Resetting the Theory of Time

Generations of physicists have claimed that time is an illusion. But not all agree. In his book Time Reborn: From the Crisis in Physics to the Future of the Universe, theoretical physicist Lee Smolin argues that time exists—and he says time is key to understanding the evolution of the universe.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. To most of us, time is real: you've run out of time; you don't have time, what time is it. But not to most physicists. Albert Einstein once wrote: People like us who believe in physics know that the distinction between past, present and future is only a stubbornly persistent illusion. Time, in other words, he said, is an illusion.

Many physicists since have shared this view, that true reality is timeless. But my next guest is not one of them. He says he thinks time is real and that the laws of physics may not be as permanent as we think they are. In fact he says the laws of nature could actually evolve and change over time, and the real existence of time might give us a better understanding of the universe.

Can we be certain that this thing called time exists? Is there any way to test that? And if time is real, what does that say about our past and future? It's all talked about by Lee Smolin in his new book "Time Reborn: From the Crisis in Physics to the Future of the Universe." He's also a founding and senior faculty member at the Perimeter Institute for Theoretical Physics. Welcome to SCIENCE FRIDAY, Dr. Smolin.

LEE SMOLIN: Thank you, Ira. It's a pleasure to be here.

FLATOW: You know, I think it is probably surprising to most people who talk about time in concrete elements like I said, what time is it, have we got time for that, that most people believe that time is not an illusion.

SMOLIN: I think so, though many people believe something also paradoxical. Many - it's certainly true that everything we experience and think and feel is experienced in a moment of time, which we experience as a flow of moments, but many of us, when we think about what we really value or really aspire to, it's to be outside of time.

We think about time of truth in different domains, in mathematics, in ethics, in religion, in philosophy. And it's often this perception that human life, which is full of change and death and so forth, can be transcended to a timeless realm. These ideas are very deep in our culture, and the physicists have just a particularly sophisticated form of it.

FLATOW: So they think that - they take these ideas in our culture, and they now build their physical structure around it?

SMOLIN: Well not consciously, certainly. But the - in my view the over-reading of the use of mathematics in physics, which is of course highly useful, but the idea is prevalent among my colleagues that there's a real world behind the world of perception and change, and that real world is mathematical, somehow lives in some domain of pure mathematical truth outside of change and outside of time.

FLATOW: So you're saying that they're living a mathematical dream, basically, that their idea of, let's say, the multiverse and string theory and that time is an illusion is all wrong?

SMOLIN: Well, yes and no - no just because you don't have to be talking about speculative ideas like string theory and the multiverse. The idea that that - as you quoted Einstein, the distinction between the past, present and the future is an illusion, this comes from very well-understood physics, in Einstein's case general theory of relativity.

But these ideas have been prevalent since Newton's physics in the late 1600s. So it's much deeper. I mean, if it were just speculative ideas, there are always speculative ideas on the edge of knowledge which are under contest at any time, but I'm criticizing something deeper and more prevalent and older in the culture of science.

FLATOW: And restate that for us. What are you exactly criticizing?

SMOLIN: The idea that laws of nature are - and you mentioned this in your opening, that laws of nature are timeless. See, I should explain a little bit how I came to change my mind about this because I came into physics to find these timeless, eternal truths, these timeless laws of nature, and then at some point I began to wonder, in the late '80s, as did others of my colleagues then, not what are the laws of nature but why are these the laws - why weren't the laws different?

Why weren't - why do we have four forces and not seven fundamental forces? Why do they have the particular strengths that they do? Why is the electron the lightest particle? Why is there a particle like an electron at all? There are many, many of these questions. And when you ask these why questions, you hit a conundrum.

I mean, one possible reason is that they're embodied in a beautiful mathematical equation, but there are many beautiful mathematical equations, and there turn out to be many similar equations that would be equally beautiful and equally compelling mathematically that don't describe the laws of our universe. So why these laws and not others?

And the conclusion I came to after some years of painful reasoning was that to explain them inside of science rather than metaphysics would require that they change and evolve in time because to explain anything within science, there has to be some causal process that makes something the way it is, and that's something that carries out in time.

FLATOW: And to do that you have to make time as a real thing.

SMOLIN: Well sure because if laws can change in time, then there's nothing beyond time. And this is...

FLATOW: Yeah, I understand. How would then - how would the laws of nature then change over time? What is the mechanism that they would be changing or change them?

SMOLIN: Well, since I'm a scientist, my job once coming to the philosophical idea that they have to change, is to invent hypotheses as to how they might change. And the whole point is that these hypotheses, since they're about the past, should be testable by observations we can make. So in the book "Time Reborn" I consider several of these hypotheses.

The oldest one, the one I've been studying the longest, is called cosmological natural selection and was in fact the subject of my first book in 1997, "Life of the Cosmos." And in that hypothesis, under that hypothesis, universes reproduce by giving birth to new universes inside of black holes, which is an old idea in the field.

And each time that happens, I presume that the laws of nature or the numbers that characterize them change slightly. And then one has a scenario very akin, very analogous to natural selection. One can derive consequences from it.

