AMA | April 2022

AMA questions - April 2022

Kathi Seeger
In your blog you wrote that you'll teach a class about "the physics of democracy". Could you tell what that's about?

Carlos Nunez
What's your opinion on how the West has dealt with Russia in recent weeks, particularly with regards to the tradeoff between stopping a tyrant vs. inciting a nuclear war?

Luc Gendrot
As a non-physicist I find myself enamoured with the concept of eternal inflation multiversal cosmologies. Intuitively an infinitely expanding series of bubble universes feels like as good a cosmology as any to get behind.
I recognize "feeling like it's a beautiful cosmology" is not a sound basis upon which to base a scientific theory, however, and I'd like to know if you could expound on what testable hypotheses are being explored in this area or have been proposed. I also know physicists tend to be wary about infinities, so I'd be curious to know what your thoughts are on the topic in general.

Craig Stevens
Newton's formulation of gravity relates the strength of the attraction between two objects to the mass of each object and their distance from each other. Einstein's formulation is based on the idea that the mass of an object warps space-time. It seems to me that under Newton's conception, light would not be affected by gravity because it has no mass, but in reality it is affected. Is it possible to derive Newton's formula for gravity from Einstein's, but making some simplifying assumptions, or are they completely separate formulas that both happen to work within different realms.

Keith
Congratulations on the Homewood Professorship at Johns Hopkins, it seems like such a great and exciting fit, best to you and Jennifer! On to the real important stuff, a huge congrats to the great seasons of both the 76ers and Villanova Wildcats. I mean what a great overall season for Team Sean Carroll! Ariel and Caliban better get max contracts. Would a Villanova championship be on par with a 76ers one for you personally? Or in general if you feel like sharing thoughts on differences and your preferences of NBA vs. college.

Simon Carter
I have just finished reading the excellent book “ How to make an apple pie from scratch” by Harry Cliff. Harry mentions Sphalerons as a potential solution to the matter-anti matter asymmetry. What credence do you give to this being correct and if not Sphalerons what do you think most likely caused the universe to be dominated by matter and not anti matter?

Tyler Ogorek
What was the inspiration behind the names Ariel and Caliban?

Robert Ruxandrescu
I have a question about spacetime vs. quantum fields: can you have quantum fields without spacetime? Can you have any kind of spacetime without any quantum field in it at all?

Nick C.
People sometimes claim that it is improbable that the physical constants of the Universe admit the possibility of anything resembling what we'd think of as life. This comes in to various other arguments (about intelligent design, the anthropic principle, the multiverse, etc.), but I always get stuck at this first point; I've never been able to see how that claim can be rigorously made. I don't understand how we would know what the range of possible values for each of these constants is or what probability distribution to assign to them. It seems like thoughtful people give this idea credence, so what am I missing?

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Stewart Hayne
In the intro to your recent podcast with Arik Kershenbaum you stated that you thought that it’s unlikely that in our galaxy, there are other very advanced technological civilizations and that if there were, it would be very easy to have noticed them already and we haven’t.
What means do we have now to detected civilization on exoplanets that are not producing result? Is it chemical signatures (perhaps spectroscopic lines) in atmospheres or some other means? I think you may have also said that the most likely means for a distant civilization to make contact would be through Von Neuman machines perhaps parking them at Lagrange points around foreign planets.

Brad Malt
In your “Aliens” podcast this month, you muse about why we haven’t noticed any extra-terrestrial technologically advanced civilizations. Could your “Looming Disasters” podcast provide part of the answer?
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Kyle Stephens
What makes for a good interviewee? Without needing to name names, has anyone stuck out as particularly good or bad at handling an interview? If so, why?

Jesse Rimler
Do you have a recommendation for someone who is interested in getting into math, for fun, as an adult? I'm looking into the Khan Academy and other resources, but I'm not quite sure what course of study is appropriate. Do you think someone who did not do well in school and has barely used math in decades should re-start at say, pre-algebra, rather than to dive in to a more interesting and advanced subject?

Antoine Choppin
Integrated Information Theory (IIT), initially proposed by Giulio Tononi in 2004, claims that consciousness is identical to a certain kind of information, the realization of which requires physical, not merely functional, integration, and which can be measured mathematically according to the phi metric. Does this theory seems appealing to you?

Scott
My kids have started asking me interesting physics questions. Recently one asked how potential energy is converted to kinetic energy in the context of classical electrodynamics (a charged particle in an electric field). I said that energy is not a substance but a really useful accounting trick that lets you keep track of the position and motion of the particle in the field without having to do numerical integration. In particle physics the energy seems to be the most important thing about any system and it is right there as H in Schrodinger's Equation. What is the right way to think about energy, useful account trick, fundamentally important, both?

Sandip Chitale
priority question. (edited)
It is said that micro-physics is time-reversible. To me what should be actually said is that the micro-physics is velocity reversible.
To me reverse time is non-sensical. What does that even mean? The direction of time is implicitly defined by the preceding events followed by succeeding events.

If we agree that time can only flow in one direction i.e. from preceding events to succeeding events. Then by definition, it does not need anything else to explain its direction. Then why do we need low-entropy at the big bang (past hypothesis)?

Thomas Prunty
Congrats on the new position at Johns Hopkins! You mentioned they are encouraging you to keep up your other activities, but I'd think something's got to give? Do you foresee a slowdown in the podcast schedule or your trade or textbook writing?

Emmet Francis
I was recently excited to receive an email from Biophysical Society saying they will put out an issue on Emergent Phenomena in Biophysics, but when reading their email, they define emergence as 'systems of many components (molecules, cells, or organisms) whose collective behavior is governed by their interactions so that the "whole is greater than the sum of its parts". '
This strikes me as more of a definition of strong emergence, which seems non-physical to me. Is there any way to reconcile this definition with physics, or have they just gotten it wrong?

Samin Tajik
Given my background in quantum mechanics, I was asked to work on a mutual project regarding quantum finance. The quantum calculation part (Bohmian Mechanics) made sense for me and the math was simple. However, when I start thinking about the results and conclusion part I suspect the whole idea, like how using Quantum Bohmian Potential one can talk about financial markets and analyze the occurrence of rare events. I remember you posted this book “quantum social science” written by the same author I am now working with, here I would really love to know your thoughts on subjects like quantum finance, and quantum social science.

Richard Graff
In your conversation with Arik Kershenbaum on alien life, aside from a brief mention of possible life in the clouds of Venus, there was no discussion of the potential for life based in the atmosphere of a planet. Is there some fundamental obstacle that would make atmospheric life, especially intelligent life, highly unlikely without some reliance on either the marine or terrestrial environments?

Amino
PRIORITY QUESTION
Do we make all possible choices at each decision point, somewhere in the quantum multiverse? If so this has unsettling implications for the importance of moral action, as others are always both maximally helped and hurt by our actions, making moral choices meaningless. Have I got the right idea or is there something I'm missing the will save me from this existentially troubling conclusion?

John Morgan
Apologies if this is answered elsewhere: why do measurements of quantum states produce definite outcomes? I have a vague recollection of an argument regarding diagonalization of the density matrix under measurement, and maybe that's related... but this isn't the kind of thing that's easily googled

Tamim M
Do you think the laws of physics are universal? Think of the most basic law. Afterall we are assuming universality when probing the universe with Webb, right?

Paul Hess
My understanding is that triggering of vacuum decay is a probabilistic quantum event: the Higgs Field would have to quantum tunnel to a new lower energy state, with an extremely tiny probability at each moment in space&time that this might occur.
If this is true, then under many worlds interpretation, would each moment of time contain a branch with an extremely thin new decayed “world” being sliced off, leaving the non-decayed portion that we continue to live in getting continually thinner over time?

Emil Rojas
From a physics POV what is a dimension? Does it differ in any way from the math notion?

Gregory Kusnick
Will you be teaching any online courses at Hopkins, or otherwise making course materials available to the general public?

Christopher Mathews
Have you ever gotten into Formula One racing? With the huge role of aerodynamics in it, I can’t think of another sport where the study of physics plays a larger part.

Alexandre Zani
It seems like we humans experience the universe in a particular basis. (moving in time, looking at things in 3d, position, not frequency for the most part, etc...) Do you think it's likely that there is similarly-interesting structure in other basis?

Roo Phillips
Listening to previous podcasts I have gotten the sense that you suspect a world that largely rejected gods and superstitions would ultimately be preferable to all, rather than one that does not (such as ours today). The reason being that a world that pursues and accepts truth is typically better off for a variety of reasons. Do I have your thinking right? If so, could you elaborate on the costs you have in mind of having gods and superstitions as part of society in our modern age?

Chris Shipton
It’s seems as humans our knowledge of the universe is increasing, but the universe is on a path towards reaching a state of highest entropy in the far future. Will there be a time that (if there are humans) we will be unable to gain new knowledge or make accurate predictions?

Vladimir Belykh
In your oral history interview, when talking about your high school years, you mentioned that you weren't good at giving talks back then.
I am also not a natural at this. I get similar comments. I use too many words to convey a thought and stumble a lot.
I am currently trying to get better at speaking because I am starting an educational Youtube channel for my business soon.
Do you have any advice on how to improve at talking to an audience that might be helpful to me and any other listeners with a similar aspiration?

Peter Solfest
If gravity can be derived from entropy, doesn't that mean it's an emergent property that can be ejected from our fundamental ontology? If that's the case, why is quantum gravity even necessary?

Brendan
I was rewatching your 2015 God and Cosmology "debate" with William Lane Craig a few weeks ago. Given the past 7 years since the debate, has there been any scientific break throughs or experiences (research, podcast interviews, etc.) that you would now include in your talking points for naturalism?

Chris Murray
The holographic principle is reminiscent of the fact in complex analysis that a holomorphic function on a disk is fully determined by its values on the boundary of the disk. Do you think this is an important connection or just a cosmetic resemblance?

Jase Forbes
PRIORITY QUESTION
If a black holes gravity causes time dilation, and hawking radiation causes the blackhole to evaporate, would the time dilation seem to accelerate this evaporation from the perspective of an infalling particle; and why, if time dilation approaches zero could said particle fall into a black hole before it evaporates completely?

Krzysztof Pieranski
I still don't get how are creativity, invention, discovery, and Eureka moments possible in the fully deterministic block universe. They all seem like a theatre in this context... What am I missing?

Owen
Just wondering why anyone at all accepts the post-Humean commonplace that you can't or shouldn't "derive an ought from an is"... If oughts aren't to be derived from is's, how should they be derived??

Fabian Rosdalen
What is your relationship to visual art (paintings, digital or not)? Do you paint, or have you ever tried painting? Do you have any favourite artists, or style?

James Nancarrow
Do magnetic monopoles actually exist and is it possible for us to create them in a particle accelerator or some other way? How much energy would it take to create one if this is even a possibility?

David Poole
PRIORITY QUESTION
It's been stated that early proponents of the Copenhagen interpretation were not interested in what was actually happening during decoherence, with the statement 'Shut up and calculate'. However, with the many worlds interpretation it seems to me you are equally dismissive when you say that the world just 'evolves according to the Schrodinger equation'. What does this actually mean? How does (say) a 60% probability evolve into the real world that we observe?

Weston manville
How do you perceive, for lack of better words, the beginning of everything and anything?
Given all the amazing experience and knowledge you possess, both philosophical and technical, I would just simply love to hear how you may describe or conceptualize that which is understandably beyond human comprehension; Is the beginning of "something" a false concept when you trace it back to the series of events that are responsible for its existence - all the way back to beyond the beginning of the universe and time only as we know it?!

Michael Bleau
Your recent episode with Andrew Leigh and episode 19 with Tyler Cowen each bring up the question of evaluating humanity’s current decisions in light of their impact on future generations.

Ford Prefect
In one of the AMAs you've described how big chunk of your work comprises of, among others, stretches of time dedicated just to thinking. Do you ever get sad, frustrated or otherwise uneasy when you don't seem to progress in any obvious way during such sessions, especially for a longer period of time? Ever feel you have wasted the time? If so, how do you deal with that? If not - why do you think that is the case?

Jim Murphy
Do you have any cute stories about meeting your wife, or maybe one of your first dates?

Cooper
Do you agree with the idea that if we find life on Europa or Enceladus then Bayesian reasoning would conclude that life is highly likely to be found in most star systems?

Jon Schoning
To be a good informal bayesian in life, is it possible to replace choosing a prior with another baysian sub-problem, pushing the choice of prior further up the stack until you reach a point closer to the edge of the system?

Russ Dill
In your podcast with Michael Dine, there was a brief discussion of ruling out physics that predict that the universe would decay to a lower energy state with some reasonable probability. Is vacuum decay actually a problem with respect to the many-worlds interpretation? Wouldn't we just be able to "ignore" any branches of the wave-function where vacuum decay occurs, so long as there is a non-zero probability that branches still exist where it has not occurred?

Josh Bauer
On what basis does one choose a meta-ethical framework? In the vein of "can't get an ought from an is," logic is out and it seems like the only foundation comes down to personal preference. But if that's the case, why do philosophers debate moral frameworks? Is "my preference is better than your preference" not just begging the question of what "better" means? And is there any hope of finding a framework that can be agreed upon across culture if it's all down to preference?

Oleg Ruvinsky
if you had to pick a philosopher living or otherwise to have a long conversation with who would that be and why?

G Clune
I watched a video with you on the Institue of Art and Ideas player in a discussion with Roger Penrose where you said 'there are people in our past who think we are in their past, that time runs in the opposite direction for them as it does for us'. Could you elaborate more on that idea. It is very difficult to wrap ones head around this concept!

Franklin Marek
I would love to know your thoughts on the cosmic censorship hypothesis and naked singularities. Do you think there is a way to get a black hole super extremal?

bitsplusatoms
Brian Greene tweeted “When you cross over the edge of a black hole, space and time interchange their roles. You are drawn toward the black hole's center with the same inevitability as you are drawn to the next moment in time.” Others have given similar descriptions.
Since space doesn’t have an arrow, and space is taking on the role of time, what accounts for the arrow of time in this case? Still increasing entropy?

Alex B
If you were placed into the plot of a scary ghost movie, how long would you make it before updating your prior to ghosts being real?

Jimi Sommer
There seems to be two irreconcilable views of progress that both point to a fundamental difference in how we create knowledge and how it grows. In one view, the difference between our theories of physics in, say, 1000 years and 5000 years, should be relatively similar (assuming of course that we continue to make steady progress and crack all the open problems). In the other view, our theories of physics in 1000 years and 5000 years will be radically, incomprehensibly different, because the growth of knowledge has no cut-off, even in any specific field. Which of these two views are you partial to, and why?

Nick G
What’s your take on Gerard ‘t Hooft and Susskind’s holographic principal as a solution to the information paradox? Just read Susskind’s Black Hole Wars and wondering if there’s any dissenting opinion among physicists. Thanks!

Derek Bayne
Now that you'll be coming to Hopkins and moving to Baltimore, will there be lots of speaking events and the like open to the public here that other philosophically inclined Baltimoreans with an amateur's interest in physics will be able to attend?

Nick Sepulveda
Do you have any advice for aspiring students of physics? I feel that self-doubt can become a hindrance on ones ability to learn the material, especially if the foundations of math aren't there to support them. Did you have any habits while you were in undergraduate studies that helped you focus on your goal?

Bruno Teixeira
I really liked the podcast with Dr. Sherry Turkle. You asked her about chatbots to keep people company and her answer was something like "totally wrong, that is a job for people". I get her point but I would like your take on my more utilitarian view: Why not both? People will continue to be selfish, sons and grandsons will continue to "forget" about their elderly, etc. While we struggle to make the world more humane, can't we (in parallel) try to help some people in another (less than perfect) way?

Preston Justice
You have done a wonderful job explaining the Schrödinger equation for those of us without a background in Physics or Mathematics (as well as why it’s important). I particularly enjoyed the Socratic dialogue in chapter 8 in Something Deeply Hidden and because of your well articulated explanations I am about 70/20 on the side of Many Worlds interpretation (I’m a good Bayesian). But I fear I can’t truly “take sides” or understand the theory to the greatest extent possible without the math, and when I look at the equation I am completely lost. Could you briefly outline the steps for understanding the equation mathematically/the prerequisite courses? And how much can someone really understand these theories, such as Many Worlds, without the Math?

Justin Wolcott
PRIORITY QUESTION: How can libertarian free will exist if all events - including the thoughts and actions of gods - are either deterministic or random?

Jeff B
Last AMA you mentioned something about different branches of the wave function potentially having different laws of physics. If this is the case, is there a mechanism by which the branches could develop new laws? What were the “original laws” at the Big Bang?

Dragon-Sided D
Many of us are still reeling at the loss of friends, co-workers, and family members to what now we now understand to be intentional disinformation campaigns. Otherwise fairly normal, seemingly reasonable people now have firm beliefs in all manner of easily falsifiable theories about diseases, about political events, and so forth.
Over the last ~2 years, have you observed this in any people in your social or professional circle, and can you offer any thoughts about ways that civil society can overcome the "pandemic of disinformation?"

V. Shannon Clyne
Are there questions other than conditions in the singularity at the beginning of the cosmos or conditions inside a black hole that require a theory of quantum gravity?

Vikki Ramsay
PRIORITY QUESTION
Although it is a true statement that all clocks tick at 1 second per second…
The GPS system & the NIST relativity experiments at Boulder, Colorado, prove that 'the duration' of a clock's second can be longer or shorter as compared to that of a comparison clock.
In examining the engineering/calibration process of GPS atomic clocks*…
Q: In that frequency & energy are proportional; When a clock engineer calibrates an atomic clock, does it require MORE energy in order to cause the clock to tick faster?

Jon
Can an electron be coerced to revolve around a positron? And if so, wouldn't this have the same spectrograph as hydrogen?

Ken Wolfe
You nad a very interesting discussion with Brian Klaas on Power and the Temptation of Corruption. Looking back on your own experience with academia and other organizations, have you reaced any conclusions on what aspect of the organization's structure or culture best works to discourage corrupt behavior?

Tyler Creighton
If you were offered the opportunity to host a popular science podcast alongside the entertainer of your choice, do you think you’d take it? If so, who would choose as your cohost?

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0:00:00.0 Sean Carroll: Hello everyone, welcome to the April 2022 Ask Me Anything Edition of the Mindscape Podcast. I'm your host, Sean Carroll. A couple of days late again, sorry about that once again. This time my excuse was for the past three weeks I've been in Santa Fe, visiting the Santa Fe Institute, as I usually do in my role as what is called a fractal faculty member. I'm supposed to go there several weeks a year, and it's like a part time position, basically. It's equal than a summer salary for those academics out there. I get my little part-time change of pace from my regular job by going to SFI. And of course, it's amazing fun to be at SFI, but I tried not to do any podcasts while I was there, because, well, for one thing, I'm supposed to be there doing SFI type stuff. And for another, I'm not at home in my office where I can control the audio quality. So I did one podcast interview, turns out that the loft that I was staying in while I was there was quite echo-y, so I went into the office to do the podcast interview. I think it did okay.

0:00:56.2 SC: I'm not gonna tell you which one it was upcoming, so if you can't tell, then I win. If you can tell, so be it. Sometimes we deal with what we're stuck with. But like I said, SFI is an amazing place. It's unique, right? It's a research institute in a very beautiful location in Santa Fe. Not the easiest to get to. I wish it were easier to get there, but you can get there. And devoted to the sciences of complexity in all of their forms. You know, the original founders were a lot of physicists; Murray Gell-Mann, Phil Anderson, George Cohen, and people who were at Los Alamos. But it's expanded by quite a bit intellectually into economics and anthropology and mathematics and a whole bunch of different things. So, I don't know anywhere else in the world, I think this is literally true, anywhere else in the world where you can just randomly walk into an interesting person walking down the hallway or even sitting in your office and interesting people will come and knock on your door and start asking you questions. Whether it's the foundations of mathematics, or the growth of languages, or how to use physics models in understanding politics or society?

0:02:01.7 SC: It's a great place. And in fact, there were several Mindscape guests who were there while I was there. Geoffrey West, of course, early guest was the former President of SFI. Melanie Mitchell, who is a more recent guest, is one of the most recent hires as a permanent member of SFI. Emily Riehl, the mathematician was there giving a talk while I was there, and this is the kind of cool people who just pass through. And partly I'm saying this because people have asked, if you haven't heard already, I'm going to become a professor at Johns Hopkins starting July 1. Homewood Professor of Natural Philosophy is my official title. I've already had people on Twitter say in all seriousness, "Oh, we don't have to listen to him anymore, he's declared himself as a philosopher." So, [chuckle] this does not bother me. I didn't want you to listen to me anyway, if that's your attitude toward philosophy. But people were asking am I still going to keep on with the Santa Fe affiliation? And the answer is yes, very much. It's very part-time, visiting there a couple of times a year. Completely compatible with what I'm doing at Johns Hopkins.

0:02:57.7 SC: So, also the last time I was at Santa Fe, it was last summer. There was still a pandemic, we had the vaccine, right? But obviously, there's still pandemic now, but there were still mask mandates, and the suggestion was, you should work from home for very good reasons. So technically I was there, but it was not a lot of interacting going on. Whereas is this time we had in-person talks, in-person lunches. Lunches at SFI are just some of the most fun events in the world. So, that was a lot of fun. That's my excuse for being late. With that, let's go.

[music]

0:03:43.0 SC: Kathy Seiger asks: In your blog, you wrote that you'll teach a class about the physics of democracy. Could you tell us what that's about? Yeah, that's gonna be one of the first classes I'm teaching at Hopkins in the fall, in September. So, some of you know, because I think I mentioned it on the podcast at some point that I'm writing a book. Supposed to be writing a book on the physics of democracy. I still am, that book is gonna appear at some point, but it's been put on the back burner while I do other things like the Biggest Ideas books. So I thought that it would be a good way to sort of keep my interest and focus on the topic while I'm technically writing other books by teaching a class. And in particular, this class is one of the new first year seminars at Hopkins. You know, Johns Hopkins is a broad-based research university, has all sorts of departments and everything, but student-wise, it is dominated by students in science engineering, pre-med, things like that.

0:04:35.2 SC: So as a result, a lot of students have been starting their college careers at Hopkins by taking nothing but large lecture classes. You know, the intro classes in these science and engineering and math fields are often just large, you're listening to the professor. Very unlike the ideal dream that you have of sitting around a table with a handful of people discussing the great ideas of the universe. So, recognizing this and recognizing that undergraduates have been kind of complaining a little bit, that their introductory experience in the university could be considered a little bit alienating, Hopkins has instituted these first year seminars, which are mandatory. Every student has to take one of the seminars when they first arrive, and the seminars are on basically anything. They're pass, fail. It's supposed to be very low stress kind of thing, but the idea is that you really dig into a topic with a professor and with your other students, right?

