• noAxioms
    694
    Well, I agree that a preferred frame is not actually incompatible with the predictions of Relativity. So, in this sense we can say that SR is not incompatible with such an idea. But, I was referring to the 'standard presentation' of SR, so to speak, where you do not define a 'preferred frame'.boundless
    Not defining something undetectable (in SR) is fine, and I suppose the standard presentation of SR is that there isn't one. But GR, to the embarrassment of Einstein, had to admit to an apparent preferred foliation (which is not an inertial frame), so SR would actually be sort of wrong if it asserted that no preferred local frame can exist, and SR has never been shown to be wrong.

    Anyway, I'd agree with what you say here. But IMO problems with locality arise if you introduce hidden variables.
    GR shows that the variable isn't hidden, but only because real spacetime doesn't conform to SR's nice flat uniform gravity special case.

    A preferred foliation is one thing. A preferred moment (presentism) is more of an offense to relativity. I've created a thread defending presentism against attacks from the relativity side and thought I held my ground OK, but I thought of another interesting one:

    If presentism is true, what is the rate of advancement of objective time? Equivalently, by how much is say a clock that tracks GMT dilated? It isn't moving very fast, but it's the depth of the gravity well I'm interested in. I thought of this when I tried to look it up. The absolutists sort of group together like the flood geologists and put out all this propaganda against Einstein, but none of those denial sites quote this absolute dilation factor, which you think would be one of their flagship points like the absolute frame. But they evade the topic. Why is that? Must be embarrasing...

    Well, AFAIK in dBB you need to somehow define a way to define an 'absolute simultaneity'.
    The one from GR is not enough?

    But in any case, non-locality is inevitable in dBB IMO. To avoid it, you either need 'retrocausality' or 'superdeterminism' but I find both ideas untenable.
    Yes, I know about the superdeterminism loophole. I also dismiss it enough to state that Bell eliminated locality and counterfactual definiteness from both being true. I see none of the listed interpretations hold both to be true, utilizing the superdeterminism loophole, so it seems the world agrees with that assessment.
  • Wayfarer
    7k
    The strategy of your argument here is an excellent example of inappropriate reductionism; you seek to explain frame dependence of motion and observer dependence of quantum state/properties as being mere instances of conceptual relations between thought and object.fdrake

    ‘Thought and object’. It is just that instinctive division which is called. Into question by ‘the observer probllem’. Anyway - thanks for your considered criticism, I appreciate the time you have taken.
  • fdrake
    1.9k
    ‘Thought and object’. It is just that instinctive division which is called. Into question by ‘the observer probllem’. Anyway - thanks for your considered criticism, I appreciate the time you have taken.Wayfarer

    If you are willing to collapse the distinction between the two, rather than merely and only 'inhabiting' the relation as correlationists describe, then the arche-fossil is successful; it at the very least forces a correlationist to choose between idealism and absurdity.

    That there is no material reality prior to the existence of humans is certainly one way to find the argument instructive.

    Anyway, was fun, even though I doubt I convinced you, I understand the arche-fossil argument in a lot more detail through rehearsing it with a willing antagonist. Thanks. :)
  • Andrew M
    598
    Yeah, that's a nice way IMO to avoid issues with relativity.

    And BTW, as I said to NoAxioms a similar problem arises in Relativity, if one wants to avoid the 'block universe idea' as suggested by Rietdijk-Putnam argument(here's the link to the Wikipedia article). There is a very nice 'insight article' on Physics Forums that gives a counter-argument (which is reminiscent of the reasoning on which, for instance, RQM is based): https://www.physicsforums.com/insights/block-universe-refuting-common-argument/.
    boundless

    Nice find with the PF article and I fully agree with it. I was going to mention the Andromeda paradox and the idea of potentiality in relation to it in my previous post. So we seem to thinking along similar lines here.

