On Thursday, August 23, 2018 at 3:16:24 PM UTC, Bruno Marchal wrote: > > > On 23 Aug 2018, at 02:05, Bruce Kellett <[email protected] > <javascript:>> wrote: > > From: Bruno Marchal <[email protected] <javascript:> > > On 22 Aug 2018, at 01:54, Bruce Kellett <[email protected] > <javascript:>> wrote: > > From: Bruno Marchal <[email protected] <javascript:>> > > 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 >
*But keep in mind that if the wf is epistemic only, it can change instantaneously with no PHYSICAL action at a distance. This is what Bruce's horse race example shows, and FWIW, my present assessment of the situation; wf epistemic only. AG * > > > > > 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] <javascript:>. > To post to this group, send email to [email protected] > <javascript:>. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit 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.
