On 14 April 2015 at 00:42, Bruce Kellett <[email protected]> wrote:
> LizR wrote: > >> On 13 April 2015 at 17:16, Bruce Kellett <[email protected] >> <mailto:[email protected]>> wrote: >> >> LizR wrote: >> >> Does the MWI predict an infinite number of branches from any >> given measurement? I'm not sure (from FOR) that the MWI predicts >> branches at all, so much as differentiation within a continuum? >> Maybe you could expand on this. Why (to keep it simple) would a >> quantum experiment with two possible outcomes not reproduce the >> correct probabilities in the MWI? (Or is that a special case >> where it would?) >> >> No, MWI does not predict an infinite number of branches for any >> measurement. It predicts a number of branches equal to the number of >> possible distinct outcomes for the measurement. >> So how does the MWI deal with a measurement with a 3/4 probability of >> outcome 1 and a 1/4 probability of outcome 2? This was Larry Niven's >> objection to many worlds back around the time he wrote "All the myriad >> ways" and it seems to me that someone else would have noticed it in the >> intervening 50 years (or whatever) ! How come anyone takes MWI seriously if >> it's actually supposed to work like this? >> > > The expansion of the wave function in the einselected basis of the > measurement operator has certain coefficients. The probabilities are the > absolute magnitudes of these squared. That is the Born Rule. MWI advocates > try hard to derive the Born Rule from MWI, but they have failed to date. I > think they always will fail because, as has been pointed out, the separate > worlds of the MWI that are required before you can derive a probability > measure already assume the Born Rule. The argument is at best circular, and > probably even incoherent. > In an article published in the 60s (I think) Larry Niven pointed out that the MWI lead to the following situation - if you throw a dice you have 6 outcomes, i.e. 6 branches. But a loaded dice should favour (say) the branch where it lands on 6. Hence the MWI doesn't work. My reaction to this (when I first read it, probably several decades ago now) was that you only have 6 MACROSCOPIC outcomes - like derivations of the second law of thermodynamics, Niven's description of the system relies on microstates being indistinguishable *to us*. But once you take this into account there are more microstates ending with a 6 uppermost - and hence a lot more than 6 branches - the MWI again makes sense using branch counting, at least for non-quantum dice (I may not have known terms like microstates at the time, nor was it called the MWI, but that was basically what I thought). Can't the same be true of any quantum event? The essential requirement is that any quantum event leads to results which can be assigned a rational number, rather than an irrational one. This gives us a finite number of branches, and counting to get the probability. Or do quantum events lead to results with irrational numbered probabilities? > > I do not take MWI seriously. > > Yes, I get that :-) -- 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 post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
