On Thursday, June 13, 2019 at 7:20:27 PM UTC-5, Bruce wrote: > > On Thu, Jun 13, 2019 at 11:23 PM Bruno Marchal <[email protected] > <javascript:>> wrote: > >> On 11 Jun 2019, at 08:14, Bruce Kellett <[email protected] <javascript:>> >> wrote: >> > > >> On Tue, Jun 11, 2019 at 3:53 PM Bruno Marchal <[email protected] >> <javascript:>> wrote: >> >> On 10 Jun 2019, at 08:54, Bruce Kellett <[email protected] <javascript:>> >>> wrote: >>> >> If retrocausality is right, then QM itself is certainly wrong. In the EPR >>> situation, the singlet state is rotationally symmetric in standard QM, and >>> this cannot be the case if that state is dependent on the future polariser >>> settings. Conversely, if QM is right, retrocausality is impossible. >>> >>> >>> If QM with collapse is right, I would understand and agree. That is why >>> Deutsch see the “retrocausality” has a semantic variant of the many-worlds >>> interpretations, but I have not entirely figure out if this makes sense >>> >> >> It makes no sense at all! Deutsch has gone completely off the rails over >> quantum mechanics. He is essentially abandoning the theory as it currently >> stands. The argument from symmetry is, to my mind, a total killer of any >> retrocausal explanation -- retrocausality must destroy the very symmetry >> that is at the heart of the QM predictions for the singlet state, Collapse >> and many worlds are all irrelevant to this argument. >> >> >> It would be nice if you could elaborate on this. >> > > The basis of retrocausality is the observation that there is no problem > with non-local influences in QM if the initial state is allowed to depend > on the final state, namely, on the settings of the polarisers in the EPR > experiment. The QM representation of the singlet state is rotationally > symmetric (about the propagation axis). This symmetry is central to the > derivation of the correlations that violate the Bell inequalities. If the > initial state is made to depend on the final polarizer settings, then the > rotational symmetry is lost. So the basis for the original correlation > predictions is lost, and the theory becomes incoherent. > > As it currently stands, the formalism of QM does not allow the singlet > state to depend on the final polariser settings, so standard QM is > inconsistent with retrocausality. It might be possible to restore the > required rotational symmetry in a wider context (taking the remote > polarisers into account), but QM does not do this. Retrocausality is a > different theory, it is not QM. And that different theory has not been > coherently worked out. > > The rotational symmetry of the initial singlet state is independent of > whether you have a collapse model, or have Many Worlds. The difference > between these two only comes into play when you include the final > measurements. So it is the retrocausal model that requires collapse -- > retrocausality cannot work coherently in a many worlds setting. > > Bruce >
The dependency of the initial and final states means the probabilities are classical and will obey the Bell inequality. This is a pretty iron clad result and I am not sure why some people persist in thinking they can get around it. LC -- 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/588f25ce-aeaf-46fd-9ba2-61f2f5fb6afa%40googlegroups.com.
