From the Beginning to Now | Lawrence Krauss | EP 182

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Hello everyone! I'm pleased today, really quite pleased to have Dr. Lawrence Krauss with me. He is an internationally known theoretical physicist, and I've wanted to talk to an internationally known theoretical physicist for about 30 years, whose research is focused on the interface between elementary particle physics and cosmology, including the fundamental structure of matter and the evolution of the universe.

Among his numerous important and interesting scientific contributions was his 1995 proposal that most of the energy of the universe resided in empty space. During his career, Professor Krauss has held endowed professorships and distinguished research appointments at major institutions all over the world, including Harvard, Yale, and CERN. He is the author of 500 publications and 11 popular books, including the international bestsellers "The Physics of Star Trek" and "A Universe from Nothing."

His most recent book, "The Physics of Climate Change," was released in February of this year, 2021. He won a major award from all three of the U.S. national physics societies, as well as the 2012 Public Service Award from the National Science Board for his contributions to the public understanding of science. He currently serves as president of the Origins Project Foundation, which celebrates science and culture by connecting scientists, artists, writers, and celebrities with the public through special events, online discussions, and unique travel opportunities.

The foundation produces the Origins Podcast, featuring dialogues with some of the most interesting people in the world discussing issues that address the global challenges of the 21st century. Thank you very much for agreeing to talk to me today.

"It's great to be with you virtually, Jordan."

Okay, so I have a question, and I'm going to jump right into it. I wrote a paper with a couple of my students. I was the final author on the paper. We tried to relate the experience of anxiety to a physical property, to entropy, which I suppose might be well-defined as a physical property.

The idea was, and you tell me what you think of this as a physicist, if you would, okay? The idea was that human beings are always trying to calculate a path from one point to another, and the length of the path is going to be proportionate, in some sense, to the energy used to undertake the task. Right? The longer the path, the more energy. Now, we generally take a path to something that we regard as valuable, and sources of energy, for example, are extremely valuable to us. And so, that might be a shortcut to doing some work because that's translatable into goods.

Anyways, the cost of the voyages is an important consideration. So, whenever uncertainty is added to a plan, it becomes more and more difficult to formulate a map that lays out the trajectory appropriately. And you need a marker for that, a psychological marker.

And so, we assume that as the certainty of the path that you're going to take, according to, you know, given a particular reward, is as the uncertainty that increased, you'd experience this unease. And the unease was a marker of the increased complexity. So, and that would be the increased entropy, in some sense, of either of the landscape or your representation of the landscape, or maybe of the disjunction between the two.

So, the first question I would have is, I guess first of all, was that a comprehensible explanation? And second of all, is that a reasonable way of construing entropy?

"Well, yeah. The answer is, it's not unreasonable in a general sense. I am very wary. I remember, you know, when I was a kid, actually in Canada, and I took, I remember I was always interested in science, but in university I took sociology. And I remember becoming fascinated at the time by various sociologists' attempts to define concepts as if borrow from physics to define concepts.

And I thought, wow, this is fascinating! As I got to know more physics, I became more wary of that application because certain things that are well-defined and appropriate in physical context become less well-defined and perhaps have less utility. They sound good in a social science paper, but whether they actually allow predictive value is the important question, right? And so that's exactly why I'm asking the question, isn't it? Because I'm sure I'm aware of that problem, and that's I wanted to see if there's some bedrock there."

"Well, you know, I think that you've got something in a sense that in physics, actually in different contexts, there's trade-offs between energy and entropy. And they're well-defined thermodynamic quantities that are defined depending upon what you hold fixed and what you don’t and how the system evolves, whether it evolves to a situation of least energy or least what's called free energy, which depends or enthalpy, which includes that entropy aspect, depending upon the specific circumstances of the physical situation.

But the complexity of a path is related to the entropy is a really appropriate approach because entropy really describes, and maybe it's probably useful for your listeners who may not be as aware of entropy as you are, that what it really describes is a macroscopic system that has many different internal states it can be in. And entropy really just describes how many internal states a system has for a given macroscopic configuration of—say—temperature and overall energy.

You know, a single particle in this box may have a restricted configuration, but the atoms in my body and your body can be in very many different configurations and still be at the same temperature. So there's a lot of entropy associated with a macroscopic object. And the more, if you wish, the more internal possibilities that a system has to explore within the confines of some external parameter that's restricting it, like the total energy of the system or its heat content or some other aspect or its volume, the more internal configurations the system has to explore, the bigger its entropy."

"So now, okay, so I was thinking, for example, I'll give you a narrative example. It's actually apropos because my car did break down today. But when you're in your car and you're driving along and everything is going according to your desires and expectations, then you're generally in a low anxiety state. But then imagine that the car emits an unexpected noise and starts to buck. Now, one of the things I've proposed is that at that point you're actually no longer in a car and that's why you get upset because the car is actually functionally described as a category.

The car is something that gets you from point A to B, and as long as it's performing that function, then that category was a very low-resolution category. That category suffices. But as soon as something goes wrong. The same thing happens when your computer does something you don’t want it to. There are so many different states that that thing could be in that your body signals that emergent complexity, and it signals the fact that you can no longer compute the cost of being where you are.

And you know there are fantasies that are associated with that that seem like attempts to map it right, like this could be wrong, this could be wrong, I might go to a crooked mechanic, I might get ripped off, I might not be able to fix this car, maybe I can't afford it, I won't get to work, like the whole panoply of possibility expands very, very suddenly, and that produces an intense physiological response, which it should do. I mean, we should have physiological responses to fundamental physical realities.

We should—most of us ignore them, and I think that's the point."

"The physiological response you're talking about is real, but in fact, when the car is operating well, all of those possibilities also exist—you just block them out of your mind. I mean, because..."

"Right. Well, that's an interesting thing too, right? Because it's appropriate in some sense. We were trying to understand, to some degree, the conditions under which it's appropriate to block them out of your mind, and it's something like as long as your predictions... But they're based on your desires. But we won't get into that. As long as your predictions match the ongoing flow of events, then you can take all of the presuppositions that order things for granted.

I mean, I agree with you completely that all those things could be going wrong at any time. The same is true of the complexity of your body, right? I mean, it isn't necessarily the case that just because you feel good right now you're going to feel good the next moment, and there's an endless number of things that can go wrong. But it's also not helpful to be aware of all of those possibilities if they're not likely to happen.

So it isn't exactly that you ignore them; it's that you assume their functional significance is zero as long as your plan is operative."

"And well, yeah, but I think it goes back to the human reason being the slave of passion. I think the point is we you're right. It's not worthwhile assuming all the negative things that can happen. If it did, you wouldn't do anything, right? If you want to take any action, if you assume all the negative things that could result from it, you probably wouldn't act at all. One of the things that I think we do, and one of the problems we have as a society, in fact, it's related to even my last book, is that we tend—one of the things that science does, which I think is so useful, is it quantifies uncertainty.

Uncertainty is a central part of science. And often, too often, journalists and other people talk about uncertainty as if it's a bad thing. In science, it's actually a very good thing because we can define, we can quantitatively say how accurate our result is or how likely or unlikely a bunch of possibilities are. I think psychologically, and that I would say that's an anxiety reduction phenomena. I mean, when you enter into a contract, you're doing that with someone too, because what you're saying is, well, I could be any number of possibilities, but contractually I'll limit myself to this manifestation, and that can make you calm and it can make us able to cooperate.

