@MoreAnonymous I don't remember any questions about interpretations of the top of my head... So we'll just have to wait and see... We have decided that questions on quantum information are on topic, if that helps?

@Mithrandir24601 to be fair measurement is a one of the tags. And the question is if Copenhagen + quasi classical apparatus circumvents a (possible) objection.

I'm guessing this is a borderline case of some sort ... And would automatically depend on the answeer the question receives? The usual non importance given to interpretations is tdue to hat what one can predict so can the other.

If you have an interpretation that bypasses that I would go far as to say it is no longer an interpretation ? To be fair I may be jumping the gun and the culptrit might be quasi classical apparatus ?? (But Im sure not all interpretations will be on board with that)?

@MoreAnonymous So, having carefully read and thought about it, I think it's a really interesting question, although I still don't know whether people will want that sort of question to be on topic here or not. I have a couple of ways I could go about seeing if I could answer it -

one (essentially your 'fourth way') would give some maths, but might not be satisfying from the interpretation point of view, as it's essentially just moving the point of wavefunction collapse. The other would essentially be saying 'Copenhagen is rubbish and we need to use more modern physics to deal with this'

I see ... If you ur of the opinion the fourth way does workout ... Then that would be enough to convert to that point of view :P But I'd also like to know a physical system where we know that the fourth way definitely does indeed work out (and the third does not)

@Mithrandir24601 Thank you for calling the question "interesting." I'm not sure if your aware of the fiasco that happened due to this question? But it did definitely propelled me to write the details and make it self contained

@MoreAnonymous there was a fiasco? I never knew, no

Well if you look at the flags for closing on the question saying it is/was unclear thats just an early indicator (thats just the tip of the iceberg) ... If u wanna know why the titanic sunk I can provide a link which show the extreme

And no I am not proud of it :/

@MoreAnonymous Well... It works out to some extent, but have you ever heard of Wigner's friend? There's a big question (in the Copenhagen interpretation) about where exactly measurement 'occurs', so if I gave an answer saying 'the fourth way is right', all I'd be doing would be shifting the point of actual measurement collapse, seemingly arbitrarily and possibly(?) defeating the purpose

@MoreAnonymous On physics? I can't see the flags, but that's a loong comment-chain

@Mithrandir24601 I am aware of Wigner's friend ... However the question clearly states if there is a physical situation the fourth way applies to and the third does not

@Mithrandir24601 yes ... it is a looonngg one :/ ... If u want I'll give u the link to save u time from investigative journalism ...

I'm pretty sure it paints a terrible picture of me ....

But I wish I had the wisdom to write such a massive post rather than just linking stuff

@MoreAnonymous Ahh, sure, this leads into the other method that I'd use to answer it, which I'm not even sure if it'd even work and would likely end up in me saying that 'Copenhagen is a bit rubbish in reality'

To be fair on the community I think I misunderstand someone else's position and thats when things start to go south ... And its not my fault in such a nuanced topic if I did ? Let alone know if my own objection has/had any kind of weight

@Mithrandir24601 I think u could just end your answer with an anti-climatic "Copenhagen is a bit rubbish in reality"

So, it would essentially be measurement device ('fourth way out') followed by some (properly applied) decoherence or equivalent

Or a series of increasingly weak interactions would do it

(OK, that's sort of the same thing, but in a different way)

@MoreAnonymous I might do :P

I see ... Also to be fair there is a link in the basic premise of my objection where the user is precisely asking for why cant the measurement be a unitary transformation .. .That question needs a new answer ....

@Mithrandir24601 if you go ffor anti-climatic ending then I will personally downvote and flag any followup question along the lines of why is "Copenhagen is a bit rubbish in reality"?

:P

@MoreAnonymous Yeah... One problem in QM: What is measurement? Another: Why do people always use states instead of density matrices when referring to measurement? Another: What's the difference between a (tossed) coin yet to be observed and a quantum state that's been measured but not observed?

To be frank if you can answer the last one then u probably have answered the previous 2