On Sat, Feb 8, 2020 at 6:45 AM 'Brent Meeker' via Everything List < [email protected]> wrote:
> On 2/7/2020 3:07 AM, Bruce Kellett 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. > > > In practice one doesn't look for a measure on specific outcomes sequences > because you're testing a theory that only predicts one probability. You > flip coins to test whether P(heads)=0.5 which you can confirm or refute > without even knowing the sequences. > The point of Kent's argument is that in MWI where all outcomes occur, you will get the same set of sequences of results whatever the intrinsic probabilities might be. So you cannot use data from any one sequence to test a hypothesis about the probabilities: the sequences obtained are independent of any underlying probability measure. It might be that every sequence you get by flipping is in the form > HTHTHTHTHTHTHT... which would support P(H)=0.5. It would be a different > world than ours, possibly with different physics; but that would be a > matter of testing a different theory. > > One of the problems with MWI is that can't seem to explain probability > without sneaking in some equivalent concept. The obvious version of MWI > would be branch counting in which every measurement-like event produces an > enormous number of branches and the number of branches with spin UP > relative to the number with spin DOWN gives the odds of spin UP. A > meta-physical difficulty is the all the spin UP branches are identical and > so by Leibniz's identity of indiscernibles are really only one; but maybe > this inapplicable since the measure involves lots of environment that would > make it discernible. > That seems to be rather beside the point. 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/CAFxXSLQCM-7Z4dnHe-siCF9eA%2B5GjzCYMBX6oYeOnr0p0iHuMw%40mail.gmail.com.