FLATOW: So every time there is a black hole, and there are many, many of them in our universe, correct?

SMOLIN: An impressively large number of them, at least a million times a million.

FLATOW: And so inside each one of those black holes, the laws of physics are being modified ever so slightly?

SMOLIN: That's the hypothesis.

FLATOW: Is there any way to test that?

SMOLIN: It makes several predictions and predictions that are genuinely testable.

FLATOW: Such as?

SMOLIN: Such as - I knew you were going to ask that.

(LAUGHTER)

FLATOW: Well...

SMOLIN: So I came equipped.

(LAUGHTER)

SMOLIN: I came equipped.

FLATOW: Are they understandable to us, is the question.

SMOLIN: Let me tell you one of them, which is easy to explain. Do you know what a neutron star is?

FLATOW: Yeah, it's a - explain it to us, what a neutron star is.

SMOLIN: A neutron star, a very massive star at the end of its life explodes in a supernova, and what's leftover, the so-called remnant, settles down and becomes quite dense. And one possibility is that it ends up as a neutron star, which is a star, something - this massive star, roughly, but with a density of an atomic nucleus. So if it has the mass of the sun, it's just a few kilometers across.

And if it's too heavy to become a neutron star so that even the nuclear forces can't hold it up from collapsing, it becomes a black hole. Now, there's a line between those, when it's too heavy to be a neutron and when it's going to be a black hole, and if our universe has been tuned by natural selection to make as many black holes as possible, which is an implication of the idea, then that line should be as low as possible.

And there's now an intricate argument I'm not going to give to our listeners which tells me that how low it could be is twice the mass of the sun. And so that's a prediction. If somebody discovers a neutron star which is, say, three time or even two and a half times the mass of the sun, I would have to say this idea is contradicted because the universe is not making as many black holes as it could.

Now new neutron stars are discovered from time to time, and their masses are measured by a variety of means, and just a few weeks ago there was a new paper in Science measuring a new neutron star mass as just at twice the mass of the sun. A few years ago there was another one also just below twice the mass of the sun.

So the prediction is holding up, but it could be falsified at any moment, which is good because that means it's real science.

FLATOW: What do your mainstream colleagues think about all of this? Do they think it's kind of nutty?

SMOLIN: No, there's a variety of responses and a variety of points of view. I think that some people - the general idea that time is real and laws evolve is embraced by many colleagues and opposed by many colleagues. It's a genuine disagreement, as there should be with any idea which is so far unproven.

FLATOW: Do you have a simple definition of time, then?

SMOLIN: Well, what I mean when I say that time is real is that everything which is real and everything which is true is real or true in a moment, which is one of a succession of moments. That's what we experience, Ira. And the question is: Is that the structure of nature? Does nature exist in a series of moments, one after the other? Is that what's really real about the world? Or is that, as Einstein said, an illusion, and there is some timeless picture which is the truer picture?

FLATOW: And your definition is that it's real, and we are existing in a series of moments.

SMOLIN: That is my hypothesis. It has consequences to be developed and tested.

FLATOW: Is it like - I'm trying to find a thought picture of it. Is it like driving on a highway, and you look out a window in passing, and every one of those is a little moment in time, but we can't see - if it's really happening, now then we can't predict the future, right?

SMOLIN: Well, we have limited ability to predict the future. Certainly the laws of nature, even if they're changing, change only occasionally or change very slowly. So within limited regions of space and time, which are quite enough for everything we'd want to do on Earth, as well as a lot of astronomy and astrophysics, we can use the laws of nature to predict the future.

But I don't believe we could use the laws of nature to predict the future arbitrarily or infinitely far in the future. And I also am playing with ideas, these are also unproven ideas, that may be in quantum mechanical systems where the future is uncertain anyway. We could set up a system in the laboratory to develop new rules, new laws.

FLATOW: All right, we're going to talk more with Lee Smolin, author of "Time Reborn: From the Crisis in Physics to the Future of the Universe," founding and senior faculty member at the Perimeter Institute for Theoretical Physics. Stay with us. We'll be right back with these new ideas about time after this break.

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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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FLATOW: This is SCIENCE FRIDAY. I'm Ira Flatow. A little science and philosophy this hour. We're talking about time, whether it's real or just an illusion, with my guest Lee Smolin, author of "Time Reborn: From the Crisis in Physics to the Future of the Universe."

You say some very interesting ideas in here, and I want to go back to something I mentioned in passing before, and that is that you do - you don't believe in the existence of the multiverse, the ideas about - that put forth by physicists, some of them with string theory, others with other theories, that say that we are one of just a countless number of universes, and that's the reason why we're here. We happen to be the right one.

SMOLIN: Well, there's some aspects of the idea that the universe may be one of a population of universes that I am willing to endorse, because in the scenario I was just describing, our universe would have daughter, child universes, and many of those - and our universe may have a parent, and so forth.

FLATOW: Coming from the black holes.

