The Trouble with Physics is a very well written overview of the state of modern physics. I've been trying to keep up with String Theory, Quantum Theory, wormholes, and all the rest for quite some time, but until now I hadn't noticed that I was looking at trees and didn't know which forest any of them were in. 's book gives a feeling for the lay of the land while he sets about laying waste to String Theory, which has been the great hope for a final unified theory for 25 years or so. I want to come back to the survey, but I'll cover what Smolin has to say about String Theory first, since that was his focus.'s book
String Theory, it turns out, is a family of theories which matches what we know about the universe in some telling details, but which has too many loose ends to give specific predictions on any of the things we know we don't know. The basic idea gives an outline for what a more specific theory would look like, but there's nothing in the outline that gives a rigorous suggestion for how to fill in about thirty parameters that it leaves open. People in the field have been expecting that if someone does the right experiment or makes the right guess about one parameter, that the equations will fall into place, and the rest of the implications will be obvious. But it hasn't happened yet, and the brightest people in physics have been pursuing this path for a couple of decades.
One of background independence that general relativity requires.'s simplest demonstrations that the field has been unproductive recently is a description of the steady progress that has been made in fundamental physics for more than 200 years. From 1780 through 1980, there wasn't a quarter century that passed without important new contributions to our understanding of the basics of matter, time, energy, and motion. But most of what has been added since 1980 is String Theory, along with Dark Matter and Dark Energy. But Dark Matter and Dark Energy are questions, not answers and String Theory doesn't make any predictions that aren't made by the Standard Model, which was completed in 1973. String Theory also doesn't seem able to produce a theory that incorporates the
standard signs are all present, and shows how it has restricted researchers' choices of what to areas to explore. It's a plausible charge; I've seen compelling cases in at least two other fields that similar dynamics prevented progress for decades at a time.is convinced that a major cause of the problem is that a form of groupthink has enveloped all of theoretical physics, enforced (probably unconsciously) by the oldest generation of theorists. He shows that the
ends with a plea that more research effort be funded in a variety of areas that are at odds with mainstream String Theory. He does a reasonable job of showing that they have some promise, though I'll admit that I'm way out of my depth by the time he gets here.
But I was really impressed by the first section of the book, in whichpresented all of fundamental physics from Copernicus, Bruno, and Galileo to the present day in a very approachable format. The focus was consistently on what pre-existing concepts were brought together in one of two ways. Sometimes the unification shows that two familiar things that are thought of as distinct are really the same thing, giving a deeper theory of both. (the Earth is one planet among several, the Sun is one star among many.) Other times, two phenomena that weren't understood well are explained as one common thing (Bacon showed that heat is a kind of motion; Newton showed that gravity explained both planetary orbits and ballistic trajectories; Maxwell showed that electricity and magnetism are the different aspects of the same phenomenon.) All of this is stuff that I have understood since high school, but viewing it this way gives me a hook to hang a few more things on. The rest of physics constitutes theories that I've been able to understand at a surface level, but which have never been integrated in any deep way. 's framework makes it possible for me to hold a few more theories in my head and see how they give shape to the entire universe.
Einstein was responsible for the next three major unifications. Special relativity forces space and time to be interchangeable in order for the speed of light to be an observer-independent limit. (Mass and energy, too, must be epiphenomena of some more fundamental construct.) General relativity showed that gravity is indistinguishable from acceleration, and that space has no geometry independent of the mater and energy that it contains. These are still a little hard for me to grok completely, but I feel much more knowledgeable about them post-Smolin. Previously, I was satisfied with being familiar with the equations, even though I didn't really understand what they implied about the universe. Now I feel like I understand them as facts about the universe, though of course it's a stretch to claim I understand how they fit together.
Even with QED, QCD, supergeometry, and the two DSRs, I am much happier that I understand what they are theories about than I was before. I've read several books on the frontiers of modern physics, but I'd have been hard pressed to say, more than a month after putting each down, what they implied about the universe. With's help, I now feel like I understand what the point of most of these theories are, and what it would mean to bring them together.