0:05:29.8 SC: I think enrollment is capped to 12 or 15 or something like that, so you get to know everybody, you're talking about things. It's the seminar, it's not a lecture, lots of discussion. Much more like the ideal college experience than you might get. So the Physics of Democracy will be a physics course, technically speaking. One of the funny things was, my physics colleagues at Hopkins apparently were not enthusiastic about teaching the first year seminars 'cause they already have their favorite courses they like to teach, with equations and lectures and all that. So I was very happy to say, "Okay, sure, I can do that for my first physics course at Hopkins." Now, as to what it is, in some sense, it's just about learning about democracy and politics and society by being inspired by physics examples. As I hinted in the intro, there was literally a talk on this topic at SFI while I was there. And I'm not trying to say that it's all physics, right?

0:06:23.7 SC: I'm not trying to say that you're gonna reduce the behavior of people in societies to the standard model of particle physics or anything like that. But I do think that the techniques and way of thinking... Ways of thinking about things that physicists get can be useful. Ideas about information flow, phase transitions, states of matter, segregation, renormalization, there's a lot of ideas that physicists have that can be productively applied to society in general and democracy in particular. Democracy in particular, because democracy is a quintessentially emergent phenomenon. It is not directed from top down. There are a lot of agents called citizens, and they vote and they sort of collectivize their decision-making in one way or another. That's an interesting question, what is the best way to do that? And then you can ask about the features, the dynamics of that decision-making, and it's very related to models in physics, where you have little tiny things that interact with each other in ways that lead to interesting emergent behaviors.

0:07:27.6 SC: In fact, when I mentioned this to David Krakauer, the current president of SFI, he said, "Oh yes, all you need to do is study everything the Santa Fe Institute has ever produced." [chuckle] Because that's what it is. I mean, when you say complex systems, what you're trying to understand is the simple emergent behavior in those complex systems. You know, the limits of how well we can understand things, what you can say, what you can't, and so forth. Ideally in a way that is universal among different kinds of complex systems, but at the very least, you can start by drawing connections between one kind and another. So, this is just helping me write a book while also chit-chatting with the students, learning about how things are going. The other course I'll be teaching will be an upper level of philosophy course on topics in philosophy of physics, where I'll cover things like the arrow of time in quantum mechanics and cosmology from a philosophical point of view, so that should also be a lot of fun.

0:08:19.1 SC: Carlos Nunez says: What is your opinion about how the West has dealt with Russia in recent weeks, particularly with regards to the trade-off between stopping a tyrant versus inciting a nuclear war? You know, I wanna say pretty well. As I mentioned on Twitter, international cooperation is generally... Suffers from being slow, right? There's a conservative-ness of bureaucratic inertia that settles in. I think that the invasion of the Ukraine has to a remarkable extent united western democracies against this particular kind of thing. It's almost without exception that NATO and NATO adjacent kind of allies have said, "No, this is not good, what can we do to stop it?" But as you hint, Carlos, there's only so much you can do to stop it when the other country has nuclear weapons. You know, to be brutally honest, and I hate to say this, If you knew for a fact that the only two choices were letting Russia conquer Ukraine or having a full-scale nuclear war between the US And Russia, that will be hundreds of millions of people dead, I think that you would have to say that letting Russia conquer Ukraine is the better option there.

0:09:30.3 SC: Hopefully those are not the only two options, and that's the trick, right? That's the art, that is the difficulty or the interesting-ness of being a diplomat in these cases, where you wanna try to avoid those two draconian options. So you want to get to a point where Russia has not conquered Ukraine without inciting a nuclear war. Now, partly that's out of your hands, right? You can try, but partly if one side starts a nuclear war, then a nuclear war has been started, right? And what can you do about that? So, what you're really trying to do is just lower the temperature, lower the percentage chance that something terrible like that is going to happen while still trying to achieve your goals. So what they're doing is diplomatic support, economic sanctions, sending some military equipment, but there's a line that they don't wanna cross. If equipment is sent, that's considered okay. That's just considered how things are done, but if actual troops are sent or even people operating the equipment sent from one country to another, then that other country now counts as a combatant in the war. And NATO countries do not want to be officially combatants in the war.

0:10:36.4 SC: Now, it's weird, you know? Just saying it out loud, these are all rules that people made up, you know? And number one, did they make up the right rules? Number two, are we sure people are going to follow the rules, even if they're the right ones? These are very murky questions, so you have to... Again, you have to balance expectations from the history of diplomacy and combat and so forth versus the possibility someone's just gonna do something completely outside the box. So, I don't agree with absolutely everything they've done, but I think that so far so good. We have not given up Ukraine, so far as I'm taping this. In fact, as I'm taping this, the most recent news is that Ukraine has begun to win back some territory, which is kind of amazing. I'm a little bit surprised that they were even able to do that. But they are and no nuclear war yet. So that's good. Fingers crossed on that one.

0:11:28.1 SC: Luke Gendrot says: As a non-physicist, I find myself enamored with the concept of eternal inflation, multiversal cosmologies. Intuitively, an infinitely expanding series of bubble universes feels like as good a cosmology as any to get behind. I realize feeling like it's a beautiful cosmology is not a sound basis upon which to base a scientific theory, however, and I'd like to know if you could expound on what testable hypotheses are being explored in this area or have been proposed? I also know that physicists tend to be wary about infinity, so I'd be curious to know what your thoughts are on the topic in general?

0:12:01.0 SC: Yeah, well, I'm not sure what to say about your statement that feeling like it's a beautiful cosmology is not a sound basis on which to base a scientific theory. It certainly shouldn't be your only basis. Science has to be fundamentally empirical, right? Looking at data, updating your priors, as a good Bayesian, right? But on the other hand, you have priors, [chuckle] that's how Bayesian analysis starts. And for me, it's just perfectly obvious, we're gonna have bigger priors on prettier, more elegant, simple scientific theories than ugly, completely ad hoc ones, right? I mean, why in the world would you not do that? So I think that it's a perfectly legitimate starting point to say, "Yeah, I'm gonna start with this particular idea 'cause I think it's beautiful," but then you have to compare it to the data. You don't stop there. That's the scientific attitude.

0:12:49.8 SC: Now, the idea of eternal inflating universes, etcetera, has been around for a while. Inflation itself sort of became officially invented, there were precursor ideas, but the official invention was about 1980, and it wasn't that many years after, by the mid '80s, we knew that inflation could lead to an infinite number of universes. It wasn't until the late '90s, so long after that, it actually became a super popular idea for two reasons. Number one, we developed theories of string theory that predicted that not only would you have an infinite number of universes, but the local laws of physics in these universes could be different. Now, again, this is something that people had thought about before. Okay, they'd hypothesized, but now you had a prediction, now you had a scheme in which that was supposed to happen.

0:13:38.5 SC: And number two, of course, we discovered the cosmological constant, and there was a pre-existing prediction for the cosmological constant from Steven Weinberg and others that said, if you have a different number of cosmological constants in different parts of the universe, and we are only selected anthropically, that is to say, we live in a world where the cosmological constant lets us live, but there's no dynamical mechanism that is picking its value, then you expect a certain magnitude. And that magnitude is roughly order of magnitude what was actually observed, okay? So that's... Both of those give a little boost to the idea. However, let's be very, very honest, number one, none of these ideas are fully baked. None of them is a rigorously defined theory. There's a set of rules, they're kind of ad hoc, you do your best to calculate things under certain assumptions, but you don't know, right?

0:14:28.5 SC: I mean, these are not, as you imply, well-tested ideas, so it could be completely wrong. And the second thing is, there are problems with it. It's not just, you know, oh, wouldn't that be great? It's that you make predictions that you don't know what to do with. People are not very sure what the predictions are even for things like the cosmological constant. So, what you're asking is, what are the testable hypotheses, etcetera. People have proposed a lots of things, but honestly, I wouldn't trust any of them. I think it's very, very important to do the work, but I wouldn't want to be premature about claiming victory on the basis of the work being done, if that makes sense. So, people are making plots about what is the mass of the dark matter or the Higgs boson is supposed to be in this kind of collective multiverse. And good for them, I think it's worth doing, but I wouldn't think that they're finally there. So, I'm not gonna give you an explicit answer, Luke. I'm just gonna say, this is something that people are working on. Hopefully, we'll get there at some point.

0:15:27.0 SC: Craig Steven says: Newton's formulation of gravity relates the strength of the attraction between two objects to the mass of each object and their distance from each other. Einstein's formulation is based on the idea that the mass of an object warps spacetime. It seems to me that under Newton's conception, light would not be affected by gravity because it has no mass, but in reality it is affected. Is it possible to derive Newton's formula for gravity from Einstein's, but making some simplifying assumptions or are they completely separate formulas that both happen to work within different realms? So the short answer to this is, you can absolutely derive Newtonian gravity from general relativity, from Einsteinian gravity. This is a standard exercise that is done in any general relativity textbook, including mine, taking the Newtonian limit. So you consider a bunch of particles...

0:16:14.8 SC: Well, I guess the important, non-trivial technical fact is this: There are two limits, the limits come into sequence. There's one limit, which is called the weak field limit, okay? And in the weak field limit, you just say all the gravitational pull is relatively weak. In general relativity terms what you're saying is that spacetime is curved, but only a little bit. It's pretty much flat. Okay? So that's a limiting case of general relativity, and it includes the solar system, all the gravitational fields in the solar system are weak. What do you mean by weak in this case, there's a numerical criterion, you can think of it as, how close are you to making a black hole, okay? Nothing in the solar system, even if you think that Jupiter or the Sun or whatever, has a lot of gravity, they are nowhere close to being a black hole. So as far as GR is concerned, general relativity, they are weak field gravity. But it also allows for things like gravitational waves or the deflection of light, which are not understood in Newtonian regime at all, okay?

0:17:14.5 SC: So there's an additional limit that you take called the Newtonian limit, which says that both the gravitational field is weak and all of the particles, all the objects in your theory are moving much slower than the speed of light. Okay? So this is part of just being Newtonian rather than being relativistic. In Newtonian mechanics, you don't have any limit on the speed of which things can move, but in relativity you do, the speed of light, and so the two theories overlap when all the velocities are very, very low compared to the speed of light. And they begin to diverge when the velocities become close to the speed of light. So therefore, if you have a relativistic theory, like GR, and you say, but I'm only going to consider situations where the particles are moving slowly compared to the speed of life, you can recover the Newtonian predictions.

0:18:06.3 SC: Now, if you notice, we did not quite, in that series of things I just said, weak field limit and Newtonian limit, we didn't quite get to a point where you could compare or think about deflection of light in the Newtonian limit. Because the Newtonian limit is particles are moving slower than the speed of light, and light moves at the speed of light. [chuckle] So that's part of the explanation for why if you're just purely Newtonian and you ask about the deflection of light, it's kind of an un-answerable question, because this idea that there's something called light, the particles of which have zero mass and they always move at the speed of light, all of these notions are just alien to Newtonian physics. So, if you want... I mean, light existed before relativity did or Maxwell's equations or whatever, but they didn't know what it was, they didn't know whether it was a wave or a particle, what kind of mass the particle would have, how fast it was moving, anything like that.

0:19:00.7 SC: So nevertheless, I think that the spirit of it is, if you have the particles that are generating the gravitational field, like the Sun and the Earth, if you have those be in the Newtonian limit, you can ask how is light deflected in a spacetime geometry, that is within that regime? And that's where you get the general relativity formula for the deflection of light. I do wanna make though one philosophy of science point here, so if Thomas Kuhn were in the audience, the guy who wrote The Structure of Scientific Revolutions, and compared different paradigms in which people work, he would have emphasized that it's not just that you start with general relativity, take some limits and get back Newtonian mechanics or Newtonian gravity, because your starting point is ontologically completely different, okay? Meaning that the actual stuff that you're describing is a completely different kind of stuff in the two theories.

0:20:00.6 SC: In general relativity, you have spacetime, it has a metric, a curvature, and the curvature responds to energy momentum. In Newtonian mechanics, you have space and time separately and there's a field, the gravitational field on top of that, that pushes things around. So it's a different language that you're speaking. And so, one of the things that Kuhn was skeptical about, but I think that you shouldn't be so skeptical about, I think that we can do better than Kuhn did, is learning how to compare the understandings that you get within different paradigms, within scientific pictures. And in fact, I would say that general relativity, Newtonian gravity is a perfect example of two very different ontologies, two very different sets of words about what the world is, that it's very straightforward to compare their empirical predictions. And the missing piece there is that in addition to general relativity as a scientific formalism and Newtonian gravity as a scientific formalism, we have our human-based manifest image of the world, right?

0:20:58.7 SC: We say, oh, I see dots on my screen of my CCD camera or I see things in the sky, etcetera, okay? And we're not comparing these two theories directly to each other, we're comparing both of them to our observations. So I think even though Kuhn would have said there in some sense incommensurable... It's not the perfect example of incommensurability, but it's in the same spirit. I think they're perfectly commensurable, and I think that all scientific theories more or less are, because you're not comparing one theory to another, you're comparing both of them to how we experience the world. Keith says: Congratulations on the Homewood professorship at Johns Hopkins. It seems like a great and exciting fit, best to you and Jennifer. Thank you, Keith.

0:21:41.8 SC: On to the important stuff, a huge congrats to the great seasons of both the 76ers and the Villanova Wildcats, what a great overall season for Team Sean Carroll. Ariel and Caliban better get max contracts. Would a Villanova championship be on par with the 76ers one for you personally? Or in general, if you feel like sharing thoughts on differences and your preferences of NBA versus college? So here's why I regret being late, 'cause as I'm taping this, Villanova just lost [chuckle] its game in the Final Four. So for those of you who don't know, number one, I was an undergraduate at Villanova University. They won the national college basketball championship my freshman year. They've won twice since then, and right now, as we speak, it's the Final Four in college basketball, March Madness. And even though they weren't quite expected to, Villanova succeeded in making it up to the Final Four, then they lost one of their best players in an injury, so he wasn't able to play in the Final Four game. And they got more or less run off the floor by the Kansas Jayhawks, who are a very high power team.

0:22:43.7 SC: And so the... As I'm taping this, what we know is that the actual championship game is gonna be been the University of North Carolina and University of Kansas. Two big public schools. So good for them, good for public education in the United States. The question that I'm not going to spend too much time on, but the interesting question is: Professional NBA level basketball versus college purportedly amateur basketball? I'm an MBA guy. I'm a more of a professional basketball guy for a bunch of reasons. Number one, it was my first love. My first true fandom in sports was when Julius Irving joined the Philadelphia 76ers in the mid-1970s, and those sixers team in Dr. Jay's day were endlessly entertaining, and of course, they won us a championship in 1983, so my heart was stolen there.

0:23:33.9 SC: I have mixed feelings about college sports in general. You know, I root for Villanova when they're playing, and it's a lot of fun to watch them, you know? There's a lot more people who get to play high college basketball than professional basketball, so it's an important thing in their lives, and I appreciate that. But yeah, college sports is just messed up for all sorts of reasons, most obviously, of which the schools and the coaches and the National Collegiate Athletic Association make huge amounts of money off of these people and the students make nothing. They get the team players, the athletes, they get free tuition at the university, but that is dwarfed by the actual amount of money that the universities are making. So it's a bit of a scam actually, and it's a scam that the professional leagues play along with, because in both college... Sorry, in both basketball and football, in particular, college basically acts as a minor league for the professional leagues.

0:24:36.1 SC: And there are even rules about how you have to go to college before you can go to the professional leagues, and that kind of makes no sense to me. I think that that's just a scheme to get people rich, other than the actual athletes doing the work. So, I have slightly mixed feelings about that. Whereas on professional basketball, everyone gets paid handsomely and you can argue the details. But also, with the current standing... The current way that the college ranks go, the very best players in college basketball only play for a year before they go to the NBA, 'cause that's what the rules let them do. So you don't get to see them progress over time in a way that you would with the professional teams. So, there you go. On the other hand, with the problem of the professional teams is that players can get traded, right? Players do get traded all the time, so in some sense, you're trying to root for this continuous Ship of Theseus in the form of the team that is constantly changing its ingredients, but somehow it works, somehow your emotions get attached to that way perfectly, effectively.

0:25:33.3 SC: Simon Carter says: I've just finished reading the excellent book How to Make an Apple Pie From Scratch by Harry Cliff. Harry mentions sphalerons as a potential solution to the matter/antimatter asymmetry. What credence do you give to this being correct, and if not sphalerons, what do you think most likely caused the universe to be dominated by matter and not anti-matter? So for those of you who are not familiar with the idea of sphalerons... You know, not many people are. In fact, most people who get PhDs are probably never exposed to... PhDs in physics are probably never exposed the idea of the sphalerons. It's something that happens late in your education in quantum field theory, in the standard model of particle physics, if that is your specialty, and it's not most people's specialty. But it's not that hard to understand the implications of it, even if the details are kind of mathematical.

0:26:19.6 SC: A sphaleron sounds like a particle, right? Like a proton, neutron, sphaleron, but it's not. It's a process really, it's a dynamical thing that can happen in the electroweak part of the standard model of particle physics. The part of the standard model that unifies the weak interactions with the electromagnetic interactions via the Higgs Boson, right? That famous thing that I wrote a book about. And the sphaleron is one of these very fun, intellectually fun exercises where you can change the topology of the fields dynamically in some quantum fluctuation, and in the process of doing that, you change the number of particles. And when you change the number of particles, you don't have to change it equally in the particle versus anti-particle sectors. Okay? You can change the total number of what we call baryons, strongly interacting particles like the proton and the neutron are baryons. So you can change baryons into anti-baryons, leptons into anti-leptons, etcetera.

0:27:18.9 SC: That's important and interesting, because as you probably know, there is an imbalance in the observed world between the number of matter particles and the number of anti-matter particles, and there's an ongoing mystery in cosmology, why is that? You may be imagined that it was just baked into the initial conditions of the universe, but for various reasons, physicists prefer to imagine that it was dynamically generated, that the universe started with an equal number, maybe zero, who knows? Of particles and anti-particles, and there was an imbalance created in matter versus anti-matter along the way. So, if sphalerons can do this, maybe they are responsible. Now, we've never seen a sphaleron, okay? These transitions are supposed to be very rare, we've never seen one in the lab, but they're theoretically on quite a sound basis. They're also not enough to get you a real physical imbalance between particles and anti-particles, because sphalerons as a class of possible things, they don't care whether it's positive mass part... Or not positive mass, whether it's positive baryon number of particles or negative baryon number of particles, okay?

0:28:22.6 SC: They don't really care whether they're making protons or anti-protons. So you need to somehow tilt the balance there. And it was Andrei Sakharov, famous Russian physicist, who really laid down the rules for when this could happen. You need departure from thermal equilibrium, you need to violate the difference between baryon and anti-baryon number, but you also separately need to violate charged parity symmetry, okay? All of these symmetries are very easily violated in the standard model of particle physics, but the rates are just so tiny that they don't explain what we actually see. So that's why there's a whole field, baryogenesis, trying to understand why there's more baryons than anti-baryons. So the question is, do sphalerons play a role in that? And the answer is maybe. There are many, many different versions of baryogenesis on the market, some of them make use of sphalerons and some don't, okay?

0:29:14.2 SC: I haven't actually followed the very most recent research in this area, it's not exactly my area. The last time I did pay attention to it, the most plausible sounding mechanism to me was some kind of something that involves neutrinos at super high energies. You know, at super high energies, you can make these neutrinos that themselves in their decays, they can be very massive neutrinos, and they can decay preferentially into either baryons or anti-baryons. So this is called leptogenesis. Neutrinos are leptons, not baryons, but then you can convert the leptons into baryons in some way. So, there are many elaborate schemes to do this, I'm certainly not an expert, so don't ask me. But it's an interesting question, because the fact that there are more baryons than anti-baryons is very empirically true, right? Like, we didn't make that up, so it's a very down-to-earth fact.

0:30:08.3 SC: The theories that we have to explain it seemed to be just a bit outside what we're able to test in the lab. So it's hard to know how to make progress in the short term, but again, just like with the anthropic principle or something like that, you gotta keep trying, you gotta keep pushing on that and try to make better predictions, and hopefully, we will figure it out at some point. Tyler Ogerack says: What was the inspiration behind the names Ariel and Caliban? Ariel and Caliban are two characters in Shakespeare's play, The Tempest, which is a favorite of both Jennifer and myself. And also, when we got them, you know they... So we got them. These are you two kittens, by the way, our two cats by now, they're five years old. For those of you who are just tuning in for the first time, I have two cats, Ariel and Caliban.

0:30:47.3 SC: We got them from a shelter, Sante D'Or Rescue here in Los Angeles. I encourage you to support or get your cats from, if you're interested. And when the kittens are in the shelter, they are just given names, they're like mass-produced names, right? So they have algorithms. So they were going through a Star Wars phase in the naming of kittens at Sante D'Or at the time, and so... Let me see if I can get them right. I think they were Jyn and Cassian, right? I think that those are from Rogue One, but I'm not sure, I'm revealing my lack of complete Star Wars knowledge right now. So, we had to figure out if we're gonna keep them what the names would be. We're allowed to change the names, etcetera. And honestly, to both of us, they both kind of reminded us of the actual characters, Ariel and Caliban.

0:31:33.4 SC: You know, in the play, Ariel is kind of angelic almost. They're both quasi-supernatural spirits of some sort, and Ariel is very light. They're both boys in the play, but our Ariel is a girl. But anyway, Ariel's very like pristine and pretty and perfect and glowing. And our little kitten Ariel is perfectly formed, very sharp features, very elegant and a little bit high-strung. Whereas Caliban in the play is more like rough and natured like and beastly. And as much as we love him, our little boy Caliban, when he was young, he's not... He's handsome, but he's not classically handsome. [chuckle] You know what I mean? He's a little bit asymmetrical. His teeth, his fangs are a little bit too long. His fur's a little bit too long. He looks so goofy, honestly, so he kinda looked like a Caliban. That was basically the answer. And their personalities worked out to be fitting to those two names, so it all came out pretty well.

