On Thu, Apr 21, 2016 at 9:49 PM, Bruce Kellett <bhkell...@optusnet.com.au> wrote:

> On 22/04/2016 5:17 am, Jesse Mazer wrote: > > On Wed, Apr 20, 2016 at 7:51 PM, Bruce Kellett <bhkell...@optusnet.com.au> > wrote: > >> On 21/04/2016 1:34 am, Jesse Mazer wrote: >> >> On Tue, Apr 19, 2016 at 8:54 PM, Bruce Kellett < >> <bhkell...@optusnet.com.au>bhkell...@optusnet.com.au> wrote: >> >>> So, the fact that these simulated results were supposed to have come >>> from an entangled singlet pair has not been used anywhere in your >>> simulation. It has only ever been used to link the copies of Alice and Bob, >>> the statistics that they observe come entirely from what you happen to put >>> in you accumulator for each setting of the relative orientations. >>> >> >> Saying the idea of a singlet pair "has not been used anywhere in your >> simulation" and then saying it has "been used to link the copies of Alice >> and Bob" seems like a contradiction--isn't the linking itself part of the >> simulation? >> >> No, there is no contradiction. You have used the fact that they are >> measuring parts of an entangled system only to link the sets of results. >> Nowhere have you used the quantum properties of the entangled singlet pair >> in the simulation to calculate the probabilities: you have imposed those >> probabilities from outside by fiat. >> > > Sure, it's a toy model so I just tailor it to give the correct statistics > for a single type of quantum experiment. But if I were to try to do the > same thing in a scheme where there *weren't* multiple copies of Alice and > Bob, so that each had to get a unique result *at the place and time they > make a measurement* (not just later when they compare results), then Bell's > theorem absolutely rules out doing this in any classical setup that > respects locality, even toy models. So, the toy model is just mean to > illustrate the principle that Bell's theorem isn't applicable to situations > where measurements don't yield unique outcomes but just yield a bunch of > different copies of a system at a given location in space at a given time. > > > interesting. So you agree that you just feed in the statistics that you > want to come out -- they do not come from any principle physics that your > computers simulate. > Yes, but they do come from rules which generate the results at each point in spacetime in a local way, depending only one what's in the past light cone of that point, and which generate the desired statistics. This proves the principle that Bell's theorem does not forbid rules of this "locally generated results on arbitrary patches" sort from reproducing the statistics of the particular experiments that Bell's theorem analyzes. Thus, Bell's theorem presents no fundamental obstacle to the hope of developing a set of rules that would generate correct results for *all* possible measurable behaviors of quantum systems, and which are still of the "locally generated results on arbitrary patches" type. Do you disagree? > > I am glad you agree that if you consider the actual physical situation, > locality is ruled out by the observed statistics. > Why should I agree to that? As I said, it obviously isn't ruled out by Bell's theorem, and if you have an alternate argument, you didn't respond to my request to present it in detail. > The fact that a measurement might yield one of a series of different > results does not alter the fact that, in the multiworlds picture, there is > only one result in each possible branch. > There are no such things as global "branches" in my toy model, only local copies of Alice and local copies of Bob that retroactively get matched up. Similarly, What Deutsch/Hayden/Rubin are all saying is that the same is true in their view of the many-worlds interpretation--there are no global branches, only local ones that join together in retrospect. If you disagree that this is what *they* are suggesting, I can give some quotes that show that this is their interpretation (along with other physicists talking about the MWI and saying the same thing--for example, I was just looking over a paper by the founder of the study of decoherence, H. Dieter Zeh, where he said essentially the same thing). If you agree this is what *they* try to suggest but think this is somehow incoherent, please present an argument for *why* it's incoherent as a general model of the laws of physics, when it clearly works fine in the toy model. > Once you accept this general principle, you can see that Bell's theorem > doesn't offer any fundamental obstacle to reformulating the general laws of > quantum mechanics in a way that yields the same predictions about *all* > observations using purely local equations, of the kind that could be > simulated on a computer where you have a bunch of separate computers > calculating how physical variables are evolving in a confined region of > space, and each computer can only get data from other computers > representing neighboring regions, in a locality-respecting way. As I said, > my reading of the non-mathematical parts of Mark Rubin's paper suggests > that the paper is coming up with exactly such a model, albeit one that is > only equivalent to a non-relativistic quantum field theory (perhaps the > math of doing it for a relativistic field theory would be more difficult). > > > If you mean that you can recover locality for measurements on entangled > pairs in this way, then you have a different theory which is not consistent > with quantum mechanics. > *Why* is it necessarily inconsistent with QM? If you want to use Bell's theorem which concerns only the observed statistics in particular experiments, then my toy model suffices to show you can reproduce those statistics with a rule of the "locally generated results on arbitrary patches" type. If you have some other argument independent of Bell's theorem, you need to actually spell it out because at this point your argument is not at all clear to me. You seem to be saying this is impossible in principle, and you're confident > enough of this to dismiss the possibility Rubin's paper has done this > without apparently understanding the mathematical details either. So, given > what I said above, should I take this to mean you think you have an > argument for the impossibility which is entirely independent of Bell's > theorem? If so you could you try to spell it out in a more detailed, > step-by-step way? > > I have done this in the thread with smitra. The min conceptual argument is > contained in the humorous little scenario I devised: > > I dream of some "XKCD-style" cartoon. Alice and Bob perform their > experiments with particular settings and get particular results, which they > separately record in lab books. Several weeks later, they meet up in a cafe > down the street for a coffee. Alice puts her lab book with her results on > the table, "Look", she says, "I got |+> with my magnet set at zero degrees > to our agreed reference orientation." There is a pause.......then Bob > slowly lays out his lab book. "Holy shit!", he says, "I also got |+> at > zero degrees to our agreed reference." They look at each other with > gradually increasing dismay........ "Fuck!", they say in unison. "That > means that we don't exist..........." Their voices fade into silence, and > then...........Nothing!. > > > The point here is that some combinations of results are forbidden. How can > this happen? > By the appropriate matching rules for locally-generated copies in different locations, as in my toy model. There's no reason you can't have something similar in a more general model, which I think is exactly what people like Rubin are presenting. > Following back the train of information exchange between the participants, > and accepting that worlds, once decohered, cannot suddenly disappear, it > becomes apparent that the zero probability branches cannot arise because > they are forbidden at the stage when A and B are still at spacelike > separations. So they are forbidden non-locally. > But that clearly isn't true in my model, so there's no reason to think it *must* be true in more general models that reproduce arbitrary quantum measurements. In my model *and* in more general models of the sort that people like Rubin seem to be proposing, until matching between Alice and Bob has happened there *are* no "branches" containing facts about both of their results, only a set of local branches for one region and a different unrelated set of branches for another region. And once the two sets of branches can interact, they can be matched up in a way that creates zero probability of matching up a version of Alice who got + at zero degrees and a version of Bob who got + at zero degrees. Jesse -- 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.