On Mon, Apr 18, 2016 at 1:37 AM, Bruce Kellett <bhkell...@optusnet.com.au> wrote:
> On 18/04/2016 2:53 pm, Jesse Mazer wrote: > > On Sun, Apr 17, 2016 at 9:19 PM, Bruce Kellett <bhkell...@optusnet.com.au> > wrote: > >> On 18/04/2016 10:11 am, Jesse Mazer wrote: >> >> On Sun, Apr 17, 2016 at 7:34 PM, Bruce Kellett < >> <bhkell...@optusnet.com.au>bhkell...@optusnet.com.au> wrote: >> >>> >>> The future light cones of the observers will overlap at a time >>> determined by their initial separation, regardless of whether they send >>> signals to each other or not. >>> >> >> Of course, I never meant to suggest otherwise. Imagining a central >> observer who receives messages about each experiment was just conceptually >> simpler than imagining an arbitrary system that is affected in some >> unspecified way by each experimenter's results along with every other part >> of that system's past light cone. But you certainly don't *need* to use >> that particular example. >> >> >> The issue is to find a local explanation of the correlations: appealing >> to some arbitrary system that is affected in some unspecified way. But my >> example shows that no exchange of information after the separate worlds of >> the two experimenters have fully decohered can ever explain the quantum >> correlations. >> > > Why do you think it shows that? Does "explain" mean something more than > giving a mathematical model that generates the correct correlations, or is > that sufficient? > > > Have you not understood my argument? The specified experiment results in > four possible combinations of results: |+>|+'>, |+>|-'>, |->|+'>, and > |->|-'>. It is relatively easy to show, either by looking at special cases, > or by consideration of a repeated sequence of such experiments, that the > probabilities are different for each of the four sets of results. The > differences in probability depend only on the relative orientations of the > measuring magnets. Conveying this angle information after the experiment > has been completed, and each of the measurements has totally decohered, > cannot explain these correlations. > > What is required is an account of how these correlations can arise > *before* A and B speak to each other, because once they have their > results in hand, it may be weeks before they actually communicate. Rubin's > argument (following from Deutsch) does not achieve this. > But as I said, you can achieve it if there is no fact of the matter about *both* results except in the overlap region of the future light cone of both measurements, where a single localized system may be causally influenced by both measurements (see below for more on what I mean by this if you're unclear). > > > This so-called "matching up" is pure fantasy. Who does this matching? If >>> the central umpire is to do the matching, he has to have the power to >>> eliminate cases that disagree with the quantum prediction. Who has that >>> power? >>> >> >> >> The laws of physics would do the matching in some well-defined >> mathematical way. >> >> >> I agree that the laws of physics will 'prevent' the formation of any >> worlds in which the laws of physics are violated. That is not the issue. >> The issue is: how do the laws of physics act in order to achieve this. Do >> they act locally or non-locally? If they act locally, then you are required >> to provided the local mechanism whereby they so act. You are not doing this >> at the moment. >> > > Similar to my question above, what do you mean by "mechanism" ? Do you > mean something more than simply "mathematical rule that gives you the set > of possible outcomes (with associated probabilities or at least probability > amplitudes) at each local region of spacetime, given only the set of > possible outcomes at regions in the past light cone"? > > > The mathematical rule that gives the differing probabilities for each > outcome depending on the relative angle of the magnets is just quantum > mechanics. But that is intrinsically non-local > I specified that I was talking about a local mathematical rule--I said the rule would give out the outcomes at one location in spacetime "given only the set of possible outcomes at regions in the past light cone". Did you miss that part, or do you disagree that if I mathematically determine the state of some region of spacetime using *only* information about the states of regions in the past light cone, that is by definition a local theory? > > You are claiming to have a local account. But I have not yet seen it. > Published attempts fail for the reasons given. > Can you actually follow the detailed math of Rubin's argument in a step-by-step way, and identify the first step that's an error? Or are you just saying that your conceptual argument is sufficient to show that any such attempt is impossible, regardless of the details? If you're making an impossible-in-principle argument, I think a simple toy model like the one I described is sufficient to show your argument must be wrong. In this type of toy model, the idea is not to simulate arbitrary quantum systems with full generality, but just to simulate the results that will be seen by a set of experimenters at different locations in space, given that they are running some specific experiment that is known to violate some Bell inequality (like measuring the spin of pairs of entangled particles with something like a Stern-Gerlach device, with each experimenter choosing randomly which of three possible axes to measure along). For concreteness you could imagine that each experimenter has a piece of paper which has written down all the results the experimenter knows about at that time (obviously they will know about their own results up till then, and they can also know about results seen by distant experimenters if there's been time for them to have received a light signal the other experimenter sent out communicating their result, in which case the paper can also record the *correlations* between one of their own past results and another experimenter's result at the same time). Given that this is the type of physical scenario we want to simulate, I'm specifically talking about a simulation that continually creates multiple copies of experimenters at each location, with the computer having a purely local mathematical rule for determining how many copies of a given simulated experimenter will have a given set of results written on their own piece of paper. You could even imagine that the simulation is being run on a set of networked computers, with each physical computer solely devoted to simulating multiple copies of a single experimenter at a single location in space, and the computers are forbidden to communicate with one another in a way that would be FTL in the context of the simulated world. My claim is that it's possible to have a purely local simulation rule of this type that has the property that if you *randomly* select one of the copies of a given simulated experimenter at any given moment, the probability that copy will have a given set of results written on their paper will match up with the probability the corresponding real-world experimenter would have recorded the same results, assuming the real-world experimenter's probabilities are determined by the laws of quantum mechanics. Do you dispute that it would be possible to have a purely local and algorithmic copy-spawning rule with this property of reproducing the statistics of the real-world experiment, even knowing the real-world experiment would violate Bell inequalities? Or would you acknowledge this could be done but say it's irrelevant to whatever argument makes you confident Rubin's paper fails to do something analogous but with more generality? Or do you think that even if my approach succeeds at doing what I describe above and Rubin's might succeed in an analogous way, any local mathematical rule that deals solely with "copies" of systems at each location in space, without assigning copies at different locations to any common "world", is a failure as a local "mechanism" or "explanation"? Jesse -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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