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Lately, I've tried to use Google in an attempt to understand the concepts of wave function collapse and quantum decoherence. So far though, things sound a bit contradictory. If the the actual existence of collapse is uncertain and the proponents of decoherence admit they haven't resolved the measurement problem, what then...if anything is on the horizon?

Qmechanic
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Marshall O'Donovan
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    This is so broad and opinion-based that I don't think it's likely to generate anything useful. People don't necessarily agree on whether or not there really is a measurement problem. Among people who think there is one, there's not necessarily agreement on what it is. Even among people who agree on what it is, there isn't agreement on whether decoherence solves it. –  Jan 22 '20 at 17:56
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    related: https://physics.stackexchange.com/q/295527/ –  Jan 22 '20 at 18:00
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    The measurement problem is like that embarrassing family member that everyone pretends to ignore. Polite physicists don't mention it, and tend to assume anyone working on it has nothing better to do. – John Rennie Jan 22 '20 at 18:01
  • @Marshall O'Donovan - maybe the horizon expands every time we reach it. Would you mind adding a bit more of what you're thinking - it's hard to guess accurately. For example where did you read or why do you think that collapse is uncertain? – Pagoda Jan 22 '20 at 20:44
  • In my view the wave function does not describe an individual system - or cat. It describes an ensemble of systems. This the essence of the ensemble interpretation. Each measurement is a draw from the ensemble. A beautiful illustration can be found at web.archive.org/web/20110114170600/http://www.hitachi.com. /rd/research/em/doubleslit.html – my2cts Jan 22 '20 at 22:59
  • Thank you Mr. Rennie. I absolutely agree with your comment about "polite physicists," if the measurement problem is ever resolved...it will be because more physicists enlist in the struggle. The polite physicists will not fight because "consciousness" has entered their realm and they just don't know what to think about it. – Marshall O'Donovan Jan 25 '20 at 17:17
  • Hello Pagoda, thanks for the comment. I read that Werner Heisenberg himself remained unspecific about the "collapse" and felt that it should not be considered a physical process. He later stated... that if the wave function is indeed real, it's collapse must be accepted as an intrinsic part of the process. – Marshall O'Donovan Jan 25 '20 at 17:38
  • Qmechanic, thanks for your response, just one more thing. The double slit experiment proved that light exhibits a wave/particle duality. During this experiment and upon observation of it's process...the wave function will and does collapse. There is no doubt about that and it's the principle reason for the awareness of "the measurement problem." – Marshall O'Donovan Jan 31 '20 at 21:55

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Your initial discoveries are correct, and already show a better understanding of this than you see in most presentations. That is, existence of collapse is uncertain, and decoherence does not on its own solve the problem.

The literature is huge and most of it is, I am sorry to say, of little value, so beware!

A paper worth the read is the one by Frauchiger and Renner, Nature Communications 2018. https://doi.org/10.1038/s41467-018-05739-8 But even with this one you should beware. The title of the paper is a bit over-stated I would say. It is not so hard to give a consistent description of the thought-experiment they describe, but at least they do give a survey of some approaches, and a reasonable list of references. The weakness of their paper is that they are a bit loose with terminology such as "rational agent" I would say.

Andrew Steane
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