’t Hooft on the Foundations of Superstring Theory

tom.stoer

This paper may be intersting:

http://www.springerlink.com/content/...74267g/?MUD=MP
On the Foundations of Superstring Theory
Gerard ’t Hooft

Abstract: Superstring theory is an extension of conventional quantum field theory that allows for stringlike and branelike material objects besides pointlike particles. The basic foundations on which the theory is built are amazingly shaky, and, equally amazingly, it seems to be this lack of solid foundations to which the theory owes its strength. We emphasize that such a situation is legitimate only in the development phases of a new doctrine. Eventually, a more solidly founded structure must be sought.
Although it is advertised as a “candidate theory of quantum gravity”, we claim that string theory may not be exactly that. Rather, just like quantum field theory itself, it is a general mathematical framework for a class of theories. Its major flaw could be that it still embraces a Copenhagen view on the relation between quantum mechanics and reality, while any “theory of everything”, that is, a theory for the entire cosmos, should do better than that.

(free access)

Demystifier

People interested in that paper might also be interested in those:
http://arxiv.org/abs/hep-th/0702060
http://arxiv.org/abs/hep-th/0605250
http://arxiv.org/abs/hep-th/0512186

atyy

Two thoughts.

1) There's a partial derivation of the Born rule by Zurek, so the question is whether string theory can derive his assumptions.

2) Since string theory seems to provide a complete theory of quantum gravity in AdS/CFT, so it may provide a concrete playground for the above aim. I don't think anyone's done that yet, but stuff like http://arxiv.org/abs/1102.2910 and http://arxiv.org/abs/1201.3666 seem like a start.

Demystifier

I am quite confident that string theory cannot do that any better than other quantum theories.

tom.stoer

Up to now string theory does have to say anything about its foundations, not about quantum theory and not even about gravity (in the most general sense).

Quantumental

Actually Zurek's derivation has been rebutted by quite a few people, among them Jacques Mallah who has this to say:

W. Zurek attempted to derive the Born Rule using symmetries that he called 'envariance' or enviroment-assisted invariance. While interesting, his assumptions are not justified. The most important assumption is that all parts of a branch, and all observers in a branch, have the same "probability". Albert's fatness rule provides an obvious counterexample. I also note that a substate with no observers in it can not meaningfully be assigned any effective probability.

He uses this, together with another unjustified assumption that is similar to locality of probabilities, to obtain what Wallace called 'equivalence' and then the Born Rule from that. Because the latter part of Zurek's derivation is similar to the DW approach, the two approaches are sometimes considered similar, although Zurek does not invoke decision theory.

atyy

Is doing no better good or bad?

Demystifier

I don't see how could that be good.

Quantumental

Why is there virtually no interest whatsoever when one of the greatest physicsts of all time is speaking his mind and providing several technical papers about his ideas?!

atyy

Because the issue is very difficult.

Quantumental

I am painfully aware of this, but so is most of the hypotheses discussed here. Why isn't his work getting any shine here?

RUTA

Who are you refering to?

marcus

That sounds like a reasonable question to ask, but the situation is complex. Obviously we are talking about Gerard 't Hooft and the "Foundations" paper that Tom linked in post#1 and the related July 2012 paper about Cell'r Automata (CA) that he cites in support of the more surprising assertions. That July 2012 paper thanks "M. Porter" in the acknowledgements. So if that is Mitchell Porter we would naturally expect him to let us know and to give us a little coaching or an intuitive leg-up.

It's normal here for the people who understand something better than the others to help by explaining it to the others.

But this for some reason must be a complicated situation, everyone is being unusually circumspect and, I would say, tight-lipped. People whom I expect have a better than average grasp of this paper are not being forthcoming about it. So people like myself (less familiar with the subject matter) conclude that there must be something delicate about the situation that they don't understand, and hold back.

