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Sep14-07, 05:56 PM
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Quote Quote by StatusX View Post

The difference in the case where we have a quantum superposition is that the dynamical equations imply that a microscopic superposition, which isn't really much stranger than, say, a superposition of overtones on a piano note, should evolve into a superposition of macroscopic objects, which is something very strange, and not something we seem to observe. The cat paradox is designed to expose this problem.
As far as I remember the cat "paradox" was orignally an attempt by Schrödinger to show how absurd QM was, i.e. he was implying that there must be something fundamentally wrong with the theory.
Now, first of all, as I have already pointed out we now DO understand why this never happens to real cats; the theory of open quantum systems as well as measurement theory is now so well developed that there is no real mystery anymore. Hence, there is no 'paradox'.

Secondly, we DO observe superposition in macroscopic objects. E.g. superconducting qubits might not be very large but they are certainly macroscopic (a few square microns, you can easily see a flux qubit in an ordinary optical microscope). The interesting thing with modern QIP (=quantum information processing) is that it has taken many problems from the realm of philosophy to what is basically engineering: in order to observe superpositions in a real experiments on superconducting qubits we use good magnetic shields, low noise amplifiers and a lot of filtering; in order to stop the "collapse" (i.e. increase the coherence time) we design the environment of the qubit in such a way as to maximize the impedance it sees (basically microwave engineering) etc. Hence, there is nothing particulary 'esoteric' about QIP anymore. I suspect many of the things we do in the lab nowadays would have shocked Schrödinger.

My point is that the cat "paradox" is not really a problem in physics anymore (and I don't think it ever was), in part simply because we got used to the idea; nowadays we instead use these effects to build useful devices. There are obviously quite a few philosophical issues, but these are largely irrelevant to the science.
It is worth remembering that thermodynamics and Newtonian mechanics also got their fair share of issues but these are rarely talked about nowadays, simply because we take those theories for granted.