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I love reviewing books - have been doing it at Goodreads, but considering moving here.

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Pattern Recognition and Machine Learning (Information Science and Statistics)

Relativity, Thermodynamics and Cosmology

The Cambridge Handbook of Second Language Acquisition

Just looking at the title gives you a large clue as to what this book is about. Woit is covering a lot of the same ground as Smolin, in *The Trouble with Physics*. Both of them argue convincingly that fundamental physics has lost its way. Superstring theory has been around for over 20 years, and it hasn't delivered on its early promises. Here are what I saw as the main pieces of evidence:

1. Problems with supersymmetry. Every particle is supposed to have a supersymmetric partner. No one has ever observed a supersymmetric partner to any known particle. The theory doesn't even predict what masses these partners should have, so it's not clear how to look for them. Very bad.

2. Incredibly bad predictions on vacuum energy/dark energy. It's notorious that natural versions of superstring theory predict a value for the density of dark energy that's at least 50 orders of magnitude too high - maybe as much as 100 orders of magnitude, or even more. As the author gleefully points out, probably the worst prediction ever made by a mainstream theory that people take seriously.

You'd think that this would be enough to sink it. But the worst part is that superstrings aren't in fact a proper, falsifiable theory. As Feynman is supposed to have said, superstring theorists don't make predictions, they make excuses. By which he meant that the framework is so loose, and has so many adjustable parameters, that any inconvenient observation can explained away. It's always possible to come up with a new variant that fits, or that at least can't easily be proved not to fit.

So, why on earth is this still the mainstream approach? Woit's argument is, more than anything, that it's down to one person, Edward Witten. Witten is incredibly gifted, and almost certainly the best mathematical physicist alive. By all accounts, he's also a very nice guy. Physicists are not just in awe of him, they like him too. When Witten started doing superstring theory, and discovered amazing new directions to explore, others followed. Unfortunately, the math required is very difficult, if you don't happen to be as smart as Witten. As Woit says, suppose you're a grad student who's spent several years of his life learning this stuff. It's hard to write it off as a bad investment. You have a strong emotional reason to want it to be right. After a while, a self-perpetuating circle is set up. Smolin spends rather more time analyzing the sociology in*The Trouble with Physics*.

So, is Woit's book just one long rant? 300-odd pages of variants on "The Emperor has no clothes"? Actually, no. The last third or so could reasonably be described in those terms. But the greater part of it is quite positive, and contains what I found to be a remarkably interesting take on quantum mechanics, presented so as to highlight the role played by the concept of symmetry. The way Woit tells it, one of most important people in the development of the field was the mathematician Hermann Weyl, who came up with some of the central ideas, and showed how mathematical ways of describing symmetries could be made into a cornerstone of the theory. There is an interesting human dimension to this as well. Weyl was not only Schrödinger's best friend and close collaborator; apparently Schrödinger was also quite happy for Weyl to be his wife's lover, while Schrödinger himself spent most of his time with another woman, who, oddly enough, has never been identified. I can't imagine why this hasn't all been made into a movie. Maybe it has, and I just don't know about it.

Woit presents a detailed account of how Weyl's ideas came to fruition in quantum chromodynamics and "The Standard Model", which he plausibly describes as one of the great achievements of science. He goes on to argue that the biggest mistake people have made has been to abandon Weyl's lead. Superstring theory no longer gives the same weight to these concepts. I'm in no way competent to judge whether Woit's arguments are correct, but they're interesting, and I hadn't heard them before.

Unfortunately, although Weyl's symmetry story is fascinating, and I applaud Woit's courage in delving so far into its details, I must warn you that he assumes a startling amount of background in math and physics. In particular, he talks more about the representation theory of Lie groups and its application to quantum mechanics than I would ever have imagined possible in what's supposed to be a non-technical book. I did courses on group theory and representation theory as an undergraduate, and I've read both Dirac on the principles of quantum mechanics and Kaplansky on Lie groups and Lie algebras. All of this stuff is very relevant to Woit's exposition, and he quotes it constantly. I still found myself struggling most of the time, and in general reading the book as poetry rather than as science. Alas, I'm not as smart as I'd like to think I am.

So, the more you know about that kind of thing, the more likely you are to feel that Woit is worth looking at. (Penrose is one famous physicist who gives this book a big thumbs-up). If you haven't got the math background, and just want to find out what the deal is with the crisis in superstring theory, I strongly recommend reading Smolin instead. They're very interesting books, and I'm glad I read both of them. But I wish more than ever that someone would sort out the mess that physics has got itself into. It's scary to see the world's greatest minds behaving like this.

