> On 15 Aug 2019, at 13:28, Bruce Kellett <[email protected]> wrote: > > On Thu, Aug 15, 2019 at 7:49 PM Bruno Marchal <[email protected] > <mailto:[email protected]>> wrote: > On 15 Aug 2019, at 02:54, Bruce Kellett <[email protected] > <mailto:[email protected]>> wrote: >> On Wed, Aug 14, 2019 at 10:10 PM Bruno Marchal <[email protected] >> <mailto:[email protected]>> wrote: >> On 12 Aug 2019, at 14:42, Bruce Kellett <[email protected] >> <mailto:[email protected]>> wrote: >>> >>> That is simply incorrect. I refer you again to Zurek, who works in a >>> basically Everettian framework, but he stresses the importance of >>> environmental induced superselection (einselection) in producing the >>> preferred pointer basis. This then breaks things, in the sense that no >>> other basis is stable against decoherence, and other sets of basis vectors >>> rapidly (in times of the order of femtoseconds) collapse on to the >>> preferred pointer states. This is the basis of the emergence of the >>> classical world from the quantum substrate. And this occurs in Everett's >>> relative state approach just as much as in a Copenhagen-like collapse >>> models. >> >> That explains why the many histories will look classical. But if I observe a >> cat in the dead+alive state, >> >> The point of the existence of a preferred basis is that you will never >> observe a cat in a "dead+alive" state. > > If that is what you mean, we both agree that Everett + Zurek solves that > problem. But the point is that If I observe the cat with an apparatus > deciding between alive and dead, I will put myself in the corresponding > superposition, unless some physical collapse occurs, but then we are no more > in Everett’s QM (QM without collapse). > > No, you do not see any superposition.
Yes. We agree on this. The point is that I will not see it, because I am part of it, nor because it would have disappeared in some way. > The cat itself is never in a superposition because decoherence brings about a > definite live state or dead state. So we do disagree, at least if you claim that the superposition state disappear and QM applies to the cat. If there is no wave collapse, saying that some unknown particle interacting with the cat demolished the superposition state means only that the particle has been entangled with the state of the cat, and that being unable to track that particle makes me unable to handle the superposition anymore, but this means that the cat remains superposed, the particle get also superposed, and my whole environment get superposed. By the double QM linearity, the superposition never disappeared at all. The cat + the particle + me + the universe evolved through a unitary rotation where I am locally described in the two terms of the wave: seeing the cat alive and seeing the cat dead. Decoherence in Everett (entanglement), and in Zurek (at least the perhaps old paper I read) does not make the “other branches vanishing”, it makes just my alternate history inaccessible. > By the time you open the box, you have also split according to the classical > basis, Ah, but that was my point. > so your probability of seeing a live or dead cat is just the classical > ignorance probability. Yes, like the H guy in Moscow and in Washington, already duplicated, but before they open the door of the reconstitution box (in the 2 cities). The H-guy is ignorant on which branch of the computation he/she belongs. > Opening the box does not collapse anything. Thanks for reassuring me. That was my point. > The point is that even if there is some superposition, it lasts no more than > a few nanoseconds. That is misleading, as some people will interpret this by a collapse. I am happy you reject that interpretation. I agree that, even we’ll before I open the box, I have already been multiplied, unless some engineer trick to isolate the cat completely, which is just impossible today. > After that time, your position is one of classical ignorance -- you are > either in the branch with the live cat, or the branch with the dead cat. Yes, like after the WM-duplication, I am either in Moscow or in Washington. Pure classical ignorance. > Opening the box does not change your relative state, or collapse anything. Exactly my point. > There is no "you" that is in a superposition of these branches (just as there > is no "you" that is in both Washington and Moscow in step 3). Exactly. In the first person perspective. Obviously, the 3p observer which looks at the entire setup can see me in both cities. The only difference with the superposition, is that the 3p-view is technically lost from the experimental local (first person plural) view. > So it is just like someone tossing a classical coin that you can't see. Yes. We do agree! (I hope you agree with this). Then with mechanism, we have a generalisation of the relative state approach, by taking all computations into account, a concept which makes sense through Church-Thesis, and if you accept that thesis, all computations are emulated in all models of arithmetic, in the (mathematical) sense I have given to John Clark yesterday. Bruno > > Bruce > > -- > 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 [email protected] > <mailto:[email protected]>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/CAFxXSLR%3DghJx6N3OsU3h%3D-jLa4QE%3DOZqA_wtt1BpLv8gctvwTA%40mail.gmail.com > > <https://groups.google.com/d/msgid/everything-list/CAFxXSLR%3DghJx6N3OsU3h%3D-jLa4QE%3DOZqA_wtt1BpLv8gctvwTA%40mail.gmail.com?utm_medium=email&utm_source=footer>. -- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/5820E569-BBC9-4091-B747-60E617176954%40ulb.ac.be.