    It also reminds me of Aristotle's future sea battle example where he contrasts potential and actual:

    One of the two propositions in such instances must be true and the other false, but we cannot say determinately that this or that is false, but must leave the alternative undecided. One may indeed be more likely to be true than the other, but it cannot be either actually true or actually false. It is therefore plain that it is not necessary that of an affirmation and a denial, one should be true and the other false. For in the case of that which exists potentially, but not actually, the rule which applies to that which exists actually does not hold good.Aristotle, On Interpretation, §9

    --

    It seems not contradictory at all for Bob to find the state of the photon still in superposition, despite the conflict wording in the article.noAxioms

    Yes, I agree - it's just what quantum mechanics predicts will happen and so it's not contradictory (or unexpected) at all. But it does challenge objective collapse theories since they modify the standard formulation.
  • StreetlightX
    3.4k
    Had also John Horgan misattributed such a view to Wheeler?boundless

    Because pop-science writers are generally trash.
  • boundless
    107
    Not defining something undetectable (in SR) is fine, and I suppose the standard presentation of SR is that there isn't one. But GR, to the embarrassment of Einstein, had to admit to an apparent preferred foliation (which is not an inertial frame), so SR would actually be sort of wrong if it asserted that no preferred local frame can exist, and SR has never been shown to be wrong.noAxioms

    Do you mean that some geometries in GR require such a foliation (rather than simply allow)?

    AFAIK, there are attempts to reconcile dBB and SR that use a preferred foliation (which is not prohibited by Lorentz symmetry) but I think that this does not satisfy many people because it goes against the 'spirit' of Relativity.

    A preferred foliation is one thing. A preferred moment (presentism) is more of an offense to relativitynoAxioms

    But is there a real difference between the two? I mean, If the structure of space-time requires such a foliation, IMO I can define a frame where all these events are present. For such a frame, there is an absolute simultaneity, which is precisely the reason why AFAIK Lorentz aether theory is criticized.

    If presentism is true, what is the rate of advancement of objective time? Equivalently, by how much is say a clock that tracks GMT dilated? It isn't moving very fast, but it's the depth of the gravity well I'm interested in. I thought of this when I tried to look it up. The absolutists sort of group together like the flood geologists and put out all this propaganda against Einstein, but none of those denial sites quote this absolute dilation factor, which you think would be one of their flagship points like the absolute frame. But they evade the topic. Why is that? Must be embarrasing...noAxioms

    I'd agree with the objection you are making. But IMO what you are saying is also a clue that one cannot make an absolute simultaneity (or rather, it is possible but would be 'hidden'...).

    The one from GR is not enough?noAxioms

    I don't know!

    Yes, I know about the superdeterminism loophole. I also dismiss it enough to state that Bell eliminated locality and counterfactual definiteness from both being true. I see none of the listed interpretations hold both to be true, utilizing the superdeterminism loophole, so it seems the world agrees with that assessment.noAxioms

    :up:
  • boundless
    107
    Nice find with the PF article and I fully agree with it. I was going to mention the Andromeda paradox and the idea of potentiality in relation to it in my previous post. So we seem to thinking along similar lines here.Andrew M

    Great. Interestingly, I discovered that the same point is made by Carlo Rovelli to defend his 'relational' view, see: https://www.youtube.com/watch?v=vbYeAaCloiM. At 4:55, Valentini makes the same question that he made in the other video (namely that different observers might disagree about what happens) and at 53:52 Rovelli answers by citing the Andromeda Paradox - so we are in good company :wink: . It is a very good discussion, BTW (other than Rovelli and Valentini, also Saunders and Wallace (and others) participate in the discussion). This might also be of interest to @noAxioms.

    It also reminds me of Aristotle's future sea battle example where he contrasts potential and actual:Andrew M

    Very interesting, thanks!
    In fact, some time ago I read a philosophy of science paper that tried to use the potential-actual distinction in SR in order to avoid situations like Andromeda Paradox. Unfortunately, I do not remember neither the title nor the author :sad:

    Yes, I agree - it's just what quantum mechanics predicts will happen and so it's not contradictory (or unexpected) at all. But it does challenge objective collapse theories since they modify the standard formulation.Andrew M

    Unfortunately, I know very little about objective collapse theories. Anyway, I agree with you. It would be interesting to see how these theories deal with this experiment.
  • boundless
    107


    I do not understand your point, actually.

    On one hand, I agree that pop-science is not always reliable. On the other hand, in this case, it seems that you are saying that John Wheeler never proposed the idea of the 'participatory anthropic principle' (or 'participatory universe') even if there are a lot of sources that claim otherwise. Am I right?
    Or you're suggesting that is their interpretation of the 'participatory anthropic principle' problematic? If so, what did he really mean?

    Thanks in advance!
  • noAxioms
    694
    Yes, I agree - it's just what quantum mechanics predicts will happen and so it's not contradictory (or unexpected) at all. But it does challenge objective collapse theories since they modify the standard formulation.Andrew M
    Since none of this is new (it is demanded by QM right from the early days), how do any of the objective collapse interpretations get around this? Does this experiment change something? Did they expect a different result? I don't think so.

