Friday, January 11, 2019

Brian Greene still plugging string theory

Sam Harris interviews Brian Greene in this two-hour video.

Greene is indignant when Harris says that string theory has failed to deliver the goods. Greene says that the theory has made great progress, and has merged gravity and quantum mechanics. The only trouble is that we do not know what that merged theory is, and it has made any testable predictions. That is not much of a criticism, he says, because no quantum gravity theory will ever make any testable predictions.

Someone asked about Bohr saying that physics is about observables. Greene prefers a wider view, and says that physics should look behind the curtain and tell us what is really going on.

So Greene can justify a string theory with no testable predictions.

Greene also defended many-worlds theory and Bohmian mechanics, altho he has not fully adopted them because the measurement problem is unsolved.

Harris points out that Bohmian mechanics is nonlocal, so doing something in one place can have an instantaneous distant effect. Greene agreed, but said that quantum mechanics is nonlocal anyway.

Greene is very misleading here. It is true that in textbook QM, if you make a measurement and collapse the wavefunction, then your knowledge of some distant particle can be immediately affected. You can say that is nonlocal, but classical mechanics is nonlocal in the same way. Bohmian mechanics is different in that it says that an electron is in one place, but its physical effects are in another place. That is a fatal flaw, since no such nonlocality has ever been observed in nature.

And any defense of many-worlds is nutty.

He gives this argument, common among many-worlds advocates, that it is a simpler theory, and thus preferable under Occam's Razor. He gives an example. Suppose a simple quantum experiments results in an electron being in one of two places, symbolized by his left hand and right hand. Suppose you then find the electron in his left hand. Under Copenhagen, you would deduce that the electron is not in his right hand. But that deduction is an extra step, and the many-worlds theory is more parsimonious because it skips that step and posits that the electron is in his right hand in a parallel universe.

It is amazing to see an educated man make such a silly argument with a straight face. The argument really doesn't even have much to do with quantum mechanics, as you could use it with any theory that makes predictions, and concoct a many-worlds variant of the theory that does not make any predictions.

Besides many-worlds, Greene defends physical theories in which anything can happen. If you assume infinite space, infinite time, infinite universes, etc., then pretty much anything you can imagine would be happening somewhere, and happening infinitely many times. In particular, Jesus rose from the dead.

Greene agrees with Harris that humans have no free will. Greene rejects Harris's determinism, but says that the laws of physics have no room for free will.

At least Greene did not go along with Harris's wacky consequentialist vegetarian philosophy.

It is too bad that Physics does not have better spokesmen.

13 comments:

  1. If I said I had a solution, and you asked where, and I said it was located somewhere in a haystack of 10^500 (this is now a very low estimate) solutions... I don't think you would consider my answer a 'solution' even remotely useful for finding a working answer.

    Nothing we can actually measure is infinite, invoking it in a relationship or ratio with anything finite is meaningless. Scientists should stay away from using the term infinite in arguments as it is untestable and resolves nothing.

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  2. "You can say that is nonlocal, but classical mechanics is nonlocal in the same way."

    Again, not sure you understand the significance of nonseperability. Can you show me a classical physics example that gives the same results as Bell's test experiments?

    As I said before, there is a physically real correlation at a spacelike separation. It doesn't matter if you think the wavefunction is ontic or not or that Bohr's distinction between the classical and quantum holds because you have a macro-level correlation in the world beyond the speed of light that anyone with eyes can observe. It really has nothing to do with false counterfactuals given that we are not trying to talk about unobserved measurements but the very ones we actually made. You can't use hidden variables, so what is the common cause? Perfect anti-correlation of spins at equal angles rids separability and correlations at unequal angles destroys hidden variables.

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  3. MD Cory, fair question. I will post an answer.

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  4. Yes, there are real correlations.

    The perfect anti-correlation of spins at equal angles is just what you expect from a classical theory, if a conservation law applies. If two identical particles get ejected from one point, then we expect conservation of energy, momentum, angular momentum, etc. So measuring one tells you what to expect from measuring the other. If you consider that nonlocal, then classical mechanics is nonlocal.

    Yes, correlations at unequal angles destroy local hidden variables. Okay, but saying that there is no local hidden variable theory allows the possibility of other local theories.

    The common cause is physical, and not described by hidden variables.

    The derivations of Bell inequalities always use something like spin, where measuring spin in one direction disrupts what would have been measured in another direction. It only seems fishy if you start making some assumptions about counterfactuals.

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    1. Bell is a statement of mathematics. Bell: "Let this more complete specification be effected by means of parameters λ. It is a matter of indifference in the following whether λ denotes a single variable or a set, or even a set of functions, and whether the values are discrete or continuous." Lambda can be psi, so QM is nonlocal. If you reject the concepts of quantum mechanics then you are overrating the accomplishments of quantum mechanics to explain the world, let alone the newfangled nonsense they are talking about now.