0:32:35.8 SC: Robert Rucksondresque says: I have a question about spacetime versus quantum fields. Can you have quantum fields without spacetime? Can you have any kind of spacetime without any quantum field in it at all? So, it depends on what you mean by can. [chuckle] In other words, in the real world, we have spacetime and quantum fields in it, at least at the level of description where spacetime exists and stuff like that, let's assume that that's a level of description at which we are working. All spacetime has Quantum fields in it, because the ingredients of the universe are points in spacetime and a set of fields defined at each one of those points, the same set of fields, right? So within our observable universe anyway, it's the same collection of possible quantum fields, the electron field, the photon field, etcetera, at every point, having a value at every point. So, can you have quantum fields without spacetime? No, because the definition of a field is something that is a function of spacetime, that's what it is, okay? Rather than something that is just a function of a point or something like that.

0:33:37.0 SC: Can you have spacetime without any quantum field in at all? Not in our universe, not in our observable universe that we know and love, you can imagine spacetime without quantum fields in it, but even that is hard. You get to stretch the definition a little bit. Because always on spacetime, you have a metric, right? You have the thing that determines the geometry of spacetime, what Einstein allows to be curved. Even if he didn't allow it to be curved, there would still be a metric, but you could sort of imagine a world that was Newtonian in spirit or even let's say a special relativistic in spirit, okay? So there's a fixed spacetime, so you have a metric, but it's not fluctuating. And therefore, there's not really a quantum version of it. It's just a fixed fact about the universe. And then you could just think about particle mechanics in that universe, that's what Newton thought about, right? Or even that's what Niels Bohr would have thought about before quantum field theory came along, quantum particle mechanics. So you can imagine a hypothetical world in which spacetime exists, but quantum fields don't. But that's not our world in which we actually live.

0:34:36.6 SC: Nick C says: People sometimes claim that it is improbable that the physical constants of the universe admit the possibility of anything resembling what we think of as life. This comes into various other arguments about intelligent design, etcetera. But I always get stuck at this first point: I've never been able to see how that claim can be rigorously made. I don't understand how we would know what the range of possible values for each of these constants is or what probability distribution to assign them. It seems like a thought... It seems like thoughtful people give this idea credence, so what am I missing? Yeah, I'm a little bit sympathetic to your worries, Nick, but I think that there is a judicious middle position here.

0:35:22.0 SC: You're absolutely right, that people do make the claim that if you think of all the constants of the physical universe, you know, the masses of the particles, the fine structure constant, the gravitational constant, what have you, the claim that is made is that if I generically chose points in the space of all possible values for those constants, most of those points would not lead to universes that allowed for the existence of life. Clearly, that claim only makes sense if you know what you mean when you say, if you generically choose some set of values. Rigorously speaking, what that means is, you need to measure on the space of all these constants. And generally, people have a measure in the back of their mind. Namely, it's a uniform measure. It's uniformly likely, let's say, that the fine structure constant, which empirically is about 100... 1/137. You could say, Well, maybe it's a random number or chosen between 0 and 1. And someone else can say, Well, why 0 and 1? Why not -1 and a billion or plus a billion and plus 2 billion, like, why did you choose that?

0:36:27.4 SC: And the answer is, nobody has any principal reason for choosing that. So there really isn't any very rigorous statement that you can make along these lines. Okay, but on the other hand, there seems to be something real going on here, you know? In the case of the cosmological constant, the vacuum energy, we don't know for sure what is the right measure to use or even if it's sensible to say that there is a measure. I mean, after all, if there's only one universe, which maybe there is, and it just has a value of the vacuum energy or the fine structure constant or whatever, what does it mean to say that it's chosen randomly from some distribution? It's not. It's just a value. It's just one thing. Okay? But okay, let's put that aside for the moment. Given physics as we currently understand it, there isn't a measure on the space of possible values of the vacuum energy, and there's also no reason why it shouldn't be at the plank scale or minus the plank scale. So it should be... It could be any number as far, as we currently know, between the plank scale and minus the plank scale.

0:37:34.5 SC: And the point of the fine-tuning argument is that in order for life to exist, it had to turn out that the values of the cosmological constant were less than something like 10 to the -120 times the plank scale, okay? In magnitude. So between -10 to -120 and plus 10 to -120. And the idea is, which I think it makes sense to me, the idea is that in the absence of any particular rigorously defined measure on the space of possibilities, that still seems like a really narrow window. [chuckle] And in fact, people like Steven Weinberg have tried to make this rigorous by saying, look, in the space of all smooth functions that you could imagine on the values of the cosmological constant, exactly because you're zooming in on such a tiny region that that smooth function will probably look flat. Probably look uniform, because most functions look flat in very, very tiny regions of space, right?

0:38:38.8 SC: Now that's a bad argument by itself, because the particular regime we're looking at for the cosmological constant includes the value zero, which might be special, there might be that there is a measure on the value of cosmological constants that is singular, that is infinitely big at zero or something like that. But we just don't know. So, I think that you're right to think that... Again, it's not finished. I could have grouped this with the earlier question. I think that there is something there, some intuition that is being pumped by this idea that the fine... That the constants of nature seem finally tuned, but it is not a rigorous argument. So the question is, what do you do about that? What do you do when you don't have a rigorous argument, but you have some intuition? So one attitude to take is, yeah, I don't trust that argument at all, right? Unless it's rigorous, I'm not gonna believe it.

0:39:28.3 SC: That's okay, you're allowed to have that attitude, but the problem is, you're not gonna get very far in real world physics, because you'll soon discover that many, many things that we are very successful at using are not on a rigorous foundation, so that's kind of a problem. The other extremist attitude is to say, you know, it's good enough. I think the argument works, therefore, the anthropic principle must be the answer to something like this. And I don't think that's right either. I think that you should sort of keep in mind that these arguments seem to make sense, but they are not rigorous, therefore we should try to do better at them. I think it is wrong either to dismiss them entirely or to take them too credulously. That's my personal attitude.

0:40:07.4 SC: Okay, I'm gonna group two questions together about aliens. Stewart Hayne says: In the intro to your recent podcast with Arik Kershenbaum, you stated that you thought it's unlikely that in our galaxy there are other very advanced technological civilizations. If there were, it would be very easy to have noticed them already, and we haven't. What means do we now have to detect civilizations on exoplanets that are not producing results? Is it chemical signatures and atmospheres or some other means? I think you may have said that the most likely means for a distinct... Distant civilization to make contact would be through von Neumann machines, perhaps parking them at Lagrange points around foreign planets. And Brad Walt says: In your aliens podcast this month, you mused about why we haven't noticed any extraterrestrial technologically advanced civilizations, could your looming disasters podcast provide part of the answer?

0:40:53.1 SC: You know, so the big question here is the Fermi paradox, right? Why haven't we detected technology-advanced aliens yet? And I think one of the reasons why this paradox is so hard or so puzzling is because it's easy to come up with reasons, such as in the looming disasters podcast, why any individual technological civilization might destroy itself. It's not that hard to imagine that possibility. But if you really thought that technological civilizations were thick on the ground, as it were, then you only need one of the ones in the past, in our past light cone, to escape killing themselves and that civilization could fill the galaxy.

0:41:34.0 SC: The important number here is that the universe is 14 billion years old. Let's give it a couple of billion years to make stars and things like that, but you can imagine that stars in our galaxy are certainly billions of years old. Okay? Our sun is over four billion years old, so maybe 10 billion years worth of star formation and intelligent civilization building. But the speed of light crosses the galaxy in 100,000 years. That's nothing. You can cross the galaxy back and forth a lot. And even if you say, "Well, I don't think they could go at the speed of light." Alright, let them go at 1% of the speed of light. Then you can cross back and forth a galaxy in 10 million years. One way or another, it's a lot less than 10 billion years that it took, that we've been making stars. So we have a really rich past of possible extraterrestrial civilizations coming into existence in our past light cone, and you have to believe that none of them have... Or it is true, let's say that, none of them have contacted us.

0:42:38.3 SC: Okay? I know that other people disagree about that, but that's my attitude towards other civilizations contacting us so far. If the contact were going on via radio signals or whatever, then it's very easy to understand why they would not contact us yet because you can easily, if you're an advanced civilization, you can easily send out radio signals that we could detect. But why in the world would you keep doing that for 10 billion years? That seems like a waste of resources, right? Whereas, if you just build a space craft and send those space craft to other parts of the galaxy and sit and wait for the emergence of life, then you can do it very easily. Or again, just move at 1% the speed of light, in 10 million years you have filled the whole galaxy. And the reference that Stewart is making to von Neumann machines is that John von Neumann figured out a way to make a machine that can build replications of... Because it can replicate itself, okay? So send out one, it's kind of like a nasty virus. You send out one von Neumann machine, it goes to another solar system, gets the raw materials, creates 10 copies of itself. They all go to other star systems, etcetera, and they park and they wait.

0:43:45.9 SC: Now, maybe you think, "Well, okay, I don't think that the civilization would want to do that." Again, the problem is you have to think that no civilization would have ever wanted to do that. And it's absolutely possible the no civilization would have wanted to do that, but at this point, to me, it just becomes easier to imagine there aren't any such civilizations. Okay?

0:44:07.3 SC: Certainly that seems more plausible to me than, "They're there, but they're not talking to us. They're waiting for us to grow up." Again, all you need is one dissenter from that consensus or something like that. And again, this is not something I have very high credence in. I'd be very happy to be wrong. We should still keep looking, blah, blah, blah, blah, blah. But to me, the simplest explanation for why none of this has happened is that there are no technologically advanced civilizations out there, probably because the various stumbling blocks or bottlenecks, I should say, in the development of complex life are hard to overcome. Here on earth, it was easy to make life, it was hard to make eukaryotic life, it was hard to make multi-cellular life, etcetera. So, I think it's just very plausible there's life out there in the universe and none of it nearby has any advanced technology. I guess we'll see.

0:44:57.2 SC: Kyle Stephens says: What makes for a good interviewee? Without needing to name names, has anyone stuck out as a particularly good or bad at handling an interview? And if so, why? Well, yeah, there's certainly things about an interviewee that makes them good or bad. It's a skill. It's not really surprising. And this comes up with me personally, because I want to, as I've said, get a lot of different kinds of people on the podcast, and one dimension that is relevant is seniority, right? There's some people you have on the podcast... This is not their first rodeo. They've been on podcasts, they've been giving public talks, they are senior people. Not only the skill of speaking and being interesting and so forth, but also the skill of having an understanding of what part of your subject matter is really interesting and being able to share it quickly, okay? Having not necessarily sound bites, but at least an ability to dive to the important part of what you're talking about and get rid of the less interesting parts. Maybe you can make it charming with some stories and stuff like that. That would be the ideal kind of podcast guest.

0:46:07.5 SC: And I remember very explicitly when I was sometime during my post-doctoral years and I began to occasionally get called by journalists writing stories about cosmology or particle physics or whatever. And part of your first response is, "Yes, but I didn't write that paper, so I shouldn't talk about it. You're asking me to talk about somebody else's paper." But it is part of the job as an academic, as a professor, etcetera, to be a spokesperson for your field, to be able to talk about it. So, you have your specific research agenda and the research you do, but you also... You don't... It's not an absolute necessity, but it's good and nice and virtuous if you have enough knowledge about the broader aspects of the field that you can intelligently talk about it and put things into context. Communicating with the broader public is part of the portfolio, of the field anyway, if not of each individual person. So, a lot of the young people... So, I like to get young people and older people. I like to get people you've never heard of and people you certainly have heard of. And the young people have not had enough time to develop these skills, so some of them are just natural geniuses at it, that's great.

0:47:20.1 SC: Others will be really good at it 20 years from now, but haven't figured that out yet. So that's one dimension on which... I'm still gonna do it, I'm still gonna invite young people on if I think they have really interesting ideas, 'cause that's how they're gonna learn, right? By being on these podcasts. And you will learn about things that you might otherwise not hear about from the older people. There's a perspective that youth and energy and vigor bring that is not gonna be there in the older people, so I think that's still very, very important. Otherwise, yeah, there's a wide range of ways to be good at being a podcast guest. Some are basically giving their talk, except it's on a podcast. Others are very happy to ramble off on tangents, whatever those tangents may be. The perfect podcast guest is one who answers the questions, but also understands that they are the expert, not me. Right? So they know better than I do what they should be talking about. So, I will ask a question and they will be able to say, "Here's the answer to your question, and also maybe the question you should have asked was this other one." Okay? I like that. That's what I'm looking for in a good podcast guest. There's also kind of trivial questions like some people just wanna give one-sentence answers all the time. Other people are not happy unless they're talking for half an hour uninterrupted, and there is some happy medium there as well in terms of podcast guests.

0:48:45.6 SC: Often I know about people's stuff from reading what they've written, their papers, their books or whatever, and I just don't know that much about their speaking style. So there's always gonna be some hit or miss, and I don't mind that. I would like more hits than misses, but the excitement, the unpredictability, that's all part of the fun. Jesse Rimler says: Do you have a recommendation for someone who's interested in getting into math for fun as an adult? I'm looking into the Khan Academy and other resources, but I'm not quite sure what course of study is appropriate. Do you think someone who did not do well in school and has barely used math in decades should restart at pre-algebra, say, rather than dive into a more interesting and advanced subject? So, I actually am not good giving recommendations, specific operational recommendations about Khan Academy or some other resources. I have a vague feeling there are a lot of resources out there. There is Khan Academy. There's Wondrium, podcast advertiser, gotta put in a good word for them. They have a lot of good courses and lectures on things like that, and there's also just other kind of MOOCS, massively online courses that you can check out, but you can Google that as well as I can.

0:49:54.8 SC: I do not know much about the details. The question that is more specific about should you start at pre-algebra rather than dive into more interesting advanced subjects. It depends. If what you want is kind of a fun, interesting diversionary, tickle-your-brain kind of introduction to some cool ideas in math, then pick up a good popular book about math. We've had people like Jordan Ellenberg, Stephen Strogatz on the podcast who have written very good popular level books on math. Tai-Danae Bradley has a website that is also a very good introduction. But if you want to really understand the deeper aspects, then you gotta start at the beginning, that's an extremely cumulative subject. I'm a big believer that it is possible to understand higher levels of math, whether it's calculus or the kind of stuff we talked about with Emily Riehl; Category Theory, very, very abstract stuff. You can understand that, but you do need the background, and pre-algebra is a good place as any to start. You need the basics of functions, pushing around functions, maybe a bit of geometry, certainly calculus, okay? And then you can go from there.

0:51:04.9 SC: And it's fun, I think it's very worth doing. The resources are out there, so I'd encourage you to at least give it a try, see how far you get. Antoine Chopin says: Integrated information theory, IIT, which was initially proposed by Giulio Tenoni in 2004, claims that consciousness is identical to a certain kind of information, the realization of which requires physical, not really functional, integration. And which can be measured mathematically according to Phi metric. Does this theory seem appealing to you? It's appealing to me, but I don't quite agree with it. And I say that with enormous caution because I'm not an expert, and I've said this, I've opined about IIT, integrated information theory, before knowing that I'm not an expert. So you shouldn't listen to my opining about it. But my vague impression is that maybe the Phi metric on some complex system that is supposed to be either conscious or not, gives you a necessary condition for being conscious. I am much less persuaded it gives you a sufficient condition for being conscious. In other words, it just seems too easy to me to imagine systems with high amounts of Phi and yet we would not recognize them as conscious. And maybe look, in some sense, that's okay.

0:52:19.1 SC: Like we did, when we talked with Stuart Bartlett about life, and he made a very good point that what we call life here on earth has a number of distinct characteristics that can in principle be separated out, right? Some systems will reproduce, others will have metabolisms of a certain kind. There's different things that you might all associate with life and you can take or leave individual parts of them. I think that consciousness is probably similar. I'd bet that there's probably a number of things that one could try to make rigorous and explicit about what is involved in what we think of as consciousness. And maybe Phi is getting at one of them, but maybe not the whole thing. But I really should learn more about it, honestly. It's one of the things on my list of things to learn more about, so I shouldn't say anything more than that.

0:53:09.8 SC: Scott says: My kids have started asking me interesting physics questions. Recently, one asked how potential energy is converted to kinetic energy in the context of classical electrodynamics, charged particle in an electric field. I said that energy is not a substance, but a really useful accounting trick that lets you keep track of the position and motion of the particle in the field without having to do numerical integration. In particle physics, the energy seems to be the most important thing about any system, and it's right there as H in Schrodinger's equations. So, what is the right way to think about energy? Useful accounting trick, fundamentally important, or both?

0:53:44.6 SC: You know, I'm on the useful accounting trick side, largely, I would say here. In fact, what you said about energy is not a substance, but a parameter, a way of thinking, a feature, a property of the physical system you're looking at, that's something I've said myself before. And I don't think that changes any from classical mechanics to quantum mechanics. The usefulness of the concept, you kind of are choosing a rhetorical strategy when you call it a useful accounting trick. It's a very useful accounting trick. It is a way of thinking about the world that is very, very powerful. I mean the existence of the desk in front of me is a useful accounting trick to talk about a whole collection of atoms and particles and things like that, but it's a very useful accounting trick. So much so that I tend to think of my desk is a real thing that is sitting in front of me. So, in quantum mechanics...

0:54:34.1 SC: Let's put it this way. In classical mechanics, if you were Isaac Newton, when you wrote down Newton's equations for physics, you never mention the word energy. The idea of kinetic energy was not one that was in Newton's toolbox. He talked a language of forces and accelerations. You have a position, a velocity, acceleration of force. Those were the fundamental ingredients for Newton. It wasn't until later, Madame Du Chatelet etcetera, that we figured out the distinction between momentum and energy, and we got the equations for them down. And then Hamilton figure out a way to do classical mechanics based on the energy.

0:55:10.6 SC: So the whole idea of Hamiltonian mechanics is just a re-write of Newtonian mechanics. It's not a new physical theory, but it's a new language in which to talk about Newtonian mechanics, where the energy of the system is the primary thing. So Hamiltonian mechanics starts with an equation for energy as a function of position and momentum. And from that one equation, it gives you a recipe for deriving all of the equations of motion in Newtonian mechanics, okay? And we call that Hamiltonian mechanics, even though it's physically equivalent to Newtonian mechanics. By the way, I have a book coming out and I will explain all of this.

0:55:45.6 SC: This is all talked about, including Hamiltonian mechanics and Lagrangian mechanics in The Biggest Ideas In The Universe, coming out in September. But in quantum mechanics, the point is that we have the Schrodinger equation, yes, and the Schrodinger equation certainly features the Hamiltonian, which is that thing invented by Hamilton, the way to express the energy of the system in terms of its velocities and its momentum. Schrodinger turns that into an operator on wave functions, but it's the same basic idea. So, I would say that energy doesn't play any more important role in quantum mechanics than it did in classical mechanics. It's just that you're using a useful accounting trick to write to the theory in a way that uses energy in a very straightforward, important, central way. So, I would say that something can be a useful accounting trick and fundamentally important at the same time, and energy certainly qualifies as well as anything that I can think of.

0:56:43.3 SC: Okay, Sandeep Chitale is asking a priority question. And so I edited this question a little bit 'cause it was a priority question, but it was long. I meant to say this in the intro, but let me say it now, 'cause now that we're in the regime where I don't get to answer every question, people wanna know why do I answer some questions rather than others. There's lots of things that go into it, and as I've said, do I personally have something interesting to say. Likewise, do I think that what I have to say it will be interesting to the rest of the world. That's also interesting. But a third criterion is I would like the questions to be short. I am not in favor of long questions because it just takes time from... They're both hard to understand, audio, visually. There's no visual, so you're just listening to my voice. And reading a question is one thing, but listening to someone say a question out loud is a different thing, so keeping the question short makes it more comprehensible to the audience.

0:57:37.6 SC: And it also is a little bit respectful of the time that it is taking away from other people's questions. Anyway, I don't mean to pick on you, Sandeep, I know you're a long time listener, and I appreciate it, but I did edit your question down, that's all I'm saying here. And if other people did not get their questions answered at all, ask how many paragraphs were in your question. And if the answer is more than one, you might have stumbled across the reason. So the question is: It is said that micro physics is time reversible. To me, what should actually be said is that micro physics is velocity reversible. To me, reverse time is nonsensical. What does that even mean?

0:58:11.4 SC: The direction of time is implicitly defined by the preceding events followed by succeeding events. If we agree that time can only flow in one direction from preceding to succeeding, then by definition it does not need anything else to explain its direction. Then why do we need a low entropy, state of the Big Bang, the past hypothesis? So there's a couple of things going on here. One is, the whole point of the arrow of time problem is that the set up that you proposed where the direction of time is implicitly defined by preceding events going to succeeding events is just not there in fundamental physics. In the equations of motion, whether they're Hamilton's equations, which we just talked about, or Newton's equations, or the Schrodinger equation or whatever, there... Time is just a label, and there is no directionality to it. So, by "just a label" what I mean is mathematically, I can invent a new time coordinate.

0:59:02.9 SC: And I can invent it by saying, "Let's let T prime equal minus T." Okay? Now the equations of either Hamiltonian mechanics or Newtonian mechanics or whatever, in some sense work equally well when you do that, letting T go to minus T. You can run the movie forward or backwards at the level of fundamental physics. The subtlety there, there's a footnote, okay, which is what you're putting your finger on when you say velocity reversible rather than time reversible, because technically... Let's think about it in terms of Hamiltonian mechanics, 'cause the interesting thing about Hamiltonian mechanics is that you don't define momentum as mass times velocity. You derive that momentum as mass times velocity, but momentum starts life as something completely independent. Okay? There's an equation of motion that says momentum is mass times velocity, but you don't assume it from the start.

1:00:00.9 SC: And there, indeed, for a typical standard kind of dynamics for physical systems expressed in the rules of Hamiltonian mechanics, to have this property that you can reverse the direction of time as a matter of parameter choice, you also need to reverse the direction of momentum, that's what you're sort of getting at when you say velocity reversible. So the rule is in Hamiltonian mechanics, I have a collection of particles, they have positions, they have velocities, or momenta. I evolve it forward in time, get some new collection of positions and momenta. I reverse all of momenta, so I create a new state called the time reversed state.

1:00:41.5 SC: Which is keeping all the positions the same, but reversing all the momenta. And then I evolve backward in time, and I can do that, I can just put minus T into the equations, then I get yet another state and I un-time reverse it. So that final state I'm gonna remove, I'm gonna reverse all of its momenta. And the non-trivial result is that process, evolve forward in time, time reverse, evolve backward in time, time reverse again, that gets you back to your initial state. That is the statement of time reverse-ability in physics. And it's just as true in the Schrodinger equation, except rather than going from momentum to minus momentum, you go from wave function to complex conjugate of the wave function. There you go. Okay? Now, the point is that when you have that property, when you have reverse-ability, the reverse-ability says that the amount of information contained in the state at any one point in time is preserved over time. You can evolve forward or backward without losing information, and that's true about micro-physical dynamics, Newtonian or Hamiltonian or Schrodinger or whatever. It's not true about macro physical dynamics, if I have...