And so I think that it's not only a scientific theory that provides that function, it's a science would be a subset of practical theory and practical theories that are very useful exactly for that reason."

"They are, but I think, I personally think more people could be—I think it would be a better—it would help people if they accepted the existence of uncertainty, you know, in a more open way. I think people are afraid of uncertainty, and I think if we, you know, including death and the universe and all sorts of other things we may talk about.

And I think accepting it as a realistic likelihood is a healthy thing because, again, it relates to some extent to some of the, I think, social problems that are happening now, of kids being coddled. If you accept that bad things can happen, then when you do anything, you know, it’s part of living, then you won't be so anxious when they do. I think, I mean, you won't be so fearful of that possibility.”

"Okay, yeah, your car can break down, but the world isn't over. You know, there's a whole series of other activities you can take place that will allow the world to go on, that will allow you to continue to function. But recognizing it, recognizing at some level a spectrum of possibilities in advance, in my opinion, and I'm not a psychologist, but in my opinion, certainly personally, I find it psychologically helpful."

"Yeah, well, it is definitely the case that's promoted among psychologists. I mean, behavioral psychologists—you may imagine that one thing you want is a theoretical configuration that encapsulates uncertainty—that's a belief system, let's say—and you measure it by its functional utility. Does it allow you to acquire what you desire when you act it out? But you need a codicil along with that, which is, well, what do you do when your theory goes wrong?

And one of the answers that's been provided to that question from the behavioral perspective is coded in narrative as well, though, is approach uncertainty voluntarily and cautiously; don't avoid it. And that triggers another mechanism, which is the capacity to explore, to generate new theories, to select among them, especially in collaboration with other people and to regenerate your pre-existing models.

So you need the model and you need a system for updating the model. And I see that expressed pretty formally in science in the scientific technique."

"Oh, it's a central part of the scientific method. And I would also argue in business and many other areas of human activity that people don't realize. Science, what I try and convince people of, they don't realize that scientists actually really like to be wrong, at least, you know, whether personally they do, it's a different question. But the process of science, it's exciting to be wrong because it means there's more to learn, first of all, and it might mean you've discovered something.

And one of the things, you know, I was chairman of the physics department for a long time, and then we started a program, a master's degree in physics entrepreneurship, which the business school dean said was an oxymoron. But I don't think so because I think scientists and business people are very similar because often what I realize we don't do well enough for children, for students, or whatever, is teach them how to fail effectively.

We give them problem sets that they're guaranteed that have direct answers and they can get the correct, and we even give them PhDs, where they're more or less guaranteed to at least come to some collusion. But in the real world of research and business and many other things, you may find that you have to learn how well the question I was asking was really not a good question. How can I use what I've already accumulated to nevertheless provide me something useful? Maybe ask a different question and go around."

"And so I think being aware, being less anxious of the fact that your planned trajectory is not going to go where you took it is actually a wonderful part of life. As, again, as a scientist, I often say when I write, you know, you probably have this problem too, you know, you write grant proposals and you write some fiction of what you're going to be studying in three years, and I always say that if I'm really doing what I thought I was going to be doing in three years, it's pretty boring.

Because what I really hope will happen is I'll be looking at something completely different because some new discovery will have come up, either from the outside world of experiment or from something I'm doing."

"Well, is it reasonable to ask you, can you remember times when that specifically happened in your career, where you had to reconfigure, and you discovered something that was worthwhile as a consequence of it?"

"Oh yeah, yeah, it's hard to imagine when it hasn't happened in some sense. I think the—well, let me give you an example. The one you mentioned, the discovery that the energy of empty space is the dominant energy of the universe.

I was studying cosmology, and, of course—and the amazing thing about cosmology is it's, over the last 30 years, turned from—or 40 years—from an art to a science. You know, I think people used to say cosmologists were never right but never in doubt. And wonderfully, what's happened, because science is an empirical discipline, is that all new whole new data sets were coming on, new machines and new telescopes, which were allowing you to make precision tests of the universe and therefore derive models that could be disproved, which is really the central part of science.

And when I was trying to understand—and I've been working on the subject called dark matter for many years—how to detect it. The fact that the most of the mass in our galaxy—in all galaxies—appears to not shine. And now we're reasonably certain it's made of some elementary particle that's different than the particles that make you and I up.

It's a fascinating thing, and I've spent a lot of my career thinking about it. But one of the reasons we became confident that that was the case, that these particles—this dark matter—was not made of protons and neutrons and the same stuff as you and I was because we built cosmological models. And we found that if this dark matter was just snowballs or, you know, or something that you couldn't see, then plugging them into our models, you couldn't get a universe that looked like what we look like today, starting from a hot big bang; you couldn't form galaxies. There wasn't enough time.

And so dark matter, it turns out if dark matter doesn't interact with light, it's easier for it to collapse early on in the history of the universe, and that gives a jump start to galaxies and et cetera, et cetera, et cetera. So we’re trying to come up with a model that really was in agreement with observation. The problem was the observations ultimately weren't in agreement with that model.

And so the question then becomes do you know what—what do you do? And so I was reasonably convinced at the time that the reason that was the case was that some of the observations were wrong, which is also something very important to realize in science—is that if there are many different observations, likely some of them are wrong.

And again, too often, journalists don't hit on that fact; you know, they concentrate on this one exciting observation, which is likely to be wrong, and when it's later on shown to be wrong, they never report on it. And that's part of the problem. But so I basically was convinced that some of these key observations were wrong because they're very difficult. And so somewhat heretically, I made this proposal—I looked, look, there was a colleague of mine at the University of Chicago, and I spent a year or two looking at all the data and saying how could it be consistent with what we—with dark matter and what would be required.

And the answer was if none of the observations are wrong, then it looks to us—it looked to me at the time like you’d have to have most of the energy in the universe reside in literally nothing. Because what observations weren’t consistent with the picture otherwise. And I was convinced at the time that the reason I was doing that was just so that people could focus on which observations were wrong and so they could see that because the result—because the proposition was so ridiculous—that empty space actually weighs something. You get rid of all the particles and radiation and everything that’s there, and yet empty space weighs something—that seems so crazy that surely it’s wrong."

"And there must be—well, it seems to violate the very presupposition that enables us to identify mass. I mean, mass by definition appears to be something—well, mass, but mass is different than energy, okay? And if you put energy in empty space, it's very—and Einstein realized this. If you put energy in empty space, it behaves very differently than it does if you put energy and matter like particles. In fact, what general relativity tells us is that mass isn't the key part that produces gravity; it's energy.

So there's this relationship between energy and gravity. Energy in different forms produces different types of gravitational attraction, and in fact, that's relevant to the history of the universe early on in the history of the universe. Most of the energy in the universe resided in radiation—hot stuff—like particles of light moving at the speed of light. They gravitate very differently than if most of the energy in the universe resides in planets or galaxies, you know, matter that's still. And so the expansion of the universe, which is gravity's response to the presence of energy, is different early on in the history of the universe when it's dominated by radiation."

"Is that one of the things that contributes to the rapid inflation at the beginning?"

