From: jos.bergervoet@nxp.com   
      
   On 19/06/17 9:31 PM, Stefan Ram wrote:   
   > Michael Cole  writes:   
   >> In my humble opinion, the \_fatal flaw_/ of many worlds is   
   >> that it is metaphysics, not science.  That interpretation of QM is   
   >> untestable. It is fun to think about, but it is a question of philosophy   
   >> that is outside the province of science.   
   >   
   >    Is the MWI a different theory ("fifth axiom") or just   
   >    an interpretation ("an irrelevant adornment")?   
   >   
   >    I'd say the MWI is not a additional "fifth axiom",   
   >    but rather a /removal/ of some rules!   
      
   So wouldn't that make it a different theory?   
      
   >    Traditional QM goes something like:   
   >   
   > D0 - A system A is described by a space H_A.   
   > D1 - States are vectors (rays) of this space.   
   > D2 - They evolve according to a unitary time evolution.   
   > D3 - Composite systems are described by tensor products.   
   >   
   > M0 - Observables are represented by operators.   
   > M1 - The Born probability rule gives probabilites for outcomes.   
   > M2 - After a measurement, we observe one of those outcomes.   
   >   
   >    But D2 and M2 are contradicting: When states evolve   
   >    unitarily, there is no need for M1 and M2. Which processes   
   >    are deemed "measurements", so that we have to use M2 and M2   
   >    for their evolution, and which aren't, so that we have to   
   >    use D2 for their evolution?   
      
   Exactly. We can define what an "interaction" between two parts of a   
   system is, but when exactly is an interaction *not* a measurement?   
   I never saw a consistent way to define the difference so they must   
   be two names for the same thing.   
      
   What you call "traditional QM" has the problem that it is ill-defined.   
   (THe term "measurement" is meaningless without a definition and all   
   attempted definitions are circular, or worse.   
      
   >    To get rid of this over-determination of physical processes   
   >    by two different systems of rules, Everett removed M0-M2.   
      
   I would agree with you that this is the essence of MWI, but others   
   insist that worlds should be "splitting off" in MWI, which is just   
   as contradictory to unitary evolution than worlds "collapsing" into   
   one. (Although usually neither of those two processes is described   
   by any rigorous mathematical time-evolution, so we remain guessing   
   what is actually meant..)   
      
   >    This is not so much like an addition of an interpretation,   
   >    it is more like a /removal/ of some interpretations!   
   >   
   >    So, MWI is just D0-D3 without M0-M2.   
      
   Perhaps MWI is indeed just QM without the additional inconsistent   
   and ill-defined additions (euphemistically called "interpretations")   
   so it is QM *without* interpretation.   
      
   But one could also argue that MWI goes further: QM with a mechanism   
   worked out to get an emerging classical behavior on macroscopic scale.   
   That of course would involve developments after Everett's work (the   
   effect of decoherence and the special properties of pointer states).   
      
   There are many ways to define what "many worlds" means. (likewise,   
   there also were many versions of the Copenhagen interpretation.)   
      
   --   
   Jos   
      
   --- SoupGate-Win32 v1.05   
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