1:01:50.7 SC: A classic example, if I have a glass of warm water with an ice cube or if I have a glass of cool water, they will both evolve into a glass of cool water. And seeing that final state macroscopically doesn't let me decide which one it came from. If I see a glass of cool water, I don't know if it just was a glass of cool water or whether it was a glass of warm water with an ice cube, they look the same.

1:02:15.1 SC: But micro-physically, I would be able to tell if I knew all of the positions and momenta, and that's why you need the past hypothesis, because the whole point is to connect the micro-physical theory to the macro-physical theory. It is a fact about the world that entropy increases over time. And we have very, very strong belief that it was lower in the past, but that's not dynamically necessary. Given the state of the world now and the microscopic laws of physics, if that's all you knew when you gave equal probability to any micro-physical state that was compatible with our macroscopic knowledge, with overwhelming probability you would predict that the past used to be high entropy. And no one thinks that's true, so you need a hypothesis that says it is low entropy at the Big Bang. Now, to be fair, the story I'm just telling you here, this is the standard story, this is what most physicists or philosophers would tell you. There are people who don't go along with the standard story. There are people who, like you say, really think that time just has a direction built into it, that there is a flow from the past to the future.

1:03:28.1 SC: I don't think that, most working physicists don't think that, but there are people who think that, okay? I still think that even if you believe that, it doesn't by itself tell you why the past had low entropy. So, the way that... To me, the logic goes in the following way: You might want to think that time fundamentally has a direction or that time doesn't fundamentally have a direction, it's just that it started with low entropy, and so we perceive it to have a direction macroscopically. But if you think that time fundamentally has a direction, you still need to explain why the early universe had low entropy. That doesn't come for granted. There's no feature about saying, "Time has a direction," that then says, "If I take the currency the universe and evolve into the past, the entropy goes down," there's no connection there. Right? So, even if you believe that time has a direction, you still need to have some past hypothesis, and once you have the past hypothesis, you don't need to assume that time has a direction because it will have a direction microscopically, even if microscopically, it's completely reversible. I think that's why most people like the past hypothesis package when it comes to explaining the asymmetry of time.

1:04:43.5 SC: Thomas Prunti says: Congrats on the new position at Johns Hopkins. You mentioned they are encouraging you to keep up your other activities, but I think something's gotta give. Do you foresee a slow down in the podcast schedule or trade or textbook writing? I get it. Thank you, Thomas. I get the concern, I've had it myself, but I guess we'll have to see, okay? I have a lot of obligations to both write things and to teach courses and things like that. I think I can do it, but we'll have to see. Maybe something will have to give. I'm not gonna kill myself or drive myself to distraction doing these things. I certainly have no plans right now to slow down the podcast schedule at any time.

1:05:20.3 SC: I did, I toyed with the idea of maybe slowing it down a fraction by instead of doing a brand new interview episode every Monday, I just make the AMAs count as a new Monday episode. Okay? So that removes one interview I need to do every month, but while still giving you a new podcast once a week. I don't know whether I'm gonna do that or not. Right now, again, that is not the plan, but that is a possible future plan if it becomes unbearable otherwise. Emmett Francis says: I was recently excited to receive an email from Biophysical Society saying that they will put out an issue on emergent phenomenon in biophysics, but when reading their email, they define emergence as systems of many components whose collective behavior is governed by their interactions, so that the whole is greater than the sum of its parts. This strikes me is more of a definition of strong emergence, which seems non-physical to me. Is there any way to reconcile this definition with physics or if they just gotten it wrong? Well, certainly, one issue in the study of things like emergence is we don't agree on the definition, okay?

1:06:24.9 SC: I can give my definition of it and someone... This literally happened not that long ago, someone in the middle of conversation says, "That's just not emergence." You can't win or lose an argument about that. It's a definition, people can just have different definitions. Okay? Now, the specific issue with the definition that you're quoting, I wouldn't necessarily say that the issue is that it's non-physical because it's strong emergence... I think it's just not very well-defined. Okay? So the whole is greater than the sum of its parts. That's their definition. What does that mean? How do I know that the whole is greater than some of its parts? How do we know what the sum of its parts is? That's why part of what one should do if one wants to have a principal discussion about these things is be a little bit more clear about what your definitions are. Do you mean that...

1:07:12.6 SC: So just to back up for those people who are not experts. I should apologize 'cause I'm sort of embedded in these debates, and I forget sometimes. There's a famous distinction between strong and weak emergence, probably the clearest version of which was given by a philosopher named Mark Bedau in a paper, I think, called Weak Emergence, 'cause people have talked for many, many years about the idea of emergence. And I think the part of the idea of emergence that everyone agrees on is there is a way of talking about a big macroscopic system that is a collection of little parts that doesn't directly refer to those little parts. Right? When you talk about the table in front of me, I can talk about the table being solid or brown or whatever, without talking about its atoms. That's a common feature of emergence. The question is, weak versus strong, are those features of the table in principle coming down to just the collective behavior of the individual atoms and particles obeying their individual lower scale laws of physics? In which case it would be called weak emergence. And what Bedau very cleverly did is said, "Look, if you have some lower level laws governing the atoms or whatever, and in principle, I could do a numerical simulation, I could put those laws of physics on a computer and I could ask what happens, and the prediction for what happens is the same as what actually happens, that's weak emergence."

1:08:36.8 SC: Okay, weak emergence is when in principle, all the behavior could have been figured out just by putting the lower level laws on a computer. And strong emergence is not that. Strong emergence is defined as something happens, but it's not what you would have predicted by putting lower level laws of physics on the computer. It's something else coming in that is somehow brand new because it is a collective. Okay? So what Emmett is getting at is that strong emergence picture is kind of suggested by this motto of the whole is greater than the sum of its parts. But it's vague enough that you're not sure.

1:09:14.1 SC: Okay? And people... And I have a take on this, which is only temporary, and I don't want to completely buy it, 'cause I'm still thinking about this myself. But I think that whether or not strong emergence happens at all depends on what your two levels are, okay? To a physicist like myself, like the microscopic level is going to be quantum field theory or atoms or something like that. And in that case, I think strong emergence just doesn't happen, because we know what the lower level things are. They're pretty simple; quantum fields, electrons, particles or whatever. They obey local equations of motion, what happens to the electron is only influenced by what's happening in its immediate neighborhood of space and time. And there's just either that theory, the core theory is either right or wrong. And if it's right, then you don't have strong emergence, and if it's wrong, then good. You win the Nobel Prize if you show that it's wrong, but no one has done that yet, okay?

1:10:12.8 SC: But sometimes you are interested in cases where the lower level of theory is not fundamental physics. Like, what if you wanna say, the behavior of a nation emerges out of the behavior of its citizens? Citizens, bless their hearts, some of my favorite friends are citizens, but they're not simple. They're themselves complex systems. So you can try your best to invent laws of behavior governing the citizens, the people in the country, but those laws are hard to pin down, hard to know that they're right, and it's hard to say that they're local.

1:10:53.7 SC: So it might very well be the case that there's some useful sense in which you get strong emergence when you connect one complex level of analysis to another, higher but still complex, level of analysis. Whereas I don't think that there's any interesting emergence of strong emergence if your lower level theory is completely simple and local, like physics is. Semine Tajik says: Given my background in quantum mechanics, I was asked to work on a mutual project regarding quantum finance. The quantum part, which involved Bohmian mechanics, made sense for me and the math was simple. However, when I started thinking about the results and conclusion part, I suspect the whole idea, like how using quantum Bohmian potential, one can talk about financial markets and analyze the current of rare events." Sorry, I... Me, Sean emphasized the wrong pronunciation there. When I started thinking about the results and conclusion part, I suspect the whole idea. In other words, suspicion is being raised about the whole idea. So I remember how you posted this book, Quantum Social Science, written by the same author I'm now working with. Here I would really love to know your thoughts on subjects like quantum finance in quantum social science.

1:12:01.2 SC: Well, you know, as someone who is trying to write a book called The Physics of Democracy, I cannot completely poo-poo the idea, but you gotta be careful. As I tried to say when I was describing the physics of democracy, I'm a believer in using insights from quantum, or from physics broadly, and certainly inspiration and analogies from physics when understanding society or other things. But that's different than saying that it is that. In other words, a financial market or a country or whatever, they are not a wave function, they are not a quantum state. You cannot just blindly apply all of the knowledge that you get from thinking about quantum mechanics to these other kinds of situations. That's not to say you can't be inspired by some of the behavior of quantum systems, especially because they're probabilistic and so forth. Probability works a little bit differently in quantum mechanics than in classical mechanics. So, very often, when people try to apply quantum mechanics to other kinds of systems, I think that they're just missing the fact that they could equally well just talk about classical probabilities, since the systems they're looking at are really classical. But I don't know of the specific examples you're talking about, so I can't judge. So, I wouldn't immediately dismiss it nor immediately take it as sensible.

1:13:19.8 SC: I would really think about whether or not you are getting something extra out of the fact that this was supposed to be a truly quantum thing rather than just a fancy and useless way of talking about classical probability distributions. Richard Graph says: In your conversation with Arik Kershenbaum on alien life, aside from a brief mentioned of possible life in the clouds of Venus, there was no discussion of the potential for life based on the atmosphere of a planet. Is there some fundamental obstacle that would make atmospheric life, especially intelligent life, highly unlikely without some reliance on either the marine or terrestrial environments? Well, you should Arik this, not me, but it's a good question. And I could easily imagine obstacles to life becoming highly intelligent and technological. Intelligence is a different thing. Intelligence could, I think, arise anywhere.

1:14:15.7 SC: What do I know? But that's what I would suspect. But technological is a little bit different. I do think that you get extra flexibility, impossibility when you kind of live near the triple point. The triple point in chemistry being the conditions under which certain things could be liquid, solid or gas. Now, a real chemist says the triple point happens when a single thing like water can be liquid, solid or gas, but forgetting about the single thing, the fact that life on earth has access to solids and liquids and gases is kind of useful if you wanna grow up to be a technological civilization. If you're literally just in the clouds of Venus, if you never go down to the ground, you don't have access to either liquid or solid, okay? So, your raw materials are much more constrained than they would be if you were down on the ground.

1:15:05.3 SC: So, all else being equal, I think it's not a surprise that we became technological here on earth with access to all these different possibilities, and maybe it's less likely if we're just floating gas bags on Venus or Jupiter. Amino asks a priority question: Do we make all possible choices at each decision point, somewhere in the quantum multiverse. And if so, this has unsettling implications for the importance of moral action as others are always both maximally helped or hurt by our actions, making moral choices meaningless. Have I got the right idea? Or is there something I'm missing that will save me from this existentially troubling conclusion?

1:15:40.7 SC: Yes, there's something you're missing, which is that not all decisions are equal, okay? And I know I've said this many times, and it's in my book, but maybe I don't say loud enough, 'cause people seem to always fall into the same, what I think is a mistake, which is if there is a... Let's say there's an electron, okay, and you're gonna put it through a Stern-Gerlach apparatus. This is for physicists out there, they know that that's how we measure the spin of an electron. It can either be spin up or spin down along some axis that you measure it in. Famously, if you prepare the electron so that its spin is pointed in the X-direction, and then you measure it along the Z-direction, okay? A perpendicular axis. So if you measure the spin of an axis... Of an electron along an access perpendicular to where its spin actually is, you have a 50-50 chance of measuring it spin up or spin down. Then you get two branches of the wave function, you have a reader, a read out apparatus that says up or down, and now you have two branches. But it's crucially, crucially, crucially, crucially important that I could measure the spin of an electron that was only 0.0001 degrees away from the Z-axis in the first place. And in that case, with overwhelming probability, I would measure it to be what the spin mostly was, mostly spin-up.

1:17:03.1 SC: It's, again, crucially important, if you're an Everettian, there are two branches after you do that, there's a spin-up branch and a down branch, but they are not created equal. They do not get equal probability, they do not get equal mattering, if you were thinking about utilitarianism or morality or choices or anything like that. Lots of things happen in the Everettian multiverse, but they don't all count equally. So, maybe in some single universe model, if you thought, "Well, if I do this, it's a good thing and that's good," then in an Everettian model, you think, "Well, if I'm probably gonna do this, that's a good thing and that's good," and all of the meaningfulness is exactly still there. It is not changed whatsoever just because of the existence of these very, very, very tiny and completely ignorable other worlds.

1:17:58.4 SC: John Morgan says: Apologies if this is answered elsewhere, but why do measurements of quantum states produce definite outcomes? I have a vague recollection of an argument regarding diagonalization of the density matrix under measurement, maybe that's related, but this isn't the kind of thing that's easily Googled.

1:18:11.4 SC: Yes. That's fair enough. It's not easily Googled. You can Google it. Whether you're gonna get a sensible answer is harder. So, the answer depends a little bit... There is an answer. The answer depends a little bit on what you mean by "produce definite outcomes". So, there's two things going on. One is that when you measure a quantum system, what that means is you bring your quantum system into entanglement with an environment, okay? And that induces branching of the wave function of the universe, so there's one branch on which the system now has one value and another branch has another value, that's why you get definite outcomes in the sense that there is one value on one branch and another value on another branch. Now, if you don't know anything about decoherence or becoming entangled with the environment, that's a much longer story. I wrote a book, you can buy it. I encourage you to do so. But there is another question, another issue here, which is maybe what you're actually getting at, which is why is it specific definite outcomes? So, there's one fact that a quantum measurement gets you an outcome. The other fact is that the outcomes it gets you are predictable ahead of time, and there's a very limited sample. So, let's just take Schrodinger's cat.

1:19:21.5 SC: That's what we always take, it's a good example. In my version of Schrodinger's cat, the cat is put into a superposition of awake and asleep. And so in the formalism of quantum mechanics, you can observe the cat, okay? And you can observe it along any basis you want, which is a way of saying that you could ask the question, "Is the cat awake or asleep?" That's a question you can ask with two possible answers, awake or asleep, and you will get a definite answer. But there are other quantum states like the superposition of awake plus asleep, and there is a perpendicular combination, the superposition of awake minus asleep. The minus sign really makes a difference, and you can ask that question in principle. In principle, you could say, I observe the cat to ask the question, "Is it in the superposition of one half awake, one over square root of two, to be technical about it, awake plus asleep, or is it in the awake minus asleep state?" Nothing in the formalism of quantum mechanics prevents you from asking that question, but in fact, when you see cats, despite jokes, the real cat's always either awake or asleep. You never see it in a superposition of both, and you cannot even choose to see it in a superposition of both. So what's going on?

1:20:36.8 SC: And that is not just decoherence, but the feature of decoherence, namely that the interactions with the environment are local in space. When you talk about decoherence and the entanglement with the environment, what you mean is there are photons, let's say, in the box with the cat, that will either interact with the cat or not, depending on whether it's awake or asleep. By which what I mean is there os a physical configuration of the cat. We're imagining that the awake cat is up and walking around and the asleep cat is lying on the floor sleeping. Okay? That's what we're imagining, just because it's our thought experiment, we can set it up however we want. And the point is that a photon that might hit and be absorbed by the cat if it were up and walking around, will miss the cat if it's asleep. But that's true for all the photons, right? There's a coherent, physical spatial extent that the cat has depending on whether it's awake or asleep. And there is no coherent physical extent it has if it's in a superposition. So, the fact that the cat is constantly being bombarded by particles that interact with it, depending on where the cat is, means that in practice, you will always observe the cat to be in a macroscopic... In a macroscopically sensible, coherent state, not in a superposition of two such things.

1:21:57.8 SC: So the bare formalism of quantum mechanics that you might learn about in a textbook would not answer this question. Most textbooks don't talk about decoherence or pointer states as they are called or anything like that, but that is the answer. Now, there's other answers and other questions that that raises about why interactions are like that, etcetera, etcetera, but that's basically the reason. There is a classical regime that you get by focusing in on states of quantum systems that are macroscopically in certain places, not super positions of being in different places, and those are the states we actually see because that's how decoherence works.

1:22:34.4 SC: Tamim M. Says: Do you think the laws of physics are universal? Think of the most basic law. After all, we are assuming universality when probing the universe with the Web Space Telescope, right? Well, we're not assuming. We're doing what good scientists do, we're hypothesizing and we're testing that hypothesis. So, for example, you could very easily hypothesize that the physics that give rise to atomic transition lines, where you can see in the spectra of a galaxy, the physics is the same in a distant galaxy 5 billion light years away as it is here, and then you can test that hypothesis. You can also hypothesize maybe it was different. If the mass of the electron or if the fine structure constant were slightly different values, then you would see shifts in the position of spectral lines that we observe.

1:23:25.8 SC: That's what astronomers do all the time, that's how you figure out the red shift of a distant galaxy, you measure the positions of its spectral lines, and those spectral lines will be moved if the laws of physics were a little bit different, and there's two things to say about that: One is that the motion is not uniform for different spectral lines. So you might say, "Well, how do you know if it's been moved? Maybe that's just what you're perceiving as the red shift." But all are different, there are many different spectral lines and they all rearrange with respect to each other in different ways if you change the underlying laws of physics. So that's different than a single universal red shift put on top of everything.

1:24:00.0 SC: And the other thing is, you might say, "Well, that's if you change the laws of physics a little bit, what if you change a lot?" Well, then, if you change them a lot and you don't expect to see spectral lines at all, maybe you have physics that doesn't even give rise to what you and I know of as spectral lines. So anyway, the point is you're being a good scientist. You're starting with a very simple hypothesis, very clean hypothesis, that the laws of physics that we observe here on earth are the same far away. And then you test that hypothesis and so far every little bit of testing we've done, whether it's for electric magnetism or for the masses of particles or for the strong interactions or whatever, they've all been consistent with the idea that the laws of physics are the same, very far away. That has nothing to say about when you're outside our observable horizon, of course. The part of the universe we can't see, the laws of physics might very well be different, that possibility literally is the cosmological multiverse. We don't know whether that's true or not.

1:24:57.5 SC: Paul Hess says: My understanding is that triggering of vacuum decay is the probabilistic quantum event. The Higgs field would have to quantum tunnel to a new lower energy state with an extremely tiny probability at each moment in space time this might occur. If this is true, then under the many worlds interpretation would each moment of time contain a branch with an extremely thin new decayed world being sliced off, leaving the non-decayed portion of what we continue to live in, that we can live in as getting continually thinner over time? Yes.

1:25:26.1 SC: I think this might be the first time my answer is shorter than the question. That is exactly what happens in many worlds. It's a smooth evolution from a wave function that says the vacuum has not decayed to a superposition of it has not decayed plus it decayed at this point, it decayed at this point, and it decayed at this point for every point in space and time where it might have decayed.

1:25:50.9 SC: And Emeel Rohaz says: From a physics point of view, what is a dimension? Does it differ in any way from the math notion? It different in some ways, of course, physicists use math, so physicists use the mathematical definition of dimension. And roughly speaking, it's actually kind of tricky to define mathematically what dimension is. But it's a standard by which you're measuring something, and those standards can be incommensurable in the sense that we're talking about earlier. So energy and length are in incomensurable, so those are different dimensions for quantities you might want to mention. In math, it is most... So we use the word dimension in slightly different senses, both in math and in physics.

1:26:28.3 SC: In math, it is very often to have your attention focused on what is called a manifold. A manifold is something that in very small regions looks smooth. Maybe I should start... Maybe I should back up. You start with geometry and flat geometry. Okay? Euclidean geometry. And in Euclidean geometry, it's very easy to distinguish between one-dimensional geometry, two-dimensional geometry, three dimensional geometry, etcetera. A manifold is a generalization of that notion that says in small regions of the manifold, it looks like Euclidean geometry with some definite dimension. So if something is a manifold in the math definition, it has a dimensionality everywhere. It doesn't change its dimensionality anywhere. Of course, that is exactly the same notion of dimension that physicists use when talking about spacetime because spacetime is a dimension. So it is nothing more or less than the number of independent, by independent we mean perpendicular, directions in which you can move. So you can move forward backward up, down, left, right, for example. Three possible directions, 'cause the direction and minus the direction count are the same.

1:27:39.1 SC: I think that's pretty much the same notion in both physics and math. Physicists often use this unit idea of dimension, like I mentioned, energy, time, length, temperature, things like that, are quantities that have units, and that's also sometimes called a dimension, but it's very, very related to the math notion. Gregory Cuznik says: Will you be teaching any online courses at Hopkins or otherwise making course materials available to the general public? I don't think the courses are online as far as I know, but I'm not there yet, so maybe. Who knows also about the future, but generally when I ever I have a course I put on either lecture notes or supplementary materials or something. In fact, you can go to my website and find such things for various courses that I've already done in the past. Look, they're generally not very good.

1:28:30.1 SC: They're generally handwritten or whatever kind of sloppy. I shouldn't even say generally. The last time I taught a course was at Caltech, I taught quantum mechanics the third quarter of a three-quarter quantum mechanics course. And I put all my lecture notes online in handwritten form because it was easy to do so, because my hand written lecture notes were actually done on an iPad. And so it was used to turn them into PDFs and put them online. For the seminars, that's not as easy a thing to do. It doesn't make quite as much sense. This was a lecture course, and so I just put my lecture notes online. Whereas seminars don't have lecture notes, you're supposed to be having the students do most of the talking. Or even if I'm talking, it will be in response to something that is organically happening in the class discussion. But there will still be a web page for every course that has readings and things like that, and you know, a syllabus and so forth. I think that's easy to put online, but I don't think there'll be any video taping going on, which look, probably that's good.

1:29:27.5 SC: For a lecture course, video taping and putting it online makes perfect sense. I actually tried to get my quantum mechanics course video taped and put online at Caltech. It didn't happen. It's one of the reasons why I became frustrated at CalTech. They were not interested in doing that. The first seminar doesn't make sense. For a seminar, you want it to be about that moment. It's not just wisdom being handed down from the lecture, it's the conversation that is going on that is more important. Christopher Matthew says: Have you ever gotten into Formula One racing? With a huge role of aerodynamics in it, I can't think of another sport where the study of physics plays a larger part. So two answers here: One is a short answer. No, I don't really know anything about Formula One racing. I do know, I have a friend, Diandra Leslie-Pelecky, who is a physicist, who wrote a book called the physics of NASCAR. Where she actually digs into the physics of car racing in general, NASCAR in particular. Not the same as Formula One, but related I think. So you can check that out if you're interested. I agree that there's a lot of physics going on, but the second part of my answer is, it's not my kind of physics.