"Well, in fact, it's not quite—you’re almost there. It turns out rapid inflation happens if at very early times in the history of the universe empty space gets energy. Empty, because it turns out if—for some reason—you empty space gets stuck and somehow it possesses energy, even if in the case of inflation, eventually it's going to release it in a hot big bang, if that energy gets stuck in empty space, empty space carries with it this property we call energy, that energy is gravitationally repulsive, not attractive. That's the key difference between energy when you put it in matter and when you put it in nothing.”

"So you said a couple of things that I want to follow up. And okay, and maybe you can take us back. So you said that in the last 25 years that cosmology has transformed itself from an art to a science, and so maybe you could tell us the science. Let's go back to the beginning, 14 billion years, and walk through it because I'm sure that—well, I certainly don't understand the role of dark matter or anything about dark matter, and I kind of had some sense of what the current cosmological theories were 20 years ago, but I really don't know what they are now. So let's go back 14 billion years and start at the beginning, if you don't mind."

"Sure, we'll try and spend less than 14 million years in describing it, but okay. By the way, before we get there, let me just end the last story by saying we made this crazy proposal because we're sure the experiments are wrong. It turned out the experiments were right, and the craziness was true, and no one was more surprised by it than me that this proposal that the energy of empty space dominates the energy of the universe was right.

It was just incredibly surprising. It was so surprising that eventually the observers who confirmed that fact won the Nobel Prize, 10 years—11 years later. Well, in your book, "The Greatest Story Ever Told So Far," you document a very large number of cases where theoretical physicists were driven to posit something they regarded as completely absurd because it seemed to fit the data assuming that something was wrong and were later shown to be right, even though they wouldn't necessarily accept that themselves."

"Yeah, exactly. In fact, one of the founders of quantum mechanics, Dirac, who's a very interesting man psychologically among other things, once said his equation was smarter than he was because he developed this equation and it predicted this new particle in nature, antimatter, and he didn't believe it, and he said it was the equation, and it turned out to be true. But anyway, let's go back to the beginning.

And well, when we go back to the beginning, this is an important difference, in my mind, science and say religion when I go back to being— I go back to as far as I can extrapolate my understanding of the laws of physics back before that. Almost anything goes. And science, we can make—and part of my job as a theoretical physicist was to make speculations, but to recognize that they were just that and look for signatures that might suggest whether those speculations were right or wrong.

So for example, I actually wrote a book called "Adam," which takes you back to the—for an individual oxygen atom from the beginning of the universe to the end, one that's in your glass of water that you're drinking right now, or during this podcast. I took it back to—not T equals zero—because literally, we don't know what happened at T equals zero, because the laws of physics, as we understand the breakdown, because the universe, if we extrapolate it back, our universe becomes infinitely dense, and that seems crazy, and the laws of gravity don't work with quantum mechanics, so we really can talk a lot about it, but it's not more than talk in my opinion right now."

"But very shortly thereafter, after that time, there's no reason to suspect that the current laws of physics don't describe what happened in the history of the universe. And again, so as soon as it comes into being, the laws come into being as well."

"Yeah, well, in fact, in 'The Universe or Nothing,' I suggested that's certainly a possibility. Maybe they pre-existed; maybe they don't. Those are metaphysical questions. But what I did show in that book, which is fascinating to me, and the fact that 30 years ago we wouldn't have even been able to ask the question, much less answer it, is that it's quite likely that our universe could and did spontaneously arise out of nothing—no space, no time, and maybe no laws.

And if you ask, what would be the properties of a universe today, 14 billion years later, that arose from nothing spontaneously, without any supernatural shenanigans, the properties of that universe would be precisely the properties of the universe we observe now. That doesn't prove that's the case; that just makes it plausible. But to me, that's a fascinating thing. And again, we never—30 years ago, we didn't have the tools to even, in some sense, ask that question.

But very—we're still estimating the birth of about 14 billion years ago, 13.8."

"Yeah, now if you actually look at the numbers which we can measure, we now know that number—13.8—to an accuracy of, you know, plus or minus of maybe a few hundred million years or two. 13.75, I think, is the most recent number. And it's amazing the fact that you can get beyond one decimal place in cosmology is just remarkable. And really, it really is a testament to the developments when I was even a young assistant professor at Yale.

I remember talking to an older colleague who said that nature would always conspire so that we could never measure the fundamental quantities of the universe better than within a factor of two because that's always been the case up to that point. Every time someone claimed to have a better measurement, you’d go out and look at astrophysical uncertainties and realize it was wrong. And now we're talking about measuring things to four or five or six decimal places. It's really—it’s really a transformation and one we're celebrating, which is what I tried to do in that book.

But the early picture that the fact that we evolved from a big bang is not in dispute. Let me make that clear. The big bang happened just like the evolution happened, and the earth is round and all the other things we know. There’s no doubt that we—of that the early history of the universe was a hot big bang."

"Now, and in fact, everything we now see—all the galaxies we now see and all the particles in those galaxies, the 100 billion stars in each galaxy, the 100 billion galaxies—all of that material was contained in a region smaller than the size of a single atom."

"And that’s just—"

"Okay, let me ask you a question about that."

"Sure."

"I mean, is it reasonable to conceptualize something like that as having a size? Because we're considering size within the universe, and it's almost—when you say that the universe at the beginning had a size, it's like it was an object in a universe that had a size, but yes..."

"That's a really good question, and I should be clearer in my language. The universe could be infinite. I want to ask as a physicist, and Wheeler would have liked this, Einstein certainly—that operational questions. I don't know how big the universe is, whether it's infinite or not. But what I do know is how big is the visible universe. So if I ask you, how big was the region, which now comprises the visible universe today, at an earlier time? That has a good—that's well defined, that region.

The size of an atom could have existed in a universe which was infinite. Even then there could have been—it could have been an infinitely dense universe that was infinitely big. So all we can ask—and this is really a big change also from when I was a student—we never, because we used to, when I was a kid or when I was even a student, we talked about universe, and universe would mean everything—that kind of ill-defined quantity, everything. What the heck is everything? Now we're much more well-defined.

We say our universe—a good definition of our universe is that region with which we could have interacted in the past and with which we will be able to interact into the future, even if the future is infinitely long. And that may not be everything, right? That could be just a small region of a much bigger thing, which we now call a multiverse."

"So it's reasonable to describe our universe as that region into which we could have had causal contact, namely which cause could have produced effect, right? And if there's any region outside of it which we can never affect or be affected by, that might as well not be considered part of our universe. That distance—that causally interactable distance—that's defined or limited by the speed of light, the speed of light, and the age of the universe."

"So, for example, in the early history of the universe, that's called the horizon, in analogy with the earth. When you look out at the earth, you can—you know, when it curves, you can only see out to a certain distance, and we call the causal horizon that region with which light could have traveled to interact with us since the beginning of time, right?

And that's the universe as far as we're concerned because nothing outside of that can affect us in any way."

"Exactly. So operationally, it's a much better definition of a universe to be that which we can be causally affected by. And because that changes with time, that's what is our observable universe changes with time. And we'll get to it because things have changed a lot in the last—"

"So does that mean that our—the universe that causally affects us is—we're at the center of it?”

"No, well, we're—well, actually, yes, and no. We're always at the center of our own universe, right? I mean, psychologically—because that's... well, but because of the causality argument that you just laid out, it seems to imply that directly.”

