On 18 Apr 2016, at 09:45, Bruce Kellett wrote:

On 18/04/2016 5:00 pm, Jesse Mazer wrote: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> wrote:The future light cones of the observers will overlap at a timedetermined by their initial separation, regardless of whetherthey send signals to each other or not.Of course, I never meant to suggest otherwise. Imagining acentral observer who receives messages about each experiment wasjust conceptually simpler than imagining an arbitrary system thatis affected in some unspecified way by each experimenter'sresults along with every other part of that system's past lightcone. But you certainlydon'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 someunspecified way. But my example shows that no exchange ofinformation after the separate worlds of the two experimentershave fully decohered can ever explain the quantum correlations.Why do you think it shows that? Does "explain" mean something morethan giving a mathematical model that generates the correctcorrelations, or is that sufficient?Have you not understood my argument? The specified experimentresults in four possible combinations of results: |+>|+'>, |+>|-'>,|->|+'>, and |->|-'>. It is relatively easy to show, either bylooking at special cases, or by consideration of a repeatedsequence of such experiments, that the probabilities are differentfor each of the four sets of results. The differences inprobability depend only on the relative orientations of themeasuring magnets. Conveying this angle information after theexperiment has been completed, and each of the measurements hastotally decohered, cannot explain these correlations.What is required is an account of how these correlations can arisebefore A and B speak to each other, because once they have theirresults 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 matterabout *both* results except in the overlap region of the futurelight cone of both measurements, where a single localized systemmay be causally influenced by both measurements (see below for moreon what I mean by this if you're unclear).This so-called "matching up" is pure fantasy. Who does thismatching? If the central umpire is to do the matching, he has tohave the power to eliminate cases that disagree with the quantumprediction. Who has that power?The laws of physics would do the matching in some well-definedmathematical way.I agree that the laws of physics will 'prevent' the formation ofany worlds in which the laws of physics are violated. That is notthe issue. The issue is: how do the laws of physics act in orderto achieve this. Do they act locally or non-locally? If they actlocally, then you are required to provided the local mechanismwhereby they so act. You are not doing this at the moment.Similar to my question above, what do you mean by "mechanism" ? Doyou mean something more than simply "mathematical rule that givesyou the set of possible outcomes (with associated probabilities orat least probability amplitudes) at each local region ofspacetime, given only the set of possible outcomes at regions inthe past light cone"?The mathematical rule that gives the differing probabilities foreach outcome depending on the relative angle of the magnets is justquantum mechanics. But that is intrinsically non-localI specified that I was talking about a local mathematical rule--Isaid the rule would give out the outcomes at onelocation in spacetime "given only the set of possible outcomes atregions in the past light cone". Did you miss that part, or do youdisagree that if I mathematically determine the state of someregion of spacetime using *only* information about the states ofregions in the past light cone, that is by definition a local theory?The local mathematical rule in this case, say for observer A, isthat measurement on his own local particle with give either |+> or |->, with equal probability. It does not matter how many copies yougenerate, the statistics remain the same. I am not sure whether yourmultiple copies refer to independent repeats of the experiment, orsimply multiple copies of the observer with the result he actuallyobtained. The set of outcomes on the past light cone for thisobserver is irrelevant for the single measurement that we areconsidering. Taking such copies can be local, but the utilityremains to be demonstrated.You are claiming to have a local account. But I have not yet seenit. Published attempts fail for the reasons given.Can you actually follow the detailed math of Rubin's argument in astep-by-step way, and identify the first step that's an error? Orare you just saying that your conceptual argument is sufficient toshow that any such attempt is impossible, regardless of thedetails? If you're making an impossible-in-principle argument, Ithink a simple toy model like the one I described is sufficient toshow your argument must be wrong.The conceptual argument is sufficient to show that Rubin must fail.Your toy model makes no impact on my argument.In this type of toy model, the idea is not to simulate arbitraryquantum systems with full generality, but just to simulate theresults that will be seen by a set of experimenters at differentlocations in space, given that they are running some specificexperiment that is known to violate some Bell inequality (likemeasuring the spin of pairs of entangled particles with somethinglike a Stern-Gerlach device, with each experimenter choosingrandomly which of three possible axes to measure along). Forconcreteness you could imagine that each experimenter has a pieceof paper which has written down all the results the experimenterknows about at that time (obviously they will know about their ownresults up till then, and they can also know aboutresults seen by distant experimenters if there's been time for themto have received a light signal the other experimenter sent outcommunicating their result, in which case the paper can also recordthe *correlations* between one of their own past results andanother experimenter's result at the same time).OK, but the past results are irrelevant here.Given that this is the type of physical scenario we want tosimulate, I'm specifically talking about a simulation thatcontinually creates multiple copies of experimenters at eachlocation, with the computer having a purely local mathematical rulefor determining how many copies of a given simulated experimenterwill have a given set of results written on their own piece ofpaper. You could even imagine that the simulation is being run on aset of networked computers, with each physical computer solelydevoted to simulating multiple copies of a single experimenter at asingle location in space, and the computers are forbidden tocommunicate with one another in a way that would be FTL in thecontext of the simulated world. My claim is that it's possible tohave a purely local simulation rule of this type that has theproperty that if you *randomly* select one of the copies of a givensimulated experimenter at any given moment, the probability thatcopy will have a given set of results written on their paper willmatch up with the probability the corresponding real-worldexperimenter would have recorded the same results, assuming thereal-world experimenter's probabilities are determined by the lawsof quantum mechanics.So the copies are running separate measurements on the sameparticle: so 50% get |+> and 50% get |->. A random selection thensimply reflects these probabilities.Do you dispute that it would be possible to have a purely local andalgorithmic copy-spawning rule with this property of reproducingthe statistics of the real-world experiment, even knowing the real-world experiment would violate Bell inequalities? Or would youacknowledge this could be done but say it's irrelevant to whateverargument makes you confident Rubin's paper fails to do somethinganalogous but with more generality? Or do you think that even if myapproach succeeds at doing what I describe above and Rubin's mightsucceed in an analogous way, any local mathematical rule that dealssolely with "copies" of systems at each location in space, withoutassigning copies at different locations to any common "world", is afailure as a local "mechanism" or "explanation"?Even if your local copy model succeeds in doing what you claim, itcannot reproduce the quantum correlations.Let me reduce this to simple steps:1) MWI is an interpretation of QM only. I.e., it reproduces all theresults of QM without adding any additional structure or dynamics.

