Thursday, August 31, 2006

Erice is beautiful

Having a wonderful time here. The mediterranean climate and light are as wonderful as I remember from many years ago.

Susskind and Douglas have been giving nice lectures on the string theory landscape. Lenny's attitude seems very reasonable. He said very clearly that string theory might be wrong, but that we could still learn from it. Personally I don't find it at all implausible that there are many universes with different physical laws and that ours is exceptional for anthropic reasons. (The earth is obviously an exceptional planet, for anthropic reasons!) However, I do think that it will be an unsatisfying end for science if the fundamental parameters are randomly determined with slight bias to accommodate life. One thing I have heard people say repeatedly here, something I've thought since I was a grad student, is that the standard model is itself an ugly Rube Goldberg contraption. Granted, it is tremendously successful in describing nature, but who ordered all of those extra generations and crazy fermion masses?

I had an interesting chat with 'tHooft about black holes and his belief that there is a deterministic structure underlying quantum mechanics. He admitted the Bell inequalities are a big problem for him and that so far he has been unable to formulate even any toy models he finds acceptable. Nevertheless he is quite sure of his viewpoint. Some of the descriptions he gave of his proto-theory seem to contain non-locality and other weirdness, but it's clear he's thought a lot about these issues. He predicted a limit to the capabilities of quantum computers as a result of his underlying description.

R.D. Kenway gave some nice lectures on the current state of lattice QCD. Very impressive recent progress on a number of fronts, ranging from chiral fermions to studies of topological charge to computation of electroweak matrix elements.

Physics is like a cloud. Looking directly at it the changes are almost imperceptible. But look away for a while, and you'll see everything has changed.

Some of the lectures are online here.

PS The main internet router broke today, so we were offline for about 12 hours while they obtained and installed a new one. Some were going nuts, but I noticed attention was more focused during the lectures. After the fancy banquet people (including me) were running back to the main building when they heard the network was back up :-)


Anonymous said...

"He predicted a limit to the capabilities of quantum computers as a result of his underlying description."

Did you ask him why he believes this? His models aren't inconsistent with quantum computers being powerful and in fact they might even lead to even more powerful computers.

A very cool example of this comes from Bell inequalities. Quantum theory violates a Bell inequality by a certain factor. But one could imagine that there is another theory which produces "stronger" correlations than quantum theory. Wim van Dam showed that in this latter case, if the correlations were as strong as possible, the communication complexity (the number of bits needed to compute a function f(x,y) when x and y are held by separate parties) is always a single bit, i.e. trivial! That's a crazy powerful model!

I actually agree with t'Hooft, in a way, but I have been developing my own crazy way to get quantum theory!

Steve Hsu said...

I didn't get a clear statement for how the limitation arises, but I got the impression it has to do with the deterministic evolution.

Anonymous said...

Interesting. Certainly determinism has little to do with computational complexity, as far as I can tell. It is quite easy to write down deterministic theories which are both more and less powerful than conventional computers.

Anonymous said...

Has t'Hooft produced any paper on this topic?

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