On Thu, Jul 1, 2021 at 2:29 AM smitra <smi...@zonnet.nl> wrote: > On 29-06-2021 01:46, Bruce Kellett wrote: > > > > I think John's trouble here is that he still adheres to David > > Deutsch's concept of worlds. Deutch talks as though every component of > > a superposition is a separate world. This leaves Deutsch no language > > to talk about decohered worlds, pointer states, and all the other > > usual apparatus of quantum interpretations. The trouble with taking > > every component of a superposition as a separate world is that in > > Hilbert space (as in any vector space) you can define an infinite > > number of different sets of basis vectors, so any vector in the space > > is represented by an infinity of different worlds, and there is no way > > to distinguish between these. > > > > I think Bruno has flirted with this idea as well. Deutsch, through his > > popular writings, has done an immense amount of harm to the cause of > > quantum interpretations. > > > > Bruce > > There ids a large body of rigorous work in this field, it's not that you > have just a handful of advocates who are defending the MWI based on > dodgy nonrigorous arguments. Of course, you can't just take nay > component of a superposition as a separate world.
But that is precisely what people like John, Deutsch, and Bruno do. > But given that Worlds > do exist A world exists. That is all that we can be sure of. > and given that time evolution is given as a linear operator, it > follows that if QM is a fundamental theory that also describes > observers, that you inevitably end up with superpositions of entire > Worlds. > Worlds have to be carefully defined. According to decoherence theory (which is also a consequence of the linearity of the Schrodinger equation), decohered worlds are truly separate and do not recombine. Non-decohered elements of a superposition do not constitute separate worlds. > > This conclusion does not depend on any assumptions of how observers > should be defined rigorously, how experiments and ultimately > observations arise out of the physics. These issues that are not yet > 100% solved, are totally irrelevant provided QM is indeed a fundamental > theory. > > It's not any different from someone claiming that conservation of > momentum may not be true. How do we convince this person that it is > true? We can appeal to fundamental laws of physics and argue on the > basis of symmetries, Noether's theorem and then say that this rigorously > establishes conservation of momentum. But the skeptic can then take > issue with the assumption about the validity of the fundamental laws, > he will insist that it's still possible for momentum to get lost. If he > does an experiment involving many particles, then he'll say that unless > you measure the momentum of each particle to infinite accuracy, you > can't really tell that momentum is conserved. He'll then turn the logic > about the fundamental laws upside down by arguing that because you can't > really be sure about momentum conservation, you can't therefore say that > the fundamental laws have been all that well established. > > Of course, there is then a lot to argue about this reasoning suggesting > that there is room for momentum nonconservation. But the arguments > against MWI (regardless of whether or not you need to add Born's rule as > a postulate and if so, regardless about any discussions about this then > invalidating the original goals of some MWI advocates), are of the same > nature. Not really. You can accept the Schrodinger equation as fundamental without agreeing to MWI. The fact that you can't derive the Born rule from the Schrodinger equation in a non-circular fashion is quite telling. It means that the Schrodinger equation is more naturally seen as a way of calculating the time evolution of probabilities. QM is a probabilistic theory, so its fundamental laws give probabilities. And probabilities are not worlds. Bruce Here you have a supposedly fundamental theory, QM and it implies > in a rather straightforward way the existence of parallel Worlds, and > because people don't like that conclusion, you have arguments against it > that can only work if QM is not true as a fundamental theory. The > problem with those arguments is then that it's invoked as a standalone > argument against the MWI. If these arguments were well motivated on > their own merits, then they would form the basis of a lot of physics > research in many different fields ranging from condensed matter, > particle physics etc. But that's not the case. > > Saibal > -- 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/CAFxXSLTzv%2ByTamQNGGuz8Qki2iokXGQUetK1qm7sASObj1L3rg%40mail.gmail.com.
