[lmm]

Nonsense. Under the Copenhagen interpretation (which I do not personally subscribe to, but it is a legitimate interpretation and it has its defenders), when one particle interacts with another particle that's in a superposition, the result is that both particles are in an entangled superposition. Cat, Geiger counter and gunpowder can thus all be in an entangled superposition; one can argue that this is absurd, but Einstein also thought that the EPR experiment showed that quantum mechanics was absurd, and actually that result has been experimentally verified.

[thisrod]

That takes me back to a slide in my physics honours talk.

1935: Einstein, Podolsky and Rosen show that quantum mechanics doesn't make sense.

1982: Aspect shows that nature doesn't make sense either.

[qznc]

I recently worked through this essay: https://quantum.country/qm

Thanks to that i understand what "Aspect shows that nature doesn't make sense either" means. I can recommend the article (and the three others) but it takes a few hours to get through.

However, the article also explains it without quantum mechanics. Polarized photons are enough to understand why our universe is not "locally realistic". Read part 2.

[phkahler]

Because nonlocality?

[bawolff]

Which part are you saying is nonsense? You just repeated what the article was saying.

[lmm]

This part of the article is nonsense:

> Since that time, there has been ample evidence that wavefunction collapse is not driven by conscious observers alone. In fact, every interaction a quantum particle makes can collapse its state. Careful analysis reveals that the Schrodinger Cat "experiment" would play out in the real world as follows: as soon as the radioactive atom interacts with the Geiger counter, it collapses from its non-decayed/decayed state into one definite state. The Geiger counter gets definitely triggered and the Cat gets definitely killed. Or the Geiger counter gets definitely not triggered and the cat is definitely alive. But both don't happen.

[bawolff]

I think the article is just saying in practise its impossible to have entanglement on such a macro scale, so in practise the geiger counter would collapse the wave function and thus the cat would not stay in a superposition state. I don't see anything contradictory in that.

But its been a very long time and my physics is pretty rusty

[ithkuil]

Yes. In practice the cat, box, posion and Geiger counter system is not a fully closed system, and it gets entangled with the observer through unavoidable interactions.

When the observer's state gets entangled with the cat's state (whether gradually or suddenly) it's still perfectly valid to say that the cat is in a superposition of being dead and alive, and so is the observer in the superposition of observing the cat dead and observing the cat alive. That doesn't mean that the observer ever can nor should observe the cat being both dead and alive.

[lmm]

> I think the article is just saying in practise its impossible to have entanglement on such a macro scale

That much is not true though. Of course an ordinary cardboard box does not thoroughly isolate its inside from its outside, but complete isolation is possible in other situations (e.g. two spatially separated labs making measurements at the exact same time, which has been done in tests of the Bell inequalities).

[phkahler]

I prefer to replace Schrodinger's cat with Schrodinger's brother. Now you claim to have a human observer in a superposition of dead and alive states. He will not suddenly experience collapse when let out of the box to greet Schrodinger. The entire notion of "wave function collapse" is a fictional construct that can not be observed because it doesnt happen.

[karlicoss]

Schrödinger's brother is Wigner's friend

https://en.m.wikipedia.org/wiki/Wigner%27s_friend

[lmm]

> He will not suddenly experience collapse when let out of the box to greet Schrodinger.

How do you know? What would you expect to be different if that was what was happening?