The possible existence of technologically advanced extraterrestrial civilizations — not just alien microbes, but cultures as advanced (or much more) than our own — is one of the most provocative questions in modern science. So provocative that it’s difficult to talk about the idea in a rational, dispassionate way; there are those who loudly insist that the probability of advanced alien cultures existing is essentially one, even without direct evidence, and others are so exhausted by overblown claims in popular media that they want to squelch any such talk. Astronomer Avi Loeb thinks we should be taking this possibility seriously, so much so that he suggested that the recent interstellar interloper `Oumuamua might be a spaceship built by aliens. That got him in a lot of trouble. We talk about the trouble, about `Oumuamua, and the attitude scientists should take toward provocative ideas.
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Abraham (Avi) Loeb received his Ph.D. in plasma physics from the Hebrew University of Jerusalem. He is currently the Frank B. Baird Jr. professor of science at Harvard University. He served as the Chair of Harvard’s Astronomy department from 2011-2020. He is Director of the Institute for Theory and Computation of the Harvard-Smithsonian Center for Astrophysics, and Founding Director of Harvard’s Black Hole Initiative. He is chair of the Advisory Committee for the Breakthrough Starshot Initiative. His new book is Extraterrestrial: The First Sign of Intelligent Life Beyond Earth.
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Sean Carroll (00:00:01):
Hello everyone and welcome to the Mindscape Podcast. I’m your host, Sean Carroll. Some of you may remember back in October 2017, astronomers announced they’d discovered an interstellar interloper in our solar system. There was an object which they dubbed Oumuamua, which was flying through our solar system. It was much like a comet, but comets come from the outer solar system. They’re in orbit around the sun, very gently, and then something knocks them out of their orbit so they dive in closer to the sun and we can see them. Oumuamua by contrast was moving so fast that it was clearly not bound to the sun, gravitationally, it came from way beyond the solar system. And after it zoomed by the sun, it’s going to return back to interstellar space.
Sean Carroll (00:00:45):
So of course, astronomers are very excited by this. This is the first ever interstellar object in our neighborhood that we could see up close and personally, and many of them analyzed it, they wrote papers. One such paper came out a year later by Avi Loeb, who is a professor at the Harvard Smithsonian Center for Astrophysics and Shmuel Bialy who was a post-doc at Harvard also. And it had the dry title of Could Solar Radiation Pressure Explain Oumuamua’s Peculiar Acceleration. And they go through and they do calculations and all these things. Near the end of that paper, there’s one little paragraph which offhandedly they say, “You know, it’s possible Oumuamua is not a rock.” It’s possible that it’s not just a naturally occurring object at all, but is in fact constructed by an advanced technological civilization outside of our solar system. And it was targeted to go near the sun, perhaps with a solar sail or something like that. Again, one little paragraph. They didn’t make a big deal out of it, but guess what? The world made a big deal out of it.
Sean Carroll (00:01:51):
This was discovered by people on the internet and suddenly Harvard scientists suggesting alien presence here in the solar system. Right? So when that happens, you have to understand when scientists think about different hypotheses for explaining the world, they’re very ready to explore all sorts of different possibilities, just because they say that a possibility is conceivable doesn’t mean they think that it’s likely or you should get excited about it, right? We’re going to put all the hypotheses on the table and then decide what we want. But given all this pressure, this sort of different things you could do, you could say, “Well, sorry, don’t take me too seriously. We didn’t really mean it, et cetera.” Avi Loeb in particular decided to go the other way. He doubled down. He said, “No, no, no. This really is possible. We should really take this seriously,” and got enormous amount of criticism for that. Many other astronomers and many people in the media said that’s not a good hypothesis. It does not fit the data. And they offered reasonable reasons to say that.
Sean Carroll (00:02:50):
So I’m not going to personally judge, whether it is likely that Oumuamua was or was not an alien artifact. We’ll talk about that in this podcast interview with Avi Loeb. But I think that there are more important things that we’re talking about.
Sean Carroll (00:03:05):
So one thing we’re talking about is Oumuamua. Okay? We’re going to talk about whether or not it is reasonable to think that this is an alien artifact or is it something else, right? Is it a rock or a comment or whatever? The second thing we’re going to talk about is what is the attitude we should have toward more dramatic ideas? Okay? So should you hide them? Should you put them front and center? Should you talk about them to other professional scientists, but hide them from the public? What should you do? The third thing we’re going to talk about is the general idea of alien civilization. Should we be looking for them? Are they likely to be out there? What should humanity’s attitude be toward this idea that we are not alone in our nearby universe? And finally, we’re going to talk about the nature of science as it is being done right now. We talked a little bit about this in last week’s podcast with Frank Wilczek, where Frank offered the opinion that a lot of his theoretical physicist friends had wandered a little bit away from data.
Sean Carroll (00:04:02):
Avi Loeb has similar opinions. Avi’s been a great, extremely respected and successful theoretical astrophysicist for a long time. He’s also not afraid of poking the hornet’s nest now and then, so Avi has very strong opinions about how science should be done, how it is being done. And we have a wonderful conversation about that.
Sean Carroll (00:04:20):
So whatever we might eventually decide about the nature of this particular thing that flew through the solar system, I’m entirely on the side of the idea that we should explore the dramatic ideas and we should take them seriously. And if they’re wrong, if we have good reason to believe that they’re very unlikely, we can discard them and get on with our lives. But as much as there is a bias towards shiny objects, right? We’re saying, “Ooh, this is a cool idea. Let’s think about this.” There’s a countervailing bias, especially among professional scientists, which say, “Look, we’re bombarded with absurd, scientific nonsense in the popular media all the time. It’s our duty to stamp it out. And therefore we should not even give any attention to these wilder ideas.” But I think we should be honest about how difficult it is to really draw the distinction between an interesting, crazy idea that is worth pursuing and something that should be dismissed out of hand. So that’s one of the issues very, very much on the table for this conversation. I think you’ll like it. Let’s go. Avi Loeb, welcome to Mindscape Podcast.
Avi Loeb (00:05:38):
Thank you for having me.
Sean Carroll (00:05:39):
So we’re going to get into some details. Obviously you talk a lot in your book about this visitor we had from interstellar space, Oumuamua, but I thought it’d be very useful to sort of lay the groundwork by letting the audience know a little bit about what sort of background beliefs professional physicists and astronomers bring to this kind of thing. So just to let people know, would you agree with me that most professional astronomers or astrophysicists spend approximately zero time thinking about alien life elsewhere in the universe?
Avi Loeb (00:06:12):
Yes, I agree. And that’s unfortunate.
Sean Carroll (00:06:14):
Yeah. But you had, even before this recent thing, you had started becoming interested in it.
Avi Loeb (00:06:19):
Right. Actually I worked mostly on cosmology, on the first generation of stars in the universe and then on black holes. But in studying cosmology, one of the interesting frontiers that I helped develop was imaging hydrogen in the infant universe based on the very faint radio emission at 21 centimeter wavelength that it produces. And for that purpose, there were a number of observatories constructed on earth, whose goal was to detect this low frequency radio emission from the early universe. And then in 2007, during a lunch, I joked with [Matia Noreaga 00:07:06] about the fact that the biggest obstacle to making these observations is radio interference from radio stations and TV stations on earth because they operate at similar frequencies. And so if that poses a challenge, why wouldn’t the same observatories be used to eavesdrop on signals from alien civilizations that are produced just by leakage of radio and TV broadcast.
Avi Loeb (00:07:34):
And then we went, so Matia said, “Why don’t we check the numbers?” We checked the numbers and we found that how to distances of tens of light years, we should be able with existing observatories targeting cosmology, we should be able to detect the radio signals from civilizations like ours. And of course we started transmitting about a century ago, and that’s an interesting coincidence that we can detect things out to the distance that our light was traveled in the meantime. And so where we might hear a response from those distances, if there is anyone out there.
Sean Carroll (00:08:16):
Well, that’s the thing. I think that a part of what I want to get down here is thinking like a good Bayesian and what our priors should be, what our expectations are. So I know that a lot of this is old ground, but let’s talk about what we expect. There’s the Drake Equation, there’s the Fermi Paradox, all that stuff. In your mind, do you think that life is ubiquitous throughout our galaxy or is it rare? And how often do you think it might be intelligent or otherwise, or is it just one of these things we have no idea?
Avi Loeb (00:08:47):
Right. Well, science is about evidence. That’s one thing that Galileo taught us that you can have a beautiful philosophical ideas that we are at the center of the universe that the sun moves around the earth. Aristotle was a very wise person, but he was wrong. And Galileo realized that and said that to philosophers, “Look through my telescope and you will figure it out as well.” And they said, “No, we know the answer. The sun moves around the earth.” And they put him in house arrest. That didn’t change the fact that the earth moves around the sun. So the bottom line is prejudice should not guide us but evidence should. Evidence or facts are those things that do not go away, irrespective what we think. And that’s what science should be all about. Collecting evidence without prejudice.
Avi Loeb (00:09:39):
Now one piece of evidence that we collected recently actually this year is that sun-like stars have a planet of the size of the earth in their habitable zone in roughly half of the cases. And that means that the earth sun system is very common. There are billions of such systems within the Milky Way galaxy and you roll the dice of life so many times, it’s very likely that we are not special.
Avi Loeb (00:10:14):
And then one of the big questions asked by Fermi, Enrico Fermi during a lunch as well [inaudible 00:10:24], about 70 years ago was if there is life out there, where is everybody, why don’t we hear from them? Now, to me, that’s not a serious concern because when a pedestrian goes on the sidewalk, the pedestrian doesn’t check every ant that is under his or her feet and we might be so common that we are of no interest to anyone and moreover we might not be smart enough to figure out that there are signals out there.
