> On 12 Aug 2019, at 14:42, Bruce Kellett <[email protected]> wrote: > > On Mon, Aug 12, 2019 at 7:36 PM Bruno Marchal <[email protected] > <mailto:[email protected]>> wrote: > On 12 Aug 2019, at 04:06, Bruce Kellett <[email protected] > <mailto:[email protected]>> wrote: >> >> If you do not measure which slit the photon went through, then the >> superposition of slits is not broken by decoherence. > Decoherence break things only if there is a collapse. > > 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, some people will still live the two alternative quasi-classical histories. > > Without collapse, even if I measure which slit the photon went through, the > two terms of the superposition continue to exist, describing me seeing both > outcomes, and both me feel like if there has been a collapse, > > No, that is not really true. Complementarity plays a role. Measurement of > which slit the photon went through is incompatible with the effective > momentum measurement that gives interference at the screen. That is > essentially why the slit measurement destroys the possibility of > interference. There is an incompatibility between the measurements -- > basically related to the non-commutation of position and momentum operators > and the Heisenberg uncertainty principle. I agree with this, but fail to see why it makes my statement above false. > > and that decoherence is physical real, but that illusion is explained by the > formalism, in a manner similar to the WM duplication: it is just first person > indeterminacy, not in a self-duplication, but in a self entanglement. > > Not really true, either. Decoherence, the formation of a stable pointer > basis, and the like, are all essential for the emergence of the classical > from the quantum, and the formation of objective physical states. This is the > operation of Zurek's Quantum Darwinism -- the environment acting as witness. > So this is third person objective physics -- it is not first person > indeterminacy. Why? The environment, in a world with brains, acts as a witness of all quasi-classical histories. Decoherence explains why those histories look very classical, but it does not select one classical history (cat alive, say), it put itself in a superposition of the (two, here) classical histories. 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/CAFxXSLRBghQR4Z1MKLdSQOGGpte7jnOjvt_vtxQ_Pohx9MDCZQ%40mail.gmail.com > > <https://groups.google.com/d/msgid/everything-list/CAFxXSLRBghQR4Z1MKLdSQOGGpte7jnOjvt_vtxQ_Pohx9MDCZQ%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/EEAEB551-0E80-4CC6-8864-7E6DBE77A548%40ulb.ac.be.
