There is then a rather separate question: Whether simple life is likely to evolve into anything we might recognize as intelligent or complex. That may be harder to decide. Some people say there are many hurdles to be surmounted in going from simple life to complex life and life on Earth is lucky to surmount those hurdles, but others suspect that life would somehow find its way to great complexity. Among my friends and colleagues, there’s a disparity of belief.
As an astronomer, I’m often asked, “Isn’t it a bit presumptuous to try to say anything with any level of confidence about these vast galaxies?” or the Big Bang, et cetera. My response is that what makes things hard to understand isn’t how big they are but how complicated they are. There’s a real sense in which galaxies and the Big Bang and stars are quite simple things. They don’t have the same intricate layer upon layer of structure that an insect does, for instance. And so the task of understanding the complexities of life is in some respects more daunting than the challenge of understanding our Big Bang and of understanding the microworld of atoms, as challenging as they are, too.
It’s rather interesting that the most complicated thing to develop in the universe—namely, human beings—are, in a well-defined sense, midway between atoms and stars. It would take about as many human bodies to make up the mass of the sun as there are atoms in each of us. That’s a surprisingly precise statement: The geometric mean of the mass of a proton and the mass of the sun is about 55 kilograms—not far off the mass of an average person. It’s surprising that this is such a close coincidence, but it’s not surprising that the most complicated things are on this intermediate scale between cosmos and microworld. Anything complicated has to be made of huge numbers of atoms with many layers of structures; it’s got to be very, very big compared to an atom. On the other hand, there’s a limit, because any structure that gets too big is crushed by gravity. You couldn’t have a creature a mile high on the Earth—even Galileo realized that. And something as big as a star or a planet is completely molded by gravity and no internal structures survive, so it’s clear that complexity exists on this intermediate scale.
Looking forward to the next decade, I expect development of the fundamental understanding of the Big Bang; I expect development in understanding the emergence and structure of the universe, using computer simulation observation; and I expect at least the beginnings of an integration between computer simulations, observations, and biological thought in the quest to understand how planets formed and how they developed biospheres.
Cosmology has remained lively and the focus of my interest. It’s not only developing fast, and of fundamental importance, but it also has a positive and nonthreatening public image. That makes it different from other high-profile sciences like genetics and nuclear science, about which there’s public ambivalence. It’s also one in which there is wide public interest. I’d derive less satisfaction from my research if I could talk to only a few fellow specialists about it. It’s a bonus that there’s a wide public which is interested in origins. Just as Darwinism has been since the 19th century, cosmology and fundamental physics are now part of public culture. Darwin tried to understand how life evolved on this Earth. I and other cosmologists try to set the entire Earth into cosmic context—to trace the origin of the atoms that make it up, right back to a simple beginning in the Big Bang. There’s public interest in how things began: Was there a beginning, will the universe have an end, and so forth.
It’s good for us as researchers to address a wider public. It makes us realize what the big questions are. What I mean by this is that in science the right methodology is often to focus on a piece of the problem which you think you can solve. It’s only cranks who try to solve the big problems at one go. If you ask scientists what they’re doing, they won’t say “Trying to cure cancer” or “Trying to understand the universe.” They’ll point at something very specific. Progress is made by solving bite-sized problems one at a time. But the occupational risk for scientists is that even though that’s the right methodology, they sometimes lose sight of the big picture. Members of a lay audience always ask the big questions, the important questions, and that helps us to remember that our piecemeal efforts are only worthwhile insofar as they’re steps towards answering those big questions.
9
Think About Nature
Lee Smolin
Theoretical physicist, Perimeter Institute for Theoretical Physics; author, Time Reborn
The main question I’m asking myself, the question that puts everything together, is how to do cosmology, how to make a theory of the universe as a whole system. This is said to be the golden age of cosmology, and it is, from an observational point of view. But from a theoretical point of view it’s almost a disaster. It’s crazy, the kind of ideas we find ourselves thinking about. And I find myself wanting to go back to basics, to basic ideas and basic principles, and understand how we describe the world in a physical theory.
What’s the role of mathematics? Why does mathematics come into physics? What’s the nature of time? These two things are very related, since mathematical description is supposed to be outside of time. And I’ve come to a long evolution since the late 1980s, to a position that is quite different from the ones I had originally, and quite surprising even to me. But let me get to it bit by bit. Let me build up the questions and the problems that arise.
