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Saturday, June 29, 2013

Reading List: Time Reborn

Smolin, Lee. Time Reborn. New York: Houghton Mifflin, 2013. ISBN 978-0-547-51172-6.
Early in his career, the author received some unorthodox career advice from Richard Feynman. Feynman noted that in physics, as in all sciences, there were a large number of things that most professional scientists believed which nobody had been able to prove or demonstrate experimentally. Feynman's insight was that, when considering one of these problems as an area to investigate, there were two ways to approach it. The first was to try to do what everybody had failed previously to accomplish. This, he said, was extremely difficult and unlikely to succeed, since it assumes you're either smarter than everybody who has tried before or have some unique insight which eluded them. The other path is to assume that the failure of numerous brilliant people might indicate that what they were trying to demonstrate was, in fact, wrong, and that it might be wiser for the ambitious scientist to search for evidence to the contrary.

Based upon the author's previous work and publications, I picked up this book expecting a discussion of the problem of time in quantum gravity. What I found was something breathtakingly more ambitious. In essence, the author argues that when it comes to cosmology: the physics of the universe as a whole, physicists have been doing it wrong for centuries, and that what he calls the “Newtonian paradigm” must be replaced with one in which time is fundamental in order to stop speaking nonsense.

The equations of general relativity, especially when formulated in attempts to create a quantum theory of gravitation, seem to suggest that our perception of time is an illusion: we live in a timeless block universe, in which our consciousness can be thought of as a cursor moving through a fixed, deterministic spacetime. In general relativity, the rate of perceived flow of time depends upon one's state of motion and the amount of mass-energy in the vicinity of the observer, so it makes no sense to talk about any kind of global time co-ordinate. Quantum mechanics, on the other hand, assumes there is a global clock, external to the system and unaffected by it, which governs the evolution of the wave function. These views are completely incompatible—hence the problem of time in quantum gravity.

But the author argues that “timelessness” has its roots much deeper in the history and intellectual structure of physics. When one uses Newtonian mechanics to write down a differential equation which describes the path of a ball thrown upward, one is reducing a process which would otherwise require enumerating a list of positions and times to a timeless relationship which is valid over the entire trajectory. Time appears in the equation simply as a label which causes it to emit the position at that moment. The equation of motion, and, more importantly, the laws of motion which allow us to write it down for this particular case, are entirely timeless: they affect the object but are not affected by it, and they appear to be specified outside the system.

This, when you dare to step back and think about it, is distinctly odd. Where did these laws come from? Well, in Newton's day and in much of the history of science since, most scientists would say they were prescribed by a benevolent Creator. (My own view that they were put into the simulation by the 13 year old superkid who created it in order to win the Science Fair with the most interesting result, generating the maximum complexity, is isomorphic to this explanation.) Now, when you're analysing a system “in a box”, it makes perfect sense to assume the laws originate from outside and are fixed; after all, we can compare experiments run in different boxes and convince ourselves that the same laws obtain regardless of symmetries such as translation, orientation, or boost. But note that once we try to generalise this to the entire universe, as we must in cosmology, we run into a philosophical speed bump of singularity scale. Now we cannot escape the question of where the laws came from. If they're from inside the universe, then there must have been some dynamical process which created them. If they're outside the universe, they must have had to be imposed by some process which is external to the universe, which makes no sense if you define the universe as all there is.

Smolin suggests that laws exist within our universe, and that they evolve in an absolute time, which is primordial. There is no unmoved mover: the evolution of the universe (and the possibility that universes give birth to other universes) drives the evolution of the laws of physics. Perhaps the probabilistic results we observe in quantum mechanical processes are not built-in ahead of time and prescribed by timeless laws outside the universe, but rather a random choice from the results of previous similar measurements. This “principle of precedence”, which is remarkably similar to that of English common law, perfectly reproduces the results of most tests of quantum mechanics, but may be testable by precision experiments where circumstances never before created in the universe are measured, for example in quantum computing. (I am certain Prof. Smolin would advocate for my being beheaded were I to point out the similarity of this hypothesis with Rupert Sheldrake's concept of morphic resonance; some years ago I suggested to Dr Sheldrake a protein crystallisation experiment on the International Space Station to test this theory; it is real science, but to this date nobody has done it. Few wish to risk their careers testing what “everybody knows”.)

This is one those books you'll need to think about after you've read it, then after some time, re-read to get the most out of it. A collection of online appendices expand upon topics discussed in the book. An hour-long video discussion of the ideas in the book by the author and the intellectual path which led him to them is available.

Posted at June 29, 2013 22:23