What Every Physicist Should Know About String Theory: Edward Witten

strings2015.icts.res.in/talkT...
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0:00:00 Introduction
0:01:05 [Talk: What Every Physicist Should Know About String Theory by Edward Witten]
0:02:46 Anyone who has studied physics is familiar with the fact that while physics - like history - does not precisely repeat itself,
0:03:13 Quantum gravity
0:07:11 If we introduce the "canonical momentum"
0:08:46 So we have found an exactly soluble theory of quantum gravity in one dimension that describes a spin
0:09:55 Just to make things more familiar,
0:12:26 For a given T,
0:13:57 Thus the complete path integral for our problem - integrating over all metrics get
0:14:47 So we have interpreted a free particle in D-dimensional spacetime in terms of 1-dimensional quantum gravity.
0:15:35 Now to do the quantum gravity path integral,
0:16:22 To integrate over the paths, we just observe that if we specify the positions y1.
0:18:00 We have arrived at one of nature's rhymes:
0:19:17 There is actually a much more perfect rhyme if we repeat this in two dimensions,
0:20:42 But now we notice that the obvious analog of the action function that we used for the particle,
0:21:30 Some very pretty 19th century mathematics now comes into play
0:23:01 To underscore how a two-manifold is understood as a generalization of a Feynman graph,
0:23:51 Now I come to a deeper rhyme:
0:26:34 Operators in quantum mechanics
0:27:36 But in conformal field theory, there is an operator-state correspondence,
0:28:31 The operator-state correspondence arises from a 19th century relation between two pictures that are conformally equivalent:
0:30:53 The next step is to explain why this type of theory does not have ultraviolet divergences.
0:33:07 It is true that, as I said, a Riemann surface can be described by parameters that
0:35:03 Instead of giving a general explanation of this,
0:36:04 Going to string theory means replacing the classical one-loop diagram
0:36:09 Going to string theory means replacing the classical one-loop diagram with its stringy counterpart,
0:36:18 19th century mathematicians showed that every torus is conformally equivalent to a parallelogram in the plane with opposite sides identified
0:36:33 But to explain the idea without extraneous details,
0:38:54 I have explained a special case, but this is a general story.
0:39:39 I want to use the remaining time to explain, at least partly,
0:40:17 We could have used in this construction a different 2d conformal field theory
0:41:09 When we get away from a semiclassical limit, the Lagrangian is not so useful
0:42:04 Many other nonclassical things can happen.
0:42:20 We can say that from this point of view,
0:43:06 This is not a complete explanation of the sense in which,

[@bonerici]

thank you ed witten.

[@RPWUKONG]

so exciting to watch this lecture.

[@DilipSadh]

Good talk... Thanks Dilip Sadh

[@Starke667]

I'm constantly amazed at this mans intelligence

[@WALLACE9009]

Very nice talk.

[@amankota2121]

thanku very much

[@joeyd1440]

World's smartest man

[@Euquila]

It is so fascinating and this guy has to be one of the brightest on the planet. I wonder if there is another framework that does not involve curved geometries / manifolds that is better suited to the problem.

[@32bikkeltje]

Thanks for posting this vid! It's nice to see something less complicated then women.

[@SVBaish]

He came to India?

[@profile1251]

IMO there's are simple reason why we don't fully understand what gravity is is because our theoretical models are wholly inadequate and incomplete, if not completely 'wrong'. Even General Relativity isn't actually perfect in charting movements of the planets and that's a very simple phenomenon but it's just the best thing we got (so far). The complete understanding of Gravity may well be centuries if not millennia away. Someday we may..

[@profile1251]

Russell K. Bonney Thanks I'll check it out. Anything that offers an alternative to General Relativity !

[@drbonesshow1]

String theory predicts far too much: a huge number of solutions known as “string vacua." However, despite the enormous number of possibilities, the string theorists can't give me one potential solution that I can apply to understanding women.

[@cloudmichael11]

Gravity is a transformation of Euclidean flat electromagnetic space which may also be generalized into mass-generalized-Maxwell's equations, see: "Reality is a Mathematical Model". The fermion model is an elementary result as expounded in "A Mathematical Preon Foundation for the Standard Model". No strings nor Higgs boson necessary.

[@gazspedding]

ed witten = a walking talking Stephen hawking..