But please don't conclude that we're not interested. I would like very much if someone would say in simple terms what 't Hooft is driving at in that July 2012 paper. It seems to be a ONE DIMENSIONAL QUANTUM FIELD THEORY realized deterministically by a series of finite state automata. In other words the whole thing sounds too good to be true, and nutty, at first hearing. I will get the abstracts.

First there was the May paper:
http://arxiv.org/abs/1205.4107
Duality between a deterministic cellular automaton and a bosonic quantum field theory in 1+1 dimensions
Gerard 't Hooft

Then the July paper:
http://arxiv.org/abs/1207.3612
Discreteness and Determinism in Superstrings
Gerard 't Hooft
(Submitted on 16 Jul 2012 (v1), last revised 15 Sep 2012 (this version, v2))
Ideas presented in two earlier papers are applied to string theory. It had been found that a deterministic cellular automaton in one space- and one time dimension can be mapped onto a bosonic quantum field theory on a 1+1 dimensional lattice. We now also show that a cellular automaton in 1+1 dimensions that processes only ones and zeros, can be mapped onto a fermionic quantum field theory in a similar way. The natural system to apply all of this to is superstring theory, and we find that all classical states of a classical, deterministic string propagating in a rectangular, D dimensional space-time lattice, with some boolean variables on it, can be mapped onto the elements of a specially chosen basis for a (quantized) D dimensional superstring. This string is moderated ("regularized") by a 1+1 dimensional lattice on its world sheet, which may subsequently be sent to the continuum limit. The space-time lattice in target space is not sent to the continuum, while this does not seem to reduce its physically desirable features, including Lorentz invariance. We claim that our observations add a new twist to discussions concerning the interpretation of quantum mechanics, which we call the cellular automaton (CA) interpretation. Detailed discussions of this interpretation, and in particular its relation to the Bell inequalities, are now included.
30 pages

Quantumental

I should probably have included that I am the one who got Gerard 't Hooft to participate over at Physics.Stackexchange about his ideas in an attempt to spread his ideas. Which worked partially and he ended up in a interesting debate with Mitchell Porter and Ron Maimon over there. But since then it's been dead silent.
If you check the citations of his papers, there are nearly zero, which is very weird when even the most crackpottery papers usually is cited a few times.

mitchell porter

At the bottom of this is the observation that a harmonic oscillator can be viewed as a system cycling through four states. If the extreme displacements are "-r" and "+r", then the four states are "at 0 and heading in + direction"; "at +r, resting, and about to head back towards 0"; "at 0 and heading in - direction"; "at -r, resting, and about to head back towards 0".

Earlier in the year, 't Hooft constructed a discrete dynamical system encoding the analogous behavior in a quantum harmonic oscillator. A quantum field is a set of coupled local harmonic oscillators, and what he did was to construct a QFT such that time evolution applied to some special basis states can similarly be represented as timesteps between particular states of the oscillators. It's a free field theory, which is how he avoids problems of entanglement.

martinbn

Why should there be any interest!? He is trying to build a hidden variable theory, and I think many people (if not most) are skeptical about whether it is possible, so why should this be interesting. Well, there is one good reason, the author, but other than that it is just an attempt for a hidden variable theory. Even if it is successful I would find it a very poor explanation. It is supposed to be an alternative of the quantum mechanical explanation, but it cannot explain without QM. If I understand correctly the explanation is that the dynamics is given by a CA but the set up is such as to give outcomes that conform with QM predictions. It looks like the claim that the truth is that earth is motionless and planets move in such a way so that from the point of view of the sun they orbit in a simple way, while we have general relativity to explain gravity.

Quantumental

Wtf how could you ever make such a far fetched comparison?
You do not have a quantum theory to explain quantum phenomena. All you've got is math.
You do not have a way of reconciling QM with GR, all you have is math that ends up not working.

Unless you can explain exactly what is going on in QM, you should really ask yourself why you dismiss 't Hoofts attempts at finding the true answer.