Every year around this time the Edge web-site posts responses from a large number of scientists to some particular question. This year the question is “What have you changed your mind about? Why?”, and the results should be posted tomorrow. John Baez has posted his answer here. He writes that he changed his mind about the question of whether he should be thinking about quantum gravity after he realized “the more work we did, the more I realized I didn’t know what questions we should be asking!”, and compares the effort to “throwing darts in a darkened room and hoping to hit the bull’s-eye.” Since changing his mind he has been working on other things, and feels that as a result “I’m making more real progress understanding the universe than I ever did before.”
I think I share John’s point of view on this in many ways, even though I’ve never actively worked on a quantum gravity research project. The problem with quantum gravity research has always seemed to me that, since you can’t measure quantum gravitational effects, you’re in great danger of coming up with lots and lots of “quantum gravities”, but unable to ever know which if any of them has anything to do with the real world. This is kind of what has happened with string theory in recent years. One hope has always been that one will find a mathematically uniquely compelling model, but that has yet to happen. To me the best bet has always been that one might understand quantum gravity by unifying it with the standard model, in a compelling way such that the unified theory explains some of the things the standard model leaves unresolved. This hope was also behind much of the original interest in string theory: it wasn’t just a quantum theory of gravity, but also a theory of particle physics that could be tested.
Like John, I think we still have a long ways to go towards understanding at a deep enough level how quantum field theories really work, and how the internal symmetries of particle physics and the space-time symmetries of gravity can be unified into a more fundamental structure. Progress towards this goal may even require new mathematics, and this means there are all sorts of things to think about and work on.
One person who hasn’t changed his mind about some things is Lubos Motl. According to his latest posting, I’m
…a typical incompetent, power-thirsty, active moron of the kind who often destroy whole countries if they get a chance to do it.
The arXiv puts out charts each year showing the number of submissions by category, the ones for 2007 are now available here. Commentary about this here and here. The general trend is that quite a few years ago the number of HEP papers leveled off, as just about all of them were posted on the arXiv. The number of math papers is still growing quickly, it is only recently that posting math preprints to the arXiv has become a widespread practice. While mathematicians probably write papers at a slower rate than physicists, there are a lot more mathematicians than particle physicists.
The end of 2007 has brought one undesirable change. Recently I was down in Princeton, and found out that the University Store, traditionally one of the best places in the world to buy math and physics books, has now gone out of the book-selling business, turning it over the Labyrinth Books. The new Labyrinth store has some math and physics books, but far, far fewer. Maybe they just are getting started, and 2008 will bring better news about this.
This past summer Terry Tomboulis posted a preprint claiming to have a proof of confinement. Recently there has been a note posted on the arXiv by Ito and Seiler claiming to have found a problem with his proof, and a response from him claiming there is no problem. I’d love to hear from an expert who has taken the time to follow these arguments carefully and can explain what is going on here.
For a recent article by Arthur Jaffe surveying the history of rigorous studies of quantum field theory, see here.
Heading off late tomorrow for a 9 day vacation in Paris. Blogging will probably be light to non-existent and it will take me longer to get around to deleting comments. Please don’t feed the trolls.
Best wishes to all for the new year….