Arcadian Functor

occasional meanderings in physics' brave new world

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Marni D. Sheppeard

Sunday, June 21, 2009

Emerging Holography

Last week's amazing twistor workshop ended Friday with an outstanding physics colloquium by Nima Arkani-Hamed, called Holography and the S matrix, but secretly about computing scattering amplitudes using twistor spaces.

He went to some effort to try to convince a large audience of theoretical physicists that there was a mysterious new, mind blowing holographic theory behind these magical simplifications in scattering amplitudes for both Yang Mills and gravity. However, unlike serious fans of thermodynamic gravities (for instance, Padmanabhan) he didn't seem in favour of a microscopic theory of gravity that was wildly different from string theory.

Some time was spent criticising the Standard Model emphasis on manifest locality, when locality should be an emergent property. In the fantastic results so far, twistor space is clearly doing holography for us, but there is a long way to go before emergent locality is properly understood. After all, if we can remove spacetime from particle physics, why not its boundaries too?


Blogger Matti Pitkanen said...

To my humble opinion space-time will stay with us. The physics in the interior of space-time represents the classical, geometric correlates of quantum physics without which one has no quantum measurement theory. In TGD framework space-time also creates correlations between 3-D surfaces (particles) appearing as its "causal boundaries" (actual boundaries or light-like 3-surfaces at which the signature of the induced metric changes).

I see the generalization of the notions of space-time and geometry as much more promising approach than trying to get rid of it. I also believe that also the good old Minkowski space has permanent place in physics because of its symmetries with generalized conformal invariance of light-cone boundary included. Also because in a wider framework it has number theoretic meaning. Also twistors are very intimately related to 4-D Minkowski space and to me look like providing a dual description.

People are endlessly introducing new mathematical frameworks but are extreme conformists - or should I say just intellectually lazy - as far as fundamental problems of physics are considered. One additional item to a long list which I have given many times. No one asks whether the radiative corrections in QFT might represent black box which should be opened in order to make progress, and QFT in standard sense is assumed to be the low energy limit of string models. At least to me a virtual particle possessing mass larger than that of the known Universe looks rather bizarre notion!

June 21, 2009 5:30 AM  
Blogger Lumo said...

Dear Kea, it's interesting & thanks. Could you please try to reproduce the arguments you've heard why the twistors (or the convergent properties of the scattering amplitudes) are linked to holography? Please feel more than free to post any of this stuff anywhere on my blog, too.

June 21, 2009 6:08 PM  
Blogger Kea said...

Hi Lubos. To me, holography is really just a buzz word, but I mention Padmanabhan because I really like the fact that he can recover Einstein's equations from thermodynamic degrees of freedom on local horizons.

Nima simply used the following arguments (it was just a colloquium) to claim that twistors are doing holography: (i) reduction in dimension (to CP3, or RP3 as the case may be), (ii) the simplification of twistor scattering amplitudes means a removal of the old S matrix picture of motion through spacetime ('coming in from infinity') to a picture where the single diagram (that replaces gazillions of Feynman diagrams) means covariant 'creation from the vacuum'. That is, there is some powerful operation of introducing new particles. Now we think roughly this way when we discuss categorification (introducing more arrow types) but personally I don't like the word vacuum, because it is imbued with far too many connotations from local field theory. But overall, Nima did a good job of explaining that the way people ususally think of locality is just plain wrong.

June 21, 2009 9:21 PM  
Blogger Kea said...

Oh, to further motivate all this, I should say, Nima started the talk with a loose discussion of measurement problems. In particular, since precise measurements eventually lead to black holes eating up the probe, we should associate ideal measurements with stuff that happens at infinity. The devil is in the details with this stringy idea of holography, but it does do a fast job of conveying a nonlocal intuition about gravity.

June 21, 2009 9:36 PM  
Blogger Daniel de França MTd2 said...

Probably this talk is about an incoming paper with the same title of the talking:

"This most recent work doesn’t appear to use topological string theory, although Arkani-Hamed et al. are rather cagey on the topic of what sort of twistor space theory is at issue. They promise a forthcoming paper entitled “Holography and the S-matrix”, with:

a completely different picture for computing scattering amplitudes at tree level than given by the BCFW formalism, that we strongly suspect is connected with a maximally holographic description of tree amplitudes that makes all the symmetries of the theory manifest but completely obscures space-time locality"

These things probably have something to do with this paper:

June 23, 2009 2:28 AM  
Blogger Daniel de França MTd2 said...

Carrasco provided further information here:

June 23, 2009 2:30 AM  
Blogger Daniel de França MTd2 said...

There is another summary here of the central topic of a report from IAS newslater, spring 2009 edition ( ):

The cover story of the newsletter is called Feynman Diagrams and Beyond, and it starts with some history, emphasizing the role of the IAS’s Freeman Dyson. It goes on to describe recent work on the structure of gauge theory scattering amplitudes going on at the IAS, emphasizing recent work by IAS professor Arkani-Hamed and collaborators that uses twistor space techniques, as well as Maldacena’s work using AdS/CFT to relate such calculations to string theory. Arkani-Hamed (see related posting here) says he’s trying to find a direct formulation of the theory (not just the scattering amplitudes) in twistor space:

We have a lot of clues now, and I think there is a path towards a complete theory that will rewrite physics in a language that won’t have space-time in it but will explain these patterns.

and explains the relation to AdS/CFT as:

The AdS/CFT correspondence already tells us how to formulate physics in this way for negatively curved space-times; we are trying to figure out if there is some analog of that picture for describing scattering amplitudes in flat space. Since a sufficiently small portion of any space-time is flat, figuring out how to talk about the physics of flat space holographically will likely represent a real step forward in theoretical physics.

June 23, 2009 2:44 AM  
Blogger kneemo said...

Ok, so is this new holography related to the idea of replacing worldlines with points in projective twistor space? If so, it seems the Riemann surface twistor diagrams introduced by Witten in arXiv:hep-th/0312171v2 would be more useful than Feynman diagrams in this new setting.

June 23, 2009 7:14 AM  
Blogger Kea said...

Hi Daniel and kneemo. Yes, Arkani-Hamed et al are very much thinking of twistor diagrams these days, as is Hodges, Mason, Sparling and no doubt many others.

June 23, 2009 8:07 PM  

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