Avi Loeb (00:10:57):
Our instruments may not be sensitive enough. We are not using sophisticated enough artificial intelligence to analyze our data. And so it’s just like having a fishing net that has too big of holes in it so that the fish go through the holes. And so the fact that we can’t detect them and that they don’t show up on our planet, I don’t think makes any difference. We just need to search with more sensitivity. If you look at the gravitational wave search, for example LIGO, for many years, LIGO did not detect anything. And then 2015, it reached a threshold sensitivity, and suddenly there was a flood of events. And by now we have more than 50 events and the Nobel prize was given for the first one of black hole mergers. And then it just shows that once you reach a threshold sensitivity, you can detect a lot of signals, but before you do that, you detect nothing.
Sean Carroll (00:11:58):
Yeah. I have sort of conflicting impulses pulling me in different directions here. On the one hand… Let’s go with the one hand first. The version of the Fermi Paradox, the idea that there could be so many civilizations out there. Why haven’t we heard them yet? The version that I’ve always found most compelling is the von Neumann replicator version, where John von Neumann suggested that you could imagine building a machine that would go out into the universe, stop by different solar systems, replicate itself, and then send out multiple copies of itself. And if this happened even once in the history of the galaxy, the galaxy doesn’t take that long to just fill up with these replicated machines. So that’s the kind of thing you might think would be easy to find here in the solar system. Do you put any credence in that kind of argument?
Avi Loeb (00:12:45):
Well, it turns out that it’s not so easy to find because right now with the Pan-STARRS survey, we can detect objects of over a hundred meters at a distance of [inaudible 00:12:59] of the earth sun separation, because we monitor the sky with high enough sensitivity. We couldn’t have done that before. And that’s why the first interstellar object was discovered in 2017. Bigger objects are more rare, and we have to wait longer before one of them crosses these distances so we can see it. And so it depends how big these von Neumann objects are. And if they are [inaudible 00: 00:13:31], tens of meters or less than we would have a hard time seeing them. If they move very fast, also astronomers would dismiss them as astronomical sources because they moved too fast across our sky. Most of the time we look for rocks within the solar system that move at tens of kilometers per second. If something would move at the speed of light across our sky, I can guarantee that no astronomer will pay serious attention to it.
Sean Carroll (00:14:01):
Right. And so you think that maybe we are surrounded by at least some density of these replicating machines. It’s possible we just haven’t noticed them yet.
Sean Carroll (00:14:11):
Yeah.
Avi Loeb (00:14:12):
Yeah. And I think what we should do is develop better and more sensitive instruments and analyze the data without prejudice. I always remember when I was a post-doc that the field of gravitational lensing became very popular. And it turned out that gravitational lenses were discovered decades earlier. And if you go through the astrophysical journal, at images of clusters of galaxies. Those images included giant arcs that were not interpreted. Nobody paid attention to them. People said, “Oh, maybe it’s scattered light. We don’t know what it.” And so only when the field became popular, suddenly people realized, “Oh, you know, these ancient images included already data that indicates that gravitational lensing takes place.” And then I think it requires us to be open-minded, attentive to anomalies. The most important thing is to pay attention to anomalies and not shove them under the rug of conservatism.
Sean Carroll (00:15:15):
Right.
Avi Loeb (00:15:16):
Because most of the time when people say, “Oh, there is something unusual, let’s not tell anyone. Let’s just say, well, it’s just noise or something.” Instead, as scientists, we should recognize that breakthroughs and discoveries occur only when you pay attention to anomalies. If you are not open to wonderful things, to new things, you will never discover them. And so I think it’s a self-fulfilling prophecy by the scientific mainstream to basically say, “We don’t want to consider anomalies. We don’t want to look at extraterrestrial civilizations, the possibility that they might exist.” And, and with that state of mind, obviously we will never find evidence for those things.
Avi Loeb (00:15:59):
But I think it’s arrogant on our behalf to believe that we are special and unique. My daughters, when they were infants, they tended to think that they are the center of the world, that everything focuses on them. Then they went to the street and saw other kids, and they got a better perspective. So the only way for us to mature as a civilization is to find evidence that we are not alone. And only then people will get the right perspective. Now if scientists refuse to look through the telescopes with that notion in mind, then we will never find it. It’s just like the philosophers in the days of Galileo. I don’t think we learned the lesson.
Sean Carroll (00:16:40):
Yeah. No, I think that’s a huge set of questions here that I do want to get to, but later in the podcast, but it would distract us from extraterrestrial life and intelligence civilization. So let’s footnote that for right now, bracket it off.
Sean Carroll (00:16:53):
Because I want to talk about this idea of the probes one more time, because there’s the idea of probes that just sort of zip by, and we can’t notice them, but then someone pointed out to me that if you think about listening for communications from extraterrestrials by radio waves or something like that, that sounds like a huge long shot, just because you need to be listening to them at exactly the right time that they would be giving out those radio waves. And maybe most civilizations are not as wasteful as us, just beaming stuff out into the sky. It might be better to imagine that if other civilizations wanted to make contact with us, they would send a kind of probe to come to the solar system and stay here either in orbit around somewhere or landing on a planet, like a monolith kind of hypothesis, ala 2001, because then you can integrate over time and you can just be ready for whenever the local life forms are ready to talk to you.
Avi Loeb (00:17:54):
Yeah, that’s an excellent point. But I don’t think that we are sufficiently interesting for them to pay attention to us. That’s one thing I wanted to mention because probably our form of life is quite common. The conditions that we have on earth are reproduced in so many other places that there is no reason for me to expect us to be the sharpest cookie in the jar. Not only that we are common, but we are not really necessarily particularly intelligent or interesting. When you look at recipe books, you can make many different cakes out of the same ingredients. And so the ingredients on earth, the chemical soup that was on earth early on, made life as we know it and us, but I’m sure we are not the most tasty cake that one can imagine out of the same ingredients.
Avi Loeb (00:18:46):
You can have much more sophisticated cakes, much more advanced civilizations, also that existed for longer than us and therefore have a more advanced technologies. And why would they be interested in us in any way? But the other thing I wanted to reinforce is your point of view, that if you look at us the way we behave, we are not doing the best things that would guarantee our survival in the longterm. We are, by developing our technologies, we develop the means for our own destruction and the same could happen for another civilization. And it’s possible that technological civilizations are short-lived because of the fact that they changed the climate on their planet, or they going to wars with each other, all kinds of other reasons. And if that is the case, most of the time you will find them dead civilizations. If you were to look at the sky and you might think, “Oh, well, then I cannot establish any evidence for their existence.”
Avi Loeb (00:19:52):
That’s not true because on earth, there used to be cultures that disappeared and we find them through archeology. We dig into the ground and we find relics that they left behind. And the same thing we can do in space. We can do space archeology and find, for example, burnt up surfaces of planets, industrial pollution of atmospheres of planets, where the industries that polluted the atmosphere are not around anymore, but the molecules that they produce are still around.
Avi Loeb (00:20:25):
We can find the photovoltaic cells coating planets. For example, if they have a permanent day side, they might want to use the light on that permanent day side to illuminate the dark side. And the civilization may be dead by now but we can find evidence for photovoltaic cells from the reflectivity of the surface, from the reflectivity as a function of wavelength, there will be an edge, photovoltaic cells have a spectral edge in their reflectants. And so the various ways by which we can find evidence, mega structures that are left behind, and then I think we should search. The key is not to believe that you know the answer in advance.
Sean Carroll (00:21:09):
Sure.
Avi Loeb (00:21:09):
That’s the lesson from Galileo.
Sean Carroll (00:21:11):
Yeah, but of course I do want to talk about this later and I’m torn between the idea that yes, we should absolutely search and it would be one of the most groundbreaking world-changing discoveries of all time, were we to discover an extraterrestrial civilization. And at the same time, we have to be able to distinguish between hypotheses that have a 1% chance of being right. And hypotheses that have a minus 10 chance of being right. Those are very different things that we should act about them differently. Right? You would agree?
Avi Loeb (00:21:41):
Yeah. But we do have one data point here and that is that we exist and that we have life on earth. Okay? And then the second data point is that earth is not rare. In fact, you find a lot of planets, the size of the earth at the right distance, from their host star to have liquid water on the surface and potentially the chemistry of life as we know it. So these two facts combined, to me indicate that we are probably not alone, that at least as a matter of scientific inquiry of what exists out there. Right now, if you look at astronomy, it’s all focused on physical objects, right? We’re talking about the cosmic microwave background. We are talking about planets. We are talking about stars or physical objects. We don’t think about biological entities out there.
Avi Loeb (00:22:35):
And that in fact, they may be very prevalent. It’s just that the signals associated with them are weak. It’s not easy to find primitive life. You could search for oxygen and methane in the atmosphere of plant. It’s not easy. The signals of a spaceship are very faint. I did the calculation. No telescope on earth can detect even a giant spaceship at the edge of the solar system. Just to give you an example, the city of Tokyo, if you put it on Pluto, then that would be at the limit of the Hubble Space Telescope. If it integrates for a few weeks, it will be able to see it. So it’s really challenging to see evidence for life at great distances. And given that and given the fact that we exist here and the conditions are replicated in so many other places, I would say that it’s very likely that we are not alone. It’s just that it’s challenging to find evidence for that.
Sean Carroll (00:23:41):
Yeah. I have to push back against this a little bit, just because there’s a little bit of a leap from, there are many, many planets out there, and many of them undoubtedly habitable in some broad classification by how we would think about it, but then you’re multiplying that big number a la the Drake Equation by the fraction of planets on which number one, life comes to exist. Number two, it becomes complicated and multicellular and number three, it becomes technological. Number four, it still survives if it’s still surviving now. Personally, I’m very happy to accept the idea that maybe the galaxy is full of life, but I’m also perfectly happy to imagine that life doesn’t very often come into existence or when it does, it just remains unicellular.
