On Mon, Dec 20, 2021 at 8:10 PM Bruce Kellett <[email protected]> wrote:
> On Tue, Dec 21, 2021 at 11:53 AM Jesse Mazer <[email protected]> wrote: > >> On Mon, Dec 20, 2021 at 7:01 PM John Clark <[email protected]> wrote: >> >>> Brent Meeker <[email protected]> Wrote: >>> >>> *> Yes, it's empirically supported; So's the Schroedinger equation. >>>> But it's part of the application of the Schroedinger equation. It's not in >>>> the equation itself. * >>> >>> >>> > I don't know what you mean by that. >>> >>> *> It's the projection postulate in the Copenhagen interpretation that >>>> applies the Born rule. In MWI it's the Born rule plus some kind of >>>> self-locating uncertainty to allow for the probabilistic observations. So >>>> those are things not in the Schroedinger equation.* >>> >>> >>> I don't know how you figure that. It has been mathematically proven that >>> the Born rule is the only way to get probabilities out of Schrodinger's >>> equation such that all the probabilities add up to 1. And Schrodinger says >>> an electron wave can be in any location, and in a camera/electron wave a >>> camera will observe the electron being in every location, and in a Brent >>> Meeker/camera/electron wave there will be a Brent Meeker for every camera >>> that sees an electron in every location. >>> >>> *> No, you can't observe the Born rule to be true any more (or less) >>>> than you can observe Schroedinger's equation to be true.* >>> >>> >>> Nonsense! Every quantum physicist alive believes the Born rule is valid >>> and they use it every day, and the reason they're so confident is because >>> the Born rule has always conform with observations and all empirical tests >>> , so it doesn't need a seal of approval from a theory for us to think it's >>> true, but a theory may need a seal of approval from the Born Rule to >>> convince us that a theory is true. That's because observation always >>> outranks theory. >>> >> >> But one of the big selling points of the MWI is to give some sort of >> objective picture of reality in which "measurements" have no distinguished >> role, but are simply treated using the usual rules of quantum interactions. >> > > At one time, that might have been a point on which to prefer MWI over > Bohr's version of the CI, but that is no longer true. Modern collapse > theories do not have to distinguish particular "measurement" events, and do > not have to assume a classical superstructure . In modern fGRW, for > example, everything can be treated as quantum, and the theory is completely > objective. > > fGRW has the added advantage that it is an inherently stochastic theory. > Probability is treated as a primitive notion that is not based on > anything else. MWI struggles with the concept of probability, and while it > has to reject a frequentist basis for probability, it cannot really supply > anything else. Self-locating uncertainty does not, in itself, serve to > define probability. You have to have some notion of a random selection from > a set, and that is not available in either the Schrodinger equation or in > self-locating uncertainty. > What does fGRW stand for? If it's stochastic, do you mean it's one of those theories that involves stochastic spontaneous collapse? Such theories are usually in principle experimentally distinguishable from QM, would that be true of this theory as well? > > > If you have to say "OK, I believe in the MWI plus Born rule for >> measurements" with there being no dynamical definition of what qualifies as >> a measurement, where the moments we call 'measurements' are just something >> we feed into the theory on a know-it-when-I-see-it basis, then this claim >> to objectivity is lost and it's not clear what theoretical appeal it has >> over the Copenhagen interpretation. >> >> Personally I still lean towards some version of the MWI being true mainly >> because you can come up with a toy model with MWI-style splitting that >> deals with Bell style experiments in a way that preserves locality >> > > No you can't. > >> but doesn't require hidden variables (see >> https://www.mdpi.com/1099-4300/21/1/87/htm ) but I see it as a sort of >> work in progress rather than a complete interpretation. >> > > They set up a contrast between realism and locality. > I wasn't linking to the paper for the argument about semantics (there doesn't seem to be any agreed-upon definition of 'realism' distinct from local realism in physics, from what I've seen) but rather for the toy model they provide in section 5 with the experimenters being duplicated when they try to measure the entangled particle. The point is that Alice is locally duplicated when she measures her particle, and Bob is locally duplicated when he measures his, but there is no need for the universe to decide which copy of Bob inhabits the same "world" as a given copy of Alice, or vice versa, until there's been time for signals limited by the speed of light to pass between them (or to a third observer). This is not the sort of "local realist" theory that Bell was trying to refute (one of the implicit assumptions in his derivation was that each spin measurement produces exactly one of two possible outcomes), but the dynamics of such splitting can be perfectly local, and it can still be true that if you randomly select one of the copies of an observer in a Bell type experiment, the probabilities that your randomly selected copy will see various outcomes can be made to match the QM predictions that violate Bell inequalities. As I said this can only be shown clearly in a toy model like the one in section 5 of that paper, but a number of physicists including David Deutsch do think that the full MWI would also respect a principle of "local splitting", although even if this can be shown in terms of the quantum formalism we still have the problem of deriving probabilities. The article on the MWI by Lev Vaidman at https://plato.stanford.edu/entries/qm-manyworlds/ discusses work on the notion of local splitting in the MWI: 'Deutsch 2012 claims to provide an alternative vindication of quantum locality using a quantum information framework. This approach started with Deutsch and Hayden 2000 analyzing the flow of quantum information using the Heisenberg picture. After discussions by Rubin 2001 and Deutsch 2002, Hewitt-Horsman and Vedral 2007 analyzed the uniqueness of the physical picture of the information flow. Timpson 2005 and Wallace and Timpson 2007 questioned the locality demonstration in this approach and the meaning of the locality claim was clarified in Deutsch 2012. Rubin 2011 suggested that this approach might provide a simpler route toward generalization of the MWI of quantum mechanics to the MWI of field theory. Recent works Raymond-Robichaud 2020, Kuypers and Deutsch 2021, Bédard 2021a, clarified the meaning of the Deutsch and Hayden proposal as an alternative local MWI which not only lacks action at a distance, but provides a set of local descriptions which completely describes the whole physical Universe. However, there is a complexity price. Bédard 2021b argues that “the descriptor of a single qubit has larger dimensionality than the Schrödinger state of the whole network or of the Universe!”' > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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