The sense of beauty leads us astray.
- James Joyce, Ulysses
Physics is in a strange state right now. On the surface, things may seem to be going well; the elusive Higgs particle was detected for the first time last year, and there are interesting signs that we may soon discover what dark matter is made of. But on the truly fundamental issues, there has been little progress. Three items in particular stand out. First, our two central theories, quantum mechanics and General Relativity, are each very successful on their own, but not compatible with each other. Second, there is no good explanation for the fact that all the physical constants of our universe appear to be finely tuned to make life possible. Third, and perhaps most embarrassing of all, no one can convincingly explain the presence of an arrow of time.
People have different strategies for dealing with these questions. Here in Geneva, the de facto
physics capital of the world, the most common approach is simply to ignore them. T, who's just published some excellent papers in his speciality, is unconcerned when he comes to dinner the other day. "Cosmology isn't physics," he says. "Physics is about things I can put in a teaspoon."
"What about stars?" I ask. I know that some astrophysicists are interested in T's work. T waves away my objections; evidently, he is talking about a fairly large teaspoon. The point he wants to make is that you can't put the whole universe in a teaspoon, even in principle. T isn't worried about questions that have to do with the whole universe. They are none of his business.
I have read several books over the last few years by people who have a different take on these issues. Paul Davies, Martin Rees and Leonard Susskind, for example, argue that there might well be more universes than the one we see around us. Perhaps there could even be an infinite number of them, all with very different properties. In that case, things are not as mysterious as they first appear. Everything imaginable happens in some universe, and in a few of them the numbers have worked out just right to produce the complex, highly structured world we see around us, in which there is a clear progression from past to future.
Some of these people have produced detailed theoretical scenarios explaining how the other universes might have come to be; Susskind's The Cosmic Landscape
describes one of the most popular versions. There is, however, the problem that we can't see any direct evidence of these other worlds, and no one is able to suggest experiments that could determine whether or not they exist. As followers of Karl Popper say, it is not clear that the theory is falsifiable. Susskind replies that he is unconcerned by this criticism: he is more worried that people will reject the right theory for nit-picking methodological reasons. But if your theories aren't falsifiable, are you still doing science? Susskind says he is. Other people are less sure. Helge Kragh, the eminent Danish historian of science, has been a particularly vocal critic.
If many physicists are refusing even to think about the fundamental problems and others are addressing them in a way which is often claimed to be contrary to the principles of science, it's reasonable to say that the field is in crisis. Smolin, a cutting-edge theoretician with a broad range of interests, has been telling us this for some time. In his 2006 book, The Trouble with Physics
, his emphasis was on sociology: he warned that research was focusing too much on string theory, which quite likely wasn't going to deliver, and argued that an attack on a broader front was required. In his new book, the point of view is more that of philosophy. He wants to reexamine the underlying assumptions and see if they need replacing. He thinks this is necessary: right now, as he puts it, people are trying to market things as science which in fact are radical metaphysical fantasies. To start with, one of his absolute demands is falsifiability.
Two themes in particular dominate the book; one, as the title suggests, is time, and the other is physical law. Smolin argues that there is a deep connection between them. In the picture of science which many scientists use without even reflecting on what they are doing, physical laws are mathematical objects. They do not form part of our everyday existence, but live in an eternal, Platonic world of abstract entities. Yet somehow these abstractions are supposed to be intimately linked to our "real" world. I thought his analysis was insightful, and helps explain why science is so often compared with religion. A scientist who subscribes to the Platonic picture is not in fact that far from being a kind of priest. He probably doesn't believe in God (most scientists don't), but he still claims to be able to mediate between our world and the eternal world of mathematics.
There is a major difference between the world we experience and the Platonic world. For us, things are constantly changing; the eternal world is frozen in a single moment. But this is exactly where science has scored its greatest victory. Starting with Galileo, scientists have found ways to conceptualize time as space. Smolin starts with the trivial example of someone throwing a ball, and considers how this can (apparently) be captured as the parabola the ball follows. The dynamic experience of watching the ball fly through the air is replaced by a static curve, or even better by the equation describing that curve. Newton extended the picture further, and Einstein completed it. Relativity fuses space and time together into the single concept of space-time.
It is all very beautiful, and Smolin, who says his first exposure to real science was reading Einstein, is particularly receptive to its beauty. But, he explains, you just don't seem to be able to progress any further once you accept Einstein's "block-universe" view. He argues that something has gone wrong, and we need to backtrack; from there, he goes on to outline the daring research program that he and his collaborators have been pursuing. First, he wants to put time center stage, and say that it really does exist in its own right. This means doing something we have been taught for a century to believe is wrong, and claiming that an absolute notion of time exists, in other words that there is a universal time according to which it is meaningful for distant events to be simultaneous. Second, and even more heretically, he wants to abolish the special status of physical laws. They will no longer be inhabitants of the Platonic world, but just part of our normal world, subject to change like everything else. He spends rather more than half of the book sketching out this framework in fair detail.
I would like to say that I was immediately attracted by the elegance of the scheme, but that would not be true. I am in fact shocked. It looks ugly, and it is very much at odds with most of the science I know. However, as the great chess master Aron Nimzowitsch used to say, the beauty of a move lies not in its appearance, but in the thought behind it. One of Einstein's basic principles, which led him to General Relativity, was that anything which acts must itself be acted on. In his case, he argued that, since space acts on matter, matter must act on space. At the time, this must have seemed crazy to many people, but now it makes perfect sense. The idea that physical laws are mutable just takes the idea a step further. And if physical laws can change, it is reasonable to argue that time needs to play a more central role; then one can go further, as Smolin does, to talk about how the laws of nature could gradually evolve over time to look like the ones we now see around us.
So I have mixed feelings about the book. My instinctive reaction is that it will probably be shown to be wrong. But that's exactly why it's science: it makes falsifiable predictions. Smolin's main competitor, the multiverse theory, is in no danger of being disproved, since the other universes aren't observable. No wonder it initially seems more attractive. And Smolin evidently knows all the angles. He's not doing this because he likes craziness; he's doing it because he's tried the obvious ideas, and they don't work.
To conclude, the thing I am most struck by in Time Reborn
is that it suggests we have reached a boundary in science. Basically, Smolin agrees with our friend T. He says that science, as we know it today, is about things you can put in teaspoons - possibly very large teaspoons, but still teaspoons. If we want to make progress on the issues currently baffling us, which concern the whole universe, we need to figure out a way of doing science that represents a fundamental break with what has gone before.
Maybe it's not possible. Maybe we've come as far as we can, and the remaining questions are simply outside the scope of scientific inquiry. But if they are things that people can understand at all, it seems plausible that the answers will be something like what Smolin presents here; perhaps not specifically this idea, but something equally bold and different. It's fascinating to read a status report from these fearless explorers on the absolute limits of human knowledge.This review is in my book If Research Were Romance and Other Implausible Conjectures