End of Time: The Next Revolution in Physics Book

People who read pop science books will know by now that the physics world is rather like that of Star Wars. The dominant String Theorists are the Empire; led by the Vader-like Ed Witten, they control the corrupt funding agencies and rule science with an iron fist. Ranged against them, we have the eccentric and charismatic Rebels. Lee Smolin's Periphery Institute is clearly the main Rebel base, and Peter Woit comes across as a typical Han Solo figure. I rather fancy Roger Penrose as Obi-Wan Kenobi and Fotini Markopoulou as Princess Leia. Luke Skywalker, alas, does not yet appear to have turned up. But I've got no doubts about Julian Barbour: he can't be anyone but Yoda. Even something of a physical resemblance, wouldn't you say?





You may have trouble with some of this book, but try reading it aloud in a Yoda voice and much will become clear. "Time, an illusion it is. Platonia, a relative configuration space it is. A blue mist, collect over Platonia it does." The blue mist, which plays a large part in the book, could be glossed as the quantum mechanical probability density function, but you may well prefer to think of it as the Force; the wave function's real and imaginary parts are the red and green mists.

I am afraid that my fluency in Yoda is limited, so I will reluctantly switch to English and leave the translation as an exercise to a more linguistically gifted reader. Joking aside, the opening part of Barbour's argument is very sensible. He starts by considering the question of what "time" is, and comes up with some good answers. He wants to go back to Mach's Principle, and think only about relative measurements: the example used though much of the book is "Triangle Space", a toy universe with two dimensions of space and one of time, which contains just three objects moving under the influence of gravity. He asks you to consider what you can do if you're just given snapshots of instants ("Nows") in Triangle Space, and shows how you can reconstruct the notion of time from them in a straightforward and pleasing way.

He takes this idea as his starting point, and then applies it to successively more complicated models of physics. It's easy to do it in Special Relativity. General Relativity is much harder, and he only sketches the argument. The problem is that a "Now" in General Relativity is a very slippery notion, since you can cut up space-time in infinitely many different ways. But I believe him when he says he's found a way to make it work there too.

He runs into the real problems, though, when he adds quantum mechanics to the mix. Here, the reasoning became hard to follow, but, as I understand him, it goes something like this. The normal (time-dependent) Schrödinger Equation makes integral reference to time, which it sharply distinguishes from space. This clashes violently with General Relativity, which views them both as parts of the same thing, and, despite repeated attempts, no one can figure out how to pull apart the four dimensions of General Relativity into three space-like ones and one time-like one in a way that will mesh with the Schrödinger Equation.

Barbour says that's because it can't be done. Instead, he makes the radical suggestion that the Universe's structure is better modeled by a version of the time-independent Schrödinger Equation, which describes static solutions to the normal Schrödinger Equation. These static solutions are the "Nows", the instants of time. The motivation is not implausible: as another reviewer points out, the time-independent Schrödinger Equation is supposed to be appropriate in situations where energy is constant and there are no external inputs. Those conditions evidently apply to the whole Universe. It's very hard to know whether to believe the argument. Your first response is that it has to be a technical trick. However, as Barbour points out, there are many examples in physics where things which at first looked like technical tricks turned out to be deep insights, and it's often best to trust the math and see where it goes.

So the Universe is technically static, and consists of a gigantic collection of "Nows". Motion is an illusion; it springs from the fact that the "Nows" are related to each other, and, crucially, that there is a tendency for them to contain "time-capsules", by which he means structures which look like records of past events; as he says, we only believe in the past because we have memories and other records of it. He illustrates using a nice example with a charged particle moving through a cloud chamber, where the track of water droplets is the time-capsule. He also compares with Leibniz's philosophy; in Leibniz's terms, the "Nows" are, roughly, monads, and there is pre-established harmony between them due to the fact that they are all solutions to the same equation.

As the book progresses, it becomes more and more mystical and Yoda-like. I had real trouble believing the final sections, which to me came across as the purest hand-waving and poeticising. In particular, he admits himself that he doesn't have a clear explanation of why the "Nows" containing "time-capsules" should tend to get high probabilities, something that is essential to the theory. But there's no doubt that he's asking interesting and original questions, and I'm certainly not competent to judge whether the answers make sense. Maybe he's right, and "time" is just one of those approximations which hold in our everyday world where quantum and relativity effects can safely be ignored, but break down in more extreme situations. If you want to read a really unusual physics book which takes the fundamental issues seriously, you might want to check this one out.