Avi Loeb (00:24:30):
Well, I call it the principle of cosmic modesty. I just believe in modesty, being humble and not believing that one is special because most of the time when you feel that you’re special, you’re proven wrong. Okay? So my tendency is to have, based on my experience in life to adopt the modesty also with respect to the cosmos and not assume arrogantly that we are special or unique. That’s a matter of preference. A lot of people prefer to believe that they’re special.
Avi Loeb (00:25:03):
Preference, a lot of people prefer to believe that they’re special and unique. I know of many people that believe so much in that notion that they never find the dates. When they go on dates, they never find a mate, someone that they can live with because they feel that they’re so special. If we adopt this notion and we don’t even search, we don’t go on a date, we don’t even check if there is anyone out there, we will live in ignorance. That’s what I hate to see that not collecting data because of a wrong prejudice is really a terrible sin for scientists. I think scientists should look for all the possible evidence without prejudice.
Sean Carroll (00:25:46):
Sure. Now, I’m a hundred percent in favor of collecting the evidence. But I do think that we need to imagine establishing some credence so we can figure out how much effort we should put into collecting this evidence. I have to confess, I’m extremely suspicious of the, we are not special argument because if you say, “Well, I’m going to be modest and assume that I’m just a typical non special person in the universe.” That’s not really very modest at all. You can flip that around by saying, “I assume that the universe is like it is here.” Which is actually not very humble. It’s pretty presumptuous. I like to just not quite draw the conclusion, I’d like to say like, “Well let’s be open-minded about this.”
Avi Loeb (00:26:31):
I should say, this is not a proposal for a thesis. This is a working assumption that allows me to go out without prejudice into the world and examine the evidence. What I’m just asking is not to block the pursuit of evidence. To give you an example, right now the mainstream of astronomy, because we detected so many exoplanets, the mainstream is advocating the construction of major telescopes, major observatories that will cost hundreds of millions or even billions of dollars to search for oxygen and methane in the atmospheres of planets. And at best, that would indicate primitive life, microbial life. There is $0 allocated in those plans for the search for intelligent life. Now, when phosphine was reported in the cloud deck of Venus, mainstream scientists argued, “Well, phosphine indeed is the result of life on earth, but on Venus, maybe it’s volcanic, maybe something else. We don’t believe it’s necessarily implying life.”
Avi Loeb (00:27:49):
I asked the same mainstream astronomers, “How dare you advocate that detecting oxygen would be indicative of life when you dismiss phosphine as an indicator of life?” Now, if oxygen can be produced by breaking water and by other natural processes, why would that say anything about microbial life? So you ask yourself what kind of molecules would convince everyone that there is life? I would say CFCs, those industrial pollutants that we produced in coolants and the industries that cannot be produced by nature. These are molecules that are extremely complex. So if we search for signatures of molecules in the atmospheres of planets, why don’t we search for CFCs as much as we search for oxygen? I would say that could be a good argument for building these observatories because everyone would agree if we detect CFCs on another planet, everyone would agree that it’s very difficult to make such molecules by natural processes.
Sean Carroll (00:29:02):
And again, all of the arguments that you have that say that we should go out there and look, I’m entirely on board with. And it’s interesting, I mean, maybe let’s delve into the psychology of this because I do also agree with you that if you say, “Well, let’s go look for this or that molecule, maybe as an indication of primitive life, astronomers and scientists get very excited.” And as soon as you say, “Well, let’s look for evidence for technological civilizations, they get nervous.” What is the psychology behind that? Is it that they worry that they won’t be taken seriously if they act to science fictioning?
Avi Loeb (00:29:39):
Well, right now it’s social pressure, and bullying and herd mentality. But if you ask yourself, why did it get to this point? There is a long tradition of science fiction and the reports without scientific credence for unidentified flying objects, UFOs. These reports are not reproducible. They are not standing up to the scrutiny of scientific evidence. They were fuzzy 50 years ago with the cameras that existed back then, and now we have much better cameras and they’re also fuzzy.
Sean Carroll (00:30:19):
So fuzzy, yeah.
Avi Loeb (00:30:21):
That tells you that something is wrong with these reports because we developed much better instrumentation to detect the unusual phenomenon. These are always on the borderline of believability, the UFO reports. So given this background, and also given the fact that a lot of our colleagues get a boost to their ego, if they belong to an elite club where they do not necessarily pay attention to what the public is interested in, but they elevate themselves to discussions on how many [angles 00:30:54] can stand on a pin? Or in other words, issues related with anti-de Sitter space that does not represent reality or issues related with extra dimensions, to which we haven’t found any evidence yet. That is considered mainstream in theoretical physics.
Sean Carroll (00:31:14):
I do know, yeah.
Avi Loeb (00:31:15):
However, it’s of little interest to the public. And elevating yourself to do intellectual gymnastics to impress your peers, to gain honors, awards and to show that you’re smart. That’s very much of the academic game rather than echoing interests of the public. And I think it’s a self-inflicted wound that academia is considered part of the elite because, it’s also for the scientists who blame that they are not paying attention to what the public is interested in.
Avi Loeb (00:31:50):
And we have the technology to address the question of whether other intelligent life exists out there. It’s JUST that we choose not to use this technology to answer this question. We choose not to invest funding even at the 10% level in search for techno signatures, whereas the rest much more funds are allocated to the search for biosignatures. Then I think it’s a matter of choice. It’s not a matter of reason. My goal in writing this book, and also I have a textbook coming out in June 2021, 800 pages long about the search for both intelligent and primitive life with Manasvi Lingham my former post-doc. My goal is to bring it to the mainstream.
Sean Carroll (00:32:41):
And now I’m completely on board in the message, and it’s weird, and it’s hard to analyze the biases of the academic community in an objective way, because who has the perspective of being completely unbiased. But I do think that there is a certain stuffiness, a certain insularity that marks certain pursuits as not academically respectable and others as a perfectly okay. And so, that’s one of the reasons why I wanted to invite you on the podcast. I’m a little skeptical, Oumuamua, but I’m very much enthusiastic about pursuing this as a serious intellectual endeavor.
Avi Loeb (00:33:19):
Let me give you another example that I actually was involved in, and that is cosmic inflation. I was in a debate with Alan Guth, in which Alan basically said that it’s a silly question to ask whether inflation is falsifiable. That in fact, it’s a framework that cannot be falsified, that whatever data we collect about cosmology about the universe can be accommodated in some version or some model of inflation, cosmic inflation. Now, that allowed. That is part of the mainstream and Alan Guth represents cosmic inflation that is very widely accepted. However, people would say, “The possibility that the signal that we detected is artificial, should not be considered because an artificial origin could explain almost everything like pulsars, other unusual phenomenon.” So I would say there is a lack of intellectual honesty in, for example, treating something like inflation or extra dimensions, or even some proposals for the dark matter.
Avi Loeb (00:34:34):
We invested hundreds of millions of dollars searching for the dark matter and many of these searches failed. We believe that it’s not the weakly interacting massive particles, that parameter space is ruled out, but nobody complains of course, it was worth checking if that idea bears any fruit. So the dark matter is not the traditional weakly interacting massive particles, that’s good to know. But at the same time people say, “Why should we spend money on searching for other civilizations if we know that we might not find anything?” Well, we do the same thing in many other aspects of science, we search for things, and we are not guaranteed to find an answer.
Sean Carroll (00:35:20):
I think there’s still some parameter space left for weakly interacting massive particles, but let’s not get into that. That’s a different podcast. But I also want to just emphasize one point that you made, and it went by pretty quickly which is that, when you are thinking about looking for evidence for extra terrestrial civilizations, advanced life forms elsewhere, you are not thinking about the CIA releasing some fuzzy videos. We’re recording this. We should tell people a couple of days after retired Israeli general says, “Oh yeah, we’re totally talking to the Galactic Federation, the Israeli and U.S. governments have just hushed it up.” You’re not talking about that.
Avi Loeb (00:36:00):
Not at all. I think this complete nonsense. I think our governments are not sufficiently competent to hide such an important revelation. Obviously if we had conclusive evidence for anything, everyone would know about it.
Sean Carroll (00:36:19):
And then the final thing before we get onto the details of your book, this has too many things to talk about here. You mentioned the fact that some of these civilizations could be archeological fines. They could have gone away and we could find their remnants, but let’s just get the timescales into people’s brains here. If they don’t go away, then we would expect that a typical galactic technological civilization would be millions, if not billions of years more advanced than us, right?
Avi Loeb (00:36:49):
That’s right. That is quite interesting because if you look at our technologies, they are evolving exponentially right now on a few year timescale. We cannot really imagine what our technologies would look like a hundred years from now, but giving it them a thousand years, a million years or a billion years, basically it would look like magic to us. We would see things that look like miracles, that we cannot really understand.
Sean Carroll (00:37:18):
Well, it creates a dilemma for those of us who would want to do science on this, which is it’s hard to know even what we would be looking for, right?
Avi Loeb (00:37:27):
Exactly. So what often you do, if you never met people and you’re about to meet the first people. Then you look at the mirror and say, “Well, maybe they look just like me.” And then it works, actually they look similar to you. As long as you have a common genetic heritage that you are connected, but when you deal with life that formed on completely disconnected planets, that is not guaranteed at all. The grass on Proxima Centauri b might not be green because that star is producing infrared light. It’s not producing visible light.
