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June 24, 2015 at 8:29 am #2386H. Dieter ZehParticipant
Shan suggested me for the Chair on Everett’s interpretation of QT, but, unfortunately, I will hardly be available during the first half of July. So I hope he will act as a Moderator himself during this time if required.
Let me make a few ´´moderating remarks´´ to begin with, however: IMO one should never discuss this interpretation in the sense of what one ´´can or cannot believe´´ or what one would like (I think nobody except some modern cosmologists LIKES Many Worlds), but rather in the sense of what the hypothetical assumption of globally valid unitarity (a global Schrödinger equation) WOULD (or could) mean. If this hypothesis does not lead to conflicts with observations (of course, it must lead to conflicts with traditional concepts – including those concerning local ´´facts´´ and ´´events´´), it would form a POSSIBLE solution to the problem of the interpretion of the empirically established formalism of QT – no matter what you are ready to believe or to regard as real.
Most participants of a forum like this may instead prefer to study possible modifications of QT that would solve the measurement problem in a certain (traditional?) sense. There are many kinds of such proposals (in spite of many no-go theorems); so I don’t see how one could make any progress in this way without any quite novel empirical support (which may then simultaneously falsify Everett!).
In particular, an objection like ´´I don’t believe that the Schrödinger equation applies to the universe´´ reminds me of the early days of decoherence, when everybody kept telling me that ´´QM does not apply to the environment´´. In fact, decoherence and Everett are both extrapolations of the validity of the quantum mechanical superposition principle. (They could later be verified in the case of decoherence.)
Since I don’t have any new arguments to offer, let me here refer to Sect. 4 of my ´´Strange Story of Particles and Waves´´at arxiv:1304.1003 (I have just posted version #13 – you may entirely skip the introductory first two sections in order to come to the point!). Sect. 4 of my Bell paper for the workshop of 2014 (see Most Viewed) may also be helpful to understand my point of view. Please note my distinction (at the end of Sect. 2 of this Bell paper) between DeWitt/Deutsch’s Many Worlds (in terms of trajectories) and the original Everett (in terms of partial waves – similar to collapse theories) – even though Everett could not yet argue quite consistently without the concept of decoherence. Some further aspects are discussed in my ´´The role of the observer in the Everett interpretation´´ (arxiv:1211.0196).
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