    Do you mean that some geometries in GR require such a foliation (rather than simply allow)?boundless
    The expansion of space is uniform only under one foliation. It isn't absolutely uniform since it seems resistant to local mass, but only under one foliation does the expansion switch to accelerating everywhere at once. Essentially, only the the frame that corresponds locally to that foliation has the property of isotropy both in what is and in appearance.

    AFAIK, there are attempts to reconcile dBB and SR that use a preferred foliation (which is not prohibited by Lorentz symmetry) but I think that this does not satisfy many people because it goes against the 'spirit' of Relativity.
    It apparently goes against the spirit of SR, and it pained Einstein to not keep that in GR. Physics is different in other frames since non-local observations are allowed in GR.

    A preferred foliation is one thing. A preferred moment (presentism) is more of an offense to relativity
    — noAxioms

    But is there a real difference between the two?
    Of course. One objectively orders any pair of events, and other may or may not attach an ontological status to each event (has or has not yet happened). A preferred foliation has no such ontological status. There is still spacetime with all events having equal ontology. Presentism has no spacetime, only space, with only current events existing (happening) and not any of the others. That sounds like a huge difference of reality to me.

    I mean, If the structure of space-time requires such a foliation, IMO I can define a frame where all these events are present. For such a frame, there is an absolute simultaneity, which is precisely the reason why AFAIK Lorentz aether theory is criticized.
    I don't understand this comment. Under presentism, there is no spacetime. Only objectively current events are present, and the other events don't exist, so can't be present.

    If presentism is true, what is the rate of advancement of objective time? Equivalently, by how much is say a clock that tracks GMT dilated? It isn't moving very fast, but it's the depth of the gravity well I'm interested in. I thought of this when I tried to look it up. The absolutists sort of group together like the flood geologists and put out all this propaganda against Einstein, but none of those denial sites quote this absolute dilation factor, which you think would be one of their flagship points like the absolute frame. But they evade the topic. Why is that? Must be embarrasing...
    — noAxioms

    I'd agree with the objection you are making. But IMO what you are saying is also a clue that one cannot make an absolute simultaneity (or rather, it is possible but would be 'hidden'...).
    No, there would still be an absolute simultaneity. I can still sync remote clocks. I just find it difficult to build a clock that is designed to run in a location of known dilation and have it compensate for that in order to record the passage of absoute time. If it were possible to do that, the objective age of the universe could be known, but we only know the figure (13.8 BY) in dilated Earth time, which is obviously running slow. The universe is older than that, but by how much is the question.
  • boundless
    107


    Thanks for the very informative answer! I need some time to think about all of this :smile:
  • boundless
    107
    You might be interested in the following article that addresses this issue:

    But it didn't take physicists long to realise that while the Wheeler-DeWitt equation solved one significant problem, it introduced another. The new problem was that time played no role in this equation. In effect, it says that nothing ever happens in the universe, a prediction that is clearly at odds with the observational evidence.
    — Quantum Experiment Shows How Time ‘Emerges’ from Entanglement
    Andrew M



    I forgot to say that I actually read the article and I found it very intriguing :smile:
  • boundless
    107



    I did some further research on Wheeler. I found this article: https://plus.maths.org/content/it-bit - it quotes a paper by Wheeler himself.

    He certainly IMHO thought that 'information' (which he believes to be 'immaterial') plays a central role and is more 'fundamental' than matter.
    But he did not seem to give a 'special role' to human observers (he seemed to have a more general idea of observer).

    I am still not sure about the 'participatory anthropic principle' thing.
  • StreetlightX
    3.4k
    Why not read Wheeler himself rather than derivative sources:

    https://what-buddha-said.net/library/pdfs/wheeler_law_without_law.pdf

    The basic idea behind the participatory universe idea is simply that what 'participates' with the universe is itself - which includes the equipment used to make a measurement (which belongs to the universe...). From the paper: "Registering equipment operating in the here and now has an undeniable part in bringing about that which appears to have happened". An 'observer' is a piece of apparatus, that's it. This, incidentally, was Bohr's position, which Wheeler understood very well.