Avi Loeb (00:38:14):
So just think, and obviously if there are animals on the permanent day side, they have infrared eyes that look very different than our eyes. And so imagining more of the same is the wrong… And I think the wrong approach. And I think we will be shocked both if we’re to meet life from another planetary system, or if we were to meet the technologies that emerged on more mature civilizations than ours. So we are out to a shock and of course, that could be one reason why we haven’t seen it yet because we’re not looking at the right places.
Sean Carroll (00:39:03):
One of the possibilities for why we haven’t seen extraterrestrial life yet, if it is ubiquitous in the universe is the idea that we can upload ourselves, our consciousnesses, our brain states into computers at some point. And right now we embodied biological organisms are driven by all of these impetuses and instincts that are given to us by evolution to survive, to eat, to reproduce, to learn. But maybe when we upload ourselves, that biology goes away and those motivations go away and people lose interest in exploring the rest of the universe. What do you think about that one?
Avi Loeb (00:39:38):
Yeah, that’s quite possible. And I think a very advanced civilizations might develop social distancing on a cosmic scale. They might create their own cocoons and then basically close themselves off and not interact with anyone because they have a very comfortable habitat that they created and they don’t need anyone. Now that doesn’t mean that we cannot detect them, they always need to produce trash because of the second law of thermodynamics. So like investigative journalists that go into the trash cans of Hollywood celebrities, we might be able to learn something about them by looking at their trash. But then it’s quite possible that they have no interest in establishing conduct. Now, I should mention to you an anecdote, one of the biggest puzzles in cosmology is what happened before the big bang. What started the universe?
Avi Loeb (00:40:37):
And then I have one possible solution for that, suppose we develop theory of quantum gravity which we don’t have right now and we understand how the universe started. And we realize that we can actually produce a baby universe in the laboratory, suppose we realize that. Then there is a solution to what happened before the big bang. And the solution is that the universe like ours produces a civilization like ours, that they gets to be intelligent enough to figure out how to make a baby universe. And then a new universe comes out of us and that will allow another civilization inside of it to create another universe and so forth. If we were to ask, where did we come from? It will be from a laboratory of a previous species that created our universe.
Sean Carroll (00:41:37):
I like that idea. It’s very similar to a paper that I actually published, but we had a natural way of making baby universes. They were not artificially created in the lab, but the spirit of it is very much the same. And to be fair, we should give credit to Alan Guth, who was one of the first people to tell us how to build a baby university in a laboratory.
Avi Loeb (00:41:55):
Yes, definitely. He did very important work. It’s just that I do not agree with some of the premises in his late life.
Sean Carroll (00:42:01):
Sure. So finally, 2017 we got a visitor from outer space. Why don’t you tell us a little bit about that?
Avi Loeb (00:42:09):
On October 19th, 2017 the Pan-STARRS Observatory on Mount Haleakala in Maui, Hawaii discovered the first object near the earth that came from outside the solar system. And we could tell because it moved too fast to be bound to the sun, and then they gave it the name Oumuamua which means scout in a Hawaiian. Interestingly, by coincidence, I visited Mount Haleakala just a few months earlier. And then at that time Oumuamua was approaching the earth rather than moving away from the earth. It was discovered once it started running away from us at a very high speed that no rocket that we have built in the past could have caught up with it. But if we would have known about it, when I visited in July 2017, then we could have designed a space mission that would meet it halfway and take a photograph.
Avi Loeb (00:43:15):
But anyway, the immediate reaction of the astronomy community was, “Oh great, we have an interstellar object. It’s probably either a comet or an asteroid, and most likely a comet, because comets are icy rocks that many of which can originate from the outer most part of the solar system, the Oort cloud. And so if other stars, heaven or Oort cloud, these are objects that are loosely bound and can easily be torn apart from their host star. And so most of the time you will get an icy rock coming from interstellar space that would look like a comet with a cometary tail.” Unfortunately Oumuamua did not show a cometary tail. It looked as if it’s maybe just a rock. So people said, “Well, okay, so then it’s an asteroid.” But then when they monitor the light from it, the light changed the brightness of the object, which is reflected sunlight changed by a factor of 10 as it tumbled.
Avi Loeb (00:44:22):
And that means that the area of the object on the sky that reflects sunlight changes by a factor of 10 as it spins around. And that is very extreme. We have not seen something like that before in the solar system. And it means that the object has an extreme geometry. And if you try to fit the light curve, it turns out that at the 90% confidence, you can show that it should be flattened, not elongated, not cigar shape, but rather pancake shape. That’s another peculiar fact about this object that became clear. The more we learned about it, the more peculiar it became. Then in May 2018, there was a paper published saying that this object exhibited an excess push away from the sun, beyond the gravity of the sun and such a push can be obtained, for example, from the rocket effect on a comet when the ice on the surface of the comet evaporates, it pushes the comet in the opposite direction.
Avi Loeb (00:45:33):
But then there was no cometary tail and the Spitzer Space Telescope looked very carefully at the environment of this object and didn’t detect any carbon based molecules, or dust or anything that makes cometary tails usually. So that was a puzzle, what is pushing this object? I wrote a Scientific American Essay in which I said, “Maybe it’s an artificial object.” And then I wrote another more extensive paper mentioning all the peculiarities. There were six of them of this object. It also regenerated in a very special frame of reference which is, I call it the galactic parking lot where if you place your car there, nobody would know where the car came from. This is called the local standard of rest. It’s the frame of reference that is obtained from averaging the motion of all the stars in the vicinity of the sun.
Avi Loeb (00:46:35):
And then, it was addressed in that frame, just like a beauty on the surface of an ocean and the sun of the solar system collided with it because of its motion relative to that frame. Only one in 500 stars is so much addressed in that frame as Oumuamua was, it was not moving at all in our local frame. Then we bumped into it like a ship bumping into a buoy. And so there were a number of these very strange facts about Oumuamua and over the summer of 2018, I realized, well, maybe it’s artificial. And then at the same time I had the new post-doc join my group, Shmuel Bialy and I suggested to him that perhaps this push that the object exhibited is as a result of sunlight bouncing off the surface of this object. And in order for that to be effective, you need the object to have a large surface area for its weight.
Avi Loeb (00:47:39):
We figured out that a Solar Sail, a LightSail would do it if it has a thickness of less than a millimeter. We submitted the paper to the Astrophysical Journal Letters. It was accepted within a few days, there were free actually said that actually there is supporting evidence that this object appears to be most likely flat rather than elongated, and that supports your idea. That’s it. We didn’t have a press release or anything, but then a couple of bloggers wrote about it and the subject became viral to my surprise, I should say, because a year before that, I wrote a paper suggesting that the dark matter may have an electric charge, a very small electric charge. To me, that’s a bigger speculation and nobody paid too much attention to that, even though it was published in prestigious journal.
Avi Loeb (00:48:43):
So then of course there was a lot response from both the public and the scientific community to this idea. But what I would like to mention is an anecdote that this year in September 2020, there was another object discovered that was not identified. There was no cometary tail, but this object seemed to move in an orbit similar to that of the earth. It was given the name 2020 SO discovered in September 2020. Then the astronomers integrated the orbita of this object back in time and found that it must’ve coincided with the earth in 1966. It turns out that in 1966, there was a failed mission called the Surveyor 2 Moon Lander and the booster of that rocket was kicked into space. Most likely that is what we’ve seen as 2020 SO. And clearly an artificially made object, and then it was hollow and they found that there is evidence from its orbit, actually for a deviation.
Avi Loeb (00:50:02):
There is evidence from its orbit, actually for a deviation as the result of the push by sunlight. And they wrote about in it’s in today’s New York times science section, it says “There is evidence that the sun pushes this object and that’s evidence that it is hollow.” And that’s interesting because we are able to recognize the artificial objects like 2020 SO, based on their orbit and the fact that they don’t show a cometary tail. To me, it reminded of Oumuamua except Oumuamua was not produced by us.
Avi Loeb (00:50:39):
The other thing I wanted to mention is when I go on vacation, I often like to be close to a beach, and I look at the seashells on the surface of the beach, and then the seashells are naturally produced an each of them, looks different from the others. But every now and then I encounter a plastic bottle that is artificially made. It’s clear that there was a civilization that produced this plastic bottle. So perhaps, or Oumuamua is a message in a bottle from another civilization, if it is a light sail and, and that’s a hypothesis that we can falsify by looking for additional objects, similar to it in the future.
Sean Carroll (00:51:33):
I think it’s definitely one worth taking seriously. Because a lot of the listeners are not going to be experts in the techniques of modern astrophysics, let’s talk first about how astronomers tackle something like this. I mean, we have telescopes and we pointed at it, but we don’t have an image of what the thing looked like, right? We tried to look for that cometary tale, but it’s just too small and faint, is that right?
Avi Loeb (00:51:56):
That’s right. It’s point like. The only way to get an image is to get close enough to it. And that is possible if the object, for example, is approaching us, because you don’t need to move very fast, you just meet it. And so hopefully next time around, if we see an object that’s weird, this Oumuamua, we will see it when it’s approaching us.
Sean Carroll (00:52:17):
It came sort of remarkably close to the sun. It was inside the orbit of mercury. And maybe that’s the selection effect that, if it had not passed within the orbit of Mars, then it just never would have even been noticed.
Avi Loeb (00:52:29):
Yeah, it was not just on its way out, but it definitely had to come very close to the earth, within the earth sun separation for us to notice it with pan-STARRS and before pan-STARRS we just didn’t have the instruments that would allow us to detect such objects. So, it’s clear.
Avi Loeb (00:52:48):
Now, the other thing I wanted to mention is a decade ago, we wrote a paper with Amaya-Moro Martin and Ed Turner forecasting how many interstellar objects we should expect and whether Pan-STARRS should see any of them. And we concluded no, if we just make a forecast based on what we know about the solar system and the rocks that exist in the solar system that could have been ejected over the lifetime of the sources … We predicted an abundance of objects that is short by a factor of a hundred, to a hundred million, then the population needed to explain Oumuamua. So the mere detection of the subject is by itself a surprise.