One way to start is with what I call “physics in a box,” or theories of small isolated systems. The way we’ve learned to do this is to make an accounting, or an itinerary—a listing of the possible states of a system. How can a possible system be? What are the possible configurations? What were the possible states? If it’s a glass of Coca-Cola, what are the possible positions and states of all the atoms in the glass? Once we know that, we ask, “How do the states change?” And the metaphor here—which comes from atomism, which comes from Democritus and Lucretius—is that physics is nothing but atoms moving in a void, and the atoms never change. The atoms have properties, like mass and charge, that never change in time. The void—which is space—in the old days never changed in time. It was fixed, and the atoms moved according to laws, which were originally given by, or tried to be given by, Descartes and Galileo, given by Newton much more successfully. And up until the modern era, when we describe them in quantum mechanics, the laws also never changed. The laws let us predict where the positions of the atoms will be at a later time if we know the positions of all the atoms at a given moment. That’s how we do physics and I call that the Newtonian paradigm, because it was invented by Newton.
And behind the Newtonian paradigm is the idea that the laws of nature are timeless. They act on the system, so to speak, from outside the system, and they evolve from the past to the present to the future. If you know the state at any time, you can predict the state at any other time. So this is the framework for doing physics and it’s been very successful. And I’m not challenging its success within its proper domain: small parts of the universe.
The problem that I’ve identified—that I think is at the root of a lot of the spinning of our wheels and confusion of contemporary physics and cosmology—is that you can’t just take this method of doing science and scale it up to the universe as a whole. When you do, you run into questions that you can’t answer. You end up with fallacies; you end up saying silly things. One reason is that on a cosmological scale, the questions we want to understand are not just “What are the laws?” but “Why are these the laws rather than other laws? Where do the laws come from? What makes the laws what they are?” And if the laws are input to the method, the method will never explain the laws, because they’re input.
Also, given the state of the universe, of the system, at one time, we use the laws to predict the state at a later time. But what was the cause of the state that we started with that initial time? Well, it was something in the past, so we have to evolve from [a state] further in the past. And what was the reason for that past state? Well, that was something further and further in the p
ast. So we end up at the Big Bang. It turns out that any explanation for why we’re sitting in this room—why is the Earth in orbit around the sun where it is now—any question of detail that we want to ask about the universe ends up being pushed back, using the laws, to the initial conditions of the Big Bang.
And then we end up wondering, Why were those initial conditions chosen? Why that particular set of initial conditions? Now we’re using a different language. We’re not talking about particles and Newton’s laws, we’re talking about quantum field theory. But the question is the same: What chose the initial conditions? And since the initial conditions are input to this method that Newton developed, it can’t be explained within that method. So if we want to ask cosmological questions, if we want to really explain everything, we need to apply a different method. We need to have a different starting point. And the search for that different method has been the central point in my thinking since the early ’90s.
Now, some of this is not new. The American philosopher Charles Sanders Peirce identified this issue that I’ve just mentioned in the late 19th century. However, his thinking has not influenced most physicists. Indeed, I was thinking about laws evolving before I read Charles Sanders Peirce. But something he said encapsulates what I think is a very important conclusion that I came to through a painful route—and other people have more recently come to it—which is that the only way to explain how the laws of nature might have been selected is if there’s a dynamical process by which laws can change and evolve in time. And so I’ve been searching to try to identify and make hypotheses about that process where the laws must have changed and evolved in time, because the situation we’re in is: Either we become kind of mystics—“Well, those are just the laws,” full stop—or we have to explain the laws. And if we want to explain the laws, there needs to be some history, some process of evolution, some dynamics by which laws change.
This is for some people a very surprising idea, and it still is a surprising idea in spite of the fact that I’ve been thinking about it since the late ’80s, but if you look back, there are precedents: Dirac. You can find in his writings a place where Dirac says the laws must have been different earlier in the universe than now; they must have changed. Even Feynman has. . . . I found a video online where Feynman has a great way . . . and I wish I could do a Feynman Brooklyn accent. It sort of goes: “Here are the laws, we say; here are the laws, but how do they get to be that way in time? Maybe physics really has a historical component.” Because, you see, he’s saying physics is different from the other subjects. There’s no historical component to physics, as there is to biology, genealogy, astrophysics, and so forth. But Feynman ends up saying, “Maybe there’s a historical component.” And then in the conversation his interviewer says, “But how do you do it?” And Feynman goes, “Oh, no, it’s much too hard, I can’t think about that.”
So having said that, it’s very audacious to say I’ve been trying to think about that since the late ’80s.
It’s worth mentioning what got me started thinking about evolving laws, and that was a comment that my friend Andy Strominger made about string theory. Andy is one of the important string theorists in the United States. Andy had just written a paper, I think in about ’88, in which he had uncovered evidence for the existence of a vast number of string theories. So originally there were five, and maybe that was not so bad; they could be unified. And then there were hundreds of ways, and then there were hundreds of thousands of ways, to curl up the extra dimensions. And then Andy identified another way to make a string theory that would make vast numbers. And he said to me, “It’s not even going to be worthwhile trying to connect this theory to experiment, because whatever comes out of an experiment, there is going to be a version that would match it.”
