Wednesday, August 15, 2012

Twistor revolution, strings, and Blackhat

Matt Strassler has an excellent posting allowing what I would call insider view to the development of particle theory during last two decades: recall that twistor revolution began around 1990 (revolutions in theoretical physics do not take place during one night!). Twistor revolutionary usually talk about N=4 SUSY or N=8 SUGRA and one might there work to be something totally unrelated to what particle physicists at CERN doing the hard computations are doing. One however learns from Strassler's posting that this is not at all the case.

The groundbreaking paper by Witten and later paper by Witten together with Britto, Cachachi, Feng led to BFCW recursion formula for tree amplitudes which has been later generalized by Nima Arkani-Hamed and others to planar amplitudes with loops. Only non-planar amplitudes are still out of reach. These papers had dramatic effects at the level of practical computation since one could replace the extremely tedious Feynman diagrammatics with twistorial/Grassmannian amplitudes constructible using only on mass shell amplitudes and recursion.

The outcome was a program called Blackhat used to analyze data at LHC, for instance analyze the data to find missing energy serving as signature of new particle not directly visible at LHC. Theoreticians Bern, Kosower, and Dixon contributed to the development of this program with their insights. To say that these persons wrote just programs, is completely misleading. They invented new methods of calculation and one can encounter these names also in twistor papers: for instance, Bern has worked with twistorialization of N=8 quantum gravity and suggested that this theory is finite. If this were the case it would prove that philosophical insights (in this case Einstein's, who was not a master mathematician in technical sense) are much more important than calculations techniques.

Strassler also expresses clearly his view about superstrings. String theory as TOE was a failure but the mathematical insights provided by it have been tremendous. Therefore we should get gradually rid of division to pro-strings and anti-strings camps. I agree. Strings can appear in fundamental physics in many manners and the super string view is only one vision about how. This vision failed as failed also standard SUSY. A creative theoretician can however imagine alternative visions about how string like objects could appear in fundamental physics and what SUSY could be, and also what color symmetry really is. In particular, a view about SUSY and interpretation of quark color not forcing proton to decay would be extremely interesting if possible at all.

My personal belief is that TGD view about strings is nearer to the truth. In this vision 4-D space-time surface is the fundamental notion and 2-D surfaces - string like objects - emerge. "Emerge" means that they are derived objects rather than fundamental ones. These 2-surfaces are also topologically extremely interesting since one can assign knotting and linking to them and in 4-D context also 2-knots become possible: this for 4-D space-time: dimension D=4 for space-time is a basic prediction of TGD too. The recent results about preferred extremals and solutions of modified Dirac equation imply that perturbative TGD can be formulated in terms of the 2-D surfaces so that one indeed obtains a representation of scattering amplitudes in terms of string like objects- in excellent approximation at least (right-handed neutrino is expected to cause very small effects requiring 4-dimensionality).


Ulla said...

Ulla said...

The wavelengths of these photons are some of the shortest distances known to science -- so short they should interact with the even smaller Planck length. And if they interact, the photons should be dispersed -- scattered -- on their trek through Planck length-pixelated spacetime.

In particular, they should disperse in different ways if their wavelengths differ, just as a ping pong ball and a softball might take alternate paths down a gravely hillside.

You wouldn't notice the scattering over short distances, but across billions of light years, the Planck lengths should disperse the light. And three photons from the same gamma-ray burst should not have crashed through the Fermi telescope at the same moment.

But they did, and that calls into question just how foamy spacetime really is. "We have shown that the universe is smooth across the Planck mass," Nemiroff said. "That means that there's no choppiness that's detectable. It's a really cool discovery. We're very excited."