1:30:32.2 SC: I don't say that in any way disparagingly, it's exactly the opposite. When you try to apply physics to the real world, suddenly all of the complications of the real world generally become important, especially with something like Formula One racing. You're absolutely right, there's a lot of physics involved, but the physics involved is not the kind of physics where you can Spherical Cow your way out of the complications, where you can ignore friction, things like that, or look at the elementary particles and get anything like that. So that stuff's much harder than what I do for a living, and so I don't pretend to be an expert on it. Alexandra Azani says: It seems like we humans experience the universe in a particular basis; moving in time, looking at things in 3D position, not frequency, etcetera. Do you think it's likely that there is a similarly interesting structure in other bases. My guess is no. Actually, my guess is that when you say that we... I agree with the presumption of the question. We humans experience universe in a certain kind of configuration that we pay attention to, certain variables are those that are observable to us in the low energy course-grained world and others are not.

1:31:41.6 SC: Okay? We see positions most obviously, and that's in part because as we said earlier, physics has interactions that are local in position, not in momentum or anything like that. And I think of this as a feature of emergence. There is a higher level emergent structure that supervenes on the lower level goings on. And I think that those emergent structures, they have a life of their own, even though they could in principle be derived from the lower level structure. The point is you don't have to derive them, okay? That's what emergence is to me. If I didn't know that my table was made of atoms, I could still talk about the table and its solidity and its height in this color and it's weight and so forth. Okay? It's compatible with the underlying structure, but I don't need to know about the underlying structure to make sense of it. And I think that the existence of such higher level structures, what Dan Dennett calls 'real patterns' is rare. I don't think that there's many, many different sets of real patterns that are useful. I think that they are precious and few in the set of all possible ways to coarse grain the underlying goings on.

1:32:54.0 SC: Because the point is not only can I look at and see the features of the table in front of me, but I can use that information to make predictions, right? I can predict that if I put the coffee cup down, it will set itself down on the table without falling through. I can predict if I try to pick up this table with one hand, I will fail. There's an enormous amount of predictive structure inherent in that pattern with very little information. I don't need to know almost anything about the individual atoms making up the table. Right? That's the wonderful ness of a higher level emergent structure. It gives you enormous handle on the world on the basis of very little input data. And I think that's very, very rare in the space of all possible things to imagine, bases, if you will in your language, to imagine observing the thing in.

1:33:36.6 SC: Rue Phillips says: Listening to previous podcasts, I've gotten the sense that you suspect a world that largely rejected gods and superstitions would ultimately be preferable to all rather than one that does not. The reason being a world that pursues and accepts truth is typically better off for a variety of reasons. Do I have your thinking right? And if so, could you elaborate on the costs you have in mind of having gods and superstitions as part of society in our modern age? I mean I think that's partly right. I wouldn't necessarily put it in exactly those words. I am in favor of truth.

1:34:05.1 SC: I suspect that everyone is in favor of truth, at least for themselves, you know? People might not be in favor of other people having the truth, that happens all the time. But they want themselves to have the truth. I don't know of anybody who actually says I would rather be wrong about the world than be right about it, right? And therefore, the fact that I don't think that Gods and superstitions are correct, truthful descriptions of the world, means that I would rather not only myself but other people understand that and accept it. I've also been very, very clear that the empirical implications and consequences of religious belief are messy, there are good aspects and bad aspects. If you said, "Well, is it mostly good or mostly bad?" I would have no idea how to start answering that question. It's very easy to point to individual really good things or individual really bad things and ignore the others, and therefore, I think you're winning the argument. I don't think that there's a rigorous way of weighing all of them. I can sort of mildly, casually suspect that in the modern world those implications and consequences are mostly negative, but I can't really back that up with a calculation or with evidence.

1:35:15.2 SC: The one thing I would point to is, we do in our world have morals, we have ethics, we have rules for behavior. What we don't have is an agreed upon way of getting them or justifying them. So we kind of agree that some things are right and some things are wrong. As a society, we are very bad at actually justifying why this thing is right and this thing is wrong. We sort of appeal to just insistence. Just like you must know this is right and that is wrong, and so forth. You go to the obvious examples and try to agree on that. And different people have, you know, there are objective moral realists, there are subjective moral people, etcetera, etcetera, etcetera. Certainly for many, many people, the justification from the moral beliefs comes from some religious belief, and I think those justifications fail, 'cause I don't believe. I don't accept the moral, the religious starting point that they have. I really think that when it comes to ethics and morality, we would have a much better conversation if we started by admitting to believe in a natural universe rather than a supernatural one. And a lot of that was evidenced in my book, The Big Picture, I try to put forward exactly that idea. So I think that's probably, in thinking about ethics and morality, is probably where our current society falls the most obviously short of where I would like them to fall if everyone being a naturalist.

1:36:44.2 SC: Chris Shipton says: It seems as if humans... Sorry, it seems as humans that our knowledge of the universe is increasing, but the universe is on a path toward the state of highest entropy in the far future. Will there be a time that if there are humans we will be unable to gain new knowledge or make accurate predictions? I think the parenthesis there are the important part. There won't be humans eventually. There will be a time when there are no humans. But there is something interesting going on here. Yes, of course, entropy is increasing. And as far as we know, it's just gonna keep increasing until it sort of levels off, it asymptotes to some maximum value, at least within any observable part of the universe. Things like knowledge are temporary. Okay? There's no knowledge at the Big Bang 'cause there's no agents having any knowledge, there's no knowledge in the far, far future, 'cause there's no agents around, everything is in thermal equilibrium.

1:37:35.5 SC: It's on that journey between the Big Bang and the far, far future that agents come into existence with a property one can call knowledge of the rest of the world; some correlations between data inside themselves; memories, laws of physics, knowledge, etcetera, and what happens out there in the world. This is a temporary feature that is enabled by the fact that entropy is increasing, but it's also going to be disabled by the fact that entropy continues to increase. So the reason why that's important is because it's easy to say entropy is increasing, it's hard to say exactly the way in which entropy increases and what are all the steps along the way, and what are all the implications of that? You might remember that Scott Aaronson and I and some students and postdocs wrote a paper about the emergence and then disappearance of complexity in a closed thermodynamic system. I'm still thinking about that stuff. In fact, I was talking about it with people at SFI this last three weeks when I was there. And there's a lot to be done about the emergence of these words like knowledge and prediction as temporary features of the universe going from low entropy to high entropy. It's not something, I don't think, that is very well understood right now.

1:38:51.7 SC: Vladimir Bellick says: In your oral history interview, when talking about your high school years. You mentioned that you weren't to go to giving talks back then. I'm also not a natural at this I get similar comments: I use too many words to convey a thought and I stumble a lot. I'm currently trying to get better at speaking because I'm starting an educational YouTube channel for my business soon. Do you have any advice on how to improve at talking to an audience that might be helpful to me and any other listeners with a similar aspiration?

1:39:18.4 SC: It's an excellent question. A very, very important question. I don't have a super good advice here. I'll mention two things that are true, but I'm not sure how helpful they are. One thing is practice. Do it a lot, right? The context in which I was talking about not being good at giving talks was that I was on the speech team, speech and debate team in high school. And there's an irony in that I was on the speech team that was very bad at giving speeches. But that's how I got better at it by just doing it a lot and doing it not just thoughtlessly, but thoughtfully, mindfully. Thinking about what was working and what was not working. Look, there are plenty of people out there who can listen to you give a talk and tell you what's going right and what's going wrong, it's hard to listen to them. It's hard to take their advice to heart and really change yourself and work at changing, but that's what you could try to do. The other piece of advice, again, not necessarily very helpful is, I don't know your personal style, but there are a lot of people who are relatively fluid and articulate when talking in conversation.

1:40:33.6 SC: And then when you put them in front of a formal crowd, they become stilted and boring and unnatural and... Why is that? It's a whole another thing. Some people just are always stilted and boring, that's too bad. But again, you can work at that through practice. But some people are different levels of interestingness depending on whether it's an informal conversation or a formal presentation. If that's the case, then you can certainly just internally work at making your mode of presentation not different when you're giving a formal presentation than when you're having an informal conversation. You can think about why is it different? And I've seen people, because I hang out with journalist sometimes, I've seen examples of people being interviewed. And before the tape starts rolling, they're joking around with the interviewer and they're very clear and charming and articulate. And then as soon as they're being recorded, they stiffen up and they get all very formal and less articulate and less interesting. And that's what I was like when I was getting talks as a high school student. So that's one trick anyway, that you can think about. Think of it more as how you would speak during a conversation. Tell some jokes, be relaxed. Don't tell too many jokes, depending on how your joke-telling skills go, but that kind of mode is what you should try to think about being in.

1:41:54.5 SC: Peter Solfest says: If gravity can be derived from entropy, doesn't that mean it's an immersion property that can be ejected from our fundamental ontology? If that's the case, why is quantum gravity even necessary. Yes, if gravity can be derived from entropy, which is... That statement is a bit of exaggeration. Gravity can't be derived from entropy, but it might have something to do with entropy, there might be a derivation that uses entropy in a central way that gets you to gravity. Okay? And if that's true, that does mean it's emergent phenomenon, it does mean it can be ejected from our fundamental ontology. It doesn't mean it's not necessary. As I like to say, there's no human being in the world that lives at the level of our fundamental ontology. Right? Just the word human being doesn't exist in the level of our fundamental ontology.

1:42:43.8 SC: We live at a higher level. We live in a world where we can see certain things, where we can predict certain things, where we can interact with certain things. None of which are from our higher level of our fundamental ontology. Desk in front of me, a classic example I've used several times already in this AMA. So we would like to understand that. Just like I would like to understand how airplanes fly, I would like to understand quantum gravity, how it emerges from these lower levels. There's more to life than the most fundamental ontology we have.

1:43:13.1 SC: Brendan says: I was watching your 2015 God and cosmology debate with William Lane Craig a few weeks ago. Given the past seven years since the debate, has there been any scientific breakthroughs or experiences that you would now include in your talking points for naturalism? The short answer is no. I don't think that there's been any scientific breakthroughs or experiences. If I were to do it again, which I have no plans to do right now, but you never know, probably my specific talking points would be different just because I have changed a little bit. I've written the book, The Big Picture, since then. I think The Big Picture was after 2015. Was it? I think so, yes. So I've thought about these issues a little bit more carefully in certain ways, about the pros and cons of naturalism. I've dwelt on and talked with other people, etcetera, etcetera. So none of the specifics would be the same, just like we all change over time, but not because of any scientific breakthroughs.

1:44:10.6 SC: I mean, look, to be super duper honest, I don't think it's a close call between naturalism and supernaturalism. Naturalism and theism. I think that sometime around the 19th Century was the last time when one could really say, "Well, maybe theism, but I'm not sure." By now, it's pretty clear, so I don't expect ongoing scientific research to have any big impact on that set of points of view I have. Unless they actually are evidence for theism, which would change my mind by a lot. But I haven't seen any of that in the last seven years.

1:44:44.2 SC: Chris Murray says: The holographic principle is reminiscent of the fact that in complex analysis a holomorphic function on a disk is fully determined by its values on the boundary of the disk. Do you think this is an important connection or just a cosmetic resemblance? So the idea here, for those of you who are not complex analysis experts, is that there is a certain... So in complex analysis, what are you talking about? You have a complex number, you have the set of all complex numbers. The set of all complex numbers is kind of like the plane, the two-dimensional plane, X and Y axis. Likewise, a single complex number has two parts, it has the real part and the imaginary part. So the set of all complex numbers, topologically, it's a plane. You talk about the complex plane. And we can have a function of that plane, so it's a function of the real part and the imaginary part of where you are on the plane. And generally, we think about complex functions on the complex plane. So we map a complex number to another complex number. Okay? There's a certain subset of those functions called holomorphic.

1:45:48.8 SC: There's mathematical conditions, you can Google them, that will tell you what a holomorphic function is, and those conditions are pretty restrictive. Most functions are not holomorphic, but some are. And a nice feature of holomorphic functions is that it's so restrictive that if you just tell me, if you have some circle in the complex plane and you think about the function being defined inside the circle, that's the disk inside the circle, then just telling me what the function is on the boundary on the circle that you've drawn is enough to completely specify what the function is inside on the disk. That doesn't bear a family resemblance to holography. Right? The holographic principle in black hole physics is supposed to be that the entire interior state of the black hole can be thought of in terms of information living on the boundary, on the event horizon of the black hole.

1:46:41.0 SC: And it's not actually a feature... This feature that a higher dimensional set of things is determined by a lower dimensional set of things is true in both of those cases. But also is true much more widely. You all know a very simple example of this, namely physics. If I give you a physical situation at a moment in time, that's enough to determine what happens in the future if it's deterministic physics. If it's Newtonian physics or the Schrodinger equation or whatever, as well as in the past, you're determining a whole space time's worth, a whole four-dimensional worth of solution to an equation just from a three-dimensional slice of time amount of information. So when you have some constraint like holomorphicity or the equations of motion of physics, it's very common. It's not magical or weird to get a full extra dimension's worth of dependants out of initial information. So that's the sense in which there is a family resemblance. It's not a very close sense. The interior of black hole is not the complex plane. In fact, it's... In the macroscopic world in which we live it's three-dimensional, not two-dimensional, so it can't be exactly the same thing. Having said that, there is a slightly similar feature that is not a holomorphic function, but a related feature, which is that if you have something like gravity or electromagnetism, you have Gauss's law, that's a way of saying the following thing: If I tell you...

1:48:14.0 SC: Let's put it this way. Let's say you have a collection of charged particles. It's actually easier to visualize for electric charge than for gravity, but it also works for gravity. If I have a collection of charged particles, protons, let's say, and there's no electron, so it's just protons. And I know that these electrons, these protons rather, are in some region of space. Then what Gauss's law tells me is that if I look at the electric field on the boundary of that region, so I have some spherical boundary surrounding the surface of the sphere, surrounding what we call in math the ball, which is the interior of the spear, the statement of Gauss's Law is that I can integrate up the electric field on the sphere, the boundary, and that tells me the amount of charge inside, inside the ball.

1:49:00.5 SC: So we can figure out a lot about the distribution of charges inside, just by thinking, just by measuring the electric field on the boundary. Maybe even not just the total charge, but a little bit about the distribution of charges by looking at where the electric field is stronger or weaker on the boundary. We can't learn everything about the charge distribution inside, because if you have a charge distribution that itself is perfectly spherical, then the size of that sphere is completely irrelevant. It's gonna give you the same electric field outside. So in conventional... And again, the same thing exactly happens for gravity. So conventionally, you can learn a lot about the gravitational or electric charges inside a region by looking at the associated fields on the boundary, but not everything. This has to do with the fact that it's a long range field, a gauge field, there's symmetries, etcetera, etcetera.

1:49:52.3 SC: You would like to promote that to something like what we think of as the holographic principle. Believe me, people have thought about this. It hasn't quite turned into a rigorous, careful identification. For example, for reasons like if you have a spherically symmetric distribution then it should look the same outside. But maybe there's something there, maybe there's something that is in the connection between long range fields and boundaries, that sounds kind of holographic. On the other hand, I kind of think that that's kind of too cheap and easy, that there is something really non-local going on in gravity because of how gravity is involved with the curvature of space time that gives rise to this holographic effect. But we'll have to see. This is a very good question. You're on the right track thinking about things like this.

1:50:43.6 SC: Jase Forbes asks a priority question: If black holes' gravity cause time dilation and Hawking radiation causes the black hole to evaporate, would the time dilation seem to accelerate this evaporation from the perspective of an infalling particle? And why, if time violation approaches zero, could said particle fall into a black hole before it evaporates completely? So I think your first half and second half of questions... I'll allow you the two questions, but they're different questions. From the perspective of an infalling particle, it's actually really subtle and interesting and am not gonna claim I understand it correctly. Usually when I say I don't understand something correctly, it's because either no one understands it correctly or because someone does, but I haven't tried.

1:51:31.0 SC: This is something that I think is understandable, and I tried a little bit, but I'm still confused about what happens from the perspective of an infalling observer when you cross the black hole event horizon. And roughly speaking, we know what happens, which is that when you're far away, you see Hawking radiation. If you start falling in, okay? You will see a slightly blue shifted Hawking radiation. You're gonna see it, you're moving now toward the black hole, so the radiation you see seems to get more energetic in some sense. But if you keep falling in as you cross the event horizon you don't see anything at all. Because from your point of view, the event horizon is not a special place. So somehow you have to sort of be feeling or noticing the black hole as an object rather than being so close up that it almost becomes indistinguishable to you. Somehow that's how the vacuum of the quantum field theory works, that it looks like empty space right there at the horizon and looks like there's a radiating black hole when you're very far away. So that's the first part of the question.

1:52:31.0 SC: The second part: If time dilation approaches zero, could said particle fall into a black hole before it evaporates completely? Yes. And that's an easy one. You can do that calculation, it's a little bit subtle because when you have a black hole that doesn't evaporate, you know, the ordinary general relativity black hole like you're reading about in my textbook or whatever, there's the even horizon. And the event horizon is well-defined, we know where it is, and it's a global property. The event horizon is the point of no return. It's the point past which if you go inside, you can never come out.

1:53:07.2 SC: If you let the black hole evaporate, in some sense everything that goes in comes out, okay? We don't understand that sense completely, but the same amount of energy, the same matter that goes in comes out. Ideally, we hope, the same amount of information. So there is no event horizon, really, for an evaporating black hole, so that complicates things. What can you do? What you can do is you can define an apparent horizon, there is a way, without making reference to the future evaporation of the black hole, there's a way of saying, roughly speaking, the radius of the black hole and a short shield metric, that a non-charged on spinning black hole is a known quantity: 2GM. Where 2 is 2, G is Newton's constant, M is the mass as the black hole. So you could just draw a sphere at a radius of 2GM and say that's apparently where the horizon is now, okay?

1:53:58.2 SC: And in that sense, that's where the Hawking radiation is coming from. And yes, particles seem to pass by that apparent horizon no problem long before the black hole evaporates. When you think about it, it doesn't take long to fall into a black hole, but it takes a huge amount of time for black holes to evaporate. So that's what you would expect. Kristoff Pironski says: I still don't get how creativity, invention, discovery and eureka moments are all possible in the fully deterministic block universe. They all seem like theater in this context. What am I missing? Well, I guess you're missing something subtle in the definition of creativity, invention and discovery. You seem to be smuggling in to the definition of these human-sounding words something that is intrinsically non-physical or non-deterministic somehow. But look, you can recognize creativity because you can look at someone's work and say, "Oh, that's very creative. You made a discovery. You made an invention."

1:55:01.6 SC: And then God shows up and God says, "You know what? The laws of physics are deterministic." Why would that change your opinion about whether or not that work of art or science was a creative or a discovery or whatever. Right? This is how higher level emerging phenomena work. At the level of the core theory of physics, there are no fundamental words called creativity, invention or discovery, there's just the quantum state of the universe evolving forward according to the Schrodinger equation. Exactly as for Lacplace's Demon, in a classical context, Laplace's Demon knows where all the particles are and where they're going. There's no such thing as temperature, pressure, entropy, any of those things, 'cause you know where all the particles are. It's only when you have incomplete information at the higher level that it becomes useful and interesting to talk about temperature and pressure and so forth. Likewise, it's only when you're talking about the human level, not the fully deterministic, fundamental physics level, that it's useful to talk about creativity, invention, discovery, etcetera. Those levels, the best descriptions we have or will ever have, are not deterministic.

1:56:05.9 SC: You're not gonna get a deterministic theory of human beings that involves only knowable things about those human beings, and that's okay. Just like flipping a coin seems to be non-deterministic to us even though we think that if we knew the exact micro state of the coin and your thumb and whatever, you could figure it out. You can predict exactly what was gonna happen. Owen asks: Just wondering why anyone at all accepts the post-Humian commonplace that you can't or shouldn't derive an ought from an is. If oughts aren't to be derived from is' how should they be derived? Well, it depends on your attitude towards oughts. The fact that you can't derive oughts from is', is just logic. There's literally nothing other than that. I can write down a set of axioms or postulates or premises, all of which say this is true, this is true, this is true.

1:57:02.1 SC: Conclusion, this ought to be true. You can't do that. It's just literally impossible simply as a matter of logic. You can do it if you smuggle in to your premises some ought, some statement about, "Well, that ought not to be true. That sounds bad, let's not do it." Or you can... Usually the way that people pretend to get around the ought/is a problem as they fake language, they prevaricate or equivocate, I should say, about the meanings of words. You can say, it is true that I don't want this to be happening. Therefore, I should not let it happen. Therefore, I ought not to let it happen. But you see, you're sort of just cheating a natural language, you're not actually deriving anything sensible. So if you wanna know where the oughts come from. I mean, strictly speaking, they're not derived. That's the answer.

1:57:48.0 SC: There is no moral realism, there is no objective fact about what ought to be done. What you can do, which I advocate doing is saying that, okay, there are subjective claims that I can make as a human being. I have things that I want to be true. I have ways that I want people to behave, etcetera. And I'm going to... In concert with other people, talking to them and thinking about what they have to say, I'm going to propose that we use the following regulations as moral guidelines. You're not driving them from anything at all, you're postulating them on the basis of what you want to be true, that's what moral constructivism is all about. And I think that's the truth, that's the way the world actually works. Again, if you think of what people actually do, it's that. They then justify it in all sorts of fancy philosophical ways, but really they have some feeling about how they would like things to be and then they justify it, but that's not really a derivation.

1:58:46.0 SC: Fabian Rose Dolan says: What is your relationship to visual art? Paintings, digital or not. Do you paint? Have you ever tried painting? Do you have any favorite artists or style? I'm a big fan of visual arts. I have art books lying around the house, etcetera. Not an expert, not super knowledgeable. When I was a... Here's something you might not know, when I was a postdoc at the Institute for Theoretical Physics at UC Santa Barbara, one of the famous physicists there is Gary Horowitz, string theorist, gravity person. And his wife Kareen was the Education Director for the UC Santa Barbara Art Museum.

1:59:23.2 SC: So she ran a program where undergraduate students could work as docents at the art museum. They could give tours and explain things to people. And so even though I was not an undergraduate student, I was a postdoc, I signed up to be a docent with Kareen Horwitz, and she loved having me because most of the young undergraduate docents were women, which they actually were way ahead of me in knowing about art, but I was way ahead of them because I had a very deep voice. And the kids who would come on elementary school, kindergarten trips to the art museum, were much more willing to listen to me because I had a deeper sounding voice. So I commanded respect among the 10-year-olds who would come to the art museum, even though I knew less about what I was talking about.

