I came across a paper that claims to prove that the Many Worlds interpretation is invalid by applying weak measurements.

The paper can be found here: http://philsci-archive.pitt.edu/9494/1/aa-mwi_further_v9.pdf

Can anyone tell me whether or not this claim holds any water?

  • $\begingroup$ Has the paper been published? $\endgroup$ – Qmechanic Jan 1 '13 at 17:43
  • $\begingroup$ I have absolutely no idea. $\endgroup$ – userrr Jan 1 '13 at 17:59
  • $\begingroup$ I searched on arXiv and INSPIRE and couldn't find any mention of this paper. (Here are some other publications by apparently the same author) $\endgroup$ – David Z Jan 1 '13 at 20:24
  • $\begingroup$ Yes he produces A LOT of papers, a quick google.scholar search reveals that, but I really don't understand his objection in this paper I linked and I find it hard to believe that it has been overlooked for so long if it indeed invalidates MWI $\endgroup$ – userrr Jan 1 '13 at 21:52

I think this comes from a misconception of MWI. That is reducing Everett Theory to a vision of "parallel worlds" that "branches" when a measurement is done.

A better way to understand MWI is to see the wavefunction as real and without collapsing. All outcome of a measurement are included in the single wavefunction, and they still interfere. Decoherence theory explains why for statistical reason this interference can be neglected and we go back to classic behavior. And in this case effectively all looks like branched parallel worlds.

If you take great care, with the protective measurement, of keeping the coherence, then you have to stick to the global wavefunction and you can't think of quantum theory as "parallel world that branches".

  • $\begingroup$ This was my initial thought too, but lateron in the paper he explicitly states that this (whatever it is) applies regardless of which Many Worlds interpretation. He even mentions David Wallace's version, which is the one you are describing. $\endgroup$ – userrr Jan 2 '13 at 19:26
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    $\begingroup$ Yes, he starts describing it the correct way, then reason with the oversimplified way. $\endgroup$ – MatthieuW Jan 3 '13 at 9:24

As far as I can see, they are simply arguing this: if one component of the wave function, namely the one that is actually measured at first, is in this world, then it must be that all other components are also. No doubt an MWI fan could argue against this, because the reality of this world is just as debatable as the reality of the many. This is philosophy, not physics.

There are alternative views, which disagree with most MWI and anti-MWI arguments. Many physicists prefer an anti-realist view of QM, but it is difficult to find philosophers who don't wince at a physicist's idea of what anti-realism is about. Most physicists are simply thinking that measurement is paramount, and our classical picture of an a priori world disagrees with experiment. But for true anti-realism one requires more: that the observer's world is itself defined by the observer's choices and experience.

So there are three basic options here: 1. many concrete worlds (MWI) 2. one concrete world (eg. Bohm) 3. no concrete worlds (anti-realism). In the end, since everyone is talking about the same mathematical QM there is no way to resolve the debate physically, without constructing a new theory that relies on one and only one of the above options.

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    $\begingroup$ I still don't understand the argument against MWI at all? I am well aware of QM interpretations, but I fail to grasp what the author is saying about how measuring one component of the WF rules out other worlds? Why must all the other components be here too, what? I'm confused $\endgroup$ – userrr Jan 2 '13 at 12:05

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