    (cf. Wheeler's comments on Bohr concept of the 'phenomenon, in the cited paper': "a phenomenon is not yet a phenomenon until it is brought to a close by an irreversible act of amplification such as the blackening of a grain of silver bromide emulsion or the triggering of a photodetector". Incidentally, this was also the point of difference between Einstein and Bohr: Einstein refused to believe the act of measurement qua equipmental intervention - or 'participation', in Wheeler's overblown vocabulary - could determine the results of a measurement, while Bohr figured this was the only consistent way to explain the results).
  • boundless
    107


    Thank you very much!

    Actually in the article I linked, there is in it a link to a paper by Wigner himself: https://jawarchive.files.wordpress.com/2012/03/informationquantumphysics.pdf.
  • Andrew M
    598
    Since none of this is new (it is demanded by QM right from the early days), how do any of the objective collapse interpretations get around this? Does this experiment change something? Did they expect a different result? I don't think so.noAxioms

    They would predict that Wigner would not see interference for sufficiently complex friend systems. So the options are to either accept the experiment's result as falsifying their theory or else show that the experiment isn't scaled up enough to trigger a physical collapse by their criterion.

    For a brief discussion of that prediction in one of the experiment's referenced papers, see https://arxiv.org/abs/1507.05255 (p18, point 1).
  • boundless
    107


    I actually thought about it but, unfortunately, I did not arrive at a satisfying conclusion.

    The expansion of space is uniform only under one foliation. It isn't absolutely uniform since it seems resistant to local mass, but only under one foliation does the expansion switch to accelerating everywhere at once. Essentially, only the the frame that corresponds locally to that foliation has the property of isotropy both in what is and in appearance.noAxioms

    Ok, that's right. Maybe the point is that the foliation is not directly observable. As you say, we can observe only a "frame that corresponds locally to that foliation has the property of isotropy both in what is and in appearance". Just a guess. As I said, I am quite at loss.

    AFAIK, there are attempts to reconcile dBB and SR that use a preferred foliation (which is not prohibited by Lorentz symmetry) but I think that this does not satisfy many people because it goes against the 'spirit' of Relativity. — boundless
    It apparently goes against the spirit of SR, and it pained Einstein to not keep that in GR. Physics is different in other frames since non-local observations are allowed in GR.noAxioms

    I see...but if this does mean that non-locality is compatible with GR (as it is usually understood) why people consider non-locality problematic?

    Of course. One objectively orders any pair of events, and other may or may not attach an ontological status to each event (has or has not yet happened). A preferred foliation has no such ontological status. There is still spacetime with all events having equal ontology. Presentism has no spacetime, only space, with only current events existing (happening) and not any of the others. That sounds like a huge difference of reality to me.noAxioms

    Well, yeah, you are right.
    But IMO this leads either to the 'Andromeda Paradox'/Riedtjik-Putnam argument scenario or some form of retro-causality.

    I'd agree with the objection you are making. But IMO what you are saying is also a clue that one cannot make an absolute simultaneity (or rather, it is possible but would be 'hidden'...). — boundless

    No, there would still be an absolute simultaneity...noAxioms

    OK, I also agree with you on this.

    Anyway, Antony Valentini proposed that cosmological observations might help to solve interpretational problems in QM. The de Broglie-Bohm interpretation actually makes the same predictions of QM only if the 'quantum equilibrium hypothesis' is satisfied, i.e. if the modulus square of the wave-function corresponds to the actual probability distribution (this assures that dBB satisfies the Born Rule). However, in general, this might be not true. Hence his proposal: maybe at the earliest stages of the evolution of the Universe, that hypothesis was not satisfied and - as a consequence - we should see empirical evidence against the Born Rule.

    Here is the link to his talk (at the same conference): https://www.youtube.com/watch?v=XYZV9crCZM8.
    Here the link to the Q&A session: https://www.youtube.com/watch?v=8qnuNLB61RA.

    I suggest these videos also to @Andrew M.

    According to the 'no signaling' theorem, if predictions of QM are satisfied there cannot be any direct evidence of violation of locality. Hence, it just seems that there is a sort of 'conspiracy' if there are non-local influence. This is actually one of the reasons I do not think dBB is true. But, interestingly, according to Valentini, this might be a clue that dBB is, instead, right: the fact that the world seems 'local' is due to the fact that the 'quantum equilibrium hypotesis' is true. IMO, his proposal however makes perfect sense in the light of dBB.

