Today is the second and last day of the YRS. The first talks were in areas of mathematical physics that I am not informed enough to comment on. One was on some sort of random walks, the second on entanglement and the third was too mathematical. You may see the program here.

The most expected talk was given by Witten and was about the Langlands program. He started giving an elementary introduction to electric-magnetic duality, magnetic monoples, Dirac strings and the quantization condition to arrive at the Montonen-Olive duality. He then explained the goal of the Langlands program, that is, to study number theory using geometry, and ended mentioning his work, that the Langlands program can be interpreted in terms of physical ingredients. Since the audience was very heterogeneous it seems he did it well.

## 5 comments:

Victor, don't you think Witten spends a disproportionate fraction of his time on mathematics-centered physics than actual nitty-gritty phenomenology?, i.e. is he really doing physics... or physics-inspired mathematics?

If most of the world is following Witten's every statement with befuddled amazement, why do we call them "physicists" then; maybe it's better to call them quasi-physicists.

Witten is an extremely brilliant individual, with far-reaching insights into deep mathematical notions; I just don't think we should call him a 'physicist', that's all. Better to refer to him as a 'phys-mathematician'.

In the String conference in Beijing Witten said that the motivation for his last work on the Langands program was his personal interest on the the coincindence of the duality and the Langlands groups. In his talk here he said that he doesn't know whether this is good for maths or physics. Of course this is a work in mathematical physics. In fact I would say that string theory is mathematical physics because it has no prediction that has been experimentaly verified yet.

Witten is clearly a very brilliant guy. It is up to him to choose to work in physics, maths or mathematical physics. Anyway I think he is clever enough to try to find any connection of string theory with experiments. So if he doesn't work in string phenomenology that means something...

who cares? when did einstein ever waste ink wondering if, in understanding reimannian geometry, he was doing physics or math? what kind of small-minded bigotry is this to wonder if it's physics, math, math-phys, or phys-math?

why is this ever worth even asking?

Your last statement just about sums up what this whole string-theory enterprise is turning out to become: meditations on various mathematical physics topics. Your remark is most likely correct: if someone like Witten chooses to spend most of his time on topics other than string phenomenology, then string theory probably isn't your quintessential physics program; I just hope most young grad students amazed and star-struck by string-theory will take note of this before taking the career plunge.

"who cares? when did einstein ever waste ink wondering if, in understanding reimannian geometry, he was doing physics or math?"

I agree that it doesn't matter if you call string theory physics or mathematical physics. The important point is that it is the most promising extension of the SM and GR we have.

"Your last statement just about sums up what this whole string-theory enterprise is turning out to become: meditations on various mathematical physics topics."

This is the wrong conclusion. I would like to have a nonperturbative framework for compactification. Only then I would be interested in phenomenology. Maybe that is the reason Witten is not doing phenomenology. Anyway you have to ask him and not jump to the conclusion that all of string theory has no physics.

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