## Wednesday, July 28, 2010 ... //

### Newton Medal talk by Witten

I have often confused Newton and Witten - a silly Freudian slip. Once he got his Newton Medal, there's a new reason for such a confusion.

Below, you will find the video from his one-hour lecture.

The first part of the July 1st Newton lecture 2010 (click this link if you don't see the videos on this page!) above is 33 minutes long, the second part below is 31 minutes long. More importantly, the videos on this page are too small and you will have to click the "screen" logo in the right lower corner for the full screen mode.

Michael Green has introduced Edward Witten. Witten paints himself as a newcomer :-) who didn't participate in many early developments.

But he reviews the history of string theory as a history of Nature that was authoritatively teaching the physicists new things that they didn't expect and that they often didn't want to be true. ;-)

This stubbornness of string theory is traced to the absence of special interaction vertices that had to be defined in quantum field theory. In string theory, interactions are automatically given by global properties of the world sheet and don't allow us to make any adjustments because the local character of the world sheet remains unchanged, whether or not the propagation of particles includes interactions.

At any rate, string theory gives us several possible backgrounds (previously: theories) only, picks its own symmetries, as well as the right spacetime dimensionality - 9+1 dimensions was one of the first things that people didn't expect and didn't want. No one sat down to find a unifying theory with extra dimensions that give them room to achieve unification and complexity more easily. Instead, all those features were imposed upon the researchers who wanted to make sense of the Veneziano amplitude.

Yes, Matt Harding was (dancing) in London, too. And everywhere else, for that matter. Thanks to Gene for the video.

In the second part, Witten focuses on supersymmetry (and supergravity), the main prediction of string theory for doable experiments. SUSY is presented as an addition of "quantum" (Grassmannian) coordinates to special relativity - similarly for SUGRA and general relativity. SUSY is a part of a much bigger structure in string theory.

A realistic draft of the real world, including quantum gravity, was a sign from the heavens (not only) for Witten. He mentions that he was shocked by the little interest that people would dedicate to many important questions. Later, alpha' mutates the spacetime in the same way as hbar mutates the phase space.

However, Witten is gradually getting from the first-revolution picture based on CFTs to the picture from the 1990s based on S-dualities, extending the old cute observations about the electro-magnetic dualities of Maxwell's theory.

String theory is not only just a straightforward quantization of a classical theory; string theory is a directly quantum theory which really explains where quantum mechanics comes from. The new viewpoint shows that there's really just one string theory and the five "string theories" in plural are just "classical" starting points for expansions.

It turned out that string theory is good not only for unification etc. but it also sheds light on other theories in physics which couldn't occur by chance. So it's almost certainly telling us deeper facts about those theories as well. Gauge-theoretical quantum pictures of black holes are shown as examples. The insights may flow and did flow in both directions.

In the last 7 minutes, Witten tries to make predictions which is always hard, especially about the future. The current research has shown that the number of possibilities has always exploded and Witten, who always wanted a unique answer, is inclined to learn a new lesson. But even if the anthropic picture with eternal inflation populating the landscape is the right answer, we need more clues to see why it's right, he says.

Finally, Witten says that there's a lot of things to do. The incomplete understanding of the theory is actually a reason why the theory continues to be exciting. It's not yet finished. During the last seconds, he receives the medal.

A recent audio interview with Edward Witten can be found in The Guardian, in the middle of comments about the ClimateGate. Witten's interview begins around 15:15 after a segment featuring a female cosmologist. Around 20:25, they switch to the ClimateGate and the whitewashes designed to hide the decline of the credibility of AGW.

See also a text that introduces the Guardian interview and other sources from Ian Sample.

Via Blog Search and a blog by P.W.

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