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MWI and special relativity

  1. Jun 26, 2010 #1
    Why is it that MWI's problem with special relativity is rarely discussed?

    From: http://plato.stanford.edu/entries/qm-everett/

    A final problem is that it is unclear how to formulate a splitting-worlds reading of Everett that is compatible with the constraints of special relativity. Suppose one opts for a strong sort of splitting, contrary to what Everett seems to suggest, where there are more physical systems after a typical measurement than before. If this involves somehow the creation of an entirely new universe (a complete copy of spacetime with an event structure, say) then when is the new universe created? One problem is in giving a frame-independent description of the creation event in the original universe, another is in making sense in relativity of an event that creates a new spacetime when all events, including the creation event, are supposed to be characterized by the local features of a particular fixed spacetime.

    Those who favor a decoherence account of splitting worlds sometimes seem to imagine some sort of "unzipping" of spacetime that occurs along the forward light cone of the spacetime region that contains the measurement interaction. While decoherence effects can be expected to propagate along the forward light cone of the region that contains the interaction event between the measuring device and the object system, and while there is no problem describing the decoherence effects themselves in a way that is perfectly compatible with relativity, there is a problem in imagining that such a splitting process somehow physically copies the systems involved. A strong picture of spacetime somehow unzipping into connected spacetime regions along the forward light cone of the measurement event, would not be compatible with special relativity insofar as relativity presupposes that all events occur on the stage of Minkowski spacetime. And if we give up this assumption, then it is unclear what the rules are for compatibility with special relativity.

    Alternatively, one might imagine that there is only one non-branching spacetime but many, equally real, physical copies of the relevant systems being created by the splitting process. But then it is unclear how this might be compatible with the conservation laws associated with the symmetries of the Lorentz group; and insofar as conservation of energy is violated, the theory is strongly incompatible with special relativity. Of course, one might suggest giving up or modifying special relativity; but such a sacrifice would only be attractive if the benefits clearly outweighed the cost, and the cost of sacrificing relativity is high given its long track-record of empirical and explanatory success. If one takes seriously the option of giving up or changing relativity in order to accommodate one's favorite reading of Everett, then it is again unclear what the rules are for theory evaluation.

    What are the opponents and proponents opinions?
    I'm tired of hearing people say Bohm is a "ugly interpretation" because of the nonlocality, when infact MWI has a unresolved problem with relativity too.
    Last edited: Jun 26, 2010
  2. jcsd
  3. Jun 26, 2010 #2


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    By treating time in QM on an equal footing with space, one can solve both the MWI-relativity and Bohm-relativity problems at once:
  4. Jun 26, 2010 #3
    Nice I will pass this paper around to some physicists I know who know relativity 1000 times more than me and get back to you.
    What have your responses from other physicists been?

    Also let me know your views on probability in the other thread
  5. Jun 26, 2010 #4


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    Possibly because very few good physicists have been working on Everett's MWI, and most of the work they did was pretty bad, so they never got very far.

    I don't know, but in the alternative MWI that I mentioned in the other thread, there are infinitely many different ways to describe the universe (what Penrose calls "the Omnium") as consisting of "worlds". The decomposition into worlds is arbitrary, and none of them is any more right than the others. This is analogous to how every coordinate system on spacetime defines a way to slice spacetime into hypersurfaces that we can think of as "space, at different times". None of them is any more right than the others.

    I think this means that an event that can be described as point were worlds split can also be described as a point where nothing of that sort happens. A "branching point" is only a branching point given a specific basis for the Hilbert space. Each basis defines a set of "worlds". The worlds defined by the given basis should be thought of as different aspects of the physical system that QM describes. This is analogous to how a coordinate system defines a set of hypersurfaces that we can think of as "space, at different times", and how spacetime is the union of all those slices.

    I don't see how SR is a problem for this interpretation, but I agree that it appears to be a significant problem for the kind of MWI where worlds split from each other in an objective way at specific events. Maybe they never got around to investigating those issues properly because they had more important problems to solve, and never successfully worked them out, in particular the problem with probabilities.
    Last edited: Jun 26, 2010
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