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  5. Bell only proved that his classical alternative to QM is nonlocal. He didn't prove anything about QM, except that it differs from his classical alternative.

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    1. Nonsense. QM is a nonlocal theory, whether reality is or not. Lambda can be psi! Furthermore, there is nothing statistical in the Greenberger–Horne–Zeilinger experiment.
      https://en.wikipedia.org/wiki/GHZ_experiment

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  6. No, lambda cannot be psi. The Bell inequality has been tested experimentally. The QM of psi was confirmed. The lambda was disproved. The whole point of Bell's theorem was to show that it is not possible to have both.

    Whether or not there is anything statistical in GHZ is irrelevant.

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    1. Yes, lambda can be psi. Good God, go read the paper! Bell simply conditionalizes on it. Bell's inequality isn't strictly about quantum mechanics. QM predicts the violation, so it's nonlocal. Your point about counterfactuals is what is irrelevant.

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    2. "Indeed, Werner’s conceit that Operational quantum physics is some newfangled theory, the likes of which never occurred to Einstein and Bell (and me) is a complete fabrication: Operational quantum physics is just plain-old vanilla Copenhagen quantum physics, the very theory that Einstein derided for its spooky action-at-a-distance. He derided it for exactly the reason illustrated in Werner’s own presentation: by taking the physical state just to be the epistemic state, the theory already commits itself to violating EPR-locality in an EPR situation. The predictive state ascribed to S1 is changed after observing the distant system S2. So if the predictive state is the physical state, then the physical state changes. The geometry of the state space plays no role at all in this argument."
      https://arxiv.org/ftp/arxiv/papers/1408/1408.1828.pdf

      Non-realists simply don't have a theory and there's nothing convincing about their arguments that such a theory would not need to revamp quantum mechanics to get anywhere.

      "At the end of the day, it may be that the lesson of Bell’s theorem is that the world is causally non-local. Or it may be that the lesson is that measurements have multiple equally real outcomes. Or it may be that effects can come before their causes. Or it may even be that no description of the quantum world can be given—although this latter conclusion seems to me to be a last resort."
      http://philsci-archive.pitt.edu/11372/

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    3. "As should be clear from a fair reading of the Bell original article, the Bell theorem starts exactly from the alternative established by the EPR-Bohm argument—namely, locality and completeness cannot stand together—and goes for the proof that, whatever form the completability of quantum mechanics might assume, the resulting theory cannot preserve the statistical predictions of quantum mechanics and be local at the same time: this means that neither a pre-existing property assumption (or ‘Objectivity’ or ‘Classicality’ or whatever synonymous one likes to choose) nor a determinism assumption are assumed in the derivation of the original Bell inequality...

      Suppose in the actual world the experimenter has chosen the axis z: if her measuring operations cannot affect by definition what axis is chosen – and what outcome has been obtained – on the other side, this holds naturally for whatever choice and this makes it invalid to claim that in an ordinary EPR argument we have adopted a conterfactual definiteness assumption in addition to locality"
      https://arxiv.org/ftp/arxiv/papers/1705/1705.01356.pdf

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  7. You provide examples of people who refuse to accept quantum mechanics. It is like finding people who are hung up on the twin paradox, and refuse to accept relativity.

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    1. Funny, they would say the same about you. You have no argument but ad hominems. Here is Bell: “THE paradox of Einstein, Podolsky and Rosen [1] was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional variables were to ***RESTORE*** to the theory causality and locality [2]” https://cds.cern.ch/record/111654/files/vol1p195-200_001.pdf

      The only position localists have left is a mystical anti-realism they can't even explain. Consistent histories just abandons logic: "But a physical theory is not simply a game for which one can impose arbitrary rules about what reasonings are permitted for the propositions of the theory; if a physical theory implies both P and Q then the logical consequences of both P and Q will hold in a world governed by that theory and there is nothing that the proponents of the theory can do to prevent that. One might try to find an actual objection against the reasoning leading to inequality (1), but one cannot simply state as a ‘rule’ that the reasoning is forbidden." http://www.scholarpedia.org/article/Bell%27s_theorem#Consistent_histories

      Ronde (2015) says Griffiths "framework" theory is contrived: "Unfortunately, still today the problem remains with no solution within the limits of the orthodox formalism. There is no physical representation of the process without the addition of strange ad hoc rules, unjustified mathematical jumps and the like. These rules 'added by hand', not only lack any physical justification but, more importantly, also limit the counterfactual discourse of the meaningful physical statements provided by the theory" https://arxiv.org/abs/1502.05396

      I don't find these kinds of ad hoc explanations even remotely convincing.

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