What Happened at the Big Bang?

I had the pleasure earlier this month of giving a plenary lecture at a meeting of the American Astronomical Society. Unfortunately, as far as I know they don’t record the lectures on video. So here, at least, are the slides I showed during my talk. I’ve been a little hesitant to put them up, since some subtleties are lost if you only have the slides and not the words that went with them, but perhaps it’s better than nothing.

My assigned topic was “What We Don’t Know About the Beginning of the Universe,” and I focused on the question of whether there could have been space and time even before the Big Bang. Short answer: sure there could have been, but we don’t actually know.

So what I did to fill my time was two things. First, I talked about different ways the universe could have existed before the Big Bang, classifying models into four possibilities (see Slide 7):

  1. Bouncing (the universe collapses to a Big Crunch, then re-expands with a Big Bang)
  2. Cyclic (a series of bounces and crunches, extending forever)
  3. Hibernating (a universe that sits quiescently for a long time, before the Bang begins)
  4. Reproducing (a background empty universe that spits off babies, each of which begins with a Bang)

I don’t claim this is a logically exhaustive set of possibilities, but most semi-popular models I know fit into one of the above categories. Given my own way of thinking about the problem, I emphasized that any decent cosmological model should try to explain why the early universe had a low entropy, and suggested that the Reproducing models did the best job.

My other goal was to talk about how thinking quantum-mechanically affects the problem. There are two questions to ask: is time emergent or fundamental, and is Hilbert space finite- or infinite-dimensional. If time is fundamental, the universe lasts forever; it doesn’t have a beginning. But if time is emergent, there may very well be a first moment. If Hilbert space is finite-dimensional it’s necessary (there are only a finite number of moments of time that can possibly emerge), while if it’s infinite-dimensional the problem is open.

Despite all that we don’t know, I remain optimistic that we are actually making progress here. I’m pretty hopeful that within my lifetime we’ll have settled on a leading theory for what happened at the very beginning of the universe.

Posted in Science, Time | 71 Comments

Memory-Driven Computing and The Machine

Back in November I received an unusual request: to take part in a conversation at the Discover expo in London, an event put on by Hewlett Packard Enterprise (HPE) to showcase their new technologies. The occasion was a project called simply The Machine — a step forward in what’s known as “memory-driven computing.” On the one hand, I am not in any sense an expert in high-performance computing technologies. On the other hand (full disclosure alert), they offered to pay me, which is always nice. What they were looking for was simply someone who could speak to the types of scientific research that would be aided by this kind of approach to large-scale computation. After looking into it, I thought that I could sensibly talk about some research projects that were relevant to the program, and the technology itself seemed very interesting, so I agreed stop by London on the way from Los Angeles to a conference in Rome in honor of Georges Lemaître (who, coincidentally, was a pioneer in scientific computing).

Everyone knows about Moore’s Law: computer processing power doubles about every eighteen months. It’s that progress that has enabled the massive technological changes witnessed over the past few decades, from supercomputers to handheld devices. The problem is, exponential growth can’t go on forever, and indeed Moore’s Law seems to be ending. It’s a pretty fundamental problem — you can only make components so small, since atoms themselves have a fixed size. The best current technologies sport numbers like 30 atoms per gate and 6 atoms per insulator; we can’t squeeze things much smaller than that.

So how do we push computers to faster processing, in the face of such fundamental limits? HPE’s idea with The Machine (okay, the name could have been more descriptive) is memory-driven computing — change the focus from the processors themselves to the stored data they are manipulating. As I understand it (remember, not an expert), in practice this involves three aspects:

  1. Use “non-volatile” memory — a way to store data without actively using power.
  2. Wherever possible, use photonics rather than ordinary electronics. Photons move faster than electrons, and cost less energy to get moving.
  3. Switch the fundamental architecture, so that input/output and individual processors access the memory as directly as possible.

Here’s a promotional video, made by people who actually are experts.

The project is still in the development stage; you can’t buy The Machine at your local Best Buy. But the developers have imagined a number of ways that the memory-driven approach might change how we do large-scale computational tasks. Back in the early days of electronic computers, processing speed was so slow that it was simplest to store large tables of special functions — sines, cosines, logarithms, etc. — and just look them up as needed. With the huge capacities and swift access of memory-driven computing, that kind of “pre-computation” strategy becomes effective for a wide variety of complex problems, from facial recognition to planing airline routes.