___________________________

I was just sent this by a friend. Well, if you can't be bothered to read the book, it's definitely giving you the essentials...

1. Problems with supersymmetry. Every particle is supposed to have a supersymmetric partner. No one has ever observed a supersymmetric partner to any known particle. The theory doesn't even predict what masses these partners should have, so it's not clear how to look for them. Very bad.

2. Incredibly bad predictions on vacuum energy/dark energy. It's notorious that natural versions of superstring theory predict a value for the density of dark energy that's at least 50 orders of magnitude too high - maybe as much as 100 orders of magnitude, or even more. As the author gleefully points out, probably the worst prediction ever made by a mainstream theory that people take seriously.

You'd think that this would be enough to sink it. But the worst part is that superstrings aren't in fact a proper, falsifiable theory. As Feynman is supposed to have said, superstring theorists don't make predictions, they make excuses. By which he meant that the framework is so loose, and has so many adjustable parameters, that any inconvenient observation can explained away. It's always possible to come up with a new variant that fits, or that at least can't easily be proved not to fit.

So, why on earth is this still the mainstream approach? Woit's argument is, more than anything, that it's down to one person, Edward Witten. Witten is incredibly gifted, and almost certainly the best mathematical physicist alive. By all accounts, he's also a very nice guy. Physicists are not just in awe of him, they like him too. When Witten started doing superstring theory, and discovered amazing new directions to explore, others followed. Unfortunately, the math required is very difficult, if you don't happen to be as smart as Witten. As Woit says, suppose you're a grad student who's spent several years of his life learning this stuff. It's hard to write it off as a bad investment. You have a strong emotional reason to want it to be right. After a while, a self-perpetuating circle is set up. Smolin spends rather more time analyzing the sociology in

So, is Woit's book just one long rant? 300-odd pages of variants on "The Emperor has no clothes"? Actually, no. The last third or so could reasonably be described in those terms. But the greater part of it is quite positive, and contains what I found to be a remarkably interesting take on quantum mechanics, presented so as to highlight the role played by the concept of symmetry. The way Woit tells it, one of most important people in the development of the field was the mathematician Hermann Weyl, who came up with some of the central ideas, and showed how mathematical ways of describing symmetries could be made into a cornerstone of the theory. There is an interesting human dimension to this as well. Weyl was not only Schrödinger's best friend and close collaborator; apparently Schrödinger was also quite happy for Weyl to be his wife's lover, while Schrödinger himself spent most of his time with another woman, who, oddly enough, has never been identified. I can't imagine why this hasn't all been made into a movie. Maybe it has, and I just don't know about it.

Woit presents a detailed account of how Weyl's ideas came to fruition in quantum chromodynamics and "The Standard Model", which he plausibly describes as one of the great achievements of science. He goes on to argue that the biggest mistake people have made has been to abandon Weyl's lead. Superstring theory no longer gives the same weight to these concepts. I'm in no way competent to judge whether Woit's arguments are correct, but they're interesting, and I hadn't heard them before.

Unfortunately, although Weyl's symmetry story is fascinating, and I applaud Woit's courage in delving so far into its details, I must warn you that he assumes a startling amount of background in math and physics. In particular, he talks more about the representation theory of Lie groups and its application to quantum mechanics than I would ever have imagined possible in what's supposed to be a non-technical book. I did courses on group theory and representation theory as an undergraduate, and I've read both Dirac on the principles of quantum mechanics and Kaplansky on Lie groups and Lie algebras. All of this stuff is very relevant to Woit's exposition, and he quotes it constantly. I still found myself struggling most of the time, and in general reading the book as poetry rather than as science. Alas, I'm not as smart as I'd like to think I am.

So, the more you know about that kind of thing, the more likely you are to feel that Woit is worth looking at. (Penrose is one famous physicist who gives this book a big thumbs-up). If you haven't got the math background, and just want to find out what the deal is with the crisis in superstring theory, I strongly recommend reading Smolin instead. They're very interesting books, and I'm glad I read both of them. But I wish more than ever that someone would sort out the mess that physics has got itself into. It's scary to see the world's greatest minds behaving like this.

___________________________

I was just sent this by a friend. Well, if you can't be bothered to read the book, it's definitely giving you the essentials...