On Thu, Aug 15, 2019 at 7:49 PM Bruno Marchal <marc...@ulb.ac.be> wrote:
> On 15 Aug 2019, at 02:54, Bruce Kellett <bhkellet...@gmail.com> wrote: > > On Wed, Aug 14, 2019 at 10:10 PM Bruno Marchal <marc...@ulb.ac.be> wrote: > >> On 12 Aug 2019, at 14:42, Bruce Kellett <bhkellet...@gmail.com> 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. The cat itself is never in a superposition because decoherence brings about a definite live state or dead state. By the time you open the box, you have also split according to the classical basis, so your probability of seeing a live or dead cat is just the classical ignorance probability. Opening the box does not collapse anything. The point is that even if there is some superposition, it lasts no more than a few nanoseconds. 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. Opening the box does not change your relative state, or collapse anything. 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). So it is just like someone tossing a classical coin that you can't see. 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 everything-list+unsubscr...@googlegroups.com. 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.