2:00:06.6 SC: You didn't have to know that much to be a docent, just give entertaining and mostly truthful exposition of what was going on. All of which is to say, I like art quite a bit. I'm a big fan, even though not perfectly knowledgeable. I have even tried to paint. I have even painted. It's been a long time since I've actually actively done it, so I can't claim that I am a painter. But my formative experience was going to a modern art museum, having the reaction that many people have looking at these very abstract kind of colorfield paintings and saying, "Well, I can do that." And then, but because I'm me, I also said, "Well look, if I'm gonna say I can do that, that's meaningless unless I do it. Right? Let's actually do it. I bought an easel and some canvases and some acrylics. Acrylics are just easier to deal with than oils if you're an amateur, and then you paint. And you realize, "Oh, guess what? I can't do that."

2:00:57.5 SC: It's actually harder than it looks to achieve the effect that are really good abstract artist achieves. So my respect for the art form went up a lot. I wish I did more painting. We don't quite have the sort of space in the house right now. Maybe I will when I get to Baltimore. Maybe we'll fire up the old painting studio again. Who knows? You never know. And then I can sell them as NFTs or something like that, and retire, that would be awesome. James Dan Caro says: Do magnetic monopoles actually exist? And is it possible for us to create them in a particle accelerator or some other way? How much energy would it take to create one, if this is even a possibility? We don't know whether monopoles exist. They could exist theoretically. By which I mean, we can construct physical theories that are compatible with all the physics that we know in the world and allow for the existence of magnetic monopoles. In fact, famously, grand unified field theories generally predict monopoles. A grand unified field theory is one that unifies not just electricity and magnetism with the weak force, like we have in the electroweak theory, but also with the strong nuclear force.

2:02:07.9 SC: Grand Unification has nothing to do with gravity. I know that the terminology can be a bit hard to follow sometimes, but literally the strictly speaking defined word within the physics community for grand unified theory is strong, weak and electromagnetism combined together. Theories along these lines were proposed, especially in 1970s. Sheldon Glashow and Howard Georgi started that trend, but many other people propose different models. And there's a really interesting mathematical fact: The whole point of a grand unified theory is that these theories that we have strong, weak, electromagnetic are gauge theories, so they're based on some symmetry group. And why do you see separate forces? Well, because the symmetry has been broken, that's why you see separate electromagnetic and weak forces because the symmetry between them was broken by the Higgs field. So grand unification imagines a bigger symmetry group, but still what we call a simple group. Usually not always, and simple in this case is not just a feeling that you have, it's the technical term in mathematics. A simple group is a particular type of continuous symmetry group. So if you combine the SU3, SU2 and U1 of the standard model of particle physics into a single simple symmetry group, and then you break that symmetry down to what we observe, SU3=SU2=SU1, then you inevitably get magnetic monopoles.

2:03:35.1 SC: That's kind of cool, that's kind of a cool result. You cannot... It's a predictive thing, you can not wiggle out of it. Of course, you can wiggle out of it by making a not simple group or something like that, but there is that conditional statement. So that's a remarkable statement, and then it also comes with a prediction, namely that the mass of the magnetic monopole particles should be of order the energy scale of which grand unification happens. So if you think about protons and neutrons, limited energy scale of about one GEV, one billion electron volts. Higgs boson, top quark are 100 GEV or a little bit more. So 10 to the two GEV. Grand unification is probably up at 10 to the 16 GEV. Way, way higher than we're looking at right now in particle accelerators. The Large Hadron Collider is at 10-T-E-V, that is is a 10,000 GEV.

2:04:26.7 SC: 10 to the four G. Still way short of 10 to the 16. So maybe you say, "Well, okay, you're predicting magnetic monopoles, but I can never make them. Right? So who cares?" Well, if you're careful, my Caltech colleague John Preskill and others pointed out that in the early universe where the energies were very high, you should make a lot of magnetic monopoles. And in fact, you can predict using a mechanism called the Kibble mechanism, after British physicist Tom Kibble, you can predict a minimum number of magnetic monopoles that you had better make. And it turns out to be way bigger than we're allowed to have. We would have easily noticed this. The overwhelming majority of matter in the universe would be in the form of magnetic monopoles if this story were true. So people caught on to this in the late 1970s. After grand unification came along, people predict there should be monopoles. People predicted that they should be abundant, and they're not. What's going on? And secretly, that fact, that puzzle was the primary motivation for Alan Guth pursuing the idea of the inflationary universe scenario. These days, magnetic monopoles are less popular. Well, I should say grand unified theories are less popular. They're not unpopular, but they did make one other, besides monopoles, they made one other prediction, which is that the proton should not be perfectly stable, it should decay.

2:05:50.0 SC: Sadly, there's wiggle room in exactly how fast it should decay, but for most of the plausible parameter space, again, we should have seen them decay. Most grand unified theories in their simplest forms predict we should have already seen proton decay. We haven't, so grand unified theories have therefore lowered in their Bayesian credence by a little bit. And therefore, the motivation of getting rid of the monopoles, the so-called 'cosmological monopole problem' is less now than it used to be. And so when people talk about inflation now, they talk about the horizon problem, the flatness problem, roughly speaking the smoothness of the early universe, but the monopole problem is still there if you wanna... Because grand unification is still possible, so that's a good motivation for inflation. Roughly, inflation can inflate away the monopole, you just have monopoles, but there's less than one per observable volume of the universe, that's why we've never seen them.

2:06:41.4 SC: David Pool asks a priority question: It's been stated that early proponents of the Copenhagen interpretation were not interested in what was actually happening during the coherence with the statement 'shut up and calculate.' However, with the many worlds interpretation, it seems to me you are equally dismissive when you say the world just evolves according to the Schrodinger equation. What does this actually mean? How does, say, a 60% probability evolve into the real world that we observe? I don't think I'm dismissive. [chuckle]

2:07:06.6 SC: I think I have a theory that says that the world evolves according to the Schrodinger equation. You can be dismissive of questions, you can think a question is not interesting and dismiss it, but this just a proposed theory of how the physical world works. You can't be dismissive of it, you can agree with or disagree with it or assign in credence to it. So my theory of the fundamental dynamics of the physical world is, it evolves according to the Schrodinger equation. What does it actually mean? It means exactly that, it doesn't mean anything different. It means that there is a state that is an element of a Hilbert space, it evolves according to an equation that was written down by Professor Schrodinger. You say, how does a 60% probability evolve into the real world? Well, you're already not being a good Everettian by saying, how does a 60% probability evolve. There's a wave function that evolves, not a probability. What you need to do is follow the evolution of the wave function. Then ask, why does it appear to us in the world as if quantum mechanical events happen with probabilities rather than deterministically?

2:08:07.5 SC: And the answer there is, as we discussed earlier, because there are different branches on which different things happen. So there are different definite experimental outcomes, but those branches are not created equally. They have different amplitudes associated with them. And you can ask, there's a much longer conversation, again, I did write a book about this that you're welcome to check out, but you can ask if I'm an agent, if I'm a person in one of these branches of the wave function, and I don't know whether I'm gonna be on the spin-up branch for the spin down branch, is there a way to assign probabilities that makes sense? And you need to define what it means to make sense and so forth. One of the criteria is that it's consistent over time, so things that people are doing over there in their experimental laboratories on Alpha Centauri are not affecting the probabilities that I would predict here on earth. And therefore, what happens is that you get the right answer.

2:09:03.5 SC: The answer is the only way to assign probabilities in this world of being on one branch or the other is what we call the born rule; the probability is the wave function squared. So it's not a probability that is built into frequencies in the world. It's a probability that is subjective, that comes out of our trying our best to figure out where we are in the world, but it does get you the right answer. Weston Mandell says: How do you perceive, for lack of better words, the beginning of everything and anything? Given all the amazing experience and knowledge you possess, both philosophical and technical, I would just simply love to hear how you may describe or conceptualize that which is understandably beyond human comprehension. Is the beginning of something a false concept when you trace it back to the beginning, to the series of events that are responsible for its existence, all the way back to beyond the beginning of the universe and time only as we know it. So as usual, there's a few things going on here in this question. I am someone who believes...

2:10:00.5 SC: And again, I'll just say it again because I always get accused of dismissing things or thinking that things are certain, even though I'm trying to assign probabilities. This is what I think at a certain level of credence. I could be wrong. But with all that said, I think that the laws of physics don't have a fundamental direction of time built into them. So I don't think that we have to think about the current state of the world as originating in the beginning then flowing into the current state. What we should think about is the whole history of the world, including the beginning and now and the future, obeying the laws of physics in some way. Now, we don't know, and this is something that it's not just, I don't know for sure, but I have strong opinions. We truly don't know with any strong confidence whether the universe had a beginning or not, that is to say whether a physical clock measuring proper time that you extended back into the past would reach a point where there was no past earlier than that, or whether it could continue forever.

2:11:05.9 SC: We don't know that. There are perfectly respectable models that have... That go either way. That have either property. Now, but you're completely right about human comprehension, and there's a good news, bad news situation here. The bad news is that the kinds of things happening at the beginning of our universe, let's call it the Big Bang, the beginning, whether or not it really was, at the beginning of our comprehension of the universe. Those things are very far removed from human experience. It's a different kind of thing happening, it's not something which our experience growing up as people in the world has equipped us to talk about, much less understand, okay? And in fact, as a practical matter, that lack of straightforward, comprehensibility and discussion, for that matter, gets in the way.

2:12:03.6 SC: It makes us make statements that upon further careful reflection just aren't very sensible. And we sometimes, as mere finite human beings, we lapse into our everyday way of thinking about the world, even in regimes where we shouldn't. Okay? That's the bad news. The good news is, man, if you're at all fair about it, the remarkable thing is not our lack of comprehension, but the presence of our comprehension. The remarkable thing is how much of the world we have come to understand. I have no idea what fraction of it is, so I have no idea how much of understanding the world we have versus how much remains yet to be discovered, so I'm making not a relative statement about the fraction that we know, but just a list of things that we know is to me utterly amazing.

2:12:53.0 SC: When you think about relativity and quantum mechanics and the Big Bang, not to mention Darwinian evolution and molecular biology and sociology and psychology, etcetera, we've learned an enormous amount, just in a couple hundred years. We live in a 14 billion-year-old universe. And in 200 years... Maybe let's give it 500 or 5000 years, it doesn't matter. It's a short period of time under which we've really been carefully using the scientific method thinking about the universe. And not only do we understand a lot of it, we understand it in terms of highly non-intuitive things, like relativity, the Big Bang, quantum mechanics, most of all. But we get it, we're able to do it.

2:13:31.7 SC: We use math, we use philosophy, we use rigor, we use data, we use Bayesian updating, all that stuff. And using these tools as leverage, we are able to develop enormous amounts of understanding and best of all, when things are really going well, not only can we understand things, but we can know where our understanding fails. We can understand that I can extrapolate beyond a certain point, but it's just guessing after that. We're not very, very certain. And that's why I can say with confidence that we are not confident about whether the universe had a beginning. We have data, we have empirical phenomenological information about what the universe was doing a minute after the Big Bang. The Big Bang... That would be there of general relativity were right, which it's not etcetera, et cetera. But hopefully, you know what I mean. But that's an enormous distance from our everyday experience, and we understand what the universe was doing. I've written papers about this myself. We understand the expansion rate in the density of the universe a minute after the Big Bang; the temperature and to a very strong level the composition of the universe. And we don't understand what it was doing a micro-second after the Big Bang. We just don't.

2:14:46.0 SC: We talk about it all the time as working cosmologists, but we know that our knowledge has given out, which to me is as impressive is the fact that we have that knowledge in the first place. So what I suspect, and now let me just get a little more poetic around it, I'm trying to be a good scientist there in saying we don't know what happened at the beginning. I don't think that what happened the beginning is beyond human comprehension. I think it's different than our everyday experience. Sure. But I don't think that it is ineffable, I do not think that it is beyond our grasp in principle. This is like when people ask me, in 50 years, what is the most amazing thing you think will happen? My favorite prediction is we'll understand what happened at the beginning of the universe. I could be wrong about that footnote as usual.

2:15:33.3 SC: But that's my feeling, 'cause I don't see any obstacles to doing it, except that it's hard. Except that we don't have any direct information, because the information about whatever happened at the very beginning of the universe is sort of transformed over time, rubbed out by either inflation or the microwave background or whatever. It's hard to get direct empirical data, but it's not impossible to build a theory that will be just so compelling and clear that I will make a statement about what happened at the beginning, and everyone going, "Yeah, it's probably true. We're not sure 'cause we can't see it, but that seems to be the right way to go."

2:16:07.2 SC: That to me is the miracle of science, that the world obeys patterns, and we have the ability to discern these patterns even when these patterns are way outside our comfort zone, way outside our everyday experience. That's the power of math and logic and philosophy and science and so forth. Tools of thinking about the nature of reality. And then it's our human duty to accommodate our understanding to those very alien terms, that's why quantum mechanics is hard, because quantum mechanics talks about the world in a way that is fundamentally different than our everyday experience. And that's why 100 years later, we don't agree about what quantum mechanics says, 'cause different human beings have different levels of cope when they're thinking about quantum mechanics. Maybe some are too willing to be radical, some are not willing enough. We're not sure yet. That's why we're talking about it, but I think we are making progress. I'm optimistic that it will happen. Michael Blau says: Your recent episode with Andrew Leigh in episode 19 with Tyler Cohen, you each bring up the question of evaluating humanities current decisions in light of their impact on future generations. And so I'm editing a little bit, but you already get the point, right?

2:17:16.8 SC: How should we evaluate humanity's current decisions in light of future generations? I'm not done talking about this on the podcast. I think this is a very crucial question. And I see strongly the arguments for two opposite lines of reasoning. One line of reasoning is basically what Andrew and Tyler would both push, namely human beings in the future are just as real, count just as much as human beings now. You would feel bad if you knew that some mild decision you made now had terrible, awful consequences for the whole future of humanity. And you would rightfully feel bad, you would think you're doing something wrong. And if you try to make that understanding kind of rigorous and think about what's going on, you might say, "Look, there's gonna be a lot of people in the future, and tiny decisions we make now can have enormous leverage over what's going to happen to them in the future. Therefore, we should take that into account at a very, very high level of concern." I get that line of reasoning. Here's another line of reasoning: We're terrible at predicting the consequences of our actions over the very, very long term. There are time scales... You can't ignore the time scales in the problem. Okay?

2:18:32.0 SC: There are things we do that have pretty clear implications on the time scale of a year or 10 years. If you think about what people might have said 100 years ago, trying to make predictions for what life would be like now. It's hard to imagine they would have done a very good job. Right? And if anything, the pace of change is accelerating. I think it's kind of not hard to imagine that we're bad now at predicting what the world will be like 100 years in the future. And a 100 years is nothing. We could imagine humanity extending 1000, a million, a billion years into the future. A billion is hard, we would evolve into something else, but you know what I mean? There might be something going down the line. So my point is that even if I care a lot about those people, I have no idea how to make their lives better. I think that's the humble realistic reading of the situation. So it's not that I wouldn't care about them, it's just that I try to be clear-eyed about what I can do about it, which isn't that much. Whereas the decisions I make might have very predictable consequences on the year or 10-year time scale. So to me, it makes perfect sense to, for all intents and purposes, discount the value of lives in the future, just not because they're not important, just 'cause I don't know what they're gonna be like, and therefore, I can't judge what to do now on the basis of that kind of analysis.

2:19:57.9 SC: Ford Prefect, probably a pseudonym, says: In one of the AMAs you described how a big chunk of your work comprises of, among others, stretches of time dedicated to just thinking. Do you ever get sad, frustrated or otherwise uneasy when you don't seem to progress in any obvious way during such sessions, especially for a longer period of time? Have you ever felt that you've wasted the time, and so how do you deal with that? If not, why do you think that's the case? Excuse me. Yeah, there's long periods where progress is not only stagnant or maybe even negative, maybe you realize that something you thought was true or you thought that you had done, succeeded in achieving, goes away. That absolutely happens all the time. I think you're not thinking about that, mostly you're thinking about sort of the time when you're just mulling or just sort of musing over what's going on, hoping for a breakthrough or whatever, those are absolutely part of the...

2:20:50.4 SC: That's part of the deal. When I was at SFI, I was joking to someone, "How do you ever get work done around here? There's too many people that are interesting to talk to." And the answer, correct answer was, "That's part of the work, that counts. You never know when that little conversation might spark something." It's less obvious than when you're just sitting silently by yourself in your own office, but still your brain can be working and moving and you can't skip that part. And it's weird for people who have different kinds of jobs where work is a little bit more evident, a little bit more manifest in the world, you're lifting something up or you're driving somewhere or whatever. If you're a writer or an artist or a scientist, there's a lot of time that is spent sitting and not doing anything. And there are things happening inside your brain that are not evident to the outside world. How do you deal with it when it doesn't work?

2:21:42.7 SC: You asked the question, do you ever feel you wasted the time? Look, you absolutely can waste time, you can waste time by thinking that something is correct and trying to build on it, or by thinking that you have a strategy for attacking a problem that turns out not to pay off. And you can waste time by playing video games or watching TV or whatever. So I'm gonna out playing video games or watching TV or eating a good meal as important self-care parts of the routine, so that's not wasting time. But the thing about the intellectual wasting time is you don't know it ahead of time. You don't know what kind of directions are gonna pay off. You can be a really great scientist and just to have sixth sense about what is going to get you in the right direction. Some people seem to have a real genius for choosing good problems and good strategies, but no one is perfect, no one gets it right all the time. So I think I don't have that much trouble living with the idea that the observable part of progress is highly sporadic and non-linear and unpredictable.

2:22:46.3 SC: Right? You're working in your work and you're working. It looks like nothing's getting done and then you make a breakthrough, but really all that previous work was necessary to get to the break through, so even if sometimes the time is wasted, I don't know it ahead of time, so I'm not sad about doing that. I just take that as part of the job. Jim Murphy says: Do you have any cute stories about meeting your wife or maybe one of your first dates? Yeah, we have a really cute story about meeting. It was back in 2006, I want to say.

2:23:17.0 SC: Yeah, it was 2006, so I was living in Chicago, but I was already sort of knowing that I was gonna to be moving to Los Angeles. Jennifer was living in Washington, DC as a freelance writer, part-time working for the American Physical Society, writing for them. And she had just come out with her first book, Black Bodies and Quantum Cats. It's a great book that I can recommend you check out. And if you think back then, 2006, this was still the early days of the modern social media landscape. There's no Twitter, Facebook, etcetera, but there were blogs, remember blogs? I still have one, occasionally contribute to it. But the idea, like just... I will tell you this. My publisher for my new book, The Biggest Ideas in the Universe, full of equations, did ask in a somewhat embarrassed tone of voice, are you on TikTok? The kids today like TikTok, and they were wondering whether or not there's anything I can do on TikTok to advertise this book. That's what you would get today. And the answer is, no, I'm not really on TikTok. And I don't think that it would help with this book. We'll see, maybe I'll have a genius idea.

2:24:23.7 SC: But at the time, in 2006, if you wrote a new book, especially as a brand new author, you'd be told to start a blog. So Jennifer started a blog that was cocktail party physics. I think the website still exists, and you can check out all the old blog posts. And again, back then, there weren't that many blogs, so especially physics blogs in particular, there was a very small number of them. You know, single digits, maybe it was double digits by them, but it was not a large number. So we were a tight knit group, and I emailed her saying, "Welcome to the blogosphere. Here's some other blogs to check out. Some tips, etcetera, etcetera." And we email back and forth and realized we were gonna be at the same physics conference in a couple of weeks. We arranged to meet up and that was that. Now we're married. I'm gonna skip some details in between, but that is how we met, through our blogs, through reading each other's blogs. And when we did get married, our marriage was announced in Nature. There was a little blurb in the beginning of the pages of Nature saying two physics bloggers get married. That's cute. Right? I think it's cute. I have different opinions on what is cute than other people.

2:25:27.4 SC: Cooper says: Do you agree with the idea that if you find life on Europa or Enceladus, I always say Insetilis, but it's Enceladus, then Bayesian reasoning would conclude that life is highly likely to be founded most star systems. Not precisely, Cooper, you know better than that, because Bayesian reasoning has two parts: It has priors and it has likelihood functions. And when you get new data, like there's life on Europa or Enceladus, then you use a likelihood function: What is the probability that life would exist on Europa, if life were everywhere versus a life were nowhere? And then you multiply it by the prior. So surely, if you find life on somewhere in the solar system, the likelihood of finding that is way bigger in a world where life is ubiquitous than in a world where life is rare. Or I should say universe or a galaxy where life is rare. So absolutely, your credence that life should be frequent in the universe should go up substantially. But what was it before? What was it before you had that measurement?

2:26:35.0 SC: If you had a prior that the probability of life was ubiquitous in the universe is 10 to the -100, then finding life on Europa is not gonna change that by that much. Now, I don't have a prior that it is nearly that tiny. So in practice, I think that finding life on Europa or Enceladus does give us a very good reason to believe that life is, maybe not most star systems, but life is frequent in the star systems that have reasonable kind of planets that given my priors, that would be my conclusion. But I can't blame just Bayesian reasoning on that or give credit to Bayesian reasoning, I have to tell you what my priors are to draw that conclusion. John Shoning also asks a Bayesian question: To be a good informal Bayesian in life, is it possible to replace choosing a prior with another Bayesian sub-problem, pushing the choice of prior further up the stack until you reach a point closer to the edge of the system. I mean, roughly, I think, no, is the right answer. You can sort of trick yourself into thinking, you can fake it, but really when people talk about priors, they talk about your current credence, that's really what you mean.

2:27:41.4 SC: What is a prior? You're not the born. Well, you're not conceived, you're a little fetus having credences for different propositions about factual statements about the world, right? You develop them over time. But we're not really talking about development in time, we're talking about intellectual development, but the point is priors are starting points. They're not finishing points. You can argue for them, but when you're arguing for them, really what you're doing is relating one prior to another. You're saying is that really, is the prior you claim... Let's say, I say I have a prior that life in the galaxy is very, very, very rare, but I also claim I have a prior that the chemistry on different planets is all the same as the chemistry in the solar system, and there are a huge number of planets, and that given the chemistry of life on a planet, it's pretty easy to make life. Then that's an inconsistent set of priors, and therefore, I can change my priors because I'm not being internally coherent. But I'm just at some point allowed to pick whatever I want. I think that the goal of justifying priors in some absolute foundational sense is not the right goal to have.

