Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: AnkitaA on 11/07/2019 10:50:40
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David asks
"What level of observation is sufficient to collapse a wave function? Does it require a particular size or chemical complexity? Is it affected by consciousness?
Or to put it another way (which is how I came to this question) if the Schroedinger's cat thought experiment is true, and the cat is both alive and dead inside its nasty box until it is observed, surely there has to be a size of box, or a cleverness of the "cat" at which it stops being true - i.e. when the sealed box gets big enough, or the cat is big and clever enough then the uncertainty resolves itself even when not observed from outside. Where is that size boundary?"
Can you help?
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The collapsing wavefunction is mathematical model, not a physical phenemenon. The "observer" in classical physics is anything capable of being changed by an interaction - geiger counter, photographic film, billiard ball, or human eye. It makes no difference whether you think it is conscious or not.
Not a good idea to talk about uncertainty - that's a function of human endeavor. Schrodinger, Heisenberg, etc., is about indeterminacy - an inherent property of the system, not its "observer".
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Schroedinger's cat thought experiment ... the cat is both alive and dead inside its nasty box until it is observed
Quantum indeterminacy clearly applies to quantum systems, like the spin of an electron in a magnetic field. It is possible to be "up" or "down", but not know which.
The point of the thought experiment was to bring this quantum state up to a more familiar level, so the non-intuitive aspects of quantum indeterminacy could be illustrated.
However, "large" systems (on the scale of a cat) also display considerable entropy, and so the moment the cat dies, it starts to decay.
So when you open the box, you find that it has not been in some indeterminate state of alive and dead the whole time, but in fact you can make a reasonable estimate of how long the cat has been dead.
In effect, the cat observes itself.
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Define 'level of observation' a little clearer David. There is something called Decoherence https://plato.stanford.edu/entries/qm-decoherence/ that might fit your question. And the idea there, as I read it, is that it should be a natural consequence of complex systems interacting forcing out a determined system aka our macroscopic world. If that is true the 'level of observation' might be translated into what 'scale of observation' is needed for it to exist.
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The posts before relate to the inherent/intrinsic? uncertainty at a certain scale as described by HUP, but our macroscopic world doesn't seem that 'uncertain', does it :) Although even that might be arguable.
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I heard that physicists are experimenting with "weak" observations, to see to what extent quantum indeterminacy is affected.
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I heard that physicists are experimenting with "weak" observations, to see to what extent quantum indeterminacy is affected.
I’ve seen some results, but they work best on large numbers of photons so you can build a picture. They can still disrupt the path taken.
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And in a larger context Collin. It touches also the idea of 'free will'', doesn't it?
A tricky one.
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I heard an interesting interview between Rob Reid & Sean Carroll, in July 2019...
- Sean Carroll is from the "Many Worlds" school of thought, and believes that the wavefunction is "all there is"
- However, he describes the other 3 or 4 most common views of quantum theory, in an accessible way
- The interview goes into what causes a wave function to collapse, in these different views
The Interview (1.5 hours) is available from podcast feeds:
Rob Reid episode 52: https://after-on.com/
Sean Carroll episode 55: https://www.preposterousuniverse.com/podcast/