John Bell Workshop 2014

Non-local beables

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  • #1636
    Lee SmolinLee Smolin
    Member

    I would like to begin with Bell’s remark on the possibility that the beables are non-local, which Tim Maudlin quotes.

    “Of course, we may be obliged to develop theories in which there are no strictly local beables. That possibility will not be considered here[1].”

    When I read that yesterday I was astounded because it made me realize that ever since encountering Bell’s theorem as a first year undergraduate I have assumed that there are non-local beables; indeed most of my work in quantum foundations has been a search for them.

    Smolin – Bell paper

    The model I have sketched shows that quantum mechanics can be recovered from an explicit hidden variables model whose beables are non-local. This is in accord with the reasons I stressed that the beables of quantum theory should be taken as non-local. I would thus propose that the ultimate legacy of Bell’s fundamental work will be the discovery that quantum theory is a description of an a-local world, which we happen to see in a phase where space has emerged. When we try to describe the physics of local subsystems of the universe, delineated by the emergent and approximate concept of locality, we are forced to neglect interactions which are really there between the subsystem’s microscopic degrees of freedom and other degrees of freedom now emerged in distant parts of the universe. These non-local interactions are mediated by relational degrees of freedom that are non-local, in the sense that they are shared between subsystems that are distant from each other in the emergent concept of locality.

    Because of the neglect of these non-local degrees of freedom, the quantum physics of local subsystems is stochastic and subject to a persistent and universal Brownian motion, which is the cheshire cat smile of the fundamental a-locality of the world. In this sense hbar is a measure of the resistance of the world to a local description.

    I very much look forward to critical comments on this proposal by members of the workshop.

    #1702
    H. Dieter ZehH. Dieter Zeh
    Participant

    I agree – but why then do we need non-local hidden variables instead of the wave function itself? Or do you think you can avoid Many Worlds?

    #1703
    Lee SmolinLee Smolin
    Member

    Dear Dieter,

    I certainly do want to avoid many worlds. For reasons we explain in our new book with Mangabeira Unger, I don’t think that the present framework of quantum theory can apply to the universe as a whole.

    I agree the wave function contains more than a probability distribution-its phase appears to be “ontic”. But I don’t like that the wavefunction influences the particle trajectories but not vise versa-that violates Einstein’s principle of reciprocity.

    One attempt to derive the wavefunction from a real ensemble within the single universe, in a way that satisfies reciprocity, is the real ensemble formulation.

    Thanks,

    Lee

    #1704
    H. Dieter ZehH. Dieter Zeh
    Participant

    Dear Lee,

    that looks like a very ambitious program. I shall try to have a closer look (even though I am not very optimistic). Perhaps you have a brief outline of its basic ideas somewhere?

    In your second paragraph you seem to be referring to Bohm. In Everett’s Many Worlds there are no trajectories.

    Best wishes,
    Dieter

    #1720
    Lee SmolinLee Smolin
    Member

    Dear Dieter,

    I’m sorry, I misunderstood you; I thought by referring to the wavefunction, as an alternative to hidden variables, you were referring to dBB.

    Everett Many Worlds fails to answer any of the questions that puzzle me about quantum physics. I can elaborate my objection to it but others such as David Albert have already done a convincing job of this, in my view.

    I do hope that my program is ambitious; I believe we have to be ambitious because the measurement problem in my view cannot be solved without completing quantum mechanics, ie seeing QM as an approximation to a different theory. And I think its likely that that more correct theory will also address the issues of giving a quantum description of spacetime and cosmology.

    You can find summaries of my present research program in the later chapters of either Time Reborn or my new book with Roberto Mangabeira Unger. Those books argue for a perspective on cosmological theories that we argue must frame any attempt to resolve the measurement problem.

    Many thanks,

    Lee

    #1733
    H. Dieter ZehH. Dieter Zeh
    Participant

    Dear Lee,
    could it be that you are just asking the wrong questions about quantum physics? Unfortunately you did not provide us with an example. As far as I know David Albert’s papers, he has mainly reformulated the traditional prejudice against Many Worlds.

    Regarding Everett, let me suggest a variation of an often quoted remark by John Bell:
    ´´It is important to note that´´ [Everett’s Many Worlds interpretation] ´´is not assumed but inferred´´ [from the Schrödinger equation]. ´´It is remarkably difficult to get this point across.´´

    Of course, nobody may be expected to believe in the validity of this global extrapolation of unitarity (we are all still searching for the truth), but everybody should be able to agree that Everett would be its (consistent) consequence if nothing else is added to the theory – and thus it appears worth being seriously discussed as a possibility. I don’t presently see any other foundation for cosmology, in particular. Everett could some day be falsified, but that would require some novel (and probably quite surprising) empirical evidence. ´´Notoriously vague´´ and speculative hypotheses, just to exclude unwanted consequences, do not appear very helpful in answering this issue.