It’s not hard to imagine how physicists would find this useful, so that’s what I briefly talked about in London. Two aspects in particular are pretty obvious. One is searching for anomalies in data, especially in real time. We’re in a data-intensive era in modern science, where very often we have so much data that we can only find signals we know how to look for. Memory-driven computing could offer the prospect of greatly enhanced searches for generic “anomalies” — patterns in the data that nobody had anticipated. You can imagine how that might be useful for something like LIGO’s search for gravitational waves, or the real-time sweeps of the night sky we anticipate from the Large Synoptic Survey Telescope.

The other obvious application, of course, is on the theory side, to large-scale simulations. In my own bailiwick of cosmology, we’re doing better and better at including realistic physics (star formation, supernovae) in simulations of galaxy and large-scale structure formation. But there’s a long way to go, and improved simulations are crucial if we want to understand the interplay of dark matter and ordinary baryonic physics in accounting for the dynamics of galaxies. So if a dramatic new technology comes along that allows us to manipulate and access huge amounts of data (e.g. the current state of a cosmological simulation) rapidly, that would be extremely useful.

Like I said, HPE compensated me for my involvement. But I wouldn’t have gone along if I didn’t think the technology was intriguing. We take improvements in our computers for granted; keeping up with expectations is going to require some clever thinking on the part of engineers and computer scientists.

Posted in Technology | 19 Comments

Quantum Is Calling

Hollywood celebrities are, in many important ways, different from the rest of us. But we are united by one crucial similarity: we are all fascinated by quantum mechanics.

This was demonstrated to great effect last year, when Paul Rudd and some of his friends starred with Stephen Hawking in the video Anyone Can Quantum, a very funny vignette put together by Spiros Michalakis and others at Caltech’s Institute for Quantum Information and Matter (and directed by Alex Winter, who was Bill in Bill & Ted’s Excellent Adventure). You might remember Spiros from our adventures emerging space from quantum mechanics, but when he’s not working as a mathematical physicist he’s brought incredible energy to Caltech’s outreach programs.

Now the team is back again with a new video, this one titled Quantum is Calling. This one stars the amazing Zoe Saldana, with an appearance by John Cho and the voices of Simon Pegg and Keanu Reeves, and of course Stephen Hawking once again. (One thing about Caltech: we do not mess around with our celebrity cameos.)

If you’re interested in the behind-the-scenes story, Zoe and Spiros and others give it to you here:

If on the other hand you want all the quantum-mechanical jokes explained, that’s where I come in:

Jokes should never be explained, of course. But quantum mechanics always should be, so this time we made an exception.

Posted in Entertainment, Science | 5 Comments

Thanksgiving

This year we give thanks for a feature of the physical world that many people grumble about rather than celebrating, but is undeniably central to how Nature works at a deep level: the speed of light. (We’ve previously given thanks for the Standard Model Lagrangian, Hubble’s Law, the Spin-Statistics Theorem, conservation of momentum, effective field theory, the error bar, gauge symmetry, Landauer’s Principle, the Fourier Transform and Riemannian Geometry.)

The speed of light in vacuum, traditionally denoted by c, is 299,792,458 meters per second. It’s exactly that, not just approximately; it turns out to be easier to measure intervals of time to very high precision than it is to measure distances in space, so we measure the length of a second experimentally, then define the meter to be “the distance that light travels 299,792,458 of in one second.” Personally I prefer to characterize c as “one light-year per year”; that’s equally exact, and it’s easier to remember all the significant figures that way.

There are a few great things about the speed of light. One is that it’s a fixed, universal constant, as measured by inertial (unaccelerating) observers, in vacuum (empty space). Of course light can slow down if it propagates through a medium, but that’s hardly surprising. The other great thing is that it’s an upper limit; physical particles, as far as we know in the real world, always move at speeds less than or equal to c.

