Trouble with Physics: Notes for a Review I. Prologue and Dramatis Personnae

Lee Smolin's The Trouble With Physics, is a long and detailed argument about the current state of physics and the nature of science by a passionate and profound thinker. Naturally, no review, much less this one, can do it full justice. These posts are my attempt to assimilate his argument and my offer to discuss the interesting questions he raises with anyone interested.

I've called the book an argument, but it is also a tale in the mode of the heroic quest. In that genre, where should I place it? Somewhere between Lord of the Rings and Jason and the Argonauts, I should think, maybe over there next to Moby Dick. The White Whale in this epic is the search for a Theory of Everything, or at least a theory of Quantum Gravity. At the risk of stretching this analogy well beyond its elastic limit, the roles of Ahab and his crew are played by the String Theorists.

Some time ago, never mind how long precisely, physics set out to achieve a unified view of all the phenomena of the world. It is a remarkable fact that this enterprise has had a great deal of success. All the phenomena of everyday life, and probably all the phenomena of any consequence in our solar system, are encompassed in just two theories. Even if we look out to the most distant regions of the cosmos there are only a couple of little exceptions.

Smolin's first chapter is a look at what he considers to be the Five Great Problems in theoretical physics: 1) quantum gravity, 2) foundations of quantum mechanics, 3) a unified theory of elementary particles, 4) how the constants of nature are chosen, and 5) the nature of dark energy and dark matter. Most physicists would agree with most or at least some of these problems. I personally would add one more: what is the nature of time? Much of the enthusiasm for string theory stems from its claim to solve 1, 3, 4, and possibly 5. The most skeptical physicists might claim that only 5) is truly a physics problem, and that the others are more like problems of philosophy.

Chapter two, The Beauty Myth is the story of unifications past. Physicists are familiar with the successful ones, but he also considers a lot of beautiful theories slain by cruel facts. The takeaway story here is that a pretty face is not enough for a good scientific theory.

Chapter Three, The World as Geometry, introduces General Relativity, the geometricization of physics, and, I think it's fair to say, Smolin's hero: Background Independence. General relativity, he says, is a background independent theory: the geometry of space and time is not the stage on which physics plays out, but a dynamical actor in the drama. The lesson he takes from this background independence is that any future theory incorporating GR needs to be background independent.

I'm not sure how seriously to take this argument. It's certainly obvious that the world does exhibit dynamical space and time, but does that fact imply true background independence? A lot of even classical General Relativity seems to consist of constructing a solution of GR with some symmetries and then treating that geometry as a background.

The chapter ends with the failure of Einstein's attempts to construct a unified field theory of electromagnetism and gravity. The problem was not that such unifications were hard to find, they were not. The problem was that none of them predicted the world we actually have. By Einstein's death, physics had moved on to other forces and other ideas, and elementary particles were at the center.

Thus, the next chapter celebrates the great unification of fundamental physics in the Standard Model. All of the forces evident in elementary particle interactions were described by the U(1) x SU(2) x SU(3)gauge theories. The next step sounds plausible even if you don't know anything Lie Groups: combining them all into an SU(5) gauge theory. It was one of those beautiful ideas that forgets to be true - protons have quite stubbornly refused to decay.

The story of supersymmetry finishes out the prologue. In case I haven't mentioned it, Smolin tells this, and all his other stories very well. He has a remarkably lucid prose style, and though I often found myself stopping to think, I was always brought up short by the ideas, not by any lack of clarity in their expression.
If the failure of supergravity to lead to a good theory of quantum gravity depressed us, though, it was also liberating. All the easy things had been tried. For decades we had tried to make a theory by extending the methods of Feynman and his friends. There were now only two things to try: Give up methods based on a fixed background geometry, or give up on the idea that the things moving through the background geometry were particles. Both approaches were about to be tried, and both would yield - for the first time - dramatic successes on the road to quantum gravity.

(To be continued)

Comments

Popular posts from this blog

Anti-Libertarian: re-post

Uneasy Lies The Head

Book Review: Anaximander By Carlo Rovelli