I finished Lee Smolin's The Trouble With Physics last night, and will write up a full review in the next couple of days. On the whole, I thought it was a well-done book, and he makes some good points. It's not without its problems, though, chief among them being the fact that the title is missing some words.

The book is really The Trouble With [Theoretical Particle] Physics, but Smolin, like the string theorists he criticizes for arrogance and narrow-mindedness, consistently talks about string theory and quantum gravity as if they were the only areas of physics that matter, and about physics in general as if the only interesting problems are problems relating to string theory and quantum gravity. This drives me straight up the wall.

Let me be perfectly clear about this: If a rampaging Calabi-Yau space comes along tomorrow and devours every single physicist working on string theory and other approaches to quantum gravity, physics will continue to be a thriving and active discipline. The rest of us will still be here, doing useful work that connects to real-world experiments. Most physicists wouldn't even notice the loss, and those who notice would probably be happier for it.

If we go another twenty years without significant progress in theoretical particle physics, with string theorists continuing to tinker with infinite numbers of increasingly baroque theories, and loop quantum gravity theorists building models and complaining about being repressed, physics will continue to be a thriving and active discipline. The vast bulk of physics activity has nothing whatsoever to do with questions of quantum gravity and unification of forces. Progress on understanding condensed matter physics, plasma physics, atomic physics, and quantum information (among others) will continue to be made no matter how far the particle theory community sinks into navel-gazing metaphysics.

There's trouble in theoretical particle physics and quantum gravity, to be sure. The rest of us are doing quite well, thank you very much, and would appreciate it if you don't burden us with your problems.

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1. Book titles should be short and punchy.

2. OTOH, it is exactly like Lee Smolin to think that he didn't leave out any words out of the title. I don't resent him for it, but it's deeply ingrained in his character.

Excellent post. Thanks for providing some perspective.

"The book is really The Trouble With [Theoretical Particle] Physics"

No, it's really

The Trouble With Quantum Gravity. Many of us theoretical particle physicists are quite happy to work on things that are experimentally testable, like TeV-scale physics that the LHC will probe, or QCD, or neutrinos, or any number of other things. I posted some anonymous comments over at Angry Physics about the breakdown of theoretical HEP groups in terms of research interests. Most of these things are not "navel-gazing metaphysics," so I don't really understand your accusation that "There's trouble in theoretical particle physics and quantum gravity, to be sure."I'm going to agree with anon. There are plenty of non-Quantum Gravity theoretical particle physicists who have very little interest in this issue.

You have a great point in this post though. I had the same issues with Smolin's title: there's plenty of physics (including particle theory) that's doing just fine, than, you.

No, it's really The Trouble With Quantum Gravity. Many of us theoretical particle physicists are quite happy to work on things that are experimentally testable, like TeV-scale physics that the LHC will probe, or QCD, or neutrinos, or any number of other things. I posted some anonymous comments over at Angry Physics about the breakdown of theoretical HEP groups in terms of research interests. Most of these things are not "navel-gazing metaphysics," so I don't really understand your accusation that "There's trouble in theoretical particle physics and quantum gravity, to be sure."Smolin mostly comes at the subject from the perspective of unification, which I think of as a particle physics issue, so I was looking for something more expansive than just "quantum gravity." I may have overshot, and slighted perfectly sensible and untroubled particle theorists in the process, in which case I apologize.

Maybe "trouble with quantum gravity and grand unification" would be more accurate?

No, it's really just quantum gravity. There's a problem with the word "unification." When a particle theorist says "grand unified theory" or GUT, they mean precisely a theory that unifies the electromagnetic, weak, and strong forces,

notgravity. This is not the same as Einstein's dream of a unified field theory for gravity plus the other forces, which is what string theory (also Smolin, at times) aims for. A GUT, on the other hand, relies purely on quantum field theory. GUT unification would happen at energy scales an order of magnitude or more below those where gravity becomes important. Those scales are still very difficult to test, but one can run measured couplings up from a low scale to see if they meet. In the Standard Model, they don't; with supersymmetry, they do. So if SUSY is observed at the LHC, it might give an indirect probe of GUT physics. Neutrino masses are another potential indirect probe of GUT physics.In short, GUTs are

really hardto test, but there might (or might not) be strong indirect evidence for them in the near future. That would still not test unification withgravity, though. Experimental tests of quantum gravity will probably require deep new insights if they are ever going to happen.No, it's really "The Trouble With Theoretical Particle Physics and Quantum Gravity". I think Chad is right, string theory is at the center of the problem, and the reason people got excited about string theory back in 1984 is that it promised not just a quantum theory of gravity, but also unification and an explanation of where the standard model comes from. This drew many particle theorists into working on the subject, and it's exactly the failure of string theory as an idea about how to get beyond the standard model that is at the center of its current problems.

You know, all the physicists I know personally these days study social networks.

Heh. Get it? "know personally... social networks"?

My Dad was a physicist, too; he designed wind tunnels, and corner cubes that are on the moon right now.

Peter, if you want to make it clear that some of these people are not solely concerned with gravity, fine; call it "The Trouble With String Theory." But "The Trouble With Particle Physics" is an ill-advised phrase, unless you

reallywant to criticize everyone studying colliders and B physics and neutrinos and QCD and improved techniques for loop calculations and all the other non-stringy things going on, just as "The Trouble With Physics" is ill-advised for the reasons Chad said.Thanks for the post, Chad. I think I'm getting a feel for the trouble with physics just by reading this comment thread.

Well said. Whatever the fundamental nature of the universe turns out to be, fluids will still obey the Navier-Stokes equation.