    [Another reason for which I do not accept dBB is its 'strange' ontology. dBB is, in fact, characterized by both particles and the wave-function. In my understanding, particles have no role except moving in a way 'dictated' by the wave-function*. The wave-function seems to do all the job. Furthermore, the wave-function is not a field in real space but lives in the 3N-dimensional 'configuration space' where N is the number of particles. This prompted some proponents to adopt a 'nomological' view of the wave-function. But IMO this is still odd: laws are generally understood to not be dynamical objects and if the wave-function is merely a law, it just seems that there is no reason why particles move in that way. In fact, some think that the wave-function is better understood as representing dispositions: https://arxiv.org/abs/1406.1371.

    *This is not true if one introduces the 'quantum potential' AFAIK. But even in this case, you still have a weird ontology where you have to make sense of particles living in our usual 3-dimensional world and an equally real field that lives in a 3N-dimensional world. And also some dBB supporters are critical of the 'quantum potential' formulation, see: https://plato.stanford.edu/entries/qm-bohm/#QuanPote

    Also, I am a bit puzzled by the asymmetry between position and other observables. QM is perfectly 'symmetrical' with them, i.e. it treats them equally. For dBB, instead, position is somewhat 'special'. The counter-argument that is found in the SEP article on 'Bohmian mechanics' does not convince me. ]



    Good find! I'll read it :smile:
  • Andrew M
    598
    Great. Interestingly, I discovered that the same point is made by Carlo Rovelli to defend his 'relational' view, see: https://www.youtube.com/watch?v=vbYeAaCloiM . At 4:55, Valentini makes the same question that he made in the other video (namely that different observers might disagree about what happens) and at 53:52 Rovelli answers by citing the Andromeda Paradox - so we are in good company :wink: . It is a very good discussion, BTW (other than Rovelli and Valentini, also Saunders and Wallace (and others) participate in the discussion). This might also be of interest to noAxioms.boundless

    Yes, another great discussion! I also liked Wallace's explanation of the wave function at 11:25.

    So here's the setup and exchange between Valentini and Rovelli:

    [4:55] Valentini sets up the scenario as Rovelli deciding to speak at the conference (or not) based on measuring a particle spin as spin up (or spin down). Rovelli measured spin up and so here they are talking at the conference. However a super-intelligent being in the future measures interference.

    [53:52] Rovelli: Antony asks, "Carlo, some super-intelligent is believing that you are not here because in his wave function you're superimposing, there's no fact of the matter. Does this bother you?"

    I think it doesn't because it's exactly the kind of thing that happens in theoretical physics all the time. I think it's very similar to what happens in special relativity. If I take Einstein's simultaneity convention, right now in Andromeda there is something which has already happened with respect to the - not the past cone but the simultaneity convention - with respect to which I haven't happened yet with respect to this.

    This makes no sense whatsoever but that's the structure of the world. The relation between when things happen for who are complicated. I think with this guy in the future, I could talk if I could survive until then, I could talk to him and we would agree and the fact that now, for him, in the future before I interact with him there is a discrepancy in what we see doesn't really bother me.

    Valentini: For him, there wouldn't be a fact of the matter about the past?

    Rovelli: That's right.

    Here's also the relevant passage from the Physics Forum Insights article that you linked to earlier: The Block Universe – Refuting a Common Argument.

    (3) All events in the past light cone of a given event are real (i.e., fixed and certain) for an observer at that event.

    The reason this accounts for all of our observations is that information can’t travel faster than light, so anything we observe at a given event can only give information about the past light cone of that event.

    So we can see Rovelli's reasoning in the above exchange. For Alice on Andromeda, Carlo on Earth only potentially exists until a local interaction (say, a telescopic observation at light speed) brings him into her present (and then past). Similarly, for Bob the superintelligent being in the future, Carlo is only potentially at the conference until a local interaction decoheres the superposition (say, Bob talks to Carlo).

    A further thought here is that I think this allows a representational interpretation of the wave function for RQM in terms of what is actual and potential for any given observer. What is locally entangled with an observer is actual (the past and present, measurements and interactions), what is not is potential (the future, spacelike separated regions, superpositions).
  • boundless
    107


    Thank you very much for the transcription!

