Friday, October 27, 2006

Teach the controversy

Aaron Pierce who is now at faculty of University of Michigan wrote a nice and wise essay for Science:
The title includes a witty analogy - I am apparently not the only one who thinks that this "controversy" about string theory and hypothetical alternatives is similar to the "controversy" about evolution and creationism. Both of these "controversies" are invented, promoted, and sometimes "taught" with a certain goal in mind and they don't reflect actual scientific results. See the Wikipedia page about the Teach the Controversy strategy to see that the two situations are essentially isomorphic.

Aaron is a phenomenologist - one of those who aren't hiding from others who spiritually live above a TeV, including the string theorists. ;-) His essay is technically a review of a blue book that all readers of The Reference Frame know and whose name will appear below. If you care why it's more relevant to review the blue book as opposed to the black book: it's because the blue book is sold better by a factor of five or so, among other reasons.

Much like Jim Cline, he starts with the difficult task of the unification of gravity with quantum field theory. Aaron explains that Green and Schwarz have made such a big impact because they showed the first theory that was not only capable to address this problem but that has also miraculously yet undoubtedly avoided some early complaints about it - namely the anomalies.

Figure 1: The Trouble With Shoes: a rise of a new technology, the fall of a foot, and what comes next

Aaron has an interesting idea that the author of the blue book is really complaining that it is no longer possible for the authors of seemingly fringe theories to get a lot of attention. The book is a lamentation for a bygone era, not an introduction to the field - because it is not too readable as an introduction for beginners.

The reason why it's no longer possible for fringe theories to get a lot of attention, Pierce explains, is simply that the bar has been raised. A new theory that would get a comparable attention would have to offer comparable results as string theory had, and no such theory is known at present.

Aaron Pierce answers the "bold claim" of the blue book that we live in an unprecedented breakdown of the marketplace of ideas in which a string-theoretical "conspiracy" has suppressed the diversity of ideas. Aaron writes that he has participated in many discussions that have revealed that the top-down theorists seem to have good and rational reasons to believe what they believe. Smolin didn't change this conclusion of Pierce: the marketplace of ideas is alive and well. Jim Cline and Barton Zwiebach came to the same conclusion.

I am afraid that the critics will argue that Aaron Pierce is a special agent of string theory from their conspiracy theories. :-)

Some of these critics often say that the difficulty of experimental testing is a characteristic feature of string theory. Aaron is a perfectionist so he offers not only a disagreement but also a full proof that it is not the case. Any theory of quantum gravity will have to face the same problem because of Wilson's insights about the Renormalization Group: all new effects predicted by any theory that can't be encoded into the shifts of the relevant and marginal couplings of the known low-energy effective theories are incredibly small.

In other words, as Aaron's colleague said, effective field theory allows you to make chicken soup without quantum gravity. ;-) Aaron cites Howard Georgi's 1993 article for the readers to comprehend the RG arguments.

Aaron explains that the recent insights have shown that the string-theoretical consistency places smaller constraints on low-energy physics than previously thought (or hoped). However,
1. it is premature to eliminate the possibility that such constraints will be found;
2. the relative ambiguity in the particle physics parameters is likely to be shared by any other hypothetical theory trying to address similar questions.
He concludes, much like Brian Greene, that despite these possible ambiguities, the questions of quantum gravity are still important and interesting. In fact, Lee Smolin agrees.

Aaron says that particle physics and mathematics owe a lot to string theory and many interesting questions could be asked about the progress in string theory. For example:
• How should science proceed if firm predictions don't appear for years?
• How do we evaluate progress if firm predictions don't exist?
• How much money should go to theories that are unlikely to be confirmed experimentally in our lifetime?
• How much credit should a field get for developing tools and results for other fields?
The Trouble with Physics only obliquely references these questions, Aaron says. It would be interesting to see them explored more fully. Meanwhile, theorists will continue to confront the thorny problem of quantum gravity with the most promising tool they can find. For the vast majority of them, this tool is string theory.

And that's Aaron's memo (and also mine, for that matter).