“Because, well, it certainly does in the sense that if you want to think of it—and this is one of the confusions that many confusions which I may add to during this podcast, but we'll try not to—is that, you know, when we look out at this thing called the cosmic microwave background radiation, it's a residual radiation left over from the hot big bang, and it comes from a sphere, if you wish, that's located with us at the center because it early on in the history of the universe, when it was hot and dense, light interacted with matter and basically followed a, you know, a random walk.

It wasn't free to travel because the whole universe was charged, and light would interact and bounce off things. But at a certain point, when the universe was about 300,000 years old, matter became neutral—protons captured electrons to form hydrogen for the most part. And neutral matter doesn't interact with light as strongly as charged particles, and that meant that that radiation, which was kind of trapped early on when the universe was 300,000 years old, could suddenly travel freely through the universe without really interacting.

And when we look out, basically we see space, and we—and the light, you know, can travel and travel, but if we're looking back further in time when we look out, and if we look out in that direction back to a time when the universe was 300,000 years old, we're kind of sort of going to see a wall, if you wish, because we can't see before that time because the light, you know, couldn't have propagated out just like it can't propagate out through a wall. Only from the surface of the wall can we see it.

And of course, so when I look at the microwave background from earth, I'm looking, if you wish, at the sphere located almost 13—well, actually, it's because the expansion universe, it's more than—it's about 26 billion light years in each direction because the universe has expanded during the time that the light has been traveling. But don't worry about that complexity. We're looking at a sphere located a certain, let's say, 20, 10 to 20 billion years light years away from us in all directions, and we literally can't see beyond that.

But the sphere we're looking at depends upon where we are. So that if we were doing the same experiment on intelligent species in another galaxy located 100 million light years away, the—literally, the cosmic microwave background that they would see would be slightly different because they'd be sent—it'd be a sphere centered on different places, and that's why, actually, the predictions we can make in some sense as cosmologists are somewhat statistical because we're talking about a thermal distribution and galaxies and lots of disorder.

And so the picture—and we've taken pictures of the microwave background—it's won at least two Nobel prizes for those pictures—the picture that we see has statistical properties which would be identical to those observed by another observer 100 million light years away, but the specifics, the hot spots on the cold spots would be different because they'd be looking at a different slice of a statistical distribution."

"Sure, okay, so that does correct me if I'm wrong, that does seem to imply that—so the universe is a globe around us—let's see. Our visible universe—the visible universe, sorry! I want to be precise with my words too, and so I move halfway across the universe, and the globe is still there, but now it's shifted that far, and so then I could move another halfway and it would shift again.

So this globe moves with the observer, so to speak, and that certainly seems to imply that it extends beyond the globe that we see because if you move it, it moves. So, and exactly, well, and it wouldn't if there was some edge, but there's no evidence of any edge, okay? I think that the point is that even before the weirdness of empty space and inflation, we used to recognize that the part of the universe we see is unlikely to be everything there is. We're limited in what we can see because of what's seeable, just like being on earth, and it's limited because of the speed of light and the age of the universe.

But also because of the way the universe was constituted in its early stages and the way it's expanded and the way it's expanded ever since. Let me throw in a wrinkle, if that was clear, now let me muddy it. Because it used to be, again, sensible when I even in my early spirit as a scientist that we'd assume the longer—the older the universe, the longer we live, the older the universe is, the more we'll be able to see, right?

Because light can travel further; the universe is expanding. But we thought at the time that that expansion was slowing down and therefore the longer we wait, the more we'll see because light from further and further objects can get to us. What's really crazy now is because we recognize that apparently empty space is dominating the energy of the universe—that's causing the universe to expand ever faster, faster and faster. And what it means is there are parts of the universe that are literally escaping from our sight.

There are parts of the universe that we will never be able to see, and moreover, even more so, there are parts of our universe that we could see now that if we were a civilization that developed five billion years from now in real telescopes, we couldn't see then because regions of the universe are eventually moving away from us faster than the speed of light and are now invisible.

So the longer we wait, the less we'll see because more and more galaxies will be literally disappearing behind the horizon. I wrote some papers about that and once a Scientific American article, and I think some of my books, that eventually—on the far future of the universe. I know we said we'd start at the past but the far future is kind of poetic because up till about 1925 the picture of the universe was quite natural based on observation—one galaxy, we saw one galaxy, the Milky Way galaxy, okay?

And beyond that, it was assumed to be eternal empty dark space. That just was static—and Edwin Hubble, who was famous for discovering the universe was expanding, did something before that! In 1925, he first realized that in fact there were other galaxies, that these things called nebulae in our galaxy could be discerned and be seen as other island universes.

So already that was a revolution in our picture of the universe. Suddenly our galaxy wasn't all there was, there were other galaxies. And then, of course, later on, he discovered the expansion of the universe. The interesting thing is that observers who evolve—and there’ll still be stars and say even up to 10 trillion years from now there’ll probably still be stars in existence and you can imagine planets around those stars and intelligent life evolving on those planets.

And astronomers would look out from our galaxy at that time; it’ll be a very different looking galaxy because the Andromeda galaxy will have collided with it and all sorts of things will happen. But they’d look out and the interesting thing is all other galaxies would have disappeared behind the horizon by then.

So observers 10 trillion years from now will think they live in the universe we thought we lived in 1925—a universe with one galaxy. And there’d be no evidence that the universe is expanding, no direct evidence, because the galaxies that are now markers that we can measure their motion away from us, they'll have disappeared. And even it turns out the cosmic microwave background will have become invisible by that time, which is another bit of evidence for the big bang.

And while some really smart scientists may come up with some pictures to say, well, really I can understand what we're seeing if we assume our universe began in a big bang, observationally, basically all the current observational markers of an expanding universe will have disappeared. And poetically, in the far future, they'll think we lived in the mistaken universe we thought we lived in—in 1925.

Because, again, it's kind of interesting. Conventional wisdom in 1925 scientifically was that the universe was static and eternal, and you may know that it was—it was actually a Jesuit priest who was also a physicist who first really suggested the big bang. And when it was later shown to be true, for a while the Catholic Church got quite excited because they argued that here was observational evidence that there was a beginning to the universe as they'd been arguing. It doesn't provide—would argue it doesn't provide any such evidence for the universe they discussed.

But it was an interesting fact that science—the model was that the universe was more or less static and eternal on large scales. And it was completely wrong. And you might say—and this is where people often, you know, write to me—they say, well, how do we know our current model isn't completely wrong? You know, if not that we had a big bang—and the answer is then there was no data, basically.

And that’s one of the biggest misconceptions about science and scientific revolutions in particular—the revolutions in physics is the misconception that scientific revolutions do away with everything that went before them. And, mm-hmm, just like they're called revolutions—in fact, I would argue that even political revolutions never do away with everything that went before them.

But in this case, they certainly don't. What survived the test of experiment before that revolution remains completely true. Newton's laws of gravity and motion may have been subsumed in quantum mechanics or relativity, but if I hold a ball up now, it'll fall just as well as described, and I can describe it—a cannonball; I can even, for the most part, calculate how astronauts are going to go into orbit without needing anything."