Sean Carroll (00:53:27):
Right. You did say about the inferred shape of it. So talk to me more because this is … I was an undergraduate astronomy major and even a graduate student, although I don’t do astronomy in any real sense. But I’ve always been enormously impressed by the ability of astronomers to take these little fragments of data, like a light curve and spin a rather elaborate tale about what we can learn. Where do you get information about, is it elongated or pancake shaped or anything like that?
Avi Loeb (00:53:56):
Yeah, so this is based on the amount of light that is reflected as a function of time. So let’s imagine that we can resolve it. Basically there is a certain surface area that it occupies on the sky. It occupies a certain area and the sun reflects off the object. We can think, for example, on satellites. So suppose we look at communication satellites. When they pass over the sky, and by the way that’s the problem for astronomy in the future, there will be tens of thousands of them that are planned for launch by SpaceX and other companies and that would pose a problem for the Vera Rubin observatory. But the point is whenever sunlight reflects off them, we can detect the amount of light that we receive. Even if we don’t resolve the object, we see how much, how much light we get.
Avi Loeb (00:54:51):
Then from this point of light and the amount of light that we get changes in time, because either the object changes its orientation relative to us, or because it spins, it tumbles. Most of the rocks do not maintain the same face in our direction because they spin and Oumuamua was spinning with a period of eight hours. So every eight hours, its brightness went from up, down, and then up again. So that was a full period of them. And then we can monitor how much light we get. When it reflects the most amount of light versus when it’s dimmer because it shows the smaller surface to us. So if you imagine a pancake like object, the change in the amount of light that you get as the object is spinning, would be different than if you were to have a cigar shaped object spinning.
Avi Loeb (00:55:54):
And so you can try and model it. Now the one thing that you don’t know is the reflectivity of the surface. Potentially there are spots on the surface that are more reflective than other parts. And that’s something we don’t know, but if you assume let’s say a uniform reflectance, then it’s very easy to try and constrain the geometry of the object from the light curve. Because we know where the sun is located. We know that where the object is located in its orbit around the sun, and we can try and model that. It’s not too complicated. I think even a high schooler can do it.
Sean Carroll (00:56:34):
Is the consensus that it is more likely pancake shape than cigar shape?
Avi Loeb (00:56:38):
There was a paper that did the analysis in great detail just a year ago by [Mishchenko 00:56:39], [Sergey Mishchenko 00:56:40] and demonstrated that and argued that at the 90% confidence level, it’s pancake shape. Before that there was also the argument that if you want it to fit the light curve, it turns out that the object with the most amount of internal motions. If you imagine Oumuamua being kicked around by all kinds of objects, obstacles along the path of its trajectory, then you would expect it to occupy the highest energy state that it can get. And the highest energy state for it would be associated with the pancake. A cigar shape would be associated with the the lowest energy state, and that’s less likely. So that argument was already made early on with the detection of Oumuamua, but what was done later with, with all the data that was collected was to try and model the light curve. And that by Mishchenko argued that at the 90% confidence it’s pancake shaped.
Sean Carroll (00:57:49):
Do we have any idea of what it’s mass is?
Avi Loeb (00:57:51):
So the mass depends on the geometry. So if you imagine it being even razor thin, like a light sail we were talking about, it’s very unlikely that it would be edge on when we look at it. A change by a factor of 10 can apply also to a very thin object. We just don’t know how thick it is and the amount of mass that it carries depends on how thick it is. All we know is that one projected on the sky, as it spins around, the area of the object changes by a factor of 10. The amount of mass I should say, if you were to assume that it’s a rock, with a characteristic density of a rock and dimensions of let’s say 100 meters in length and 10 meters in width, then you would get something that is …. From the fact that it’s a member of a population of objects of similar properties, you would get that you cannot easily explain its existence with what we know about planetary systems. We are off by orbits of magnitude. It’s just difficult to produce. You need a quadrillion such objects produced per star and the amount of mass that each of them carries makes it quite difficult to explain.
Avi Loeb (00:59:18):
Amaya-Moro Martin wrote a couple of papers on that, how difficult it is to produce if it’s a rock. So many of them so that we will see one within a few years with Pan-STARRS. However, if you make it like a light sail, it doesn’t carry as much weight, actually. A quadrillion such objects would carry the mass of an asteroid that has a size of roughly a kilometer or so. In principle, that will not be a lot of mass associated with Oumuamua it’s very thin.
Sean Carroll (00:59:58):
Yeah. In the interest of still normalizing the expectations for what kinds of things might be out there for our audience, astronomers have thought about this a lot, but maybe the people in the street haven’t. You’ve mentioned rocks and you’ve mentioned comets. And so those are a little bit different, right? Rocks are solid and comets are made of ice or other volatile things that can light up when they come near the sun. And maybe there’s some sort of in-between thing where there’s a loose agglomeration of rocky and icy things. We think that all of these things are in our solar system, we find them, but the Oort cloud and maybe the Kuiper belt very far away are more icy, more Rocky? [crosstalk 00:10:42]
Avi Loeb (01:00:44):
Since you did your PhD at Harvard, I should mention the story starts with Fred Whipple that used to be at Harvard. I think he got the idea, it wasn’t clear at his time what these comets are. He came after going through Harvard yard, during a snow storm, he came up with the idea that they might be dirty ice. It turns out that the more likely icy dirt. So in other words, it’s mostly a rock. I mean, comets are mostly a rock and they have some water ice on them. One thing about water ice to keep in mind is, it doesn’t go to liquid if you warm it up in space. In order for water to go to liquid as we find on earth, you need an atmosphere, you need an external pressure, and that doesn’t exist on a small rock in space.
Avi Loeb (01:01:50):
So if you warm it up, when the rock gets close to the sun, the ice sublimates directly into gas and that’s what we see as the cometary tail. We see the gas that is created by warming up the ice. So the solar system had basically the debris that was left over from the formation of the sun created this proto planetary disc. A disc of material that was orbiting the sun and small dust particles collided to make bigger and bigger rocks. Beyond a certain distance from the sun, there was water ice, because it was too cold in that disc and water could not exist in gas form so it solidified into ice. That’s how you get these icy rocks in the outer part of the solar system, where the conditions were cold enough for them to form.
Avi Loeb (01:02:47):
These are relics of the formation of the solar system. You have all these rocks moving around, and some of them were kicked by planets and occupy the Oort cloud. Some of them were donated to our solar system from other stars as well. So they are orbiting the sun at great distances that go out to a hundred thousand times the earth, sun separation. Whenever one of them passes close to the sun, we see it as a comet. Every now and then we also get some objects to collide with the earth. That’s what killed the dinosaurs. Unfortunately the dinosaurs didn’t have a science and astronomy so they couldn’t have studied the sky. As a result, they saw this giant rock heading their way, and they couldn’t do anything about it. Hopefully by Pan-STARRS, by monitoring the sky, can alert us to any dangerous rock that is heading our way. And perhaps we can give it a nudge so that it will not hit the earth
Sean Carroll (01:03:51):
Here in our solar system then we have these rocky things and these snowballs, these comets, and presumably some of them are kicked out of the solar system. From either random jigglings due to planets, or maybe in other circumstances, there could be explosions or collisions. So therefore we would expect some flux of interstellar visitors here visiting us right?
Avi Loeb (01:04:12):
Definitely. In fact, Oort cloud extends half way to the nearest star, the Alpha Centauri system. Those Oort clouds, if each star has an Oort cloud around it, you can think of them as billiard balls that are touching each other. So space is full of these Oort clouds. It’s easy for a star to pass near an Oort cloud of another star and tear it apart. Basically get some objects kicked out and therefore the interstellar space is full of objects. It should not be a surprise that some of them enter the solar system. That’s what we calculated a decade ago, but we just didn’t expect an abundance so large as to explain Oumuamua like object. Because what we calculated is the natural density or abundance of such objects is not high enough for Pan-STARRS to detect any of them. But apparently it did.
Avi Loeb (01:05:14):
I should say there was a second object, interstellar object detected. That is by an armature Russian astronomer called Gennadiy Borisov. He built a telescope and detected what looked like a regular comet that is not bound to the sun. Then people came to me and said, “Well, this one looks just like a regular comet, this interstellar object, doesn’t it convince you that Oumuamua was also natural?”
Avi Loeb (01:05:43):
And my answer to that was, “You know, when I went on a date, the first date with my wife, she did look special to me and the fact that I met many other people afterwards didn’t change that opinion.” So the fact that we saw Borisov looking like a typical comet didn’t make Oumuamua more typical.
Sean Carroll (01:06:04):
I guess the thing that is most provocative about Oumuamua is the combination of the fact that on the one hand it did accelerate. I mean, there was some non gravitational push, which by itself is not surprising because comets do that when gases light up and push away. But on the other hand, we didn’t see any such out gassing, is that right? Is that the real tension that we’re working to fix here?
Avi Loeb (01:06:27):
That’s the main peculiarity that it exhibited an extra push without a cometary tail. That led the few mainstream astronomers to come up with innovative ideas. For example, maybe it’s a hydrogen iceberg, something that we have never seen before. The problem with that, we wrote a paper about this with Thim Huang, showing that in hydrogen iceberg would not survive the journey. It would evaporate over the millions of years that it takes it to reach us from a distant molecular cloud. The reason that the hydrogen iceberg was proposed is because in that case, you would not see a regular cometary tail. It would be made of hydrogen that is an invisible gas. Also because it’s so light, it would give more of a push. Well, first of all, hydrogen icebergs were never seen, but moreover we have good theoretical reasons not to expect them to exist.