That first fact, the universal constancy of c, is the startling feature that set Einstein on the road to figuring out relativity. It’s a crazy claim at first glance: if two people are moving relative to each other (maybe because one is in a moving car and one is standing on the sidewalk) and they measure the speed of a third object (like a plane passing overhead) relative to themselves, of course they will get different answers. But not with light. I can be zipping past you at 99% of c, directly at an oncoming light beam, and both you and I will measure it to be moving at the same speed. That’s only sensible if something is wonky about our conventional pre-relativity notions of space and time, which is what Einstein eventually figured out. It was his former teacher Minkowski who realized the real implication is that we should think of the world as a single four-dimensional spacetime; Einstein initially scoffed at the idea as typically useless mathematical puffery, but of course it turned out to be central in his eventual development of general relativity (which explains gravity by allowing spacetime to be curved).

Because the speed of light is universal, when we draw pictures of spacetime we can indicate the possible paths light can take through any point, in a way that will be agreed upon by all observers. Orienting time vertically and space horizontally, the result is the set of light cones — the pictorial way of indicating the universal speed-of-light limit on our motion through the universe. Moving slower than light means moving “upward through your light cones,” and that’s what all massive objects are constrained to do. (When you’ve really internalized the lessons of relativity, deep in your bones, you understand that spacetime diagrams should only indicate light cones, not subjective human constructs like “space” and “time.”)

Light Cones

The fact that the speed of light is such an insuperable barrier to the speed of travel is something that really bugs people. On everyday-life scales, c is incredibly fast; but once we start contemplating astrophysical distances, suddenly it seems maddeningly slow. It takes just over a second for light to travel from the Earth to the Moon; eight minutes to get to the Sun; over five hours to get to Pluto; four years to get to the nearest star; twenty-six thousand years to get to the galactic center; and two and a half million years to get to the Andromeda galaxy. That’s why almost all good space-opera science fiction takes the easy way out and imagines faster-than-light travel. (In the real world, we won’t ever travel faster than light, but that won’t stop us from reaching the stars; it’s much more feasible to imagine extending human lifespans by many orders of magnitude, or making cryogenic storage feasible. Not easy — but not against the laws of physics, either.)

It’s understandable, therefore, that we sometimes get excited by breathless news reports about faster-than-light signals, though they always eventually disappear. But I think we should do better than just be grumpy about the finite speed of light. Like it or not, it’s an absolutely crucial part of the nature of reality. It didn’t have to be, in the sense of all possible worlds; the Newtonian universe is a relatively sensible set of laws of physics, in which there is no speed-of-light barrier at all.

That would be a very different world indeed. Continue reading

Posted in Science | 25 Comments

Gifford Lectures on Natural Theology

In October I had the honor of visiting the University of Glasgow to give the Gifford Lectures on Natural Theology. These are a series of lectures that date back to 1888, and happen at different Scottish universities: Glasgow, Aberdeen, Edinburgh, and St. Andrews. “Natural theology” is traditionally the discipline that attempts to learn about the nature of God via our experience of the world (in contrast to by revelation or contemplation). The Gifford Lectures have always interpreted this regime rather broadly; many theologians have given the talks, but also people like Neils Bohr, Arthur Eddington, Hannah Arendt, Noam Chomsky, Carl Sagan, Richard Dawkins, and Steven Pinker.

Sometimes the speakers turn their lectures into short published books; in my case, I had just written a book that fit well into the topic, so I spoke about the ideas in The Big Picture. Unfortunately the first of the five lectures was not recorded, but the subsequent four were. Here are those recordings, along with a copy of my slides for the first talk. It’s not a huge loss, as many of the ideas in the first lecture can be found in previous talks I’ve given on the arrow of time; it’s about the evolution of our universe, how that leads to an arrow of time, and how that helps explain things like memory and cause/effect relations. The second lecture was on the Core Theory and why we think it will remain accurate in the face of new discoveries. The third lecture was on emergence and how different ways of talking about the world fit together, including discussions of effective field theory and why the universe itself exists. Lecture four dealt with the evolution of complexity, the origin of life, and the nature of consciousness. (I might have had to skip some details during that one.) And the final lecture was on what it all means, why we are here, and how to live in a universe that doesn’t come with any instructions. Enjoy!

(Looking at my YouTube channel makes me realize that I’ve been in a lot of videos.)