"Yeah, the developmental psychologist Piaget studied Kuhn's scientific revolutions, and his objection essentially was that when a child undergoes a cognitive restructuring, the new structure incorporates all of the knowledge of the old one, plus some new knowledge.

So it could be revolutionary, but it still subsumes it. Exactly. And that's exactly what happens in science. So it's not as, so we have a lot of data with which we can test ideas and I'm certain that there's much more we don't know about the universe than we do. What people don't realize is, or don't give credit to, is that there's a lot we do understand.

And any new picture, a new understanding can, will not be able to disagree with the observational evidence that the universe is expanding, that there's a hot cosmic microwave background, all of the things we now have discovered that we didn't know about in 1925. And so whatever our picture is of the beginning of time or the end of time in a hundred years may be very different.

But we know the—it's not—we're not going to ever say the age of the universe is no longer 13.7 billion years old. We—that's going to remain true. What happened at the beginning could be completely revolutionarily different, and what happened, if you want to think about before the beginning—if there even makes sense to describe it before—and it may not make sense because time itself could have originated."

"Let me ask you about that for a second."

"Sure, okay."

"Sure. Well, I thought a lot about time a long time ago, and it struck me that time is—we mark time by change. And so then I thought, well, why not dispense with time as a concept if we mark it by change? Time is average change; if nothing changes, there’s no time. So if there’s nothing happening, there’s no time. There’s no before that time; there’s an event, and then if there’s no event till the next event, there’s no duration between those two things—if there’s only that event and then the next event."

"So, I mean, is there any reason to assume that there’s anything about time that is independent of change?"

"Well, you know, that's obviously a very deep question, and a lot of people spend a lot of time—and time, I think, far too much time talking about time in physics. Time and space are not different; they're both, if you wish, parameters that simply describe when events happen and where they happen. And that’s it.

And it turns out that that’s the playing field on which the laws of nature play out. The playing field happens to be in spacetime. And time is no different than space in principle, except in fact, in practice, time seems very different than space. We can go backwards in space, but it’s not clear we can go backwards in time, and that has caused a lot of people, a lot of philosophers and then physicists a lot of problems— a lot of mental gymnastics.

But even— but you could argue that time is a parameter, and I could replace that parameter by some other parameter that is equivalent to time. And you could say that that parameter was change, like the parameter you talked about. And then if there isn't any T change, then you’d say, okay, well, that’s—you could say that that parameter isn’t— it isn’t changing.

And you mean there are changes happening all the time at the microscopic level, right? I mean, there's an indefinite number of changes. And so statistically, you can extract out an average from that, and you can—you can experience that as duration, and you can define that as time. But if there isn't anything there except one event and then the next event— well, that's it, there's no time there; there's an event and then there's the next event."

"Well, that’s—that’s where I disagree with you, I guess. That's right because if nothing is happening literally, if nothing's happening, then time is an irrelevant concept. But so, to some extent, in space—and to some extent it's physics because really what we're interested in is describing the process of events, in particular, the prediction of events.

And that process for going by from event to event is parametrized by a useful quantity called time. But if nothing's happening, you're right; it's completely arbitrary. But then we won't—it wouldn't be worth having; we wouldn't be having this conversation because nothing would be happening."

"So back to the beginning. Now, my understanding—I don't understand why there is something once something is created, because as far as I could tell, and I don't think I was disabused of this notion with the—I finished reading "The Greatest Story Ever Told So Far" this week.

Why weren't there equal amounts of matter and antimatter produced at the beginning so they just disappeared? Everything just disappeared. That's a good question, and we assume—does that have anything to do with uncertainty, with the fact that there wasn't equal numbers produced?"

"Well, look, the point is that we don't have an answer to that question. And by the way, I think that's really important as a scientist. Too few people, you know, journalists always want answers, and people are always disappointed when they say we don't know. But I think it's probably one of the most important things that we and parents and teachers should get more used to saying because it means there's more to discover, and that’s wonderful.

So the answer is we really don't—it's one of the biggest questions that’s really provoked much of the field of research that I've been involved in since I was a student. I remember Steven Weinberg wrote about it when I was a graduate student and got me interested in the whole subject.

We now know that we live in a universe that's made of matter, and we try and measure antimatter, and there's minuscule amounts of it, and we think most of it's caused by high-energy collisions between particles, and causing graves, as far as we can see. And there are real tests we can do. For a while, people thought maybe we lived in a universe that had equal amounts of matter and antimatter, and they were separated.

You know, there were matter regions and antimatter regions. But it turns out there are tests you can do to test that, and all of those tests demonstrate, as far as we can tell, that there—know that the universe is made of matter, not antimatter. Which, again, is arbitrary because, of course, if we lived in the universe made of antimatter, we’d call it matter. And, you know, and there’d be anti-lovers living in anti-sitting anti-cars making anti-love, and all of that, it wouldn’t be different for the most part."

"But the paradox here is at early times, the universe is very very hot, and when it's so hot, you—one of the central parts of relativity is that energy can turn into matter, and matter can turn into energy. So particles of light with enough energy can collide together and produce particles of matter, okay?

But when they do that, if they have enough energy—but since antimatter and matter have exactly the same mass, particles that collide will produce equal amounts of matter and antimatter. If two photons, at very high energy, collide—and they don't collide very easily—but if they do, they'll produce particles and antiparticles equal in equal numbers, partly because of the conservation of charge, right? The photon doesn't have any charge, and therefore whatever comes out of the collision has to have no charge, so if it produces an electron, it'll have to have a positron—the equilibrium."

"So the all those interactions of elementary particle interactions don't really distinguish between matter and antimatter, and therefore at very early times, if you were a creator, if you were creating a universe, and it was very hot and dense, the most reasonable thing would be for it to have equal parts of matter and antimatter. Okay, but somehow..."

"So that's the reasonable assumption for the beginning of time, that the universe had equal amounts of matter and antimatter in a very hot dense plasma. How do we get to a universe that just has matter?"

"Well, that is the interesting question, and it turns out, by the way—and I know you're interested in what you would call Soviet things. You're like the art and everything else, and you probably—and Alexander Solzhenitsyn—"

"No, I collect it; I don't know if I like it."

"Yeah, okay. You collect it, but I do collect it. But I think I would say but Andrei Sakharov was a very famous physicist who’s actually probably the father of their hydrogen bomb, but he was also, as you know, won the Nobel Peace Prize because he became a dissident. Interestingly enough, one of his major—well, in retrospect, one of his major contributions to science was he actually asked in, I think it was 1967, well before any of the physics actually allowed any of the—he came up with three criteria by which a universe that started out with equal amounts of matter and antimatter could evolve into a universe which just had matter.

They’re called the Sakharov conditions, and there are three of them. One is that you have to depart from thermal equilibrium because if you're in thermal equilibrium, everything remains the same. So nothing's going to happen, right?"

"Okay, thermal equilibrium, like the air in this room, okay?"

"So there's a place where uncertainty seems to be relevant because if the principle of uncertainty holds, you wouldn't have thermal equilibrium; you'd have unavoidable variation."

"Well, no, but you do have local thermodynamic equilibrium in this room. There are local variations. The thing about thermal equilibrium is, and you're right, in fact, what you just said, there's right. Normally we talk about thermal equilibrium being a global thing, but we can also talk about microscopic equilibrium.