`What do you mean by QM? I am not sure I agree with you. Everett did`

`not talk about a new intepretation of QM, but about a new formulation`

`of QM. And he is right in the sense of the logician. Before Everett:`

`QM was formulated roughly SWE + Collapse + an implicit dualist theory`

`of mind or of scale (mircro/macro). Everett's QM is SWE, the abandon`

`of collapse, + a mechanist theory of mind, with the implicit use of`

`the FPI.`

`For a logician, if QM (without collapse) is formalized, you get an`

`"Herbrand minimal model" which contains already all relative state`

`(like we get them already in the sigma_1 arithmetic with the Mechanist`

`Hypothesis in the Cognitive Science).`

`Given the linearity of the tensor product and the evolution, we can`

`only abstract away the self-superposition, although we would have to`

`take them into account if we get a quantum brain (and here the SWE`

`give non ambigous result where a collapse theory has to first make`

`more precise how the (non local) collapse is made physically.`

2) The QM state describing an entangled singlet pair does not referto, or depend on, the separation between the particles.

`OK. But the singlet state describe an infinity of Bob and Alice with`

`their spin correlated, yet both of them see their own particles with a`

`random result, as none of them know in which universe they are. They`

`know only one thing for sure: their spin are correlated, and remains`

`so independently of the distance.`

3) The quantum calculation of the joint probabilities depends on therelative orientation between the separate measurements on theseparated particles.

No problem.

4) This quantum calculation is the same for any physical separation,since the singlet state itself does not depend on the separation.

No problem.

5) The quantum calculation is, therefore, intrinsically non-localbecause it does not depend on the separation, which can bearbitrarily large.

`This does not follow. It would be if the state |psi> = (|+>|-> - |->|`

`+>) would be interpreted by We know that Alice has a particle in`

`state |+> or in state |-> and Bob the opposite. But the state (|+>|->`

`- |->|+>) means eaxctly that neother Alice nor Bob know in which`

`universe they are. It could be one with |+'> or |-'> or whatever.`

6) Since MWI does not add anything to standard QM, and standard QMgives a non-local account of the probabilities we are considering,any MWI account must also be intrinsically non-local.

Proof?

`Don't invoke Bell's theorem, because it assumes Alice and Bob are in`

`the same reality, where without collapse, the measurement of Bob and`

`Alice propagate only locally from multiple Alice to mutiple Bob, as`

`describe by the superposition singlet state (in any base).`

`If I find some time, I might try to describe this with the density`

`matrix formalism, which I think can make this more obvious.`

`One physical reality, and/or hidden variables specifying unqiueness of`

`state + Violation of Bell's inequality entails non-locality. That is`

`shown by Bell's inequality violatin.`

`But without "collapsing" a wave at a distance, the apparent non-`

`locality comes only from Alice or Bob determining in which universe`

`they are. There are just no reason they found themsleves in the same`

`universe. If they can compare the results, it is only after the`

`contagion of their superposed state with each other, and in that case,`

`the statistics implies the Bell correlations, without any physical`

`action at a distance. You need to transform the pure state in some`

`mixture, before the measurement to get non-locality, but such mixture`

`are local and different for each Alice and Bob in the superposition`

`state, so you cannot take them as definite like if Alice or Bob could`

`know that in advance.`

`It is "shocking" because it is really the self-multiplication which`

`explains the apparent non-locality, but then that was also the case`

`for the apparent indeterminacy.`

`Put in a different way: when Alice and Bob make their measurement,`

`they might get result violating the correlation, but that would make`

`their belonging to different cross-product term of the final`

`superposition, so they would not been able to compare those forbidden`

`results.`

Bruno

You appear to be disagreeing with step 5 here -- by relying on a non-standard notion of locality.Bruce --You received this message because you are subscribed to the GoogleGroups "Everything List" group.To unsubscribe from this group and stop receiving emails from it,send an email to everything-list+unsubscr...@googlegroups.com.To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.

http://iridia.ulb.ac.be/~marchal/ -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.