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From my layman's perspective, it feels like the many worlds interpretation is invoked out of the inability to explain why one observation occurs out of many possibilities. Given no explanation why one particular observation occurs out of many, we say all events took place... so there's no need to explain why 1 particular event happened anymore.

To me, it looks like this doesn't fix anything, just sweeps it under the rug... there's still the question "why did I observe this particular event when I could have observed multiple others"... ie: "why am I in this world instead of another" So the need to explain the "specificity" of our experience is still there. If there are multiple versions of me, the question still exists, "why am I this version?".

Is my impression false? Is there more to the many-worlds interpretation than I'm thinking?

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    $\begingroup$ Yes your impression is false. Many-world explains the specificity of our experience as due to our indexical uncertainty in the quantum wave function. There is nothing mysterious here. If there are two copies of you, then there are two version of you asking "why me?" in the exact same sense that you can ask "why is an apple an apple and not an orange" in an ordinary non-many-worlds universe. Of course the reason an apple is an applie and not an orange is not a particularly difficult or deep question. $\endgroup$ – user1247 Feb 16 '16 at 15:47
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Before the MWI, there only used to be wave-function collapse models, which had a problem in the sense that they would require a non-unitary measurement operator in order to make the wave-function collapse into a particular eigenstate. However, there was a problem, that is, time evolution is determined by unitary operator, and no combination of unitary operators can lead to a the non-unitary measurement operator. MWI had a means to tackle this problem by suggesting that wave-function collapse doesn't take place, rather reality is presented as a branched tree with all possible outcomes realized. Thus the problem is well-motivated, although it's solution may be difficult to accept or test. The quantum to classical transition in this model is realized by utilizing decoherence approaches.

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Your impression is false.

For your defense, the name "Many World Interpretation" is misleading. It seems to means the theory is "parallel worlds" explaining something (here quantum randomness).

Actually, here the theory is quantum mechanics, that explains outcomes of countless experiments. Everett has shown that "Collapse of wavefunction" was unnecessary. "Parallel worlds" are a consequence of this theory, not its premise.

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  • $\begingroup$ Down vote due to uninformed grief against MWI... $\endgroup$ – ch7kor Feb 16 '16 at 17:08
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"why am I in this world instead of another"

The answer is that you are in all of them, along with the various outcomes of the measurement. And they are all asking this question.

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No, I think you are kind of close there. In actuality it's even a little worse than that. The WMI stems from an outright false analysis of the measurement process as requiring some form of memory possessing special "observer" which is embodied with such miraculous capabilities as (this is literally from Everett's paper) "the machine has perceived A" or "the machine is aware of A"... which sounds like a naive end run around saying "a human observer has perceived A" which, for whatever reason, seems to be important to him. No such thing is ever necessary for a physical "measurement" to take place. The interaction of a local quantum system with the physical vacuum is perfectly enough to produce a lasting record. A wonderful example of that would be CMB photons, which are the lasting record of quantum events that happened just 300,000 years after the big bang. Except for scattering on interstellar gas and dust every one of them marks the optical transition of a hydrogen or helium atom from a higher to a lower quantum state.

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    $\begingroup$ (1/2) I am not the downvoter, but for any modern proponents of MWI of which I am aware (I can't say what Everett specifically thought) this seems almost exactly backward. The logical progression is the following: if we take the wavefunction as physically real, meaning that for example an electron in a position superposition really is in some sense in either/both/neither locations, then this should be possible for an arbitrarily large macroscopic object as well, and in particular a person. $\endgroup$ – Rococo Feb 16 '16 at 17:07
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    $\begingroup$ (2/2) Of course, in the latter case there is a decoherence time that is essentially instantaneous, but an extremely complex macroscopic superposition is still a superposition nonetheless. In this sense, MWI is an attempt to treat systems that are considered to be "observers" exactly the same as any other quantum mechanical system. $\endgroup$ – Rococo Feb 16 '16 at 17:07
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    $\begingroup$ You said to me in other discussion that "Copenhagen 1925/1927 can possibly be seen as a crude subset of what we are using today, but the basic ideas are all there". In similar sense, I believe that MWI is considered by its proponents differently than in the original paper. For example, some may think "Many" as a countable number, some may think it as uncountable. Some (for example I) may just use term "Many worlds" to highlight that there is no evidence of non-unitary wave function evolution and that the observer is no different, (related to what @Rococo said). (I am not the downvoter either!) $\endgroup$ – Mikael Kuisma Feb 16 '16 at 17:29
  • $\begingroup$ @Rococo: I am simply citing from Everett's paper which I have right here. Don't blame me for what he wrote. I am not sure why anyone would take the wavefunction "for real" anymore than they would take a Newtonian force "for real". Both are descriptions of reality on different levels, none of them is reality itself. An electron is not in a superposition. A quantum field is. That's a totally different ontology and important because the electron is not an object in the proper theory but just a property of an object, which removes all the quantum mysticism from the picture. $\endgroup$ – CuriousOne Feb 16 '16 at 20:52
  • $\begingroup$ @Rococo: The "extremely complex superposition" is, in most cases, one or a few photons that are leaving at the speed of light as soon as you are leaving the mean field. People have gotten themselves into a frenzy about what a quantum experiment is. It's usually a rather simple affair where massive fields (baryons, usually atoms) transfers energy to massless ones (the em field, i.e. photons). The photons leave the crime scene at the speed of light which leads to the scale separation that one needs to freeze the local state. No magic. $\endgroup$ – CuriousOne Feb 16 '16 at 20:55

protected by Qmechanic Feb 16 '16 at 15:40

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