On Sun, Feb 9, 2020 at 2:33 PM 'Brent Meeker' via Everything List < everything-list@googlegroups.com> wrote:
> On 2/8/2020 6:53 PM, Bruce Kellett wrote: > > But it is implicit, or even explicit in Bruno's model. It's also >> consistent with Barbour's model. >> > > It can be consistent with as many models as you like. It is simply not > Everettian QM. It is some ad hoc concoction that totally undermines the > point that was the basic attraction to Everett in the first place. People > like Carroll and Wallace laud Everett because they see it as quantum > mechanics in the raw -- the Schrodinger equation without extraneous > additional assumptions. You seem bent on adding all these extraneous > assumption, most of which are not even consistent with the Schrodinger > equation, and still claim that you are talking about the same model. > > > I think Everett assumed Born's rule as a kind of weight attached to each > branch; so there was only one branch per result and the Born rule was > assumed. > This is close to what Everett did. But Kent also considers a toy universe of this sort. As long as there is only one branch per result, weights such as those Everett proposed are purely decorative -- they fulfil no functional role and the arguments against the "no weight' multiverse goes through unchanged: weights of the sort Everett proposed do not solve the problem of probability, not do they make the theory scientific in the sense that data can be used to test he theory. Kent also considers a toy universe more along the lines of the one you propose. When an experiment is performed, the universe is deleted, and successor universes created in which the outcomes are treated differently: for example, there are more new universe created for some results than for others. The number of such successors may be large, or even infinite. In the absence of data to give probability estimates, the inhabitants have no way to detect that the outcomes are being treated differently, or how many successor universes are being created. However, after N runs, there will be a large number of branches. Kent is not convinced that this is enough, but he feels that it might be a step in the right direction. "If we could argue, perhaps using some form of anthropic reasoning, that there is an equal chance of finding oneself in any one of the branches, then the chance of finding oneself in a branch in which one concludes that the branch weights are close to the number of identical branches created for each result would be very close to one." He concludes: "It seems hard to make this argument rigorous. In particular, the notion of 'chance of finding oneself' in a particular branch doesn't seem easy to define properly. Still, we have an arguably natural measure on branches, the counting measure, according to which most of the inhabitants will arrive at (close to) the right theory os branch weights. That might perhaps be progress." The trouble, of course, is that any such theory with multiple replicated branches for each experimental result goes far beyond Everett's ideas, and is certainly not a natural extension of the Schrodinger equation. Other theories about the origin of weights and probabilities in Many-worlds theory seem all to fall foul of Zurek's observation that such arguments are inherently circular: they rely on distinguishable observers in distinguishable branches, and such can arise only through the processes of decoherence and the approximate diagonalization of the density matrix. And, of course, such arguments all depend on the notion that small amplitudes correspond to low probabilities -- which is just the Born rule. 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 everything-list+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CAFxXSLTTRkjZz2X62%3DSfiK3M4XuaJkyiuNA1P8%3DxciTs0m0O%2Bg%40mail.gmail.com.