Avi Loeb (01:07:35):
Then another idea was maybe it’s a dust bunny, the kind of things you find at home when you don’t clean a home very often. The idea there is that maybe it’s an object that is a hundred times less dense than air. So it’s very fluffy and porous and that kind of an object can be pushed by sunlight. So it doesn’t need to be a light sail, it could be a dust bunny. Here again, I have a problem with this survival over millions of years in the interstellar medium. I just have a hard time imagining a dust bunny of the size of a football field spinning around every eight hours and surviving a journey of millions of years. You know, it’s just less plausible to me.
Avi Loeb (01:08:24):
But I should say that while people were coming with these challenging scenarios and these are people from the mainstream, other people from the mainstream were arguing, “Forget about it, it’s natural. And that’s it. End of argument. There is nothing to discuss.” I find this to be very strange situation where some people have a hard time explaining the facts that we know and others are claiming “Forget about the facts let’s move on, business as usual.”
Sean Carroll (01:08:51):
So I mean, the nice thing about the light sail hypothesis is that it would be something which would be big and flat. Very, very thin, but also robust against it surviving for a long time in interstellar space.
Avi Loeb (01:09:02):
Exactly, that’s one thing we checked in the paper, that was the first thing we checked. Will it survive all the dust that is bumping against it and the interstellar medium, the radiation so forth. We found that there shouldn’t be any problem. I mean, this is a falsifiable, unlike inflation, it’s falsifiable hypothesis in the sense that, we just need to find another object that shows similar properties and then, take a photograph of it or, or just get more data on it. I’m just proposing this conjecture as a testable hypothesis. This is nothing different from suggesting that the dark matter has a small electric charge that you can test in the laboratory in principle or any other scientific inquiry. It’s only the emotional blockage or that the [inaudible 01:09:59] that is put by the scientific community that prevents us from going in these directions right now.
Sean Carroll (01:10:05):
My impression is that the biggest challenge to the light sail idea is the tumbling. You wouldn’t quite expect a light sail to tumble in the exact way that this one does, but am I right about that? Or did I mix that up?
Avi Loeb (01:10:17):
You’re right if it’s functional, if it’s something that was designed to maintain its integrity in a way that, it’s operational right now. But if it’s just a piece of equipment that is defunct by now or serve some other purpose, I’m not sure, this is guesswork. The question is what really physically speaking, what is this object? What’s the geometry? What is it made of? Is it shiny? Just a shiny rock or is it shiny because it’s made of metal? That’s a simple question.
Avi Loeb (01:10:53):
It turns out the Spitzer space telescope did not detect any heat coming from it. Given the amount of sunlight that it reflected, it looks like it was more shiny than an average asteroid or comet. It’s just a very simple question. What is it made off? How does it look? And we can answer this question with existing technology. We just need to monitor the sky for more of the same.
Sean Carroll (01:11:20):
We’ve been talking and been serious scientists for a while. Now we can let ourselves speculate a little bit more. If it is artificially constructed by an alien civilization, why would they do it? What is your idea about what purpose this thing could have served to its initial constructors?
Avi Loeb (01:11:42):
So again, I go back to the evidence and this object was in the local standard of rest and sort of the galactic parking lot, a place where you can’t really trace where it came from and why would it be in that frame? One possibility is that there is an array of these things, and they’re used for navigation or as relay stations for communication, there could be many possibilities. Why would you construct a set of systems that are addressed in the galactic frame? That’s one possible use that if you were to navigate through the local volume of the galaxy, you want to have signposts, or if you wanted to communicate, perhaps relay stations if you send out spacecrafts. I mean, it’s not clear to me and it could just be some debris leftover from equipment that is dysfunctional by now.
Avi Loeb (01:12:46):
The point of the matter is that we can tell it’s something artificial, can tell the difference from a rock. Clearly if a caveman were to find a cell phone, the caveman based on experience would say, it must be a shiny rock. Because that caveman saw rocks all of his life, that’s the thing that he’s familiar with. But obviously with more sophistication that caveman will conclude, “Oh, this is an unusual object and not something that I’ve seen before.” We can attempt to do the same by getting more data, rather than claiming one thing or another based on prejudice.
Sean Carroll (01:13:30):
Presumably we did listen to see whether there were any radio signals or other things being given off that would be manifestly artificial coming from Oumuamua, but we didn’t find any.
Avi Loeb (01:13:40):
Yeah, in fact a couple of weeks after it was detected, I visited Yuri Milner’s home in Palo Alto and discussed with him the possible use of the telescopes that Breakthrough Listen has access to, to monitor if there is any radio signals coming from Oumuamua. That was done and nothing was detected, but it doesn’t tell us much because perhaps we were not listening at the right frequencies. Even if it’s transmitting, it could be transmitting at times that are special, not when it was passing near us. So although interesting, that possibility, there was no signal detected. That possibility is ruled out, that it was transmitting at the frequencies that we were listening to. I mean, it’s of limited use for ruling out an artificial origin.
Sean Carroll (01:14:35):
Let’s again be a little bit more speculative now, late in the podcast. This is how we get. So you mentioned there was at the Breakthrough Starshot Program, you’re heavily involved, Oumuamua aside, in our attempts to contact or communicate or visit potential alien civilizations elsewhere?
Avi Loeb (01:14:55):
Yes. I chair the advisory board for Breakthrough Starshot, which is an initiative –
Avi Loeb (01:15:03):
Breakthrough Starshot, which is an initiative attempting to develop the technology that would allow us to visit other stars. The idea there is that by physically visiting the neighborhood of a planet, we can learn much more about whether life may exist there. The only problem is that the nearest star, Proxima Centauri, is a four and a quarter light years away. So it takes light four and a quarter years to reach us from that star. In fact, next to Proxima Centauri, there is a planet, Proxima B, in the habitable zone, and if there are people out there, they still do not know the results of the election of 2016, because those signals will get there only in February, 2021. It just shows you how long it takes for signals to get from one star to another.
Avi Loeb (01:16:04):
But that means that if you want to reach the nearest star within our lifetime, meaning within 20 years or so, which is the goal that [Uri Menor 00:01:13] posed when he came to my office and asked whether I would like to lead this project. If you want to do that, you need to send a spacecraft that moves at the fifth of the speed of light. That is very challenging and that’s the technology that Breakthrough Starshot is focusing on. When he asked me, I told him, “Well, I have to think about it with my students and post-docs.” We thought about it for six months and then we came up with the suggestion that the only technology that works is pushing a LightSail with a very powerful beam and having a payload that is very lightweight, only a gram of material that has a camera, communication device, navigation device. That’s possible with present day miniaturization of electronics.
Avi Loeb (01:17:08):
Then with the LightSail technology, if you have a laser of 100 gigawatts shining on a sail that is roughly the size of a person outside the atmosphere, you can launch the sail to a fifth of the speed of light over a few minutes, by which time it will be five times farther than the moon is from us. Then if you launch it in the right direction, it can carry the electronics to the destination and take a photograph of the planet. So that would be a way of getting there quickly enough. Otherwise, if we were to send, for example, New Horizons or Voyager One- and Two- like missions, it would take them 50,000 years to reach Proxima Centauri. That’s the time that elapsed since the first humans left Africa. So if you want it to get there today, we would’ve needed to launch the spacecraft when the first humans left Africa.
Sean Carroll (01:18:17):
But these a breakthrough Starshot one gram little fellows would be … they wouldn’t be landing anywhere. They’d be passing through these other solar systems at point five-
Avi Loeb (01:18:28):
By the way, I should mention that if there are one gram spacecrafts flying through the solar system, we would never notice them.
Sean Carroll (01:18:37):
Well, I was going to say that the idea of this, you would push it and you’re pushing the one gram by itself, or is there a little sail attached to it?
Avi Loeb (01:18:46):
There is a sail attached to it and the sail weighs roughly a gram as well.
Sean Carroll (01:18:50):
Yeah. Okay.
Avi Loeb (01:18:52):
But since it’s so thin, it’s less than a micron in thickness, maybe a 10th of a micron and roughly the length of the height of a person. That is sufficient to bring the payload to a fraction of the speed of flight. Payload is attached to it. There is the question of what geometry to give to the sail. It’s not clear that the flat geometry is optima because it may not ride in a stable fashion on the laser beam. So we considered, for example, a sphere or other geometries. But it’s still work in progress. We are currently addressing three challenges in this project. One is developing what we call the photon engine, which is the laser that produces the very powerful beam on earth. The second challenge is the LightSail making it of sufficiently strong material that is highly reflective and doesn’t absorb much of the laser light because otherwise it will burn up quickly. The third challenge is communication at those great distances. That’s not easy. If you want to transmit a photograph from the distance of Proxima Centauri B to the earth, it’s a major challenge actually.
Sean Carroll (01:20:18):
Yeah, no, no. I can imagine that. Just to be super, duper clear, the idea that you’re sketching kind of bears a family resemblance to your idea for ʻOumuamua with the very large difference that ʻOumuamua is not moving anywhere near that fast.
Avi Loeb (01:20:32):
That’s right. The reason I thought about the LightSail in the first place is because I was engaged in this project. Now, if you look at the history of the search for extraterrestrial signals, when we developed radio technology for communication purposes, then we started to search for radio signals from the sky. When we developed lasers, we started to looking for that. I mean, obviously our imagination is limited by the technologies that we have, and we cannot imagine things that we have not mastered ourselves. So I find it completely natural to consider what we know. So since we are developing LightSails and Breakthrough Starshot is not the first to embark on this challenge and The Planetary Society launched LightSail 2 and JAXA, the Japanese space agency, had a demonstration of a LightSail. So this is maybe the wave of the future in terms of space exploration, and if we are working on that, why not imagine that another civilization already mastered this technology and it’s very common?
