> On 23 Aug 2018, at 02:05, Bruce Kellett <[email protected]> wrote: > > From: Bruno Marchal <[email protected] <mailto:[email protected]> >>> On 22 Aug 2018, at 01:54, Bruce Kellett <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> From: Bruno Marchal <[email protected] <mailto:[email protected]>> >>> >>>> The other sort of infinity, the one which I think you disagree with, is >>>> typical for the superposition of tensor products, like the singlet state >>>> ud - du. Before measurement Alice has the same probability of finding u, >>>> or d for any measurement she can do in any direction. Both Alice and Bob >>>> are maximally ignorant of their possible measurement results. The MW on >>>> this, or a MW way to interpret this, to keep the rotational symmetry, is >>>> that we have an infinity of couples Alice+Bob, with each couple being >>>> correlated. If not, some implicit assumption is made on u and d, like it >>>> is a preferred base. >>> >>> But the problems with any such suggestion are obvious. Firstly, Alice does >>> not choose her measurement angle in that way, so there is no >>> super-superposition created. Secondly, this construction does not restore >>> the rotational symmetry in any case. You might have an infinite number of >>> Alices, measuring the singlet at all possible angles, but that >>> multi-multiverse is not rotationally symmetric either! All it needs is for >>> Alice number 7,234,826 to poke her tongue out and the rotational symmetry >>> is lost! Of course, you could add yet more multiverses to cover every >>> possible deviation of Alice from the stationary state. But the process >>> rapidly becomes ridiculous. >>> >>> So this Rube Goldberg construction of additional multiverses of >>> superpositions does not actually restore stable rotational symmetry. So why >>> propose such a construction? William of Ockham will rise >>> out of his grave to haunt you for such pointless extravagance of >>> entities! >> >> Alice destroys the rotational symmetry in all its universe. Not of the whole >> wave, where Alice does not exist as a determinate subsystem. > > I can't really parse this. The point is that when Alice interacts with the > singlet with her magnet she destroys the rotational symmetry of the state. > This symmetry is not restored by considering and large system, or the whole > wave. If anything, enlarging the context in this way simply lessens any > symmetry that might remain. > > I think what you have in mind is a situation such as arises if you shine a > light through a small aperture. The photon emerges as a spherical wave, with > the rotational symmetry of such a (hemi-)spherical wave. If there is a > hemispherical screen downstream, the photon will interact with the screen at > some single point. If you consider only one branch of the SWE evolution, this > interaction point breaks the rotational symmetry. But if you consider all > branches of the wave function together, there is a branch for every single > point at which the photon can hit the screen, so that the symmetry is > preserved in the wave function as a whole -- over the ensemble of all > branches. But that is a situation in which the environment with which the > photon interacts is itself symmetrical. If the screen, rather than being a > smooth equidistant hemisphere, is just the rough walls of the laboratory, > there is no symmetry in the points at which the photon can hit the walls, and > the rotational symmetry is lost, even in the wave function as a whole, even > by considering the superposition of all possible branches. > > The take away message from this is that the symmetry of the original system > can be lost by interaction with a non-symmetrical environment. The boundary > conditions of the total system may not have the symmetries of the original > state. So loss of symmetry is ubiquitous in the universe, even for Everettian > no-collapse quantum mechanics. If you introduce a non-symmetrical interaction > into the system, the symmetry is lost. That is all that is happening with the > measurement of the spin projection of the singlet state by Alice. Your > idiosyncratic interpretation of the tensor product, and your insistence the > the symmetry be preserved regardless of the non-symmetrical environment, are > just misguided. There is no need to try to preserve symmetry given > non-symmetrical boundary conditions. > > Since the symmetry is broken, the singlet state no longer exists in its > original form, and the state that Bob measured is affected by the measurement > Alice makes. There is no more to it than this. If Alice and Bob are > space-like separated, there are some interpretational issues with this > instantaneous influence at a distance.
Nice to hear that. It was basically my point.We have never disagreed except on some definition. I use “symmetry” in a larger sense, and I take superposition at face value, independently of the base, making the superposition of tensor products into “many superposition”, which indicate the relative state locally accessible by the observers. > But that just means that quantum mechanics is not fully integrated with a > total quantum theory of space-time. Yes. > No need to get agitated by this -- ride with it until we have a more complete > theory. In the meantime, this is what is meant by non-locality. It means violation of Bell’s inequality. I get agitated only by those implying the existence of instantaneous physical action at a distance, that’s all. 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 post to this group, send email to [email protected] > <mailto:[email protected]>. > 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
