> On 20 Aug 2018, at 13:18, Bruce Kellett <bhkell...@optusnet.com.au> wrote: > > From: Bruno Marchal <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>> >> >> > On 19 Aug 2018, at 21:36, Brent Meeker <meeke...@verizon.net >> > <mailto:meeke...@verizon.net>> wrote: >> > >> > >> > But Alice and the detector are not in a singlet state and when you combine >> > them in a product with the singlet state the result is no long >> > rotationally invariant. >> >> The rotational invariance of the singlet state has not been broken, and in >> principle Alice can get back to it by quantum memory erasure, unless >> collapse. > > You didn't respond to my earlier post in which I discussed the symmetry > breaking occasioned by Alice's measurement interaction with the singlet > state. I copy the relevant parts of my earlier post here: > > "The fact that Alice's interaction with the state is unitary and can be > reversed does not mean that the original symmetry still exists in some sense. > If I place a large weight at some point on the circumference of a bicycle > wheel, the rotational symmetry of that wheel is lost. The fact that I can > reverse the process by removing the imposed weight does not mean that the > altered wheel is still rotationally symmetric in some wider view.”
OK, but when the heavy object is removed, at that moment, the symmetry is back. Then, when Alice makes the measurement, the symmetry is lost from her point of view, but the general symmetry of the state has not changed. It is only not retrievable by Alice (unless quantum erasure, amnesia, etc.). > > and later in the same post: > > "It seems that you are basing your conviction I have no conviction. It just that I claim that there is not yet a proof that there are FTL physical *influence* in one semi-classical universe which would be a branch of the universal wave. Violation of Bell’s inequality can be explained by “Bertlmann socks” (common cause) in the MWI, without a too much “classical” (naive) conception of world. My point was just a reply to Clark, and honestly it looks to me you have oscillated on this. > that all physics is ultimately local on the idea that all interactions are > unitary transformations of the universal wave function. That is not my argument, except if you use this to show that a classical computer can emulate a quantum computer. On the contrary, I thought that any physics emerging from arithmetic would be “non-local”, with apparent FTL influence, but later I realise that this would be of the white rabbit style of events. That should be excessively rare. > But that is not sufficient. You have also to postulate that the wave function > itself is actually local. I don’t see what you mean by this. The wave spread locally, even singlet. It has the shape of e^iH(t). Only its collapse brings a genuine FTL. > And we know that that is not true. Because non-separable, that is, non-local, > states do actually exist within the universal wave function. As Maudlin > points out, the basing an argument for locality on the wave function fails > because the wave function itself is not a local object.” I will wait reading maudlin 2011. Locality is a space-time notion, as your appeal to EPR = ER suggests. I do not understand what it would mean for a wave to be non local. In fact, without any collapse, I do not see how QM could generate an instantaneous FTL influence. And the argument of Bell’s inequality is not valid, as I gave an interpretation (à-la Many-Minds) where EPR is recovered without FTL, by using common cause. I agree that a singlet state remains rather weird, but I think that this is the case in all interpretation or theories, and that MW is the one the most plausible (indeed enforced by independent non physical argument). 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 everything-list+unsubscr...@googlegroups.com > <mailto:everything-list+unsubscr...@googlegroups.com>. > To post to this group, send email to everything-list@googlegroups.com > <mailto:everything-list@googlegroups.com>. > Visit this group at https://groups.google.com/group/everything-list > <https://groups.google.com/group/everything-list>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- 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.