Sean Carroll (01:21:43):
Well, given that we are just beginning to even contemplate these technologies and think about them, whereas other civilizations we might bump into have been around for who knows, hundreds of millions of years longer, is there some credence to the idea that we should be prudent and not draw attention to ourselves? Should we be worried about letting people know that we’re here?
Avi Loeb (01:22:04):
I think it’s prudent to actually look and not make too much noise, but unfortunately the cat is out of the box. We already transmitted. We were careless over the past century. The loudest signals that we produced were with anti-ballistic missile radars. So after the Second World War, there were these radars, very powerful radio transmitters, that were searching for ballistic missiles from the ground. Their beams were extremely powerful. They can be seen by our radio telescopes across distances of tens of light years. So we already left some imprint and we should hope that nobody hostile is on the other end receiving it, because eventually we will find out if there is such entity.
Avi Loeb (01:23:10):
I think it’s prudent not to make too much noise, to just search for evidence for what is out there. Because based on human history, there were lots of predators. Cultures that were more advanced and were trying to concur new lands to harvest the resources there and dominate those lands. So there is no reason for us to be too loud. I think we should be quiet and first listen.
Sean Carroll (01:23:42):
That certainly makes sense to me. I know some people are very eager and convince themselves that if a civilization becomes officially technologically advanced, it must also be benevolent. But it’s a big risk to take, right, when we don’t really know for sure.
Avi Loeb (01:23:57):
Yeah, it’s a big risk, and by the way, speaking about risk, I do think right now all of our eggs are in one basket, the earth. It would make a lot of sense to spread the eggs in different baskets. So that if something catastrophic happened on Earth, because we misbehave or because of some catastrophe, at least humanity will exist somewhere else. It’s sort of like the Gutenberg revolution with the printing press. Before that, there were very few copies of the Bible and each of them was handwritten and very precious. But as soon as you made the duplicates with a printing press, each copy was not as valuable. If something bad happened to it, you could always find other copies. I think we, as a civilization, if we find life as we know it very precious, we should produce copies and send them to places. So going to Mars is a good idea, going beyond the solar system is a good idea. We cannot rest assured that if we stay here on Earth, that things will go our way.
Sean Carroll (01:25:08):
What is your attitude toward the fact that other stars are very far away, vis-a-vis our ability to get there? Do you think that it makes sense for human beings?
Avi Loeb (01:25:17):
I don’t think need to get there. I just wrote a Scientific American article called Noah’s Spacecraft. The idea was what is the modern version of Noah’s Ark? So Noah was worried about the flood and he collected all the animals. According to the mythological story of the Bible, he collected representatives of elephants and monkeys, all the animals, put them on a big ark that he constructed so that they would survive the flood, so that the precious life on earth would survive the flood, the great flood. You can imagine doing the same thing with a spaceship, but my point is that this could be a CubeSat you don’t need Noah’s Ark, which by the way, the Bible mentions the dimensions of and there were 100 meters by 10 meters and so forth. Very similar to the dimensions of ʻOumuamua.
Sean Carroll (01:26:11):
That’s what I was going to say, yeah.
Avi Loeb (01:26:12):
But getting back to the point, with the CubeSat, you can put a very capable computer on board and a 3D printer and artificial intelligence, equip the computer with the ability to store all the genetic information, let’s say about the life forms that we find on earth, and then if we understand how to make life artificially, then you can imagine that the 3D printer, once it gets to a place where there are raw materials, it could make life as we know it there. So instead of transporting, like Noah’s Ark, transporting people to places, you can reconstruct them there by just carrying the information about their DNA and using 3D printers to make life as we know it in distant locations. So that’s my version. Just the CubeSat. You don’t need a giant Noah’s Ark for that purpose.
Sean Carroll (01:27:18):
Well, I have a couple of questions about that. Would it be the right thing to do? Would it potentially get in the way of indigenous life growing up?
Avi Loeb (01:27:29):
That’s a good question. It depends how much you value our life relative to what may happen elsewhere naturally. If you’re a naturalist like Thoreau was … I live very close to Warden Pond where Thoreau wrote his book, and if you are naturalists like Thoreau was, then you would argue we should avoid contaminating other places with our life as much as possible, because nature is precious, we should let … and if we perish on this planet, so be it because that’s our natural way. So you can argue that. You can say, “Whatever happens to humanity on earth, that’s our fate. If we perish here and nobody hears about us in the distant future in the universe who cares? The universe is large. Lots of things are happening in it and we don’t amount to too much. We shouldn’t assign significance to our life.”
Avi Loeb (01:28:33):
But on the other hand, if you think, “Oh, actually we value life very much and we want to maintain its longterm future, then you want to make many copies of it. I’m sure there will be people on both sides. I think the naturalist approach would be less popular based on the way we behave with our industries and how much care we take of our planet. If you look at it right now, I think that most people care about reproducing themselves rather than maintaining the environment.
Sean Carroll (01:29:11):
So many things to talk about here. Yes. I think that there’s … I’m intrigued by this. I would want some sort of dead man switch, some sort of dead planet switch. Like if we destroy ourselves, then we spread ourselves elsewhere, but otherwise we can be a little bit more circumspect.
Avi Loeb (01:29:25):
That’d be interesting. Yeah. It reminds me of what, at some point, a friend of mine said, that he wants to have on his website a button saying, “Click here after I die.” Then when you click there, you will find the full obituary that includes all of his scientific accomplishments.
Sean Carroll (01:29:53):
Oh. There you go. Why not?
Avi Loeb (01:29:53):
It’s a similar idea that when catastrophe hits only, then you activate your plans.
Sean Carroll (01:30:00):
Let me give you the chance to say one more thing about what you’ve alluded to already, which is sort of the lessons for this kind of discussion we’ve been having for how science is done, both within academia, choosing topics and valuing certain kinds of research being done, but also the fact that whether we like it or not, some of our research is carried out in the public eye, and the public on the one hand wants to trust science, on the other hand, science is sometimes not done yet. And how do we make that balance?
Avi Loeb (01:30:32):
Yeah, so I think the most undervalued quality that I would like to highlight is innovation. I think it’s extremely important for the scientific community to encourage, to cultivate innovation. Right now it doesn’t look like that. A lot of the funding for grants is given to mainstream ideas that just add the nuance on an existing theme. The reason is simple. Because the people on the committees, the selection committees, are mainstream people that want to create echo chambers where they advocate how significant their contribution to the field was. And the way to achieve that is by educating students to reproduce what you’ve done, and so that you get this echo chamber of people saying the same things with more details.
Avi Loeb (01:31:23):
It’s just a mechanism for boosting their ego in some sense. If you have people like that on selection committees, they would try to fund projects that support their activity throughout their career, and continues to do along the same line rather than innovate and criticize and be open-minded about alternatives.
Avi Loeb (01:31:49):
I think that’s bad for science. In fact, if you look at the public sector, the commercial sector, you find that companies like Google do have within them blue sky research. That was true of Bell Labs in the old days and a lot of innovation came from that, a lot of Nobel prizes. So if the commercial sector recognizes the value of innovation more than the academic community, that’s an unfortunate situation that we’re at. I think it should change. I think there should be a fixed fraction of the funds allocated to innovative thinking. It will also change the atmosphere, there would be less bullying of anything that looks different. If you go to kindergartens, you see kids always bullying those that look different and the scientific community does the same thing. Whenever a proposal for an idea that is different than the one that is commonly adopted is made, then people bully that proposal.
Avi Loeb (01:32:58):
I think that’s bad for the health of the field. It’s bad for science. We should be open-minded. We should criticize based on evidence and rational arguments. So that’s point number one. The second is kids often are innocent when they explore the world. They don’t do it for boosting their ego and so forth. I would very much like my colleagues to behave more like kids, like being open-minded and discussing possibilities without dismissing them ahead of time. I wrote an article about this to the Harvard Gazette in which I encouraged my colleagues to behave more like kids. That that would be my wish, both in terms of funding and in terms of interactions with each other. I see that a lot of work needs to be done to make the scientific inquiry more honest and straightforward.
Sean Carroll (01:33:58):
No, I’m 100% in agreement with you there. I’ve come across the bullying if … There’s a thing that grows up as a scientist matures, where they try to discriminate between good work and bad work, and it’s not always completely objective and they have their biases and it’s just remarkably fast how quick scientists can knock down work that they’re not familiar with. But on the other hand, I recognize there’s a lot of crack pottery out there also, and it is not worth supporting. So it’s just so hard to get that balance exactly right.
Avi Loeb (01:34:27):
Yeah, but you see, this is called natural selection. I think the evidence and data should be the rulers, rather than people’s opinions. So what you find are fields that are saturated with subjective judgments as to what is appropriate to look at without any evidence. You have string theory for five decades being very popular, no evidence and it’s now not even predictive as to what we might look for in order to falsify it. You just have these cultures that are self perpetuating without a need for evidence anymore. Evidence is not the oxygen that drives them. It’s more intellectual gymnastics. I find that dangerous because that’s the way Aristotle operated, the ancient Greeks. We’ve learned a lot since then, that evidence is extremely important for the progress that we have and we’ve made progress, but there is some retreat and are even people advocating that we live in a simulation, which I find just like being on drugs in a way.
Sean Carroll (01:35:39):
Well, this is exactly the problem. One person’s scientific investigation is another person’s waste of time. So I’m agreeing with you in principle. I don’t have any concrete suggestions for making it better, but it’s something that we should try to think about. But let’s close up by asking a very different question. You’re very well known for working on many different kinds of things. We’ve been talking about the search for extraterrestrial life and ʻOumuamua and stuff like that, but you’re also the founder of The Black Hole Initiative and so forth. Let me give you this opportunity to say what is the most interesting thing you’re working on right now that has nothing to do with extra terrestrial life?
