I saw this:
http://aeon.co/essays/is-the-many-worlds-hypothesis-just-a-fantasy
In this article the author raises a number of intriguing philosophical challenges against the so-called "many worlds" interpretations of quantum theory. In particular, the author appears to argue that it is "philosophically and logically incoherent", suggesting that it must contain one or more logically contradictory statements. However, is there actually such a statement? Looking over the objections, I'm not entirely sure I find them convincing, but would be curious to hear from philosophy experts as to exactly whether or not these hold any ground. I've examined quantum mechanics quite a bit, and am not sure that the argument given here properly characterizes it - but nonetheless, I also am open to being totally, and completely wrong, and that's why I want to ask about this. And I'm posting it on this forum because I'd like to hear it from a philosophy pov, not physics, since that's what the author is challenging it upon.
In particular, the points he raises against the many worlds theory are:
The time when the "worlds" split apart is not well-defined - it relies on the same vague notion as Copenhagenism does for the collapse, namely "when a 'measurement' occurs" which is a concept from intuitive natural language, not formal, rigorous mathematics. However I'm not sure this is a fair characterization. The "splitting of worlds" is nothing else than the uncompromising application of the Schrodinger equation to everything, as much as possible. When a particle collides with a barrier in a tunneling event, there is a splitting - this requires no vagary, it can be seen right in a direct simulation. When these superposed waves collide with detectors that read which side the particle went through, then the detector system is predicted to form a superposition by the same equation applied to the combined particle + detector system as a whole. The "branches" come from that alone, the expansion of superposition due to the linear nature of the equation, not some ill-defined process. The wave is in a very high-dimensional space, so we have no real hope of simulating this on a computer, however. Granted that as it's a smooth evolution, there is not a precise instant where the branches form, but it, I'd believe, has the same qualitative character as the initial splitting of the particle.
The formation of many worlds undermines the concept of "I", namely that the bifurcation of a human under the Schrodinger evolution renders it meaningless. How exactly it does this is not clear from the author's description. To me though, it seems, why can't we just imagine the different branches to be literally different people? If they diverged soon after one's birth, then they could be considered as similar to twins separated at birth, arguably rather different people altogether. But perhaps someone here more well-versed in this issue could actually elucidate this in a logically well-parsed-out manner.
The interpretation has no way to prove or refute its truth, there is no way to detect the "parallel universes". However, this seems to be a problem that plagues all quantum interpretations - we do not, with the framework of existing quantum theory, have any way to tell them apart, because the actual predictive theory of quantum mechanics is the math, which gives one tool - the Born rule - to connect the wave functions to the results of experiments, and that is shared by essentially all interpretations. The one exception may be the "objective collapse" interpretations as these actually do in fact predict a slightly altered statistics (but then again one can also fudge them so as to make this undetectable in light of new data coming in - but I'd think that at some point that would have to necessarily degenerate to special pleading and we'd have to say it's less likely this interpretation is true.). Any actual resolution would seem contingent upon discovering something beyond quantum mechanics that sets one interpretation as the correct one (while also rendering quantum mechanics only an approximate theory to something deeper) - which is exactly what the advocates that the author dismisses argue.
There's others too, but I think I'll stop here. So I'm curious: do these problems pose an intractable philosophical challenge that renders MWI useless? The other thing I notice is that he seems to rely heavily on popular-culture and layman characterizations of the theory, instead of the actual theory itself.
If anything, to me the big problem with MWI is the one which inspired it: the problem of reconciling the unicity of our observations of the universe and experimental measurements with the inherent pluralism of the Schrodinger equation. In particular, given that it involves a bifurcation of the observer as per Schrodinger, it is not clear why our train of subjective experience must follow only one path, and furthermore, what determines which path it follows (e.g. why does this coincide with the Born rule statistics?).
