Parallel Universes

2 Replies to “Parallel Universes”

1. This might just be me, but as best I can tell these results of Wallace and Saunders (see here and especially this review and references therein) that are being touted in the above articles are way more philosophical than physical… even by the standards of the interpretation of quantum mechanics community! [And let me hasten to add I’m a guy who actually enjoys and respects the whole debate on interpretations of quantum mechanics. 🙂 ]
   Correct me if I’m wrong, but Wallace and Saunders new results are in fact philosophical arguments about the meaning of “emergence” and “experience.” These philosophical arguments are then used say one can reject as philosophically incoherent the 2 most common objections to the notion that Many Worlds explains Born’s rule for probabilities and resolves the measurement problem. That is:

   (Long-Standing Objection 1) Decoherence only solves the preferred basis problem once you define what systems are interacting and what their interacting Hamiltonian (and also once you make certain assumptions about the initial state to allow for stable classicality rather than oscillations between having coherence and not)
   (Wallace and Saunders Resolution 1) Nope. It’s all good. It’s fine for systems to be “emergent”, especially as it’s damn hard to think of how to define objects intrinsically.
   (Long-Standing Objection 2) As nice as it would be to believe that counting the Many Worlds gives an objective basis for good ol’ frequentist probability (i.e., there is an actual ensemble of many worlds so the usual presupposition of drawing at random from a big ensemble can be the objectively true and not just a convenient fiction), there is no reason to believe that conscious observers in a Many Worlds universe would experience this branching as frequentist probability.
   (Wallace and Saunders Resolution 2) Well, I don’t understand Wallace’s and Saunder’s argument but it seems to be that they argue that under certain plausible definitions of what would constitute an idealized rational, conscious observer, they would indeed rationalize the branching as probability. (This application of decision theory to Many Worlds in particular is the culmination of a program started by David Deutsch a long time ago… and the news hook for articles claiming Wallace and Saunders have proven Deutsch right.)

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2. “I keep wondering how I can find my way to a parallel universe where I don’t spend my time reading those articles . . .”
   But that’s the point Dave, you already are there — relax. 🙂

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