2:28:50.2 SC: We human beings are not disembodied, logical reasoners. We're part of the world. We have pictures of what makes sense to us and what doesn't make sense to us, and that's where we get our priors from, and that's okay. That's not a mistake. That's not a bug. It's a feature of how the system works. Russ Dill says: In your Podcast with Michael Dine there was a brief discussion of ruling out physics that predicts the universe would decay to a lower energy state with some reasonable probability. Is vacuum decay actually a problem with respect to the many worlds interpretation? Wouldn't we just be able to ignore any branches of the wave function where vacuum decay occurs so long as there's a non-zero probability that branches still exist where it has not occurred. So this is just... Maybe you know this, Rus, but this is just a quantum suicide experiment, right? You're asking yourself if I have some quantum event, which is set up in such a way that on one branch of the wave function I instantly die painlessly not knowing even what happened.

2:29:44.2 SC: On the other branch of the function, I continue to live. That is literally an implementation of this vacuum decay scenario, and there's an argument that says, look, on the branches where you don't exist, you don't care. You have no feelings, you're not sad, you're gone. The only caring that is involved with you is on the branches where you exist, and therefore, why is this bad? Why should you feel bad about this? But you kind of should be suspicious about these words from the start because already you've made a huge classic mistake in many worlds analysis, you're talking about you as if you exist on more than one branch at once. You're saying there's the you on this branch, the you on the other branch. Those are separate people. It's not that there's a you that exists and you that doesn't exist, it's that there's a person who has lived and a person who's died. Those persons are both sharing a past you that is a feature that is different in Everettian logic than in the usual single world way of thinking about the world. But they're different people. They're like identical twins.

2:30:46.8 SC: No one ever says, "It's okay if I kill this one identical twin, because they still in the other denial twin that's living." They're different people. It's exactly the same for these kind of quantum suicide vacuum decay experiments. The point is that right now, I have value in continuing to exist. I would be sad now if I thought that I was gonna die in a minute, even if that death was completely painless and even if after death, I didn't feel anything. I'm sad now about that future prospect. And my claim is, you should be sad in exactly the same way if your quantum descendants on all the different branches of the wave function are gonna die, exactly that amount of sadness. Maybe not the same sadness as if all of them are gonna die, but there's still some sadness there. So I think it does matter. I don't think you just ignore the branches on which you don't exist anymore than you ignore a future in which you don't exist, which after all, if you go far enough in the future, is all the futures. You will not exist in them.

2:31:47.0 SC: Josh Bower asks: On what basis does one choose a meta-ethical framework. In the vein of can't get an ought from an is, logic is out and it seems like the only foundation comes down to personal preference. But if that's the case, why philosophers debate moral frameworks? Is it my preference is better than your preference, not just begging the question of what better means... Sorry, is my preference is better than your preference not just begging the question of what better means, and is there any hope of finding a framework that can be agreed upon across culture if it's all down to preference.

2:32:16.1 SC: So I think that, again, my analysis of how you should build a moral framework is more or less what people actually do. The statement is there's no claim that is very effectual to the point of saying, my preference is better than your preference without, as you say, knowing what better means. But you can say, here's what my preference is. And there's two things, two places to go from there: One is, as you said earlier, preferences are often not internally coherent, okay? So there's the whole process of taking a list of preferences, each of which seems perfectly plausible, and systematizing them and saying, "Okay, what is the general principle from which these preferences might grow?" That's how you get things like utilitarianism or deontology or virtue ethics. It depends on what your preferences are.

2:33:05.2 SC: You can actually land on an ethical system that says my preference is the most happiness for the most people. And then you try to say, well, what does that mean? Right? What does happiness mean? How do I add it up? How do I make it the most? What kind of people count? All those complicated questions come out of that. And then the other aspect is you talk to people, you realize you're not the only person in the world, maybe other people's preferences are different, and there's two things: One is that you can shape each other's preferences, you can give a sales pitch saying, "Look, if you think that that's important, you should also think this is important." That actually happens in the world, that is not some weird mistake, that is how things work.

2:33:45.6 SC: And the other thing is you can disagree, there could be people who will just fundamentally disagree. And this dream of imagining the correct moral framework in which everyone agrees that it's right and obeys it, is entirely implausible in my point of view. And that's why I think it's very important to have political social structures that allow for disagreement, where people can accept that they disagree on some things, agree to agree on other things, and on the basis of what they agree on, build a society in which they can work with people with which they disagree about some things. Sometimes the disagreements will be so large that you can't live with them, and that's when you throw them in jail or go to war or run away or whatever it is you have to do. Again, as you see from all the examples, these are all things that really do happen in the world, it's not just some hopeless mess. It's how life has lived, and what I'm really advocating is not a change in how life is lived, but an acknowledgement that that's how life is lived rather than inventing false goals of having perfect agreement, perfect foundational establishment of the moral rules or whatever you might hope to get.

2:35:00.0 SC: Oleg Ravinski says: If you had to pick a philosopher living or otherwise to have a long conversation with, who would that be and why? So I'm not sure what say you about this. So the answer is, I don't know. That's a short answer. I don't know. I don't have an answer to this. The reason why I chose to answer the question... I'm trying to do this without dismissing the question, but I wanna indicate that this is not my kind of question to which I have good answers. Okay? And maybe it's interesting why I don't have good answers to this question. And the cheap and easy way to say it is that I don't like heroes, I don't like hero worship. And I know that you didn't it mention here. I'm not trying to pick on you here, Oleg, but the kind of idea that there are great people, great men, great women, whatever, who you would really like to talk to that would change your life. I just don't like that whole idea. I like ideas, right?

2:35:54.8 SC: And I think that of the people who I've known there have been really good ideas that a lot of different people have had. Now, of course, some people seem to be better at having good ideas than others, there is no rule that says that all people are equally interesting or good to talk to. But the point is, I just don't conceptualize what I want to do as I would love to talk to this person. That's just not my goal in life. I'd love to talk about these ideas with people who are interested in it and have interesting things to say about it. And that'll be different for all sorts of ideas. So I'm sort of wimping out of answering the question, but I'm trying to explain why I'm wimping out.

2:36:36.4 SC: I just don't have a list of people who I'd really like to talk to. I'm reminded of the story, which might be completely anecdotal or even completely fake, but apparently Marcel Proust, the great French writer, and James Joyce, the great Irish writer, once shared a cab, or they shared to ride anyway, and there was someone else in the cab. And the other person, the onlooker was asked like, what did they talk about, the great minds? And the answer was, they were silent the whole ride. They didn't have anything to say to each other. Just because a person has great ideas or is accomplished or moral or whatever, doesn't mean they're a great person to talk to always.

2:37:19.2 SC: And vice versa, there can be charming conversationalist who are not necessarily gonna be building the next great scientific theory or technological advance, so I'm just a pluralist about ideas and experiences and people and all those things. And I know that even some of the smartest and best people in the world have their flaws. So again, I don't... I'm not so silly as to think that I wanna talk to every person equally, but I don't have a list of top five that I would really just be dying to talk to. I'm sorry.

2:37:47.9 SC: G. Clune says: I watched a video with you on the Institute of Art and Ideas player in a discussion with Roger Penrose, where you said there are people in our past who think we are in their past. The time runs in the upside direction for them as it does for us. Could you elaborate more on that idea? It's very difficult to wrap one's head around this concept. I'm not gonna say too much about it, 'cause I think that some people here listening have heard me talk about it a lot, but it's the whole subject of my book From Eternity to Here, if you wanna take that far into it. The crucial thing is... Two crucial things: One is that I think that the arrow of time, which defines the difference between past and future, is entirely down to entropy increasing over time.

2:38:29.7 SC: Entropy used to be lower in the past, it will be higher in the future. And within our observable universe, entropy has just been increasing. So everyone in our observable universe agrees on the same direction of time. The second thing is there could be more to life than the observable universe, and so this is an outgrowth of a model that I proposed with Jennifer Chen back in 2004, a cosmology model where there are baby universes. So there's individual small pockets of universe, small compared to the whole thing, they're still very, very big, pockets of universe that have a low entropy end and a high entropy end. And the collection of all of these takes the form of... There's a moment of time where the entropy is as low as it ever gets.

2:39:22.2 SC: It doesn't mean it's low, that's the great thing about our model. It doesn't mean it's low. It's just lower than it is at other times. Okay? It's a relative measure. And on one side of time, you have these baby universes being created with low entropy and then increasing in entropy away from that middle moment. And on the other side of time, you also have baby universes been created with low entropy and growing with entropy in the direction away from that middle moment. So there's a crossover moment in which the arrow of time goes away from it in both directions. So therefore, oppositely oriented on different sides of that moment. If you hear noises in the background, I have a big box that Caliban just jumped into. So there's a kid running around in the box, I think is Caliban... Let me check.

2:40:10.9 SC: Oh, I was wrong, it's Ariel. She's jumping around in the box. Caliban is more of the box jumper, but two kitties, you never know. Anyway, I hope that explained that. The point is, the thing that saves you from any conceptual worries here is that the people for whom we are in their past are not only really, really, really, really far in our past, but so far that there's no connection, there's no communication, there's no way of talking to them that would get you in trouble. Okay. Franklin Merrick says, I would love to know how your thoughts on the cosmic censorship hypothesis... I would love to know your thoughts on the cosmic censorship hypothesis and naked singularities. Do you think there is a way to get a black hole super extremal?

2:40:54.0 SC: Roughly speaking, no. So the cosmic censorship hypothesis, which goes back to former Mindscape guest, Roger Penrose, though he invented it long before he was on the podcast, basically says that there are singularities in nature, but they're hidden behind event horizons, that's what we think is true for ordinary black holes. Right? And as far as we know from numerical simulations and analytic investigations of general relativity, this is almost true, but not quite. So you can actually show, there was great work done by Matthew Choptuik, for example, that if you pick your initial conditions with infinitely precise specification of where you start, you can get a naked singularity.

2:41:36.6 SC: Strictly speaking, by the rules of the game, the cosmic censorship conjecture is not true. And so I think... I'm not gonna remember the details of this, but Kip Thorne has a bunch of bets with Steven Hawking and other people. And I think that one of their bets was about cosmic censorship, and I think that... I forget who was is on what side, but they conceded the bet anyway because of this work by Choptuik. I think Hawking conceded the bet. I think he was wrong about this one.

2:42:01.2 SC: But I kind of am not that invested in this particular result because I don't think the classical general relativity is the right theory of the world. The world is quantum mechanical. And I think that there's a whole way of thinking about classical general activity that pretends that classical general activity is right and takes it to its extremes and asks what happens in these incredibly dramatic situations. Whereas I think that in nature, once you get to these incredibly dramatic situations, classical general activity isn't gonna be right in a big way. So the very vocabulary we use to talk about it, singularities, horizons, they're just not gonna make sense, not gonna really apply. That's my actual feeling about cosmic censorship.

2:42:47.7 SC: Bits Plus Atoms says: Brian Green tweeted when you cross over to the edge of a black hole, space and time interchange their roles. You're drawn toward the black hole center with the same inevitability as you are drawn to the next moment in time. Others have given similar descriptions. Since space doesn't have an arrow, now this is the question, and space is taking on the role of time, what accounts for the arrow of time in this case? Is it still increasing entropy. Okay, so I have to shatter a few idols here. Brian is a good friend of mine, Brian Green, and he was a former Mindscape guest, and his statement in that tweet is entirely wrong.

2:43:22.7 SC: It's just not true that space and time interchanged their roles. I know exactly why he would say that, there are coordinates that we put on space time, and we put them on space time for good reasons having to do with the symmetries that exist in space time, etcetera, etcetera. And in the usual coordinate system that we use outside a black hole, you have a radial coordinate that tells you how far away you are from the black hole, and of course, you have a time coordinate as well as angular coordinates. And the role of the radial coordinate and the time coordinate switch inside the event horizon.

2:44:01.1 SC: Okay? So what that means is the coordinate R, the distance from the black hole, the radial distance, the distance in the straight line from the center, is what we call a space like coordinate outside the event horizon. You move along, you change your position in space not in time. Whereas the T coordinate, the time coordinate is the time coordinate. Those same coordinates exist and can be discussed inside the black hole. By the way, I have a book coming out that explains this in great detail, this is all explained in The Biggest Ideas. Inside the event horizon, the R coordinate moves in a time-like direction, the T coordinate moves in a space-like direction. So that's why people say space and time interchange their roles. But they didn't. What changed their roles was space and time coordinates, but who cares? Coordinates are made up by human beings, they're not out there written in space time. You don't bump into R and T, those are just a way that you used to describe it.

2:44:57.7 SC: You could, and very often do, use better coordinates, in which case it's not true that they switch their identities at all. So what follows from that is the following statement: You are drawn toward the black hole center with the same inevitability as you're drawn to the next moment in time. Not also... I mean that's closer to being accurate, but still not accurate because what you're drawn to is R equals zero, the radial coordinate equals zero. That's where the singularity is. But the point is, it's not the center of the black hole. It's just not. It's a moment in the future. We know what a center is, it's a location in space at the middle of some spheres. That is not what our equal zero is. It's not a location in space, it is a moment in time, 'cause now R is a time-like coordinate. So the point of the tweet is correct, the point is once you are inside the black hole, you are drawn toward the singularity with the same inevitability as you move towards the future, but the words in which it's particularly expressed there, I just completely disagree with as a correct way to think about what general relativity is really saying. And so for the arrow of time: Time is just time, it doesn't matter what coordinate you use. And yes, it is still due to increasing entropy.

2:46:11.8 SC: Alex B says: If you were placed in the plot of a scary ghost movie, how long would you make it before updating your prior to ghosts being real. This is an excellent question. I know that it sounds like a silly question, but I think it's a really important question. If you wanna be a fair, legitimate, rigorously thinking Bayesian naturalist who doesn't believe in ghosts, you have to say, "Okay, what is the evidence that would take for me before I started believing in ghosts. And it would be pretty far... " Let's put it this way.

2:46:38.6 SC: I think it'd be pretty far now compared to what it would have been a thousand years ago. Both because our knowledge of the physical world was not as good back then, and therefore. It was much more reasonable to believe in ghosts, but also because we have experience now with magicians, with illusionists, with fakers, right? And so we know that there's a lot of data, a lot of experiences, a lot of things you could notice that might naively point you in the direction of believing in ghosts that could be easily faked. And you have to take that into consideration. You have admit that that's a possibility when you're doing these kinds of calculations. But the thing is, if ghosts really existed, it wouldn't be subtle, it wouldn't be hard to notice, it wouldn't be like you heard a bang in a room you thought was empty or you saw a smudgey reflection in the mirror or something like that. The ghosts could just come up and say hi. Right? Why not? If they really existed. I think this is a more logical argument in the case of God existing than ghosts, 'cause I don't know what the rules about ghosts are. But somewhere along those lines, almost no collection of bangs in the night and things falling over and smudges in the mirror or in photographs would make me change my priors very much.

2:47:58.0 SC: But some very noticeable manifestation of someone who I knew to be dead, who would give a convincing description of who they were and what they knew and answer some questions about the afterlife, etcetera, I would be willing to change my priors. I don't know exactly how quickly it would take, but I would get there, I promise. Jimmy Summer says: There seems to be two irreconcilable views of progress that both posit a fundamental difference in how we create knowledge and how it grows. In one view, the differences between our theories of physics in, say, 1000 years and 5000 years should be relatively similar. Assuming, of course, we continue to make steady progress. On the other view, our theories of physics in a 1000 years and 5000 years will be radically incomprehensibly different because the growth of knowledge has no cut off even in any specific field, which of these two views are you partial to and why? I'm not completely sure I understand the two different scenarios, but I think I have a vague idea. And the short answer is, I don't know. I think that it's important to stress two things, and these are two things that I think are just obviously perfectly unmistakably true.

2:49:05.4 SC: Yet people like to emphasize one and forget about the other. One thing is, we don't know what's gonna happen in the future, as far as scientific knowledge is concerned. We've lived through a series of revolutions in science that have completely changed our point of view of the world, and so it's completely allowed to imagine that revolutions will continue. And like you say, things are gonna be completely different in the future. There's no way that you can principally argue... Sorry, argue in a principled way that that's impossible, that there can't be huge revolutions coming.

2:49:40.0 SC: The other thing that is true is, as I said before, we know a lot more about the fundamental nature of reality now than we did 500 years ago. Maybe we're close to being done. That is absolutely a possibility. Scientific progress doesn't have momentum. It's not like, well, we've had a bunch of revolutions in the last 500 years, therefore, ergo, we will have a bunch of revolutions in the next thousand years or the next 500. We don't know, it's possible. You're literally asking a question about something that is precisely what's impossible to know, because if we knew the answer to that, we'd be much closer to just doing it today rather than a thousand years from now. If I don't know what the revolution is gonna be, I can't tell you how likely it is that it's gonna happen. Right?

2:50:24.5 SC: So I'm kind of wishy-washy on this one. I think we should just absolutely keep an open mind. I know a lot of people like to, you know, argue on the basis of history or logic or whatever, that either things are almost done or they're nowhere near done. I have no idea, and of course, this is something where I am always misunderstood because I make the point that the laws of physics underlying everyday life are completely known in terms of the core theory. People, because people have short attention spans and have difficulty having ideas stick in their minds, they think I'm saying we're close to understanding everything, which is explicitly what I'm not saying, and I try very hard to make the difference clear. People don't wanna hear the difference, so that's why I'm completely happy to say I have no idea whether or not we will have revolutions in our fundamental understanding of reality. But 1000 or 5000 years from now, there will still be atoms and we still believe in the electric magnetic force and in electrons and protons and neutrons evolving according to the core theory.

2:51:25.0 SC: Nick G says: What's your take on Gerard 't Hooft and Susskind's holographic principle as a solution to the information paradox? I just read Susskind's black hole wars and wondering if there's any dissenting opinion among physicists. Well, I think it's a crucially important insight, maybe not everyone agrees.

2:51:41.7 SC: But I think that the standard view among working theoretical physicists these days is that holography, the idea that what's happening, a black hole can be represented by information spread across the boundary of the black hole, across the event horizon, is both true and important. I think that's the consensus. It's not... Maybe consensus is too strong. I think that's the most common view. Okay? There's absolutely some decent. There always is dissent. Physicist love them. They love the descent. And I love them for it. It's not by itself a solution to the information paradox. There had been over the last, let's say, five years, a couple of times when people have claimed to have solutions to the information paradox, and I think that some of them represent genuine progress, genuine new ways of thinking that might very well be helpful. Here on the podcast, we talked to Netta Engelhardt, who's one of the leaders in this field. And she and her colleagues have done absolutely important work that sheds light on how information might come out of black holes. But as she said, as I said, we're not done yet. It's not the solution. We're not there. Okay? So I think it's an important step along the way. It's insight. And it's not the final answer. That would be my opinion.

2:53:02.0 SC: Derek Bain says: Now you'll be coming Hopkins, moving to Baltimore, will there be lots of speaking events and the like open to the public here, that other philosophically-inclined Baltimoreans with an amateur's interested in physics will be able to attend? I suspect. Yes, I suspect that's the answer. There are... Johns Hopkins has a pretty vibrant community interest in science and communication and outreach. Science is a big part of the university. Science, engineering medicine, as I said. But there's also humanities departments and writing departments, etcetera, humanities institutes. There's a lot of social science things going on, so it is a very rich source of things like that, so I cannot say exactly what they will be, but I predict that they will exist. There you go.

2:53:47.9 SC: Nick Selbodata says: Do you have any advice for aspiring students of physics? I feel that self-doubt can become a hindrance on one's ability to learn the material, especially if the foundations of math aren't there to support them. Do you have any habits while you were an undergraduate that helped you focus on your goal? These are, again, really important questions to which my own ability to give advice is very limited, I think in part because it's one thing to do it. I made it through graduate school, became a professor, etcetera. It's a completely different thing to be able to say what you did. There's plenty of people who are good at basketball, who couldn't coach basketball to save their lives. And so I don't know whether or not I could articulate what was important along the way, some things that I did and some things I didn't. And the other reason is 'cause everyone's different, right? So the things that work for me might not work for you. I don't think that self-doubt was one of my biggest obstacles. I had obstacles. In fact, if anything, my obstacle was, I used to think, "Oh, everything will be fine." And that was my obstacle. And maybe I should have had a little bit more self-doubt, but that's not the right way to spin it. The right way to spin it is not doubt versus confidence.

2:54:58.4 SC: But I do think that it's crucially important to constantly be aware of what you're doing and why you're doing it, right? It can be easy... Academia for better, for worse, think about academia versus becoming a musician, right? Yeah, there's similarities, there's many more people who wanna be professional musicians than can be, just like there are many more people who wanna be professors who can be. There's a lot of knowledge and work you need to do, there's a good amount of luck you need to succeed along the way, but academia has a more or less structured way of doing that success, right? You go to undergraduate, you go to graduate school, postdoc, junior faculty, senior faculty. Whereas being a musician, you can toil away for years and then be an overnight success. Many overnight successes toiled for years and years to get there, but it's much less predictable. It's much harder to know what the next step should be in order to succeed. In academia, you very often know what sort of you're expected to do next. Expected to write a PhD thesis, defend it, get a postdoc, write papers. The expectations are pretty clear. And actually, that can stifle creativity a little bit, right? You can have your mind focused on that next step to the detriment of thinking about the longer term. Am I working on the right projects? Am I in the right place? How should I maximize my opportunities going forward when I take the next step, etcetera.

2:56:24.2 SC: So that was my flaw, that I was too focused on the next year, not on the next 20 years, rather than... And again, I thought I would continually think that it'll be fine. If I'm blaming myself for not getting tenure at Chicago, it's because I thought, "Look, I'm doing great, I'm writing all these papers they're cited, I've had a lot of students." The idea that they would not give me tenure literally never occurred to me as a serious thing to worry about. I had plenty of friends who were assistant professors at the time who were just fretting about getting tenure, and I just didn't. I'm like, they'll recognize that I should get a tenure. And I was totally wrong 'cause I was not very smart. But of course, that's not... There's absolute reality to the worry about self-doubt. There are other people... I've known people who are brilliant, who are great at doing science, and who didn't seem to know it themselves. Students of my own, who I've had to say, "Oh no, you'll be great." I worry that I don't say that enough to my students, 'cause to me it's obvious they're great, the ones who were great, most of them, maybe all of them. But maybe I don't say it enough 'cause to me it's obvious, and I have a standard for comparison that they don't.

