Wednesday, June 05, 2013

David Gross on youth, revolutions, conservatives, QM, QFT, QCD, ST, multiverse etc.

Wired has reprinted an interview of Simons Science News with David Gross:
Nobel Laureate Says Physics Is in Need of a Revolution
Well, I don't think that the title accurately summarizes what Gross said.

He mentioned that he was attracted to physics as a kid, partly by Einstein's and Infeld's book when he was 13. He gives some clues to the interviewer about the meaning of quantum mechanics, fields, quantum fields, asymptotic freedom, and so on.

His adviser Geoffrey Chew has ordered Gross to spark a new revolution by showing that quantum field theory is fundamentally wrong and one needs some revolutionary self-determining theory based on no special "elementary" particles, one satisfying the bootstrap paradigm. Instead, Gross ended up showing that quantum field theory works very well. Thank you.

The younger big shots understood his or their discoveries quickly; the old chaps didn't know quantum field theory well enough so they needed some easily understandable experiments to grasp the idea of the seemingly "unphysical" quarks.

At any rate, this story about an old revolutionary who hires a young gun but the young gun ends up being conservative is presented as something that is rather standard in science. Heisenberg, Dirac, and Bohr were already old chaps who were expecting a new revolution but the Standard Model that ultimately explained the data did nothing of the sort. Instead, it provided us with a conservative accurate reductionist theory based on the well-established concepts and postulates that have passed the tests of time.

You may see that the usual stereotype that the young people are rebels and old people are conservatives doesn't always work in physics – its converse arguably works more often.

Gross interprets string theory as a part and parcel of quantum field theory and in his conventions, it's therefore another continuation of this evolutionary process, not a revolution. In later paragraphs, he makes it clear, however, that the whole portion of quantum field theory that wants to describe quantum gravity well does need string theory and not just the "old things" about quantum field theory.

He says that the landscape of googol-to-the-fifth vacua makes no sense to him. Although I agree with most things he says about the multiverse story, he seems a bit irrational to me when he assaults the very *landscape*. The landscape is just the set of solutions and it is as large as Nature and mathematics decide, not caring whether or not the set and its size "makes sense" to a Gross.

Laymen misinterpret any uncertainty as a "wild guess". In science, uncertainty may be put under control and its existence is actually essential for a proper scientific understanding of anything. In the absence of experiments directly settling questions, we must rely on other scientific methods and we may arguably get very far with them. Philosophy isn't one of them; if a philosopher can offer musings that contribute to physics, he or she is actually doing physics.

The interview ends by not so controversial statements that science describes objective laws and patterns because even the human mind is a physical object. Maybe the author of the question wanted Gross to talk about the interpretations of quantum mechanics but he didn't understand it that way.

1. "Gross: First of all, string theory is not a theory. The Standard Model is a theory. String theory is a model"

I don't agree with that. I see SM as a model of QFT. String theory on the other hand, like QFT, *is* a theory (especially after the advent of M theory).

2. Right, I surely know where you're coming from and agree with that. String/M-theory has been unified into a single structure and all the approaches etc. are just solutions to the same theory that can no longer be separated to individual ones - in the same sense in which the set of QFTs may be divided to subgroups.

In combination with Gross' statement about the landscape, I sort of became worried that Gross hasn't understood this lesson of the duality revolution. At the same moment, I know many papers he wrote that make it very hard to believe that he could have misunderstood the lesson.

The idea that "string theory is a framework just like QFT is a framework" is correct to the extent that one doesn't know which string vacuum should be picked much like one doesn't know which QFT should be picked. At this level, the situations are analogous. But it's still important for the inner structure of the logic that the individual QFTs are separated theories while the vacua of ST can't be separated to intelectually separate pieces.

Whether some vacuum selection wisdom in string theory is waiting to be discovered is an open question but the unity of string theory is not. Because of this connectedness, string theory may also *not* be considered as some corner of a generalized quantum field theory. Quite on the contrary, string theory is the beef and skeleton connecting almost everything and it's the non-gravitational QFTs that are limits of this structure. Non-gravitational QFTs are like nails of a human, and the human is the whole QFT+ST structure most of which is given by the stringy beef. The nails may only be isolated from each other because they're limits (G goes to zero, well-below-Planck-scale effective theories) of the body that is dominated by the beef.

3. alejandro riveroJun 5, 2013, 11:41:00 AM

About Chew school, David Kaiser wrote in 2002 a paper "Nuclear Democracy. Political Engangement, Pedagogical Reform, and Particle Physics in Postwar America"; it is in a ISIS/jstor paywall, http://www.jstor.org/stable/10.1086/344960 , but it can be found also googling around. I think to remember that there was also some recollections about Chew and the RadLab in one of these meetings on the early history of string theory, perhaps a narrative from Ramond or from Schwarz.

4. alejandro riveroJun 5, 2013, 12:03:00 PM

I still think that the history had been different if Chew's students had been aware of the existence of three and only three light generations. Schwarz "dual quark-gluon model of hadrons" had been used to bootstrap the squarks and sleptons from gluon strings terminating in the five light quarks. Of course, this had been a very different history, specially the connection with gravity.

5. That was a great interview with David Gross. Thanks for sharing Luboš. We are still at the chimp stage of evolution... One always believes that great physicists can "see the matrix" and show it to us. They tell you what they know. Frustratingly not enough but still, it has already been a lightning revolution!

6. On other physics blogs, I have seen people using the "string theory is a framework" phrase as a means to "calm down" aggressive sourballs in the meaning of "string theory is not a theory, it is just a framework to do useful calculations and it does not have to have anything to do with how the real world works" or something along these lines...

Guess who said this ... ;-)

Now I'm going to read the interview and then the next TRF article :-)