    So we can see Rovelli's reasoning in the above exchange. For Alice on Andromeda, Carlo on Earth only potentially exists until a local interaction (say, a telescopic observation at light speed) brings him into her present (and then past). Similarly, for Bob the superintelligent being in the future, Carlo is only potentially at the conference until a local interaction decoheres the superposition (say, Bob talks to Carlo).Andrew M

    :up:

    A further thought here is that I think this allows a representational interpretation of the wave function for RQM in terms of what is actual and potential for any given observer. What is locally entangled with an observer is actual (the past and present, measurements and interactions), what is not is potential (the future, spacelike separated regions, superpositions).Andrew M

    Yeah, I'd agree. Both the representionalist and the non-representionalist views are possible. Rovelli himself wrote against a 'realistic' interpretation of the wave-function: https://arxiv.org/abs/1508.05533.

    Actually, this interpretation of the wave-function is also held by some Copenaghists. For instance, Abner Shminoy wrote in the older version of the SEP on Bell's Theorem:

    There may indeed be “peaceful coexistence” between Quantum nonlocality and Relativistic locality, but it may have less to do with signaling than with the ontology of the quantum state. Heisenberg's view of the mode of reality of the quantum state was briefly mentioned in Section 2 — that it is potentiality as contrasted with actuality. This distinction is successful in making a number of features of quantum mechanics intuitively plausible — indefiniteness of properties, complementarity, indeterminacy of measurement outcomes, and objective probability. But now something can be added, at least as a conjecture: that the domain governed by Relativistic locality is the domain of actuality, while potentialities have careers in space-time (if that word is appropriate) which modify and even violate the restrictions that space-time structure imposes upon actual events. The peculiar kind of causality exhibited when measurements at stations with space-like separation are correlated is a symptom of the slipperiness of the space-time behavior of potentialities. This is the point of view tentatively espoused by the present writer, but admittedly without full understanding. What is crucially missing is a rational account of the relation between potentialities and actualities — just how the wave function probabilistically controls the occurrence of outcomes. In other words, a real understanding of the position tentatively espoused depends upon a solution to another great problem in the foundations of quantum mechanics − the problem of reduction of the wave packet.

    The link is to the section 'Philosophical Comments' of the article - Shimony lists other possible positions.

    There are different takes. For IMHO a very interesting Neo-Kantian non-representionalist reading (among the 'Copenaghists'), check this article of Michel Bitbol (I already quoted it in this thread - I quote it again here for convenience): http://www.bourbaphy.fr/bitbol.pdf (according to him, Bohr's epistemology was close to Kant's views...). Or, if one prefers the video of the talk: https://www.youtube.com/watch?v=pYRLapWBqJY.

    Another instance of interpretation of the wave-function in terms of potentiality-actuality can be found in this paper by Kastner et al: https://arxiv.org/abs/1709.03595.
  • noAxioms
    694
    Since none of this is new (it is demanded by QM right from the early days), how do any of the objective collapse interpretations get around this? Does this experiment change something? Did they expect a different result? I don't think so.
    — noAxioms

    They would predict that Wigner would not see interference for sufficiently complex friend systems. So the options are to either accept the experiment's result as falsifying their theory or else show that the experiment isn't scaled up enough to trigger a physical collapse by their criterion.
    Andrew M
    That is one thin explanation. If what Alice did wasn't complex enough to objectively collapse the wave function, she should be able to measure the subsequent superposition herself and not leave it to Bob. Of course, QM theory won't allow that, so the 'thin' explanation see to go against QM itself.
    Of course maybe I just don't understand this explanation. I have not read your link and am not sure that I would find the answer there satisfactory.
  • noAxioms
    694
    Maybe the point is that the foliation is not directly observable.boundless
    It seems not to be. It would probably violate SR if it was.
    As you say, we can observe only a "frame that corresponds locally to that foliation has the property of isotropy both in what is and in appearance". Just a guess. As I said, I am quite at loss.
    Yes. What is: Space is expanding everywhere equally(ish) at all simultaneous points. I say 'ish' because it expands more in empty places than crowded places, but not more in any particular direction. This isn't true in other frames.
    Appearance: Space appears to be expanding equally at all points at some fixed distance from any observation point. So space is expanding close by, but not expanding say 6 billion light years away. Doing these sorts of measurements is how they determined the acceleration of expansion in the first place. You can't measure what is now, but you can measure how it appears now.

