On Tue, Feb 11, 2020 at 11:16 PM Bruno Marchal <[email protected]> wrote:
> On 7 Feb 2020, at 12:07, Bruce Kellett <[email protected]> wrote: > > On Fri, Feb 7, 2020 at 9:54 PM Lawrence Crowell < > [email protected]> wrote: > >> On Thursday, February 6, 2020 at 10:59:27 PM UTC-6, Bruce wrote: >>> >>> >>> This argument from Kent completely destroys Everett's attempt to derive >>> the Born rule from his many-worlds approach to quantum mechanics. In fact, >>> it totally undermines most attempts to derive the Born rule from any >>> branching theory, and undermines attempts to justify ignoring branches on >>> which the Born rule weights are disconfirmed. In the many-worlds case, >>> recall, all observers are aware that other observers with other data must >>> exist, but each is led to construct a spurious measure of importance that >>> favours their own observations against the others', and this leads to an >>> obvious absurdity. In the one-world case, observers treat what actually >>> happened as important, and ignore what didn't happen: this doesn't lead to >>> the same difficulty. >>> >>> Bruce >>> >> >> This appears to argue that observers in a branch are limited in their >> ability to take the results of their branch as a Bayesian prior. This >> limitation occurs for the coin flip case where some combinations have a >> high degree of structure. Say all heads or a repeated sequence of heads and >> tails with some structure, or apparent structure. For large N though these >> are a diminishing measure. >> > > I don't think you have fully come to terms with Kent's argument. How do > you determine the measure on the observed outcomes? The argument that such > 'outlier' sequences are of small measure fails at the first hurdle, because > all sequences have equal measure -- all are equally likely. In fact, all > occur with unit probability in MWI. > > > Each individual sequence of head/tail would also occur with probability, > in the corresponding WM scenario, and in the coin tossing experience. > OK. So what relevance does that comment have? In the MWI, what you describe is what has motivated the introduction of a > frequency operator, and that is the right thing to do in QM. > What frequency operator? The trouble with any attempt to pretend that the number of copies of any branch is related to the coefficient or weight of that brranch in the superposition is that any such operator violates unitarity. It would, in fact be nothing more than the von Neumann projection operator in disguise. You are not going to rescue Everett in that way...... > I think you might confuse the first person and the third person points of > view, in the WM-scenario and in the MWI (which is coherent with your > non-mechanist stance). > That is your favourite rejoinder to any argument that you do not like. It is just a meaningless straw man -- there is no relevant 1p/3p distinction in operation here. From the 3p perspective, with unitary evolution (Everett), all sequences of results occur with unit probability: the sequences do not depend on the weights, so the sequences are the same whatever the initial state. From the 1p perspective, an individual sees one of these sequences when he performs repeated trials. The probabilities that he might infer from the data cannot reflect the branch weights -- because the sequences are independent of the branch weights. The theory has failed. 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLT9_t0g53ByCkMQR%3DWS3jADEW_mwmrrWKd_zz_0zWoRAg%40mail.gmail.com.
