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  What are the 't Hooft papers about classical models underlying QM?

+ 7 like - 0 dislike
2946 views

Gerard 't Hooft states on his webpage:

I have mathematically sound equations that show how classical models generate quantum mechanics.

Also, there are some interesting discussions here on Physics SE about the question, see for example Discreteness and determinism in superstrings and Deterministic quantum mechanics [or searching for "+hooft +determini*"] and the links therein.

Which of the 't Hooft papers in arXiv should I read in order to grasp the question? Could anybody provide an ordered list? I would like to restrict myself for the moment to those strictly related to quantum mechanics, to grasp the ideas within a known framework. (I have seen that the question extends to the realm of string theory, where I am for the moment nearly ignorant.)

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user Eduardo Guerras Valera
asked Dec 20, 2012 in Theoretical Physics by Eduardo Guerras (435 points) [ no revision ]
@David Zaslavsky: thanks very much for the edit (I always welcome corrections to my non-native english), but, could you re-formulate it again in some other way? Because now it seems that 't Hooft models generate the whole foundations of QM, which is not true. As I have so far understood, they are able to reproduce some simple systems. That is why I wrote 'underlying classical models behind QM' instead 'generating QM'.

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user Eduardo Guerras Valera
Ah, I just used the wording from the quote. Anyway I fixed the title, hopefully that's okay. (You can always make such edits yourself, you know.)

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user David Z
It's trivial to see that 't Hooft's models can't emulate a single quantum system for various simple reasons. One of them is that 't Hooft's models disagree with the superposition principle, the fact that for any two states $\psi_1,\psi_2$, an arbitrarily complex combination $a\psi_1+b\psi_2$ is an equally allowed state of the system. This principle or postulates underlies all of quantum mechanics and may be verified in as simple systems as 1 qubit. Because 't Hooft constructs "his foundations" to explicitly contradict this postulate, they can't agree with anything in proper quantum mechanics.

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user Luboš Motl
@Qmechanic hm, I wouldn't have thought this needed soft-question. Maybe I'm wrong?

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user David Z
@DavidZaslavsky: I removed the soft-question tag again.

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user Qmechanic
It is absolutely not a soft-question. What I request is that some theoretician selects for me the paper(s) by 't Hooft that contains the essential idea in a more or less advanced stage and (if possible) before he extends the question to strings. If I were a physicist in the 1920s I wouldn't want to struggle against the Einstein paper with the previous, wrong version of the field equations (of 1915 or so?), or study all Einstein papers about inertia, but rather I would want a direct reference to the 1916 paper in Annalen der Physik. I am not asking for any popular description...

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user Eduardo Guerras Valera
I am working in lensed quasar spectra and in large scale structure computer simulations, this 't Hooft question is far from my field, and I don't want to devote days studying all papers that may seem related. I'm simply asking that some of you theoretical physicists select for me which paper I should study to grasp the question. I have a more or less solid background in QM but have not yet studied strings seriously.

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user Eduardo Guerras Valera
There's this little point that @Motl failed to grasp about these models: It's the "ontological, true" events described here that are such that any superposition of such events is NOT an ontological event. That's just like cats: the dead cat is ontological, the live one is, but any superposition of the two isn't, or at least, that's the case in our models. Now the superposition of the two cats DOES obey Schroedinger's equation. What I have done is take all "ontological" states of a system and look at the equations they obey. Now superpositions of ontological states also obey the equations.

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user G. 't Hooft
Our theory is now that physicists describing the real world have no way of knowing whether they are describing an ontological event, or just any other solution of their equations (except when it's about cats, where we think we DO know!). The simple reason for this is that Schroedinger's equation is linear. We keep that property throughout. But now I add something new: a true, ontological state should, some way or other, evolve to become again a true, ontological state. That's just a constraint on the set of Schroedinger's equations that we impose. What's wrong with that? Nothing of course,

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user G. 't Hooft
except that it raises the suspicion that what's really happening in this world might be just these ontological states, and the rest is due to our limited understanding, somewhat contaminated with some sort of religious feeling that God likes to superimpose. So, the answer to @Motl's objection is that it's our equations used to describe observed reality that allow for superpositions, not reality itself. I thought that this statement would be trivial and unimportant, but if not understanding it causes someone to reject the models first-hand, apparently the statement is important after all.

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user G. 't Hooft
I don't know if it helps you but here is a list of his papers: staff.science.uu.nl/~hooft101/gthpub.html

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user kaj dijkstra

1 Answer

+ 1 like - 0 dislike

Well since this is a request for a reference to a paper one need not be a theorist.

I would start with the last reference 't Hooft himself gives in the paper found in the link at Physics SE. The last reference there is on the non-string model: "The mathematical basis for deterministic quantum mechanics" (arXiv:quant-ph/0604008).

Abstract:

If there exists a classical, i.e. deterministic theory underlying quantum mechanics, an explanation must be found of the fact that the Hamiltonian, which is defined to be the operator that generates evolution in time, is bounded from below. The mechanism that can produce exactly such a constraint is identified in this paper. It is the fact that not all classical data are registered in the quantum description. Large sets of values of these data are assumed to be indistinguishable, forming equivalence classes. It is argued that this should be attributed to information loss, such as what one might suspect to happen during the formation and annihilation of virtual black holes.

The nature of the equivalence classes is further elucidated, as it follows from the positivity of the Hamiltonian. Our world is assumed to consist of a very large number of subsystems that may be regarded as approximately independent, or weakly interacting with one another. As long as two (or more) sectors of our world are treated as being independent, they all must be demanded to be restricted to positive energy states only. What follows from these considerations is a unique definition of energy in the quantum system in terms of the periodicity of the limit cycles of the deterministic model.

You could then follow backwards in time the references of this one.

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user anna v
answered Dec 20, 2012 by anna v (1,985 points) [ no revision ]
thanks very much. I'll have a deeper look at this paper.

This post imported from StackExchange Physics at 2014-06-14 12:53 (UCT), posted by SE-user Eduardo Guerras Valera

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