then the quantum collapse must correspond to a real physical process.
Not according to Many Worlds. Waveform collapse has never been experimentally observed. Every observation is as would be predicted by simple decoherence.
For the most part, but violations of Bell’s inequality can also be explained by action at a distance. The impossibility result in this paper is nevertheless really old. For example, conditional swap tests are well studied and incompatible with any statistical interpretation of the wave function (in the same slightly stronger sense of this paper). There are experimental results that invalidate these interpretations quite directly. The view of the wavefunction as a reflection of statistical ignorance has not been tenable for a very long time. The interesting thing here is the non-trivial attention part.
I think there is some confusion going on here. Bell’s theorem tells you that local hidden variables cannot reproduce quantum mechanics, i.e. that the uncertainty in quantum outcomes is not like the uncertainty of a coin toss in that “if you hit a coin in the same place with the same force, it does the same thing,” as Persi Diaconis said. This does not settle the question of whether wavefunction collapse is a physically real event or just a calculational tool that lets you predict what nature will do with some accuracy without giving you any hint into how it is that nature is doing it.
The paper shows that this “quantum-state-as-statistical-calculational-tool” approach is inconsistent with a few reasonable assumptions.
Also, Many Worlds does tell you that quantum collapse corresponds to a physically real process, namely the usual linear evolution rule. It tells you that the “extra” measurement phenomenon postulated by other interpretations is not really there. So none of this is in conflict with MW; in fact, it adds credibility beyond Bell’s theorem.
I don’t consider decoherence the same thing as wave-form collapse. Wave-form collapse seems to imply that it suddenly collapses into an eigenstate, rather than just slowly morphs from one blob to two.
I am treating “wavefunction collapse” as a generic term for “whatever it is that causes ‘me’ to see the outcomes that I do.” Orthodox views treat this wavefunction collapse as an extra “measurement” rule and then mumble around the issue of what exactly constitutes a measurement, usually trying to say that none of it is ‘physically real’ so such questions are moot. Many Worlds treats the wavefunction collapse as a parochial artifact of having been in a particular Everett branch and figuring that out by becoming entangled with some particular other particles.
But I agree that if one defines wavefunction collapse to be only that sort of instantaneous updating to only one particular state that the orthodox views take, then Many Worlds language just does away with it all together. I prefer to use the same term for both phenomena because I have found that it helps people who are uneasy with MW to realize that it’s not all that weird.
In my view, the result of the linked paper weakens the orthodox position of denying that “wavefunction collapse” is physically real.
This result is much stronger than Bell’s theorem. I don’t understand all the details but it seems to apply in a much broader range of contexts. ETA: To be more clear, Bell’s Theorem applies to entangled particles. This doesn’t seem to require entanglement as long as there’s not too much pathological behavior.
Wasn’t this already proven by Bell’s Theorem?
Not according to Many Worlds. Waveform collapse has never been experimentally observed. Every observation is as would be predicted by simple decoherence.
For the most part, but violations of Bell’s inequality can also be explained by action at a distance. The impossibility result in this paper is nevertheless really old. For example, conditional swap tests are well studied and incompatible with any statistical interpretation of the wave function (in the same slightly stronger sense of this paper). There are experimental results that invalidate these interpretations quite directly. The view of the wavefunction as a reflection of statistical ignorance has not been tenable for a very long time. The interesting thing here is the non-trivial attention part.
I think there is some confusion going on here. Bell’s theorem tells you that local hidden variables cannot reproduce quantum mechanics, i.e. that the uncertainty in quantum outcomes is not like the uncertainty of a coin toss in that “if you hit a coin in the same place with the same force, it does the same thing,” as Persi Diaconis said. This does not settle the question of whether wavefunction collapse is a physically real event or just a calculational tool that lets you predict what nature will do with some accuracy without giving you any hint into how it is that nature is doing it.
The paper shows that this “quantum-state-as-statistical-calculational-tool” approach is inconsistent with a few reasonable assumptions.
Also, Many Worlds does tell you that quantum collapse corresponds to a physically real process, namely the usual linear evolution rule. It tells you that the “extra” measurement phenomenon postulated by other interpretations is not really there. So none of this is in conflict with MW; in fact, it adds credibility beyond Bell’s theorem.
I don’t consider decoherence the same thing as wave-form collapse. Wave-form collapse seems to imply that it suddenly collapses into an eigenstate, rather than just slowly morphs from one blob to two.
I am treating “wavefunction collapse” as a generic term for “whatever it is that causes ‘me’ to see the outcomes that I do.” Orthodox views treat this wavefunction collapse as an extra “measurement” rule and then mumble around the issue of what exactly constitutes a measurement, usually trying to say that none of it is ‘physically real’ so such questions are moot. Many Worlds treats the wavefunction collapse as a parochial artifact of having been in a particular Everett branch and figuring that out by becoming entangled with some particular other particles.
But I agree that if one defines wavefunction collapse to be only that sort of instantaneous updating to only one particular state that the orthodox views take, then Many Worlds language just does away with it all together. I prefer to use the same term for both phenomena because I have found that it helps people who are uneasy with MW to realize that it’s not all that weird.
In my view, the result of the linked paper weakens the orthodox position of denying that “wavefunction collapse” is physically real.
This result is much stronger than Bell’s theorem. I don’t understand all the details but it seems to apply in a much broader range of contexts. ETA: To be more clear, Bell’s Theorem applies to entangled particles. This doesn’t seem to require entanglement as long as there’s not too much pathological behavior.