SMOLIN: Coming from the black holes. But in these cases, the population of the universe is organized according to progeny, according to inheritance. There's a lot of structure. And we can use that structure to make predictions, as I was describing. What I'm against, and what I argue - and what I think nobody's really answered these arguments. What I argue is that to postulate that our universe is simply one of a population of simultaneously existing universes that have no relation to each other, and that just have randomly chosen laws, that idea takes us outside of science, because it's not verifiable or falsifiable.

No postulate - no hypothesis about those other universes can be checked experimentally, because they don't - they have no influence on our own. And I think it's very important to draw a distinction between making up stories that might be true and science.

You know, the rock-and-roll band They Might Be Giants has a song about what's science and what's not that I think nails the matter. So if a rock-and-roll band can understand it, I think anybody can understand it.

(LAUGHTER)

FLATOW: In other words, you're saying what - science requires that you are able to make predictions about your theory and test them. And you're saying this multiverse can't really be tested. So it's more a theoretical belief in something than being a scientifically valid theory.

SMOLIN: That's what I think. And this is a lively debate that goes on within the community of theoretical physicists and cosmologists, and it has been going on for about 20 years.

FLATOW: What about time as a fourth dimension? You know, we always talk about that. Is that true?

SMOLIN: Well, time is nothing like a dimension. If there's - what's characteristic about a dimension of space is that you can choose to go to the left, to go to the right. Where you are in space just represents your perspective, and you can choose, to some extent, your perspective.

We have no choice about going forward in time. We have no choice about where we are in time. We have no choice about the fact that almost everything that goes on in our lives is irreversible and can't be restored or reversed. So there is - it is true that within the mathematics that we use to discuss space and time, there is a certain mixing of space and time in relativity theory, and this is very useful.

But this doesn't imply that space is - that time is just like another dimension of space. The mathematics is very useful, especially for relativity theory, but in my view, it's been over-interpreted.

FLATOW: Is there a way to prove that time exists?

SMOLIN: You know, there's no way in science to demonstrate a philosophical hypothesis, a broad philosophical hypothesis like that. I see philosophy and philosophical statements like that as inspirations, as motivations for a scientist like myself to invent ideas, to invent hypotheses which can be tested.

So if we can make a hypothesis about how the laws of nature have evolved in the past, and if that has predictions which are verified and which are not falsified, it makes it more plausible that time is real and laws of nature are temporary.

FLATOW: So you're saying that the laws of nature, as they do in biology, as Darwin would talk about in nature and biology, the laws of physics also have natural selection to them?

SMOLIN: Yes. There's a historical story about how the laws of nature came to be. And, by the way, I'm not the only one who's been thinking these thoughts. Richard Feynman speculated in an interview with Hermann Bondi that perhaps there's a historical dimension to physics which we're missing. Perhaps laws of nature change.

A number of other eminent physicists through the 20th century have speculated about this. The philosopher Charles Peirce, the inventor of American pragmatism in the 1890s, came to the same conclusion I came to very painfully much, much later, and it would have saved me a lot of time to know about this philosophical background here.

Charles Sanders Pierce wrote in 1893 that the only way within science - I'm paraphrasing - to have an explanation for what the laws of nature are is if they're the result of evolution in time.

FLATOW: And did anybody listen to them?

SMOLIN: I'm listening.

(LAUGHTER)

SMOLIN: I think the difference - as I said, the difference between making a speculation on a broad scale and doing science is when you make a particular hypothesis that's testable. And that's - I discuss several of those in the book, and they recount papers that I've been publishing over since 1992 in this area.

FLATOW: What would your idea about time solve? What problems would it solve that are still bugging us with our current view about the universe?

SMOLIN: In fundamental physics, I'll mention three. One of them is what chooses the laws of nature. The second one is the question of the unification of gravity with quantum theory, the so-called problem of quantum gravity, which is my main work that I've contributed to in physics. And there the disappearance of time is a crucial feature of some approaches and a crucial stumbling point that we've been unable to proceed beyond for several decades.

And the third is the foundations of quantum mechanics. The foundations of quantum mechanics is a highly successful theory of small parts of the universe, but it makes no sense when applied to or extended to a theory of the whole universe. And it turns out that the issue of time is paramount here, and if we're - you see, we're not allowed, in the standard mathematical formulation of physics, to use the word now. We're not allowed to treat as real or objective a distinction between the past, present and the future, because we have to imagine that there's a picture which is outside time in which the - what moment it is now plays no role.

And I've been able to make hypotheses about the foundations of quantum mechanics, which give a different account of the meaning and implications of quantum physics in which the distinctions between the past, present and future play a central role.

FLATOW: All we need to do is find the evidence for that, then, to prove you're right.

SMOLIN: Again, that formulation seems to imply predictions. We're working on it in some discussions with experimentalists right now.

FLATOW: All right, Dr. Smolin, I wish you good luck. It's a fascinating book. Lee Smolin is author of "Time Reborn: From the Crisis in Physics to the Future of the Universe," and also founding and senior faculty member at the Perimeter Institute for Theoretical Physics. Thank you, Lee, for taking time to be with us today.

SMOLIN: Thank you, Ira. It's a pleasure to be here. Thank you.

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