And it took a lot of people a long time, until the early 2000s, to catch up to that. But I was really struck by that conversation and then went away and wondered about this: How could you have a theory that accounts for the selection of laws from a vast catalogue of possible laws? And not only that, there are some mysteries about why the laws are what they are—because they seem to be very special in certain ways. One way they’re very special is that they seem to be chosen in such a way that it leads to a universe with an enormous amount of structure. With structure on every scale, from molecules and biological molecules, to biological systems themselves, to all the rich variety of structures on the Earth and the other planets, to the rich structures of galaxies, to clusters of galaxies on this vast array of scales.
The universe is not boring on any scale you look at it. It’s very structured. Why? And there turned out to be two connected reasons. One of them is that the laws are very special. One way they’re very special is that they have parameters in them, which take values that we don’t know the reasons for. These are things like the masses of the different elementary particles—the electrons, the neutrinos, the quarks—and the strengths of the fundamental forces. I’m talking about thirty numbers that we just put into theory from experiment. And then we have a model—the standard model—which works very well. But we don’t understand why those numbers are what they are. So I started to imagine a scenario where the numbers could change in some violent events. Maybe the Big Bang was not the first moment in time; maybe it was a violent event where our universe grew out of some previous universe, and maybe those numbers altered the way that when a new individual is born the genes are different from the parents’.
And I started to play with that idea and began to see how you could use the principles of natural selection to make predictions about our present universe. These predictions test the scenario that the laws have evolved in a particular way. A thing I understood from that: There was already speculation about multi-universes and our universe being one of a vast number of other universes, and there was already the use of the anthropic principle to pick out our world. But I realized you can’t do science assuming that our universe is one of a vast array of other universes, because we can’t observe any properties of them. And I’ve been making this argument forever, and it doesn’t seem to penetrate to some people, that science is not a fantasy story. It’s not a Harry Potter story about magical things that might be true. Science is about what you can verify—hypotheses that you can test and verify. If you’re making hypotheses about many universes that exist simultaneously with us with no connection to our own, you can’t verify those hypotheses. But if you’re making hypotheses about how our universe evolved from past universes, you’re making hypotheses about things that happened in our past and there can be consequences that you can verify. So through this, I came to the idea that laws must have evolved in time. And that was the idea of cosmology and natural selection.
Now, meanwhile most of my work has been about making the quantum theory of gravity. And in quantum gravity, we apply quantum mechanics to the equations of Einstein’s general theory of relativity and we come up with a theory that has no time, fundamentally. This is a point that Stephen Hawking made, that Julian Barber has made, in many different ways. The variable time—the dependence of processes on time—just disappears from the fundamental equations of quantum cosmology, of quantum gravity applied to cosmology. And time is set to emerge when the universe gets big, in the same way the temperature emerges as an approximate description of the energy contained in a lot of molecules moving around randomly—where pressure emerges as a summation of all the forces coming from all the collisions of an atom on a wall.
But time is nowhere in the fundamental equations of quantum cosmology. And I was working on the equation of quantum cosmology for many years, first with Ted Jacobson and then with Carlo Rovelli. We solved a form of those equations, and that was the main root of my work in quantum gravity. So for many years I had these two parallel things going on: one in which laws were evolving in time and the other in which time was emerging from laws, which therefore implied that the laws were timeless.
And because the first thing was a kind of side project—i
t was a kind of thing I had thought about occasionally, on the side of my main work—it took me a long time to realize that there was a contradiction between those two stories. I’m a little bit ashamed about that, but it’s better to lay it on the table. And several things happened which made that contradiction very evident and made me deal with it. One of them was in the quantum theory of gravity itself. There turned out to be technical issues realizing the picture of time emerging from a timeless quantum cosmology. This isn’t the place to talk about technical issues, but something I’m convinced about is when a technical issue hangs around for many years and many people work on it and nobody solves it, it may be that you should reexamine the ideas behind it. Maybe it’s not a technical issue. Maybe it’s a fundamental conceptual or philosophical issue.
And indeed this is something that Feynman said to me when I was a graduate student. He said there are things—again, I’m not sure why I’m invoking Feynman so much, but why not? He said, “There are things that everybody believes, that nobody can demonstrate. And you can make a useless career in science . . .” He probably put it in an even harder way, “You can waste your time and waste your career by trying to work on things that everybody believes but nobody can show, because you’re probably not going to be able to show them either, if a lot of smart people couldn’t show them. Or you can investigate the alternative hypothesis, which is that everybody’s wrong.” And this always comes back to me, this, with Feynman’s voice. He, at the time, was thinking the confinement in QCD was wrong, and he was probably wrong about that, but nonetheless he made a brave effort to prove confinement.
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