Avi Loeb (01:36:20):
Well, we think that we discovered the nearest black hole, and it’s about a thousand times the mass of the sun and it’s at a distance of a few hundred light years from us. Completely unexpected, we found some evidence for it. The paper is being refereed right now. To me, that’s very exciting because a black hole is a place … If I’m asked what would I like to visit, I would like to visit the vicinity of a black hole. Not get into it, because then you have a limited life inside before your body gets torn apart, but looking at it from a close distance would be quite amazing. So actually at a conference, at the annual conference of The Black Hole Initiative that we have at Harvard that I’m the founding director of, I once suggested in my closing remarks …
Avi Loeb (01:37:18):
I said that a black hole represents one place where you can actually test string theory, and the string theorists should plan on a field trip. If we have a nearby black hole, we should go there in the next conference so that they will test the theory by entering the black hole and getting close to the singularity. When I suggested that, Nima Arkani-Hamed shouted from the audience, “You must have an ulterior motive for sending string theorists into a black hole,” to which I didn’t respond.
Sean Carroll (01:37:53):
You did not respond, and I will not make you respond right now. We’ll let the audience think about that. So Avi Loeb, thanks so much for a incredibly provocative and fascinating conversation.
Avi Loeb (01:38:01):
My pleasure. Thank you.
[/accordion-item][/accordion]
Photons can have a certain twist. Intentionally twisted photons could be communication?
Maybe binary stars could have sub-text intentional pulses in them, an evolution of that clicking sound we hear.
Maybe superior life forms have no need to travel, just talk to each other, and engage in multi-million year conversations, and these are going on now?
Maybe entanglement of atoms could be directed and acted on by a higher life form– to have spooky action at a distance, sent to a target a thousand light years away.
The “Three Body Problem, that Chinese Trilogy, we use the sun to lens our broadcast.
Personally, I think its going on, we just dont recognize the signal, can’t pick it out from the noise.
Bob Newhart 70’s comedian, had a recent joke. A guy returns from Mars: “Are the aliens more advanced than we are?”, “yes, the returning astronaut tells them, about 6 weeks”.
Did he say the Ort Cloud reaches half way to Proxima Centari? 2 and one eighth light years, ?
Maybe a light sail rotates to prevent heating.
I think its ridiculous to assume predators in space. If you master the environment of a solar system, anything that evolves would be able to amply meet its own needs.
Millions of years to evolve. If we had that, wouldn’t it be great to read Sci-Fi that showed blue whales, dogs, squids, and orangutans all evolve, some of whom evolve past our own evolving ability, but share the Earth and the aliens are just from our own evolved ecosystems. Maybe one day I work for a dog, or a blue whale, or a crow?
I also think we should not put anymore pollution into the atmosphere, and the indulgence of space travel is way down the list for first actions with limited resources. If we could just sit quiet for 5 or 10 centuries, the Mozarts and Einsteins and Newtons will naturally come. What’s the need for immediate science progress.
Thanks for indulging the idle speculation of a non-scientist. I think half the motivation for cosmology is to dream.
Fun one today.
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This is very interesting. But I wonder what you think of the videos that were published by the New York Times and also in other places that showed UFOs that were picked up by the USA Navy pilots? Avi did say something about all the photographic evidence being fuzzy but these objects were tracked and accompanied by the commentary of experienced pilots. What do Avi and Sean think they are?
In response to HAL,
I highly recommend you have a listen to Joe Rogan’s podcast with Avi that he just released. It goes for about 2hrs on essentially the same topic as what Sean has discussed here with Avi, but Joe being Joe, is happy to entertain ideas that Sean, respectfully, is not.
There is no one out there, we are Alone!
The chance of life occurring from non-living molecules is so low that even if all Planets in all 10^500 Universes try it simultaneously for billions of years, it still wouldn’t have right odds to create a simple reproducible life molecule let alone a primitive cell.
Well, Arrokoth, the small Kuiper Belt object visited by New Horizons in 2019 apparently is formed by two (two!) almost pancake-like objects fused together, so maybe ʻOumuamua is natural after all 🙂
Anyway, this was an interesting conversation, for sure!
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There are times when a voice in the wilderness is the one saying the truth. This is not one of those times.
Hi Sean,
Your Mindscape podcast is a trusted source of good thinking (which is a scarce commodity in the Internet these days). Your episodes present an in-depth look at topics dealing with science and society with characteristic intellectual integrity. Thanks for your efforts.
Your recent conversation with Avi Loeb, however, did not measure up to your high standards of intellectual integrity. Here is why: 1. Words matter, and in this society, scientists need to understand that they have a responsibility and be very careful about the ideas they communicate and how they present them; 2. The choice of topic (‘evidence’ for alien intelligent civilizations) is particularly challenging given the tendency of certain audiences to appropriate unsound claims in the name of science and the media readiness to amplify them; and, 3. The arguments presented by Prof. Loeb were weak (some even silly) and throughout the conversation he made categorical statements against the “main stream” scientists which were unfair, unjustified and damaging, but you seemed to agree with everything he said and did not challenge him. Let me elaborate.
We scientists in general are not very savvy when choosing how to engage with the media. Some scientists love having their names reaching headlines and to reach that goal, they sacrifice honesty and rigor. We have seen the public relations damage generated, case after case, of scientist rushing to the press to present their spectacular discovery only to see them proven false shortly after. BICEP2, OPERA, Life in Venus, Life in Mars, come to mind. I think you would agree that these careless false positives result in eroding the trust that the public has in science. Claiming that we have evidence for alien civilizations should raise red flags all over. The claim has all the marks of a premature, unjustified and exaggerated claim.
The main argument presented by Prof. Loeb is the classical “mystery therefore miracle” argument loved by creationists. He insisted that main stream scientists are a bunch of conservative minds afraid of looking at the telescope (yes, he compared us to those who refused to look through Galileo’s telescope afraid of seeing their worldview crumbling). Not only that, we are also corrupt! (the grant referees only give grants to projects that support their pet theory). How can you allow these categorical statements go unchallenged?
Prof. Loeb referred to the “arrogance” of us weak little humans pretending to be the only intelligence in the vast universe. But, wait a minute, his argument that “there is no natural explanation” is even more arrogant! What the argument implies is that we have exhausted all possible natural explanations (and he is sure, right?) Isn’t that arrogance? He knows ALL the physics that there is and he knows that ALL the physics knowledge has been exhausted and yet it does not explain Oumuamua. Is he sure we have explored ALL possible natural explanations? What if there is a prosaic explanation? Low probability accidents happen (the meteorite that killed dinosaurs 65 million years ago…), what if Oumuamua is a big sheet of solid ice chipped away from a collision of a meteorite with a frozen ocean in some far away planet, or some other ‘low probability’ accident? Bayesian thinking (as you pointed out) is of great help here: a natural explanation (however outlandish and unlikely) is orders of magnitude more probable than alien civilizations (is that arrogance?). We have evidence that low probability accidents do happen. We have zero evidence that alien civilizations exist (and are within reach and are interested in sending us – weak and little terrestrials – signals). You should tell Prof. Loeb how to update probabilities.
Prof. Loeb made use of the argument of falsification to support his claim (while also using it to criticize inflationary models). Someone needs to explain Prof. Loeb how falsification works. He said that his “alien civilization hypothesis” is falsifiable because we can simply keep looking and at some point in time, we should find another instance. In contrast – said Loeb – inflation is not scientific because the model can be adjusted to explain any observation (or absence of it) that experimentalist come up with. This is totally wrong. Assuming that the Popperian criteria is a good discriminator (which is not, as has been amply shown by multiple critics, such as Van Orman Quine), saying that “seeing more instances” is a falsifiable prediction does not constitute validation of the hypothesis as a legitimate scientific hypothesis. What if the alien civilization in question decided to send us just one probe? How many years do we need to wait with lack of positive observations before we can give up and discard the hypothesis? Given the paucity of rare astronomical observations, this hypothesis will be classified as a scientific hypothesis for the next few million years (that is, if we follow the misleading version of falsifiability that Loeb is using). At least inflation (or some of the various version of inflation) does make bold and falsifiable predictions in the spirit of Popper (i.e. the index of the power spectrum of primordial perturbations).
In summary, it is irresponsible for a scientist (a reputable one, as expected from a Harvard Professor) to use on-line platforms and the media to spread highly speculative claims in the name of science. This type of hype exacerbates the already toxic issue of public trust in science. So, please Sean do plan a follow up episode, do not leave Loeb off the hook, challenge him.
It seems to me that the guest told the name of Nima Arkani-Hamed at the very end of the podcast, but the name in the transcript appears as Neymar Connie Hammad. It could be worth correcting that, unless the mistake is mine.
@Sergio Torres: thank you for your very well written criticism of this episode. This episode also triggered a my skeptic mindset. So when I assume that there’s probably no other intelligent life I’m arrogant? That’s not a scientific argument at all.
Scientific American published an article in september 2018 called “Are Humans Alone in the Milky Way?” with the subtitle “Why we are probably the only intelligent life in the galaxy” which has a lot of arguments why the chances are extremely small.
For example, it took almost 2 billion years to evolve from single cell organisms (Prokaryotes) to the next step (Eukaryotes) and then another billion years to form multicellular life.
Another example: the goldilocks zone in the Milky Way where life is possible. When you get closer to the center there are to many gamma-ray bursts and further on the outside where stars are to sparse for enough metals to build up to form rocky planets.