    I see...but if this does mean that non-locality is compatible with GR (as it is usually understood) why people consider non-locality problematic?
    All of relativity seems to depend on locality, while QM interpretations might have other ideas. It is why I resist interpretations that discard locality in favor of counterfactual definiteness. I just don't see how relativity can make sense without locality. One can blatantly change the past, not just events outside one's future light cone.
    That and the fact that counterfactual definiteness has all sorts of seemingly paradoxical philosophical baggage that goes away if you don't accept the principle.

    Well, yeah, you are right.
    But IMO this leads either to the 'Andromeda Paradox'/Riedtjik-Putnam argument scenario or some form of retro-causality.
    Don't get your Dutch names wrong... I've got one myself.
    The Andromeda thing and the Rietdijk-Putnam thing are pretty much the same, and are only paradoxical if you try to combine assumptions from both interpretations of time. All that proves is that they are not both correct.
    Presentism demands an objective ordering of events (although no particular one), but a preferred folation does not demand a preferred moment in time.

    Anyway, Antony Valentini proposed that cosmological observations might help to solve interpretational problems in QM. The de Broglie-Bohm interpretation actually makes the same predictions of QM only if the 'quantum equilibrium hypothesis' is satisfied, i.e. if the modulus square of the wave-function corresponds to the actual probability distribution (this assures that dBB satisfies the Born Rule). However, in general, this might be not true. Hence his proposal: maybe at the earliest stages of the evolution of the Universe, that hypothesis was not satisfied and - as a consequence - we should see empirical evidence against the Born Rule.

    Here is the link to his talk (at the same conference): https://www.youtube.com/watch?v=XYZV9crCZM8.
    Here the link to the Q&A session: https://www.youtube.com/watch?v=8qnuNLB61RA.
    Way to kill an afternoon, eh? Thank you for the link. Not sure how much I'm interested in sinking an interpretation that I've already listed as low probability. I'd rather see them sink RQM. Always best to have ones own cage rattled once in a while.
  • boundless
    107
    It seems not to be. It would probably violate SR if it was.noAxioms

    Same impression!

    Doing these sorts of measurements is how they determined the acceleration of expansion in the first place. You can't measure what is now, but you can measure how it appears now.noAxioms

    Ok, thanks! I think I'll revise GR and cosmology. I admittedly do not know very much about both.

    All of relativity seems to depend on locality, while QM interpretations might have other ideas. It is why I resist interpretations that discard locality in favor of counterfactual definiteness. I just don't see how relativity can make sense without locality. One can blatantly change the past, not just events outside one's future light cone.
    That and the fact that counterfactual definiteness has all sorts of seemingly paradoxical philosophical baggage that goes away if you don't accept the principle.
    noAxioms

    :up: I agree! I would add the 'no signaling' theorem.

    Don't get your Dutch names wrong... I've got one myself.noAxioms

    Ops! Sorry!

    The Andromeda thing and the Rietdijk-Putnam thing are pretty much the same, and are only paradoxical if you try to combine assumptions from both interpretations of time. All that proves is that they are not both correct.noAxioms

    Right :smile:

    Presentism demands an objective ordering of events (although no particular one), but a preferred folation does not demand a preferred moment in time.noAxioms

    Maybe dBB requires a preferred moment in time and not just a preferred foliation, then! (alternatively, a preferred foliation without a preferred moment in time and retro-causality.)

    Way to kill an afternoon, eh?noAxioms

    LOL, yeah!

    Thank you for the link.noAxioms

    You're welcome :wink:

    Not sure how much I'm interested in sinking an interpretation that I've already listed as low probability. I'd rather see them sink RQM. Always best to have ones own cage rattled once in a while.noAxioms

    I see! That's perfectly reasonable :smile:

    Actually, I admit that dBB (in some forms*) is my third favorite interpretation. After all, it is still somewhat 'odd' but at the same time counterfactual definiteness is very intuitive. But as I mentioned before I find (among other things) this 'oddness' as an indication that some kind of 'paradigm change' is required. Also, it seems that, in general, there is a trend to more and more 'counter-intuitiveness' in physics...Hence, I lean towards RQM and Copenaghen.

