On Sunday, November 20, 2022 at 6:29:00 PM UTC-6 Bruce wrote: > On Mon, Nov 21, 2022 at 2:52 AM smitra <smi...@zonnet.nl> wrote: > >> Probability cannot be a fundamental concept in physics as explained >> here: >> >> https://www.youtube.com/watch?v=wfzSE4Hoxbc > > > I'm afraid Deutsch is a bit too glib in this lecture. He hasn't, despite > his best efforts, removed probability from physics. For example, in quantum > mechanics, he has not explained why, if one measures the z-spin of a > spin-half particle prepared in an eigenstate of x-spin, one gets only one > result -- either z-spin-up or z-spin-down. If one has eliminated > probability, one should be able to explain which result one gets, and why. > It is no solution to say that with many-worlds, that both results are > obtained by disjoint copies of the experimenter. The experimenter is just > one copy, and one would have to explain the result for each individual > separately. Many worlds does not explain why I, for example, see only > z-spin-up and not z-spin-down. To make sense of that, we need a viable > concept of probability and the Born rule. > > Bruce >
As I see it quantum mechanics has features of being a type of Bayesian update system with mutual information. A single system can give a string of outputs, say by running an electron through a sequence of Stern-Gerlach experiments, which will give a statistical distribution of outcomes based on the orientation of the different SG apparatuses. However, to understand the statistical properties one must perform this experiment multiple times, for to assume any string of outcomes with a single electron gives the total statistical distribution is to assume the ergodic principle. Bayesian statistics is not entirely consistent with the ergodic principle. I see this as holding regardless of what interpretation of quantum mechanics one holds to. With science in general experiments are performed on multiple systems and with repeated trials, whether the experiments test the effectiveness of a medication or are looking for the Higgs particle. Science addresses nature not in some existential level according to what always "is" with a system, but rather as a set of outcomes of various trials. The nature of quantum wave function is not explicitly knowable. Bohr said the wave function is just a predictive device meant to predict probability outcomes, and it has no effectiveness at telling us how an outcome obtains. This is the epistemic perspective. Everettian MWI is an ontological interpretation, but again it gives us no information for predicting any particular outcome. This appears in what I have seen so far of this what Deutsch is trying to argue. In effect this is an appeal to some type of local hidden variable. Since neither epistemic or ontic interpretations tell us anything about how an outcome applies, the existential nature of the wave function is not decidable. A quantum interpretation is not something that is proven by quantum mechanics. It can only be consistent with quantum mechanics, say in that it does not contradict quantum mechanical results. The Bohm QM interpretation originally proposed a local hidden variable, but since this contradicts QM and so the Bohmians accepted a non-local hidden variable or "beable," within a rather clumsy system. Deutsch is attempting to localize a hidden variable IMO. This interestingly points to issues with quantum gravitation. One of the things that is strange is that in cosmology a lot of what we think of as hard facts about physics do not apply. One of these is conservation of energy. There are various types of solutions to the Einstein field equation. These are from the close field to far field, Petrov type D solutions corresponding to black holes, type II and III solutions that correspond to intermediate gravity field, and type N solutions that are far field solutions and gravitational waves or radiation. These have dynamics on a contact manifold determined by Nöther’s theorem and Killing vectors. These also have a distribution of occurrences in the world. The universe does not, and further it has only one outcome. Quantum cosmology is not something that fits within a standard scientific paradigm. All of these ideas of multiverse, or black hole vacuum generation of cosmologies and so forth are so red-shifted away that we may never be able to observe any consequence of them. This is particularly the case with inflation. In effect these sorts of “pre-cosmic” theories may be sort of quantum gravitational hidden variables that are completely unobservable. I think that Deutsch is proposing something that is a type of hidden variable that will contradict QM on some level. Deutsch has proposed these things before, where at one time he said there splitting of the worlds was determined by some scalar field that an experimenter could observe and predict the outcome. 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 everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/b6af7ed4-b846-42ec-918b-f4f79339ebfcn%40googlegroups.com.