    All the best for 2015
    Dieter

    #1762
    Lee SmolinLee Smolin
    Member

    Dear Dieter,

    Thank you for your remarks. I couldn’t disagree more, on substance as well as methodology. First, I don’t agree that the Everett interpretation is “inferred” rather than invented. Without an operational hypothesis as to how the mathematical symbols correspond to measured values a theory, any theory, is just empty mathematical formulas. Any assertion of a connection between mathematical expressions and measured values relies on metaphysical and ontological assumptions. You cannot pretend otherwise. When you do so you are just refusing to expose your own metaphysical assumptions or expose them to criticism and debate.

    Second, while I agree it is a fair question to ask whether Everett is cogent taken on the assumption the current formulation of QM is correct, I don’t agree that it is. To my understanding, the following criticism has never been successfully answered: there are an infinite number of branches where Born’s rule is not satisfied and an infinite number where it is. To assert we are in one of the latter requires we make additional assumptions, extraneous to the theory, thus negating the claim that the theory produces its own interpretation. Attempts by Saunders, Wallace etc to provide a convincing basis for this step in decision theory are impressive but don’t change the outcome, as they also rely on extraneous assumptions.

    Third, there is a whole suite of arguments that establish that QM as currently formulated cannot be applied to the universe as a whole. These go under the name of the cosmological fallacy. I won’t repeat these here as they are lengthy and they are the core of my last two books, Time Reborn and The Singular Universe and the Reality of Time. A summary is in my paper Temporal Naturalism, arXiv:1310.8539. We strongly welcome criticism of these arguments as we believe they are crucial for the future of physics.

    Finally, I would argue on historical and methodological grounds that if a theory has been on the table for more than 50 years and has not succeeded in answering objections posed to it or convincing critics, and has no empirical support (not shared with many other approaches) our presumption should be that it has failed. We should put it aside and encourage ourselves and especially young scientists to put forward new ideas and new hypotheses which have a better chance of succeeding.

    I would apply this both to Everett and dBB.

    Best wishes,

    Lee

    Many thanks,

    Lee

    #1763
    H. Dieter ZehH. Dieter Zeh
    Participant

    Dear Lee,

    thanks for your response, which may help at least to locate the source of our disagreement a bit better. So here are a few further remarks in reply.

    You may call it a hypothesis that I am using an ontic interpretation for the wave function (superposition) – very similar as in collapse theories, for example. However, I think that there are excellent arguments for this physical (ontic) interpretation of this general superposition principle, and it is the reason why I do not need any ´´operational hypothesis´´: all physical operations must be described by the dynamics of the wave function. What I do need, though, is a new definition (based on empirical knowledge) of subjective observers as parts of the physical world in terms of the wave function (von Neumann’s psycho-physical parallelism). [I do not want to explcitly ask you to read my papers and books, but a look at my contribution for this workshop might already answer some of your questions, including those discussed below.]

    Your objection about an infinite number of branches (most of them incompatible with the Born rule) is a very old hat – but nonetheless quite inappropriate. These branches are not objectively and not precisely defined, they are not infinite (although even Everett thought so), and there is absolutely no reason to regard them as ´´equally probable´´. You need weights for them in a very specific sense (that I have often discussed – for example in my contribution to this forum). I do not know any interpretation of QM that does NOT postulate Born’s rule in some sense. (Indeed, all fundamental elements of a physical theory must be empirical.) I have never referred to decision theory in this context, since (1) I do not understand the meaning of the ´´agent´´, and (2) I do not see any problem in postulating my subjective probabilities. (They have no objective meaning, since objectively there is only ONE quantum world – one superposition – according to Everett.)

    I do not know what you call the ´´cosmological fallacy´´, but I may understand your traditional reservations for applying quantum theory to the universe. However, what does your assumption of nonlocal ´´ontic phases´´ then mean, and what limits their validity in a chain of unitary interactions, which would otherwise lead to a superposition of many worlds? Extrapolating the known basic laws and concepts is the most conservative or the only way to construct ´´physical cosmology´´. The alternative is simply to shut up. Classical cosmology is certainly ruled out, in particular after the success of decoherence in deriving classical concepts in wave mechanical terms (including the spacetime metric – see Claus Kiefer’s contributions in the literature), while I would regard any cosmology that is based on new and not yet confirmed physical theories (such as strings) as no more than ´´educated science fiction´´. It is a shame that such things are nowadays taught students as ´´science´´ (even if they may form interesting mathematics). You may well suggest novel theories that are intended even to explain the wave function, but you cannot expect us to accept them before their novel consequences or their empirical foundation have been confirmed.

    Everett’s theory has been SUCCESSFUL for 50 years or more, since it never required or assumed any new physical hypotheses. It has always predicted that there are no novel phenomena that go beyond von Neumann´s pragmatic collapse (now as a ´´collapse by convention´´ in accordance with decoherence – but without a collapse as a dynamical process). So what is missing in principle with respect to quantum mechanics and perhaps even quantum field theory (save the usual technical problems for interacting quantum fields)?

    Best wishes,
    Dieter

    In case you do want to read more non-technical details about my interpretation of QM, here is a link:
    http://www.rzuser.uni-heidelberg.de/~as3/ParticlesOrWaves.pdf

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