And there are variations, but what happens is that in thermal equilibrium one particle turns into another particle. You know, collision, but an equal number of collisions happen in the opposite direction, so there's lots of things happening, but they’re all happening in equal opposite ways so that no global properties are changing."

"Okay, so thermal equilibrium but you—okay, the second is that you have to have some physical process that tells the difference between particles of matter and antimatter. Because if the physical processes don't tell the difference, then nothing's going to start a situation that has equal numbers and change it to a situation that has unequal numbers.

This property is called it—it happens to be a—the laws of physics that tell you matter and antimatter—the laws of physics are the same for matter and antimatter are related to two symmetries of nature, something called charge conjugation and variance, which tells you that positive and negative; there's no difference between positive and negative. It's just an arbitrary thing.

And it turns out there's no difference between left and right. If those—if those laws of physics at a microscopic level obey both of those properties, then the laws of physics will not distinguish between matter and antimatter; only if, though that's violated. That’s called CP, charge and parity. Only if CP is violated can you, by some microscopic physical law, can you evolve from a system with equal number of particles and antiparticles to one that hasn't.

And the third is something called, well, we call it baryon number non-conservation, but basically, matter is made of protons. Okay? And you know, electrons are a little, obviously protons and electrons wake up atoms, but electrons are very little mass; most of the mass in your body is protons and neutrons, they're called baryons.

Okay? And clearly, if you want to end up with a universe full of protons and neutrons, and more protons and neutrons, if you wish, than antiprotons and anti-neutrons, then there has to be some process that makes protons when there weren't protons to begin with. So those are three—so that's thermal equilibrium, CP and violate—so violation of thermal equilibrium, violation of CP invariants, and some process that violates what are called baryon number."

"And he wrote those down, and what's amazing is at the time he wrote them down, the laws of physics obeyed thermal equilibrium, and the universe obeyed CP and obeyed baryon number. So there's no evidence that you could ever do that. And what's been remarkable is that over the last 50 years of so, as we've studied the microscopic laws of physics, we've discovered both that CP is violated by microscopic laws, and we've discovered processes that could have happened in the early universe that would violate that thermal equilibrium, that nice general, what you call adiabatic expansion of the universe. There could have been abrupt processes during which the universe departed from thermal equilibrium by natural processes that we could describe—in fact, we know there were some of them.

We know, if you read my book, we know, for example now, that the two forces of nature—electromagnetism and the weak interaction—that now appear very different, early on in the history of the universe, actually represented two different sides of the same coin. They were really part of a single more unified force, okay? And the point where the universe cooled down enough so that suddenly electromagnetism began to behave differently than the weak interaction as the universe cooled down, and things suddenly began to behave differently—that’s what we call a phase transition.

And phase transitions are places where you can depart from thermal equilibrium. Right? If I—I think I don't know if I use the example in the book, but—and I grew up in Canada, so the example is beer—but if you have a party and a beer party, and you forget to put beer in the refrigerator, you put it in the freezer, and you forget that you put it in the freezer, and the next day you take it out of the freezer, and it’s frozen solid, I mean, it’s not frozen solid; it’s still liquid, but you—you click the—you take off the top, and suddenly it freezes instantaneously, and the bottle breaks.

That’s a phase transition because when the beer was being held under high pressure, it wasn't in—at low temperature; it wasn’t really in thermal equilibrium. When you opened it up, then it could suddenly go into thermal equilibrium, and the preferred state to be in—the thermal equilibrium—was ice, and suddenly boom, and break it."

"So thermal equilibrium, so, so phase transitions are places where you can violate thermal equilibrium momentarily before the transition completes. There’s a theoretical explanation for how the antimatter-matter—well, the point is there’s no one theoretical explanation, but we now know all the parts of the Sakharov requirements for generating matter—a universe that had an asymmetry are possible in nature and are suggested.

I should be a little more careful. We know phase transitions happened in the early universe; we know CP is violated; baryon number we don’t know to be violated, but all of our models that extend what’s called the standard model of particle physics naturally produce at very early times models where baryon number is violated. So it’s not implausible; it’s certainly not implausible. And so all those things exist, and our current picture—it’s really quite—having said all of that—that’s complicated. The current picture that is a little simple.

And it’s really remarkable: it says that what happened is there were equal amounts of matter and antimatter, and a physical process happened sometime between the big bang and the time when the universe was about a millionth of a second old that caused a very slight excess—one part in a billion more particles of matter than antimatter. And that’s all you need. You might say, why is that the case?

Because we now live in a universe that’s just matter. Well, if I have one, let's say there's a billion and one particles of matter and a billion particles of antimatter, what will happen as the universe evolves? The particles of matter will annihilate with the particles of antimatter, producing radiation. But there’ll be one leftover particle that couldn’t find the particle antimatter to annihilate.

So what you’d expect is roughly a billion particles of radiation in the universe for every particle of matter. And when we look out, that’s exactly what we see. The cosmic microwave background contains roughly a billion—one to a billion to ten billion photons throughout going throughout all of space for every proton in the universe. So in fact, while we think, we really live in a universe of matter, what we really live in is a universe that’s mostly radiation polluted by a little teeny, teeny bit of matter—one part in a billion.

But that teeny bit of matter is enough to make all of the gas stars and galaxies in you and I. So, like one of the things that I’d like to think of in physics is it makes us more and more insignificant as human beings in a cosmic sense. We realize we used to think we’re the center of the universe; we’re the son of the sun. You know, the sun went around us.

It’s been a series of these kind of Copernican revolutions where the earth isn’t the center of our solar system, but the sun isn’t the center of our galaxy. But our galaxy isn’t the center of a cluster of galaxies, and our cluster of galaxies isn’t the center of the universe. And now we find that most of the particles in the universe aren't even made of the same stuff as we are.

So it pushes us more and more to feeling marginal. And I find that, and a lot of people say, well, that should make us feel sad. But to me, it makes me feel more precious rather than less precious. It’s like, obviously, we’re getting into the realm of psychology, but my psychological response is, hey, the fact that the universe is accidental as far as I can see and was created without any supernatural shenanigans, the fact that we’re cosmically irrelevant, the fact that the universe is going to go on without us—all that doesn’t make me feel sad; it makes me feel I should enjoy my brief moment of the sun.

I should enjoy my brief, you know, four score and ten, or hopefully more, and years, and it and it makes this accident of life on earth remarkable that we—that evolution has endowed us with a consciousness so you and I can have these discussions. So I don’t find a pointlessness of the universe to be depressing; I find it rather the opposite.

And I often—and this may be an area we disagree in; I don’t know—but one of the bits of semantics that I’ve tried to fight is this notion of loss of faith, like losing your faith is a loss. But to me, losing my faith in those fairy tales at least or those incorrect explanations is not a loss; it’s a game. It’s a—it’s—and using that terminology makes it seem like people always write to me, I now recognize that I don’t believe the Bible stories. But what am I to do? I mean, how can I deal with this loss?

And I think they’re conditioned to feel like they have a loss. I don’t think so. I think you can at least—you can psychologically create a picture where you don’t feel that’s a loss; you feel, in fact, you’ve gained something. And actually, it’s the way I feel about many things in life when I’m being well adjusted, which is a small percentage of the time, to be clear, when I have a loss, I often reflect on it afterwards and realize in fact how I’ve gained that what seemed to be a traumatic experience or, in the end, produce something which is much more valuable—and of course it’s a rationalization probably, but it allows me to deal with those things.