2:57:38.1 SC: So sorry, I don't have good advice for dealing with the self-doubt other than... I tend to think that self-doubt itself is not the target. In other words, if you're trying to say, how do I deal with self-doubt, the cheap answer, which I suspect has some correctness to it, is do awesome things and your self doubt will go away. Really put whatever abilities you have into succeeding. Again, I've known a lot of people, graduate student level, who thought like if only they could be introduced to the famous professors at conferences than they would be fine. And I have to tell them, it doesn't do any good to be introduced to the famous professors, if they say, "So what are you working on? What do you do?" And you don't have a good answer. You gotta have this stuff, you gotta have the accomplishments, and those accomplishments might be passing your qualifying exams or getting a good grade or even just coming to understand something difficult in physics, but that's gotta be your focus. And I tend to think that the other things will come along with it. Not painlessly, not without work. But once you keep doing good things, you'll eventually say, "Ha! Yeah, maybe I can do this, maybe I'm pretty good at this after all." It's doing the good things that has to come first.

2:58:57.7 SC: Bruno Texara says: I really liked the podcast with Dr. Sherry Turkle, you asked her something about chatbots to keep company, keep people company, and her answer was something like, totally wrong, that's a job for people. I get her point, but I would like your take on my more utilitarian view. Why not both? People will continue to be selfish, sons and grandsons will continue to forget about their elderly, etcetera. While we struggle to make the world more humane can't we in parallel, try to help people in some other less than perfect way. So I am inclined to be on your side, Bruno, in this point. Why not both, right? Like if there is a chatbot that helps someone feel wanted or loved or whatever, why not? If the alternative is not having that and they don't feel love from a utilitarian perspective, if you wanna be utilitarian about this, that doesn't seem like the way to go.

2:59:48.3 SC: Let me just put... And I'm not gonna conclude with any definitive statement here, but let me put two other thoughts into your mind. One is, it can certainly be easy to say, "Oh, we're just helping a little bit and it's better than the alternative." And use that as an excuse to not do something really better. To say, well, we can't do everything perfectly, so we'll give them chatbot. We can't give them a real human being who cares about them, so they can talk to the computer and kind of use that either explicitly or implicitly as a reason not to do something more meaningful with a real human being that loves them in some way. Okay? So I think there's a practical matter. You can not get around the idea that that's a possible failure mode in that particular way of thinking. And the other aspect is, even if it works in some sense to let an elderly person or someone who doesn't have a lot of friends or whatever it is to feel human connection by talking to a chatbot, I think that Cherry's point is it's not human connection, it's just not.

3:00:52.3 SC: It's fake. And so even if, again, in a utilitarian way, you're giving them some momentary pleasure, you're not giving them what they think they need to get that pleasure. It's kind of fake pleasure. This is not a perfect analogy, but imagine the classic science fiction example of a happiness drug. We have drugs that are pretty close to that, right? There's a drug you can take and you're just happy all the time. If you thought that the goal of life was to be happy all the time, maybe you just take that drug and sit in your chair and waste away and die, but you're happy all the time. Right?

3:01:25.2 SC: There's something in that that is unsatisfying to us, even if we started by agreeing that we just wanna be happy all the time, there's something that is not genuine about it, and so I think an argument can be made. And again, I don't know how far to push the argument, but I think an argument can be made that even if a chatbot does a really good job of cheering someone up, it's not a replacement for an equally good job and a precisely equally good job done by a real person. There's something genuine about it, and again, I would love to articulate that in a more complete way, but I'm just gonna put the idea into your head that maybe that is something to take seriously in this discussion. Preston Justice says: You've done a wonderful job explaining the Schrodinger equation. I particularly enjoyed the Socratic dialogue in Chapter 8 of something deeply hidden. Well, by the way, thank you for saying that, Preston. It's interesting. The dialogue in Chapter 8 was an experiment, and my publisher was willing to let me do it, but was a little bit skeptical. And I think that some people loved it and some people hated it.

3:02:23.7 SC: Which is more or less, I guess, what I should have expected, but I'm thankful to the people who loved it. Because of your well-articulated explanations, I'm about 70-20 on the side of the many worlds interpretation. And you say I'm a good Bayesian, but I think I a good Bayesian should have credences that add up to 100 and so... Maybe you mean 70-30? I fear I can't truly take sides of understand the theories of the greatest extent possible without the math, and when I look at the equation I'm completely lost. Could you briefly outline the steps for understanding the equation mathematically, the prerequisite courses, and how much can someone really understand these theories, such as many worlds, without the math. I think you can understand them without the math, but it's not... There's two things that happen when you don't have the math. One is, you're not gonna understand it as well. I do think you can get the point, but because you're learning it through words and analogies and things like that, the sort of penumbra of the point is harder to get, all the implications of the point are harder to get. If you knew the math, then you could figure out what the implications of them are, but as long as things are in words, they're gonna be fuzzy, and therefore, the further you go away from what you really and truly know, the less confident you're going to be.

3:03:33.4 SC: So that is a problem. I forget whether I just said there are two things I wanna say, but let me just say that for the moment, but I do think you can understand things at a pretty good level if there's... But you're gonna understand points rather than the whole landscape, if you know what I mean? The second thing is that I am writing a book. The book that is coming out in September, The Biggest Ideas in the Universe is just the classical stuff. Okay? So Hamiltonian mechanics in there, black holes are in their, general relativity, but no quantum stuff, that will be the second volume, which will hopefully come out next year. But we did do the videos. You can check out my videos where I do the math starting from not doing the math. It's for people who don't know the math ahead of time.

3:04:18.2 SC: It's hard. It's hard to follow without knowing the math ahead of time, but I try to teach you calculus and complex numbers and things like that up to the Schrodinger equation. You don't get very far into the Schrodinger equation, solving it and things like that, because that requires more time, but the videos are there if you're interested. For your actual question, briefly outlining the steps. Well, you need calculus, all the calculus you can get. So integrals and derivatives are what are important in calculus. For quantum mechanics, there's two other things, and... Sorry, integrals and derivatives, but also differential equations. That's crucially important. So an equation that does not just say the derivative equals a number, but derivatives of some functions are equal to other functions of other things and other derivatives, and that's the whole field of differential equations, crucially important to understanding quantum mechanics. And the two other things crucial for quantum mechanics, one is complex numbers, complex variables, the wave function itself is complex. There you go. And the second thing is linear algebra, which is the theory of matrices and diagonalizing them and finding eigenvalues all over the place. Literally the name of Schrodinger's paper where he invented the Schrodinger equation is quantum mechanics as an eigenvalue problem.

3:05:30.3 SC: And the word eigenvalue appears in linear algebra, the theory of matrices, okay? And Heisenberg's version of quantum mechanics was matrix mechanics. You need to know matrices. And you can learn all those things. Those are all things that typical math or physics students learn their first or second year of undergrad, so it's not like it's very, very, very far away if you wanna dive in. Justin Walcott says: Priority question, how can Libertarian-free will exist if all events, including the thoughts and actions of gods, are either deterministic or random? That's an easy one, they can't in that case. Libertarian free will, the word libertarian is very important here, it means that it is not reducible to the laws of physics. So somehow agents have to violate laws of physics. So there are not laws, either deterministic or random, that tell you what's gonna happen. That's it. I don't believe in libertarian free will. I'm a compatiblist about determinism and free will, so I believe in both deterministic laws and free will at the level of an emergent higher level description. Jeff B says: Last AMA you mentioned something about different branches of the wave function potentially having different laws of physics. If that's the case, is there a mechanism by which the branches could develop new laws? What were the original laws at the Big Bang?

3:06:49.2 SC: So we don't know, this is all speculative stuff like. Okay, the short answer is that we don't know. I'm actually thinking about it though. Quantum mechanics, cosmology, these are things that don't go well together, but we can sort of speculate on the basis of we know a lot about, individually, quantum mechanics and cosmology. So one thing... I wrote a paper last year with Jackie Lodman, who was an undergraduate at Caltech, on energy non-conservation in quantum mechanics. The idea being that measurement could change the average energy of the branch of the wave function you're on. And I think that people will debate about the words, the meaning of the word 'energy' and whatever, but I think the physics that we describe in that paper is rock solid. It's baby quantum mechanics. There's not a lot there to disagree with, but what it implies from the many world's perspective is that if you can think about the wave function of the universe as a superposition of different kinds of states, right? That's what quantum mechanic says. And what happens as time goes on, is that you narrow down what parts of the wave function are contributing to the super position you're on, that's why the energy can change, 'cause you're not participating in all of the previous states. You're sort of, well, there were a lot of possibilities at it together, but now I picked out one.

3:08:08.5 SC: Okay? I think it's true, and this is far from established, but I think it's true that that can appear as changing the laws, changing the laws that apply on your specific branch of the wave function. So to answer your question, the original laws or whatever laws govern the whole collection of all the branches of the wave function of the universe. And the ones that you observe on any one branch might be a subset, and therefore, look different than that. So it's not really that the branches are developing new laws, it's that the apparent laws you observe seem to be changing with time because you're sort of participating in less and less of the wave function of the universe. Again, speculative stuff. We don't know if that's what actually happens. Dragon Sided D says: Many of us are still reeling at the loss of friends, co-workers, family members, to what we now understand to be intentional disinformation campaigns. Otherwise fairly normal, seemingly reasonable people have firm beliefs in all matter of easily falsifiable theories about diseases, political events and so forth.

3:09:11.2 SC: Over the past two years, have you observed this in any people in your social or professional circle? And can you offer any thoughts about ways that civil society can overcome the pandemic of disinformation? Well, it's a crucially important question, and my thoughts are not very strong on this. And in part they're not very strong because I appreciate the difficulty of the social science question that is being asked here. Research in these areas are hard and it's easy as Tin Wen would remind us, it's easy to fake yourself into clarity, to go, "Oh, this is the reason why people are so susceptible to disinformation." and then the data turn out not to bear that out, but you stick with your previous opinion. We're all susceptible to disinformation, depending on our pre-existing prejudices. So I don't like to be very definitive about how to combat these things. I have people in my family friend circle who have been susceptible to this, but not really my close friends or professional circles. No one in the Caltech Physics Department is falling prey to these conspiracy theories and disinformation that much, or at least I haven't noticed. Of course, we've also been in pandemic, so maybe I haven't talked to them enough. Maybe I don't know.

3:10:31.8 SC: How can civil society overcome it? You know, there's two things. There's sort of like the blunt thing and then there's the more subtle, systematic thing. The blunt thing is, we have to be good role models, we have to give good information. It's kind of easy and fun to point out people being dumb, but that's not actually very constructive. It doesn't convince them to be right, even when people are in the grips of some terrible disinformation conspiracy theory, you still gotta treat them like a person and make them want to change their minds. You don't make them want to change their minds by berating them and telling them that they're stupid. You have to give them an off-ramp. You have to explain, "Well, does this thing that you're saying really compatible with this thing?" Have you ever thought of the possibility that something else is going on? They have to make the journey themselves, and you can guide them and help them, but you can't just say, "Oh, you're an idiot, please believe me instead, that will never work." The other thing, the more systematic thing is ask why they believe it in the first place. Why would some people fall for these things.

3:11:40.6 SC: Let's take an extreme example. As a basketball fan, I'm well aware that Kyrie Irving, who's one of the best basketball players on the planet, is also a conspiracy theorist. Literal Flat Earth conspiracy theorist. Didn't take the vaccine for COVID, etcetera. Many people have made fun of him. Okay, I don't need to add to that. So instead, let's ask, why would any... Someone who has all the resources in the world, why in the world would they believe in the flat Earth conspiracy theory, right? I mean and ask it in a sincere way, don't ask it just in an eye-rolling way, like why in the world would that happen? Like no, really. Why would someone believe that? Look, it's not because they actually have been thinking about all the possible scientific evidence and said, "Okay, in my considered opinion, I think the scientific evidence is better explained by flat earth." That's not why. There are other reasons why. One big factor is maybe the people in the establishment have been telling them that the Earth is round, not flat, and the people in the establishment have been telling them a lot of other false bullshit at the same time. Maybe that is what they believe. Maybe they are built to be skeptical of received wisdom, and maybe that's not completely crazy, right?

3:13:00.0 SC: Maybe they have been lied to or maybe they've been misled or discriminated against or whatever. Try to open yourself up to the mental space that these other people have and ask, "Okay, why would anyone feel that way? Why would they feel like they've been lied to? Is it because they've been lied to? Is it... " I mean, by the good people as well as the bad people, the people we'd call good and bad. And ideally, this is just impossible in practice, but the sort of ideal state would be one in which people in our society didn't feel that way. And it's because all people in our society were respected and successful, right? I think that if we lived in a society where people were educated and not discriminated against and were told the truth by the establishment, etcetera, etcetera, susceptibility to crazy conspiracy theories would be a lot less. It's much harder to achieve that kind of systematic societal change in any easy way, but I think that's where I would ultimately wanna go. The Shannon Cline says: Are there questions other than conditions in the singularity at the beginning of the cosmos or conditions inside the black hole that require theory of quantum gravity?

3:14:10.9 SC: Well, it depends what you mean by require. Again, what questions do you want to ask? Okay, look, my favorite example is the Sun. The Sun in the sky, depending if it's day time or night time where you are, if there are clouds, but you know what the Sun is, right? Well, what is it? What do you mean you know what the sun is? What is the Sun? Well, you say it's a collection of plasma, protons and helium and things like that. Well, okay, what are those things? What do they do? Well, one thing is they are a source of gravity. The Sun creates a gravitational field, it warps the space time around it. It affects the evolution of the Earth's orbit. We can all agree on that. That is described in our best scientific understanding by general relativity, the theory of gravity that Einstein gave us. There's another thing the Sun does for us, it gives us energy. Light coming from the Sun, how does that happen? Well, through nuclear fusion, ultimately fusion of protons via various cycles into heavier elements, which is a completely quantum mechanical process.

3:15:14.6 SC: You cannot describe nuclear fusion without quantum mechanics, so to understand what the sun is, you need to describe it simultaneously using the language of general relativity and quantum mechanics, but we can't. We can't do that, at least not completely. We can fake our way into get the right answer. Okay, 'cause we know what the right answer is. But we don't have a single principled, fully rigorous theory that describes the Sun simultaneously as a source of light and a source of gravity. Now again, in the regime where it's the weak field limit, etcetera, we can do fine.

3:15:50.3 SC: But a full theory isn't there for that. So there's very few... To get to the spirit of your question, there's essentially no conditions that you bump into in your everyday life where you need quantum gravity, but the world is both quantum and and gravitational. And I'm a believer that there is a way of describing the world that is correct and complete and that requires quantum gravity. Thicke Ramsey says: Priority question. Although it is a true statement that all clocks tick at one second per second, the GPS system and the NIST relativity experiments at Boulder proved that the duration of a clock second can be longer or shorter as compared to that of a comparison clock. In examining the engineering calibration process of GPS atomic clocks, in the frequency and energy of proportional, when a clock engineer calibrates an atomic clock, does it require more energy in order to cause the clock to tick faster?

3:16:46.2 SC: So I know this is a priority question. I'm gonna address it without answering it because I need to un-ask it because I don't think that the words quite hang together in the right way. So first you say, these experiments prove that the duration of clock second can be longer or shorter as compared to that of a comparison clock. The comparison there is just not an innocent clear thing because the only time that the clocks move at apparently different rates is when they are in different positions, when they're not located at the same place, so how do you compare them? You need to look at how they are reading things out with light, with photons coming from the clocks to your eyes. And it takes time for the light to come to your eyes, it takes time for light to go from one clock to another. So you're not actually comparing them at the same time, at the same point in points in space time, you're inventing a procedure for comparing them. And the procedure might be good or bad, but there's a reason why I don't like to say that clocks change their rates in a gravitational field, because it relies on extra baggage that I don't want to have to assume.

3:17:56.8 SC: What I can say is that if you start two clocks at the same position in space and time, and then move them around and then bring them back, they will not necessarily have measured the same elapsed duration, but that's a different kind of thing. That's more accurate than what you said, but it's not exactly what you're trying to get at, because what you're trying to get at is like you say, frequency and energy, proportional frequency is one over time. So therefore, does it require more energy? I have to once again say, what do you mean by energy? Energy is not a Lorentz invariant concept. Energy depends on your frame of reference.

3:18:33.1 SC: Just think about a photon going by, right? You can measure the energy of a photon, collect it in your little calorimeter, measure its energy, but then the same photon had you been moving toward it would have a shorter frequency and therefore more energy. So there's no fact of the matter about what the energy of the photon is. It depends on your reference frame, and that's true not only promotions, but also for locations in a gravitational field. So that's why I don't like to talk this language, I like to talk a language of what is happening in the reference frame of the thing you're talking about. And in that reference frame, the amount of energy, which is a well-defined quantity now, 'cause I told you what reference frame you're in to make a clock tick is the same for every physical clock made out of the same stuff.

3:19:19.8 SC: That's how I like to say it. Anyway, your mileage may vary for other people. John says: Can an electron by coerced to evolve around a positron. And if so, wouldn't this have the same spectrograph as hydrogen? So, for the first part, yes, it absolutely can and has been. There's something called positronium, which is an electron and a positron in a balanced state with each other. Wouldn't this have the same spectrum as hydrogen?

3:19:43.5 SC: No, because the mass of the proton is very different than the mass of a positron, so therefore, you're gonna get a different spectrum. One way of thinking about this is you know, think about the Sun going around the Earth, right? If you replace the Sun with something the size of the Earth, the period of the earth's year would be very different. The energy involved, the binding energy between an Earth and an Earth is very different than the binding energy between the Sun and the Earth. Likewise, the binding energy between a proton and electron is different than the binding energy between an electron and a positron, so the spectrum is gonna be different. Ken Wolfe, says: You had a very interesting discussion with Brian Kloss on power and the temptation of corruption. Looking back on your own experience with academia and other organizations, have you reached any conclusions on what aspect of the organization's structure or culture best works to discourage corrupt behavior? So here's the bad news. It's a very, very good question. The bad news is, I think the thing that the most important aspect of making sure a culture discourages corrupt behavior is having non-corrupt people at the top of it. Having the best people, the most influential important people in the culture, be good people.

3:20:56.7 SC: That is not sadly a fact about the organization, that's a fact about the people. But if you have bad people at the top, it's just hard for any amount of organizational safeguarding to prevent bad behavior throughout the whole organization. That is a... I'm not a social scientist, I should say, and that is my very personal, very non-evidence-driven judgment. So I might be wrong about that, but there you go. If you insist on organizational aspects that might help along the way, I kind of would point to transparency. A lot of organizations, certainly universities and university departments, instantly try to protect themselves and cover their asses. When something bad happens, it's like shut down communication, don't talk to anybody, we'll figure it out. This creates a culture of not discussing bad behavior because no one's listening, they can just cover it up, etcetera. I think more transparency, more openness are very helpful, but I don't know how to really achieve that in any systematic way, so there you go. And last question, Tyler Creighton says: If you were offered the opportunity to host a popular science podcast alongside the entertainer of your choice, do you think you'd take it. If so, who would you choose as your co-host? No, I wouldn't take it.

3:22:20.2 SC: Good question, Tyler. And I know there are people out there, we have friends, very good friends, who do exactly this, host popular science podcasts or shows or give live talks. Both a science professor or a scientist and an entertainer of some sort. I love the format, I think it's great. It's a wonderful way of making things seem a bit less intimidating, a bit funnier and especially, crucially important, reeling in the scientists when they get a little too deep into the woods, into the details. Some scientists, even the great ones that explaining and being popularly understandable, even the best need some reeling in sometimes. So I get the format. It is not my format.

3:23:06.1 SC: As I said before, I'm in some sense not here for outreach. It's not why I'm doing this right now. Outreach in the sense of taking things we know and explaining them to people. Both because I'm interested in learning myself, so my goal here isn't to say things I already know. If I know them, it's much less interesting to me in the podcast format. My books that I'm writing, The Biggest Picture, Biggest Ideas books, that's all pedagogy, that's all outreach, that's all explaining things that we know. I very explicitly, in choosing the topics of the book, eliminated the parts that were speculative. I don't talk about baryogenesis much less... I don't even talk about inflation for that matter, that much. Super string theory, quantum gravity, none of that stuff, it's about the well-established stuff. But that's not the podcast thing for me. For me, the joy of the podcast is that, number one, I'm learning things as I'm saying, I'm talking to people who I want to learn from. Okay? That's crucially important for me, and I think that having a co-host who was an entertainer would not help me in doing that. Maybe I'm wrong about that, but I think that I can ask the questions that I wanna know the answers to in a more direct way. And the other is even more lofty, I'm not sure if it's achieved, but a harder goal that I still am gonna cling to is not just me learning new things, but actually generating new ideas, doing real intellectual work.

3:24:37.2 SC: I want the podcast not just to be a recitation of known true things, but an exploration of learning and creating new true things, giving ideas to me and to the guests and to the audience, ways of thinking that weren't previously there. A true intellectual contribution, not just explaining ideas, but generating them. And again, that's not going to be abetted by having an entertainer alongside. So again, I think that the reasons to have an entertainer along with a scientist as podcast hosts make perfect sense for certain goals, those are not my goals. My goals are to really be out there at the edge. I'm gonna be demanding of you folks. I'm gonna stretch your brain sometimes. Sometimes it'll be easy and fun, but sometimes it will be a little bit brain-twisty. Hopefully, the goal is every single podcast makes you think in a new way. And I think... There's only an hour or so. I know that some people have three-hour, five-hour podcasts, but I have people who's time I respect, who I don't wanna take that much time. So between one and two hours is about how long I'm gonna talk to somebody.

3:25:49.2 SC: It's hard to have a sufficiently efficient conversation in that period of time that you can really gain new knowledge and get to the frontier of ideas and play around with them, and that's what I wanna do. So in my incredibly hubristic thought process, I think that I do that better by myself than with an entertainer along my side. So that's my choice, but again, let the ecosystem be diverse, let everyone do their own thing. Listen to lots of different people. Hero worship goes both ways. I don't worship other people, no one should be worshipping me. Thankfully, that's not the world's biggest problem right now. So I don't need to worry about it too much. But listen to lots of different people think about it. Draw your own conclusions. Get some thoughts. That's why we're here on the Mindscape Podcast. Thanks so much for the support of Patreon members who are asking the questions here. I forgot to mention this in the introduction, I'm supposed to say, the AMA is funded by Patreon supporters. Thank you very much for all that support. I appreciate it immensely. Keeps us going, keeps the podcast humming along, and I think at pretty high level. I'm very happy with how the podcast is going as we near our 200th official episode. Want to do something for that. Alright, thanks very much. Take care, have a good month. Bye bye.