    *(I do not like the purely 'nomological' view where there is no physical explanation of the movements of the particles - I prefer the 'dispositionalist' version. Also, I think that I am in the minority but I find the 'quantum potential' formulation interesting - after all, the 'classical limit' becomes quite intuitive if the contribution of the wave-function is seen as additional force.)
  • Andrew M
    598
    That is one thin explanation. If what Alice did wasn't complex enough to objectively collapse the wave function, she should be able to measure the subsequent superposition herself and not leave it to Bob. Of course, QM theory won't allow that, so the 'thin' explanation see to go against QM itself.
    Of course maybe I just don't understand this explanation. I have not read your link and am not sure that I would find the answer there satisfactory.
    noAxioms

    Obective collapse theories (such as GRW and Penrose's) are physically different theories to standard QM. I don't know what specific explanations they would give for this particular experiment. But they make predictions for Wigner's friend-style experiments that make them experimentally differentiable from standard QM.

    As Brukner says in that link (my italics):

    In my eyes, outcomes 1 and 2 would indicate fundamentally new physics. I will not consider these cases further and regard quantum theory to be a universal physical theory. This leaves us with situation 3 as the only possible outcome of Deutsch's thought experiment. The outcome is compatible with the Everett interpretation: each copy of the observer observes a definite but different outcome in different branches of the (multi)universe. The outcome is compatible with the Copenhagen interpretation too, but it is rarely discussed what the implications of this claim are for our understanding of physical reality within the interpretation. The rest of the current manuscript is devoted to this problem.On the quantum measurement problem - Caslav Brukner

    I'd rather see them sink RQM. Always best to have ones own cage rattled once in a while.noAxioms

    I'd be curious to know your thoughts about the RQM questions from my earlier exchange with boundless here.
  • Andrew M
    598
    There are different takes. For IMHO a very interesting Neo-Kantian non-representionalist reading (among the 'Copenaghists'), check this article of Michel Bitbol (I already quoted it in this thread - I quote it again here for convenience): http://www.bourbaphy.fr/bitbol.pdf (according to him, Bohr's epistemology was close to Kant's views...). Or, if one prefers the video of the talk: https://www.youtube.com/watch?v=pYRLapWBqJY.

    Another instance of interpretation of the wave-function in terms of potentiality-actuality can be found in this paper by Kastner et al: https://arxiv.org/abs/1709.03595.
    boundless

    Thanks for the links! I had a quick skim. I find Rovelli's approach more natural than either of those. Bitbol's approach seems overly metaphysical and Kastner's approach is non-local.

    Actually, this interpretation of the wave-function is also held by some Copenaghists. For instance, Abner Shminoy wrote in the older version of the SEP on Bell's Theorem:

    There may indeed be “peaceful coexistence” between Quantum nonlocality and Relativistic locality, but it may have less to do with signaling than with the ontology of the quantum state. Heisenberg's view of the mode of reality of the quantum state was briefly mentioned in Section 2 — that it is potentiality as contrasted with actuality. This distinction is successful in making a number of features of quantum mechanics intuitively plausible — indefiniteness of properties, complementarity, indeterminacy of measurement outcomes, and objective probability. But now something can be added, at least as a conjecture: that the domain governed by Relativistic locality is the domain of actuality, while potentialities have careers in space-time (if that word is appropriate) which modify and even violate the restrictions that space-time structure imposes upon actual events. The peculiar kind of causality exhibited when measurements at stations with space-like separation are correlated is a symptom of the slipperiness of the space-time behavior of potentialities. This is the point of view tentatively espoused by the present writer, but admittedly without full understanding. What is crucially missing is a rational account of the relation between potentialities and actualities — just how the wave function probabilistically controls the occurrence of outcomes. In other words, a real understanding of the position tentatively espoused depends upon a solution to another great problem in the foundations of quantum mechanics − the problem of reduction of the wave packet.

    The link is to the section 'Philosophical Comments' of the article - Shimony lists other possible positions.
    boundless

    Thanks, that was interesting. So my suggestion differs in at least two ways. First, as with Rovelli, I think that quantum mechanics is local. Second, as with Aristotle, potentialities don't "do" anything, only actual systems do.

    Instead, the term "potential" provides a natural way for Wigner and his friend to describe the scenario from their own perspective and also to describe the scenario from the other's perspective.

    So when the friend (Alice) measures spin up, that actualizes (i.e., realizes) the particle's spin potential for her. But she also knows that both the spin and her subsequent measurement of the spin are only potentials for Wigner until Wigner measures the friend's system in that basis.

    The actual/potential terminology combined with RQM's relationalism provides an ordinary language abstraction over the underlying mechanics. That abstraction preserves locality, factual definiteness, freedom of choice and, crucially, a referent within the universe that provides a view from somewhere (i.e., the system's reference frame).
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