Lecture One: Cosmos, Time, Memory (slides only, no video)
Slideshare

Lecture Two: The Stuff of Which We Are Made

Lecture Three: Layers of Reality

Lecture Four: Simplicity, Complexity, Thought

Lecture Five: Our Place in the Universe

Posted in Big Picture, Philosophy, Religion, Science | 11 Comments

Talking About Dark Matter and Dark Energy

Trying to keep these occasional Facebook Live videos going. (I’ve looked briefly into other venues such as Periscope, but FB is really easy and anyone can view without logging in if they like.)

So here is one I did this morning, about why cosmologists think dark matter and dark energy are things that really exist. I talk in particular about a recent paper by Nielsen, Guffanti, and Sarkar that questioned the evidence for universal acceleration (I think the evidence is still very good), and one by Erik Verlinde suggesting that emergent gravity can modify Einstein’s general relativity on large scales to explain away dark matter (I think it’s an intriguing idea, but am skeptical it can ever fit the data from the cosmic microwave background).

Feel free to propose topics for future conversations, or make suggestions about the format.

Posted in Science | 54 Comments

Leonard Cohen

What a goddamn week. Leonard Cohen, one of the greatest singer-songwriters in living memory, has died at age 82. His music meant a lot to me personally, as it did to countless others. Usually sad, sometimes melodramatic, always thoughtful and poetic and provocative. I never met him in person (though I did go to a couple of concerts), but he lived not too far away from me in LA, and somehow felt as if I knew him. We’ll miss you, Leonard.

Let’s hope he was right about this democracy thing.

Posted in Music | 30 Comments

The Future of Democratic Values

Hey, did you know we are having an election here in the United States? I think I saw it mentioned on TV. Whatever your preferences may be, everyone eligible should try to get out and vote.

This election has, without a doubt, been somewhat unique. I’m cautiously optimistic that Hillary Clinton will win, that we will celebrate the election of the first female President in the history of the republic, and that she will do a relatively good job — although as a good Bayesian I know that empirical predictions are never certain, and in an atmosphere like this uncertainty runs relatively high.

Even if Clinton wins and the U.S. avoids complete embarrassment, I’m still very worried about what this election has revealed about the state of the country. No matter who our next President might be, there are real reasons to be concerned that the U.S. is veering away from some of the foundational principles that are necessary to a functioning democracy. That may sound alarmist, but I don’t think it’s unwarranted. Historically, democracies don’t always last forever; we’d be foolish to think that it can’t happen here.

This isn’t a worry about the specific horrible wrongness of Donald Trump — it’s a worry about the forces that propelled him to the nomination of one of our two major political parties, and the fires he so willingly stoked along the way. Just as a quick and hopelessly incomplete recap:

  • Trump built his early political notoriety via “birtherism,” explicitly working to undermine the legitimacy of our elected President.
  • He has continually vilified immigrants and foreigners generally, promoting an us-against-them mentality between people of different races and ethnicities.
  • He has pledged to violate the Constitutional principle of freedom of religion, from banning Muslims from entering the country to tracking ones that are here.
  • His campaign, and the Republican party more generally, has openly engaged in suppressing the vote from groups unlikely to support him. (“‘We have three major voter suppression operations underway,’ says a senior [Trump] official.”)
  • He has glorified violence against protesters who disagree with him.
  • He has lied at an unprecedented, astonishing rate, secure in the knowledge that his statements will be taken as true by a large fraction of his intended audience.
  • He has presented himself as a uniquely powerful strongman who can solve problems through his personal force of will, and spoke admiringly of dictators from Vladimir Putin to Kim Jong-un to Saddam Hussein.
  • He has vowed that if he wins the election, he will seek vengeance on those who opposed him, including throwing his opponent into prison.
  • He has repeatedly cast doubt on the legitimacy of the election outcome, implying that he would refuse to accept the result if he lost.
  • He has pointed fingers at a shadowy global conspiracy in charge of world finance, often with explicitly anti-Semitic overtones.
  • Several Republican politicians have broached the prospect of refusing to confirm any Supreme Court nominees from a Democratic President.
  • A government agency, the FBI, has interfered in a Presidential election.
  • Republicans have accused Democratic officeholders of being traitors.
  • A number of Trump supporters have spoken of the prospect of violent resistance if Clinton is elected.

