On Tue, Apr 12, 2022 at 4:58 PM smitra <smi...@zonnet.nl> wrote: > On 12-04-2022 01:17, Bruce Kellett wrote: > > On Mon, Apr 11, 2022 at 10:47 PM smitra <smi...@zonnet.nl> wrote: > > > >> On 11-04-2022 14:02, Bruce Kellett wrote: > >>> On Mon, Apr 11, 2022 at 5:35 PM smitra <smi...@zonnet.nl> wrote: > >>> > >>> The trouble with this is that the entanglement spreads only at the > >>> speed of light or less. If faster than that, then it is npn-local. > >>> Alice and Bob make their separate measurements at spacelike > >>> separations. So if the entanglement resulting from Alice's > >> measurement > >>> affects Bob's measurement, that that is FTL or non-local. > >> > >> In the MWI Alice's measurement does not affect Bob's measurement. > > > > That is your contention. > > It's not just 'my contention"" it is implied by the rules of QM when we > omit collapse. > > > But if Alice does not make a measurement, Bob > > gets both up and down, 50/50. If Alice does make a measurement, then > > the Alices branch in which she got up does not have a Bob who saw > > 50/50 up/down. So Bob's result is clearly affected by Alice's > > measurement. > > No it isn't because Bob is not located in one or the other branch before > he observes what Alice has found.
Wrong. Bob does not have to observe anything. He is automatically split into two copies -- one in the sector in which Alice saw up, and the other in the sector in which she saw down, when the forward light cone from Alic'e measurement intersects his position. He does not have to observe anything to be split in this way. Before he makes that observation, > Alice is in a superposition of both possibilities. No, she is not. By decoherence she has definite results in both sectors, and Bob sees her in both of these sectors since Bob splits along with the rest of the world. And we know that, in > general, if you are going to assume that the measurement results exist > prior to measurement that will introduce non-local effects. > No one in this discussion is assuming that measurement results exit prior to measurement. But I would certainly claim that measurement results can be definite and exist before a third party becomes aware of them. The measurement splits the observer, the device, and the rest of the world as it becomes entangled with the result through decoherence. Bob, if he is some distance away, is also split when the forward light cone from the event entangles him along with everything else. He need not be aware of this. Physics is an objective science. It doesn't depend on what people are aware of or conscious of. And in each branch, Bob's result is affected by Alice's > > measurement. The measurement outcomes are correlated, after all, and > > that is what correlation means -- the results are not independent. Not > > independent means that if one of the pair does not make a measurement, > > then the results for the other are different. (Counterfactuals rear > > their ugly head here.) > > > > But because both branches objectively exist, and Bob can end up in > either one, But he actually ends up on both of Alice's branches, carrying different results to each branch. he's identical in both before he observes Alice's result, > his results remains random even after Alice makes her measurement. > The point I was trying to make is a simple logical one. If Alice's and Bob's results are truly local and independent, then there is no correlation between them. The fact that they are correlated means that they are not independent. If their measurements are not independent, even at spacelike separation, then a non-local influence is implied. You can't have it both ways. If local and independent then no correlation. If there is a correlation, then they are not independent and the measurement of one party influences the results that the other can obtain, in a non-local way. 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. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLTvXBXrbwfS2oUN_P5uOJm-eHx_1DJ9M2ZN0QYqn3ynDA%40mail.gmail.com.