Anyway, that’s my little bit of psychology, my little bit of pop psychology for our discussion. I'm tempted to take it in the direction, but I think I'm going to continue to torture you about the structure of the universe.

I could do that because one of the things that I hope your listeners will know is that you and I are going to have a podcast on my podcast. I can’t wait to have you on my podcast. Maybe we’ll be in together in the same room, and then I will do—I will torture you."

"Okay, okay, that sounds great. I'm looking forward to that a lot!"

"Okay, so matter pops into being essentially after things cool down to some degree and the—there are different—there aren't exactly different laws governing the universe before that, but what would you say the allowances that the current laws make have a remarkably powerful effect before that?"

"Yeah, yeah, absolutely. The form that the laws—I mean, the laws of physics do evolve at energy scales, and which laws are important at different energy scales are different. So certain laws of physics—even if they don’t change at all, certain things are more important early on, and then other laws become important, more important later on, like now.

Obviously, electromagnetism on small scales is incredibly important; it governs all the biology, all the chemistry, all of the things that we see in around in the world around us, at early times it was nuclear physics and particle physics that the laws of the strong and weak interaction that were determining what was going on. But you're right eventually—and it took a while. It took a long time before the universe became dominated by matter.

Even when the universe was one second old and a temperature of about 10 billion degrees, there weren’t even elements. All of the light elements, hydrogen, helium, and lithium were, if you wish, created by nuclear reactions in the first five minutes of the universe, which is why Stephen Weinberg's book called "The First Three Minutes" talks about that. So those were the only elements created at the beginning of time, hydrogen and—they're created from the lightest upward."

"And that's basically the way that things go across the entire—yeah, you start with protons and neutrons, but neutrons are actually unstable, so they decay into protons. It’s very fortunate; it turns out if you want to believe in coincidence, this is really quite amazing. It's very fortunate that it works out that the neutrons live about 10 minutes.

And if I had a neutron here and held it in my hand, in 10 minutes, on average, it would decay. Well, you and I have more neutrons in our body than protons. How can that be the case? We've been talking for a lot more than 10 minutes, I'm sure your listeners are quite aware of that, but the reason is if you put a neutron in a nucleus, it can become stable, okay?

And it's really quite fortunate that all the neutrons that are more or less—the many of the neutrons that now exist in the universe got trapped in the form of helium and lithium because protons—hydrogen just has a proton and electron, okay? There’s a heavy hydrogen, which is deuterium, which is a proton and a neutron electron, and some of that was created in the universe too.

But helium has two protons and two neutrons, and so by those neutrons being—by helium forming, by a series of remarkable nuclear reactions, the universe, if you wish, stored the neutrons that otherwise would have decayed away into protons. And there'd be no neutrons left in these—and so they've been stored ever since that time, for the most part."

"Yeah, they have been, exactly. And so those—the neutron and, of course, other neutrons have been created in the fiery cores of stars. So what happens is—and I talked about it in the universe, or nothing in a lecture I gave you, that sort of was the formation of that book.

And I'm not the first person to say that, I know Carl Sagan talked in different ways, but it is really true what’s important for the psychology that you study is carbon, nitrogen, oxygen, phosphorus, iron—all of those things—none of those elements were created in the big bang. All of those elements were created much later, literally billions of years later, in the fiery cores of stars where nuclear reactions happen.

And that means something that is really truly the most poetic thing I do know about nature. That every atom in your body, in the first approximation, all the carbon, all the oxygen was created inside of a star. And that means, you know, it’s getting into the realm of the stars, you know, and not just forge inside the star, but in order to get into your body, that star had to explode.

So all the atoms in your body—and in fact, probably they've been in many stars because you've probably— many generations they've experienced the most catastrophic explosion in nature—a supernova. Every atom in your body has experienced that at least once, if not many times.

It's—you are stardust, it's—I mean, you know, it sounds, you know, it's so remarkable that it sounds cliched."

"Yeah, yeah, exactly!"

"But it’s when I really like the discussion of love, yeah, exactly, it is the case. But you know what makes it less remarkable for me as an analogy I gave is that the atoms in your left hand could have come from a different star than the atoms in your right hand. I just find that amazing. Anyway, it doesn’t matter; whatever turns you on."

"So what do you think, okay, so now we're at the point in the story where atoms are beginning to form, and they're starting with the simple forms, and that's it within the first three minutes."

"Yeah, and five minutes, and the first five minutes. And so, and then, so it's hydrogen first, and then it's helium—and then it's..."

"Let me even correct you again because, well, correct me. The nuclei of atoms form, but there were no atoms until the universe was 300,000 years old because it was so hot that when atoms exist, when protons and neutrons capture electrons, right, then you get a whole atom. But in the early history of the universe, it was so hot that when an electron got captured, it got knocked out again.

So there were only these nuclei which were charged of protons and electrons and everything, and it was a plasma of these things. Only when the universe cooled down to about somewhere about a thousand degrees or so—maybe ten thousand degrees, somewhere in that region—was the universe cool enough so that protons could capture electrons and neutral hydrogen would form.

And those were the first atoms, literally, atoms—neutral atoms—that existed in the universe, and that's when, if you wish, the cosmic microwave background separated from matter because then once matter became neutral, instead of being a bunch of charged objects, then light and matter kind of decoupled.

And that was a momentous period, and that was the first moment that neutral atoms began when the universe. So that's about 300,000 years. Yeah, and then not much happened! I mean, it was, it was, um, and the dark ages, if you wish, because, you know, there were no stars, it was just matter and radiation, but the original was fairly uniformly distributed, and it’s understanding and cooling unbelievably uniformly distributed.

This was one of the big surprises. Einstein, in order to make a model of the universe, your models are simple, so you, you know Einstein and others would make models in which the universe was uniform because only then could you do the calculations. But then when we look out, we discovered empirically this remarkable fact which for a long time was quite surprising and now we have this idea of inflation that in principle explains it, but it is that the universe is uniform across regions that could never have been in causal contact before today.

That’s really important; the region way over there could not have communicated that region over there before today, but they have the same temperature to one part. It’s remarkable! The universe is unbelievably. And that’s the cosmic background microwave radiation."

"Yeah, you’re talking about it; it’s the same in every direction. In every direction, right? And since matter was... coupled the radiation, the more or less distribution of matter is uniform around the universe. But now it’s not because you and I are in, you know, in different places and you know that you shouldn’t matter."

"But it sounds like it’s another one of those situations where small discontinuities at the beginning were enough to produce very large differences across time, exactly. Because gravity is attractive—that's the key point.

So if you have small lumps anywhere, a little small excess here will begin to grow, and then that snowballs, so to speak, and that’s exactly the case. There were small—and this is another amazing fact which is not appreciated enough. The small fluctuations in the microwave background, we think, are due to quantum mechanics.

Yeah, I was thinking about the quantum uncertainty, sorry, it’s not that we—these are literally quantum lumps, if you wish, in order to—in order to get those because there’s quantum discontinuity, discontinuity, uncertainty on microscopic scales that causes clumping."

