Video is now available of David Gross’s colloquium this past week at NYU, which had the title Quantum Field Theory: Past, Present and Future. It’s quite interesting to compare his current point of view to that of ten years ago. The earliest substantive post on this blog was this one, which reported on a similar sort of talk by Gross, of similar length, also here in New York.
If you look at that blog post, you’ll see that I found myself in strong disagreement with many of the main arguments Gross was making back in 2004. Remarkably, ten years later, there’s relatively little I would disagree with in his NYU talk on much the same topic. Back in 2004 he was predicting the imminent discovery of supersymmetry at the LHC, in the current talk supersymmetry was not mentioned at all. I think the negative LHC results have had a very real effect on his thinking.
His 2004 point of view on string theory was that it was a better, more fundamental replacement for QFT. His arguments for this weren’t very good then (see the old blog posting), and he seems to now have wisely abandoned them. Instead, the first hour of his talk was all about the story of our increasing understanding of the power of QFT. From there, he argued that there’s some larger framework that we don’t understand, which includes our current understanding of QFT, as well as things like quantum states that look like strings. He likes to refer to this conjectural new framework as QFT/string theory. Interestingly, there was no reference at all to “M-theory”.
Gross’s current vision of the future comes down to something close to mine: some yet undiscovered new ideas will tell us something new about the QFT framework, and this will show us how to make progress on quantum gravity and unification. I’d add something more specific, that previous progress came from understanding new ways of exploiting symmetries in QFT, so future progress may very well be of that same general nature. He pointed out that the story of past QFT progress was often that people had decided that something dramatically different was needed, but ended up realizing that they just needed to solve some very technical issues, not move to something very different (e.g. proper handling of renormalization and of gauge symmetry was needed, not new degrees of freedom).
In the question and answer period Gross made clear his distaste for the string theory landscape. About all he would say about anthropics was “Oy-vey”, and that it’s nothing but a cop-out. He characterized the supposedly finite number of “string vacua” with stabilized moduli and positive CC as likely irrelevant, since you don’t know what theory they are a solution to, and there’s an infinity of other solutions to the kinds of equations you’re considering.
All in all, I found watching this quite encouraging. Seeing one of the great elder statesmen of the field stop promoting failed ideas, challenge dubious received wisdom, and move on to a more promising take on where the field should be heading is cause for optimism. I hope younger theorists will pay attention.
There is a brief mention to M-theory around 1:30:30.
Yes, some are sick and tired of claims such as “Theory of Everything” (i.e. everything except the standard model), “multiverse” (a coverup for the failure to explain the Universe) and so on. More prudently, string theory can be seen as a framework that gives certain insights in quantum field theories.
listening to the talk, I get an impression that differs from yours. My impression is that Gross is still a full believer in string theory, but that he acknowledges that critics have a point. It seems to me that his retreat is only tactical; he avoids the issues that are easily criticized, while still being convinced to be correct on the large picture. String theory is still what he wants and thinks correct. He still believes in supersymmetry and higher dimensions.
On the other hand, maybe you are right, and there is hope for improvement.
Gross is a good speaker and fun to listen to. However, nature couldn’t care less about his beliefs. They are no more than far fetched speculations involving huge extrapolations.
He talked about Feynman diagrams but said nothing concrete. It would have been more useful if he, for example, had said something about “Amplituhedron”. Is it really a breakthrough in quantum field theory, as it is advertised to be?