On Sun, Apr 17, 2016 Bruce Kellett <[email protected]> wrote:
> > Consider the following: Alice and Bob perform their experiments on the > entangled pair and record the results (magnet orientation and outcome) in > their lab books. They then go on with other things. Some weeks later they > meet up at a cafe down the street for a coffee, and there compare their > results. This is the first time that any explicit information about magnet > orientations and results has ever been exchanged. And yet Alice and Bob > meet in the same world Alice and Bob meet in 4 different worlds because there are 4 different ways their lab books could be. > > > How do you prevent the situation in which, when they compare their lab > books, they find that they both used the same magnet orientation and both > recorded |+>? If the a massive particle decays into 2 lighter particles such that one is spin up and the other is spin down then the world splits into 2, and in one I get the spin up and you get the spin down and in the other I get spin down and you get spin up. In no universe do we both get spin up because that would violate the laws of physics. The MWI doesn't say everything happens, it just says everything that doesn't contradicts the laws of physics happens. > > The situation before even more bizarrely extreme if you consider the > situation in which Bob and Alice do a long series of trials of the > experiment before they meet to compare notes. They each have a series of > |+> and |-> results, with corresponding orientations, But the probabilities > calculated from these sequences must match the quantum predictions, even > though no intermediate exchange of orientation information ever took place. > Note also that if the initial separation is sufficient, or if the repeat > rate was sufficiently high, they could both accumulate these long sequences > of results before their future light cones ever intersected. The records > are fixed and unchangeable before any information exchange ever takes place. We know from experiment that things are bizarre. Suppose that Bob is 10 light years from Alice but they are not moving with respect to one another, then there are in the same frame of reference and can agree on simultaneity. So simultaneously they both intercept a stream of entangled particles that originated a billion years ago a billion light yeas away and they measure the spins of their particles, and they both get a apparently random string of ups and downs and they record the results on a paper. Alice then gets into her spaceship, which moves at 99% of the speed of light and after 10 years meets Bob and they compare records. Only then do they realize that Bob's apparently random sequence of up's and downs are exactly the same as Alice's. Thus either the entanglement propagate s instantly and things are not local, or the paper records change depending on who is looking at them and things are not realistic, or things are not deterministic and the identical sequence of measurements was just a astronomically unlikely coincidence. John K Clark -- 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.