"Well, eventually it allows clumping to occur, yeah—the point is that we don’t see quantum fluctuations on our scales, but remember the entire observable universe was once inside a region that’s the size of an atom, and those scales, quantum fluctuations are very important.

And what's amazing is those quantum fluctuations got frozen into the microwave background characteristics in ways that we can predict and describe, and those quantum fluctuations later formed all the stars and galaxies and everything else because they were lumps.

So we really are macroscopic manifestations of quantum mechanics, if you want to think of it."

"Okay, so let me ask you a question about that quantum fluctuation. So there's uncertainty of location, and posit location, and speed. Yes, I’ve got that right?"

"Yeah, there's uncertainty in the combination, okay, but that uncertainty is real enough so that in that relatively uniform background, there were actual, let's say, fluctuations, there were discontinuities of position that were sufficient to cause—they're not only were inevitable; they're required."

"Yeah."

"And right—but that's really—that's—that's a real—that's an actual phenomenon."

"Oh, it's even more—not only more real and more—but it's also more wild than you just said that what you just said may not surprise people. But what's even weirder is when you go to the smaller scales, for very—there's another uncertainty principle in quantum mechanics since there’s a position and momentum uncertainty, but there’s a energy and time uncertainty, and the certainty is if you can measure a system for only a short time, then your ability to measure its energy is very uncertain.

So if you can measure it for a longer time, your uncertainty of energy goes away; if you measure it for a small time, your uncertainty of energy gets very large. Okay? And that means for very short times, empty space can burp out particles and pianti-particles.

You say, well that violates the conservation of energy? Because there’s nothing there to begin with. And you know when I pump out a burp out of an electron or positron suddenly there are particles. Is that how black holes evaporate? That is a mechanism by which black holes can be thought of as evaporating, if you want to get there."

"Right, because they—they—particles pop up; you can continuously—some of them fall into the black hole. That’s one way of describing Hawking radiation. It’s a—not a bad analogy; it’s got problems, but it’s not a bad analogy."

"But in real—I'm glad I'm not completely off the wall here."

"No, no, no, you're dabbling around. No, you're so far you haven't—except your questions about time, you're right on track. Anyway, so this says that particles can suddenly spontaneously burp out of nothing because as long as they disappear again in a time so short that we can’t measure their existence, they don’t violate anything.

They don't only violate energy conservation if we could measure them. Now, that sounds crazy, and it sounds like it sounds something like potential. Well, it’s—or to be—well, that’s right; they have potential to do things, but to be less generous—they sound like talking about how many angels can dance on the head of a pen, right?

Because if you can’t see them, if you can’t see them, then what the hell does it matter? The point is we can't see them but they have indirect effects. That’s what's remarkable. So we know that process is happening, not just because physicists like me say it’s happening, but because if you take, say a hydrogen atom—you got a proton, an electron—laws of quantum mechanics that Dirac developed allow you to calculate the energy levels that that electron can have around a proton, and that determines the colors of light that's emitted by hydrogen, right?

Okay, we can compare those predictions with observations, and that’s one of the bases of knowing that quantum mechanics works—this discrete set of light that's emitted by hydrogen. Well, it works, but it doesn't really work because it turns out, at a gross level, it works, but when you try and measure things at the level of one part in a thousand or so, it doesn't work.

It turns out the energy levels aren’t exactly what you’d think they were. Why is that? That is because the proton—the hydrogen atom isn't just a proton-electron; it's a proton-electron, but in the atom, virtual particles are popping in and out of existence. And say an electron positron pair pops in into existence in the atom, in the atom, within the confines of the electron."

"Yeah, exactly, in that region. Well, it’s happening everywhere in space, but it’s also happening in atom. But in that region, during the time before that electron-positron pair disappears, the electron in that pair will want to hang around close to the proton because negative charges are attractive and positive charges, whereas the positron will be kind of repelled, and that’ll change the charge distribution inside the atom in a way that we can calculate in a way that makes every atom somewhat unique."

"Well, it’s not totally unique. Every atom is experiencing the same thing because what's happening is the particles—I mean, what’s happening again statistically is that all those virtual particles and anti-particles are changing the spectrum of hydrogen of all hydrogen atoms by the same amount because they’re happening so fast. They’re changing that spectrum in a way that we can calculate, and it is one of the triumphs of theoretical physics that, using a theory called quantum electronamics developed by Feynman and others and building on what Dirac—we can calculate to 14 decimal places.

14 decimal places from first principles what the spectrum of hydrogen should be and how those virtual particles could change that spectrum. And when we compare with observation, it's bang on; there’s no other place in science that we can make a theoretical prediction from first principles and compare it to 14 decimal places with observation and get the right answer.

So that tells us that those virtual particles that we can’t see are really there, okay? And that means empty space is much more complicated than we had assumed before, which is part of what led you to the hypothesis that empty space was... "

"Okay, so that's all part of the background for that. So empty space is a seething pool of virtual particles popping in and out of existence constantly, and that does sound a lot like potential, like... "

"Yeah, and that means not only has a potential but it can have—but that effect can cause empty space to have energy. In fact generically, you would expect empty space to have energy, so you might say, what's so surprising?

So, it's not surprising that empty space has energy. What's surprising, in a sense, is that empty space has so little energy."

"You might wonder why—why does it have energy if the particles sum to zero over a short time? Well, that's a really good point, and the answer is a little more complicated and it is that, let me give you an example from quantum mechanics. So if I have a—, what the famous quantum mechanical example of a potential well, I have a little U-shaped well, right?

And if I have a ball on that well, you know, it'll roll down the ball, but friction will eventually cause it to rest at the bottom at the lowest energy state, right? It’ll lose energy by friction along the most energy state; it turns out in quantum mechanics because energy states are quantized.

In such a potential well, the lowest energy state is not at the bottom of the potential well; it's a little bit above the bottom. And so the ground state—the lowest energy state that an electron can have trapped in a well is not at the bottom of the well; it's actually—it actually has a little bit more energy than the bottom because the energy states are quantized."

"Classically, the energy—that means it can’t get to zero. It can’t get to zero. That’s a generic property of an electron in a potential well."

"It’s an amazing fact! So that’s called the ground state energy in quantum mechanics, and is there a why to that? I mean, you said it’s because it’s quantized, and well, I presume that's an explanation, but it’s not an explanation I understand."

"Okay, okay. Again let me give you a heuristic explanation that you might get better. You might not like it as much, but it’s one that I use in my own mind, so maybe it’ll help. Remember we tell us—in quantum mechanics, particles are also waves, right?

So the electron has a wavelength, okay? I don’t know if you play music; do you play music at all?"

"Badly, me too. Very badly, but I like to play."

"Okay, so when I hit a piano key, I hear a note. Why? Because that string has a certain length, and the only—and there are vibrations that can be on that string—but the only vibrations that persist are ones that have a very specific relationship with their wavelength to the length of that string. That’s called resonance, right?

So, and that’s why, because they go along the string, it comes back, then it bounces back and comes along and reinforces, but only when the wavelength in that case is exactly equal to the length of the string will you have resonance; will the string be able to persist.

Okay, now, the electron has a wavelength, and the way to think about a stationary state of the electron is it’s like it’s like a resonant note in a musical instrument. So I have a potential