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’t Hooft on the Foundations of Superstring Theory

  1. Oct 1, 2012 #1


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    This paper may be intersting:

    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)
  2. jcsd
  3. Oct 1, 2012 #2


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  4. Oct 2, 2012 #3


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    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.
  5. Oct 3, 2012 #4


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    I am quite confident that string theory cannot do that any better than other quantum theories.
  6. Oct 3, 2012 #5


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    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).
  7. Oct 3, 2012 #6
    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.
  8. Oct 3, 2012 #7


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    Is doing no better good or bad?
  9. Oct 4, 2012 #8


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    I don't see how could that be good.
  10. Oct 6, 2012 #9
    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?!
  11. Oct 6, 2012 #10


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    Because the issue is very difficult.
  12. Oct 6, 2012 #11
    I am painfully aware of this, but so is most of the hypotheses discussed here. Why isn't his work getting any shine here?
  13. Oct 6, 2012 #12


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    Who are you refering to?
  14. Oct 7, 2012 #13


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    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:
    Duality between a deterministic cellular automaton and a bosonic quantum field theory in 1+1 dimensions
    Gerard 't Hooft

    Then the July paper:
    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
    Last edited: Oct 7, 2012
  15. Oct 7, 2012 #14
    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.
  16. Oct 7, 2012 #15
    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.
  17. Oct 7, 2012 #16


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    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.
  18. Oct 7, 2012 #17

    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.
  19. Oct 7, 2012 #18
    So what do you want instead of math, literature? Math is the only thing you'll ever get.

    If there's any issue with reconciling QM and GR, it's that GR needs a modification. Not QM.

    So what are the unresolved issues in QM that need extra understanding? Non philosophical ones please, just ones that make sense.
  20. Oct 7, 2012 #19
    Not really sure how you can be so certain about that?
    What makes you so certain that QM is correct and GR wrong?

    Also, ofcourse the unresolved issues will stem back to the fact that either you have to close your eyes and accept magic (indeterminism) or you have to come up with a deeper theory
  21. Oct 7, 2012 #20
    So what if I said that determinism is magic? You're just stating your opinion. There's no single observation, experiment or even theoretical reason to suspect that there should be something else behind the theory. It's just like saying "oh i don't like differential geometry and the way it explains GR, there has to be something more like algebra there". Why, or how do you reach such a conclusion?

    QM is by far the most complete, tested and accurate theory in physics. It doesn't fail anywhere, whereas classical mechanics does fail in various places. Why assume then that determinism is more fundamental, or preferable?

    I'm not saying that GR is wrong, it' just incomplete, at higher energies it needs new degrees of freedom. It's just more plausible that we only need to modify GR, than the whole Standard Model which is based on QM. The SM makes incredibly accurate predictions, all of them verified. There's just no reason to look for stuff that doesn't need to be there. Looking for hidden variable QM is just like looking for pink unicorns eating lava in the center of the earth. Sure they might be there, but what makes you think that? Just because it's possible doesn't mean it's at all worth investigating.
    Last edited: Oct 7, 2012
  22. Oct 7, 2012 #21


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    I think it is very important what 't Hooft is doing, and in fact -maybe subjective- very very interesting. First of all he makes a connection between classical and quantum models. He is not alone in this. Wetterich makes a interesting connection between a classical Ising model and the quantum physics of fermions, Hossenfelder takes plancks constant and G to zero at high energies, giving nature a classical as well as a quantum phase. Futhermore, there is a big trend of studying information theory and thermodynamics in Gravity describing it as a thermodynamic equation of state, still allowing for underlying classical theory for the microscopic degrees of freedom (as I understand it...). To me it does not seem crack-pottery at all.

    't Hooft does not make the claim (yet) that he is describing models of nature, but he has clearly described the path to reach that:

    "We set out to follow the following strategy: turn a simple, exactly soluble cellular automaton into an exactly soluble quantum field theory, derive its hamiltonian, and subsequently add interaction terms. The hamiltonian will receive small, local corrections so that now a cellular automaton can be mapped onto an interacting quantum field theory. From there, find our way to the Standard Model."

    The fact that he is using a discrete space, gives a classical description of superstringtheory and gets around the Bell's theorem should wake us all up. Stay tuned!

  23. Oct 7, 2012 #22
    This thread would be a good place to mention another recent idea of 't Hooft's that isn't getting any attention, what I call his "conformally constrained QFTs". Reality according to 't Hooft seems to be: cellular automaton -> strings -> "conformally constrained QFT" -> standard model.
  24. Oct 7, 2012 #23
    I guess we just have a irreconcilable difference of opinion when it comes to metaphysics.
    I consider indeterminism to be unscientific and in the same realm that I place solipsism.
    Please explain to me how it is that a particle is indeterministic, yet it follows the Born Rule? Why would it, why wouldn't it rather be completely impossible to calculate the probability?
    Think about it, you're claiming that a particle is indeterministic but that there is a limit to it's indeterminism so that it always follows the Born Rule and I ask WHY? Why does it follow the Born Rule. It just SCREAMS: "hidden cause."

    If indeterminism *could* even in principle be true, then the Universe should not be possible to model at any scale. What do we find? Determinism. ALL THROUGHOUT the history of scientific inquiry we found a new layer and a new layer of determinism the deeper we peeled back and now because we have hit a barrier we should conclude "Oh yeah indeterminism is true" ? I don't think so, but you are free to.

    If that is your position then go ahead, since you think it's worthless to look for such causes I guess all I can say is that I appreciate the input, but it wont help this thread to discuss this further with you.
    Last edited: Oct 7, 2012
  25. Oct 7, 2012 #24


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    There are many physicists in the foundations community who believe the study of foundational issues, e.g., measurement problem, EPR-Bell phenomena, Born rule, etc., will bear on the unification/reconciliation of GR and the Standard Model. Smolin and ‘t Hooft are two of the most famous examples, but having attended several conferences in foundations of physics, I can tell you there are many more. The physics community has worked on this problem for decades without finding a solution, so why not welcome new approaches? You don’t have to participate, nor even keep abreast of them, but I don’t see why you would revile them.

    As for why ‘t Hooft’s idea isn’t getting more attention here, I don’t think there’s a conspiracy :smile: Many technical approaches to foundational issues with implications for unification have been published. They don’t get a lot of air time in forums such as this because they require committed study to fully appreciate/understand and haven’t produced results commensurate with such an investment. When someone produces a new theory that formally unifies GR and the SM, and yields new physics, then the community will invest the time and energy necessary to learn it. At that point, enough people will understand and appreciate it that it will be discussed extensively on Physics Forums.
  26. Oct 7, 2012 #25
    But who/where/what?
    Everytime I find a new paper discussing some of these issues they usually just assume "standard QM" and aren't really looking for a deeper answer with a few exceptions, like you mentioned.
    But were are the "many more" people?

    I understand this and don't think there is any conspiracy. It's just a bit depressing to see the reception a potentially revolutionary idea like the one he got in mind gets when we take into consideration that there are really no other satisfactory answers at the moment.
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