This is not a list of “why Donald Trump is a bad person who is disastrously unqualified for the Presidency”; that would be much longer. Rather, I wanted to highlight features of the campaign that are specifically attacks on (small-“d”) democratic norms and values. The assumptions, often unspoken, by which legitimate political opponents have generally agreed to operate by over the course of the last two centuries and more. Not all of them, of course; there are glaring exceptions, authoritarians who have run roughshod over one or more of these norms in the name of personal glory. History generally looks down upon them, and we consider ourselves fortunate that they didn’t have greater success. But fortune can run out.

The most worrisome aspect of the situation is the very real prospect that these attacks on the foundations of liberal democracy will not simply disappear once Donald Trump rides off into the gold-plated sunset; that they will be seized upon and deployed by other politicians who couldn’t help but notice Trump’s success. If that’s the case, we will have a real reason to be concerned that American democracy will stop working, perhaps sooner rather than later. I don’t think it’s likely that such a disastrous scenario would come to pass, but one has to balance the small likelihood against the devastating consequences — and right now the probability seems closer to 0.05 than to 10-5.

Democracy is a curious and fragile thing. It’s not just “majority rules”; crucial to the project are the ideas that (1) minority rights are still respected, and (2) in return, losing minorities respect electoral outcomes. It’s the second of these that is under siege at the moment. Since the time of the Federalist Papers, it’s been understood that democracy is an attempt to provide common self-rule for people who don’t agree on everything, but who at least share the common values of democracy itself. Having strong, even extremely passionate, political disagreements is inevitable in a democratic system. The question is whether we cast those with whom we disagree as enemies, traitors, and cheaters who must be opposed in every measure at every turn; or as partners in a grand project with whom we can fiercely disagree and yet still work with.

I don’t claim to have a complete understanding of how we got to this precarious point, though there are a number of factors that certainly have contributed. Continue reading

Posted in Humanity, Politics | 72 Comments

Entropy and Complexity, Cause and Effect, Life and Time

Finally back from Scotland, where I gave a series of five talks for the Gifford Lectures in Glasgow. The final four, at least, were recorded, and should go up on the web at some point, but I’m not sure when.

Meanwhile, I had a very fun collaboration with Henry Reich, the wizard behind the Minute Physics videos. Henry and I have known each other for a while, and I previously joined forces with him to talk about dark energy and the arrow of time.

This time, we made a series of five videos (sponsored by Google and Audible.com) based on sections of The Big Picture. In particular, we focused on the thread connecting the arrow of time and entropy to such everyday notions of cause and effect and the appearance of complex structures, ending with the origin of life and how low-entropy energy from the Sun powers the biosphere here on Earth. Henry and I wrote the scripts together, based on the book; I read the narration, and of course he did the art.

Enjoy!

  1. Why Doesn’t Time Flow Backwards?
  2. Do Cause and Effect Really Exist?
  3. Where Does Complexity Come From?
  4. How Entropy Powers the Earth
  5. What Is the Purpose of Life?
Posted in Big Picture, Science, Time | 27 Comments

Live Q&As, Past and Future

On Friday I had a few minutes free, and did an experiment: put my iPhone on a tripod, pointed it at myself, and did a live video on my public Facebook page, taking questions from anyone who happened by. There were some technical glitches, as one might expect from a short-notice happening. The sound wasn’t working when I first started, and in the recording below the video fails (replacing the actual recording with a still image of me sideways, for inexplicable reasons) just when the sound starts working. (I don’t think this happened during the actual event, but maybe it did and everyone was too polite to mention it.) And for some reason the video keeps going long after the 20-some minutes for which I was actually recording.

But overall I think it was fun and potentially worth repeating. If I were to make this an occasional thing, how best to do it? This time around I literally just read off a selection of questions that people were typing into the Facebook comment box. Alternatively, I could just talk on some particular topic, or I could solicit questions ahead of time and pick out some good ones to answer in detail.

What do you folks think? Also — is Facebook Live the right tool for this? I know the kids these days use all sorts of different technologies. No guarantees that I’ll have time to do this regularly, but it’s worth contemplating.

What makes the most sense to talk about in live chats?
Posted in Internet, Personal | 41 Comments