What causes quantum uncertainty?

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What causes quantum uncertainty? My friend who's working for Apknite says that detectors are not the cause of wave collapse, because you are measuring something that isn't remaining in the same state.
 

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atyy
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The cause of quantum uncertainty is unknown, and cannot be answered at the present state of science.
 
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The cause of quantum uncertainty is unknown, and cannot be answered at the present state of science.
It's caused by observables not commuting. Why do say position and momentum not commute? The answer is symmetry as can be found in chapter 3 of Ballentine - QM - A Modern Approach. The hidden assumption is it proves certain observables defined by symmetry have exactly the same relationships as classical physics. Taking Erenfest's Theorem into account it makes sense to define these operators as their corresponding classical quantities. To bring the correspondence into logical order you define momentum and position operators as the quantum operators found from symmetry, then say the corresponding quantities from Erenfest is their definition classically. So the question is why does symmetry and the above logic lead to exactly the same definition found in classical mechanics? I am not sure the exact reason is known, but we have some very advanced QM experts that post here who may be able to elucidate it further. My suspicion is Feynman's Path Integral approach has something to do with it.

Thanks
Bill
 
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