Apparently particles can be anywhere when not observed. How strong is this theory really? Okay the wave-function can be collapsed through observation but how are we so sure that when an object is not being observed that it is in potential states? How are we so sure whether or not the wave function is collapsed by a conscious observing force other than us? And is superposition an assumption due to the fact that when we observe waves they act as particles, so we assume that everything has different potential until measurement; when really we don't know for sure whether it is that an object is in potential states or a conscious observance by a higher power already puts things in order already eliminating this potentiality?

  • $\begingroup$ A couple of remarks. A conscious observer is not needed for collapse. Also, try avoiding the word 'potential', use 'possible' instead (potential has a specific, different meaning in physics). And lastly: how then do you suggest we interpret the fact that we can prepare $N$ particles in the same way but find that e.g. after waiting a while $N_A$ of them are measured in state $A$ and $N_B$ in state $B$? Superposition works very very well, what's the reason for your doubts? $\endgroup$ – Wouter Mar 20 '14 at 22:09
  • $\begingroup$ We are not a 100% sure about superposition, but quantum theory has never been disproved by any experiment afaik and so we are pretty sure. If you can find a better theory that survives those countless experiments, and in addition also explains other unexplained phenomenons, such as quantum gravity, then you will most likely win a Nobel prize. $\endgroup$ – Hunter Mar 20 '14 at 22:15
  • $\begingroup$ Wouter, my doubts are due to the possibility that superposition is possibly a wrong explanation of the phenomena. I don't know what your talking about when you say a conscious observer isn't needed for a collapse, I don't know what these alternative(s) are but still conscious observance does indeed collapse wave function. So if the Copenhagen interpretation or superposition are false then a great explanation is a conscious observance external of our five senses such as a collective consciousness or omnipresent God. $\endgroup$ – user42407 Mar 20 '14 at 22:48
  • $\begingroup$ @user42407 A goldfish can collapse the wave function just as well as a human being. So can a dust particle or a ray of light. Consciousness is not a prerequisite for wave function collapse (although such interpretations have been proposed in the past). In any case, the Copenhagen interpretation is still widespread but I really don't think it should be. Note, however, that there is definitely no consensus (yet) among physicists about the interpretation issue. $\endgroup$ – Wouter Mar 21 '14 at 0:31
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    $\begingroup$ I like to think most who have seriously thought about this tend to go for alternatives to the Copenhagen interpretation, but this post by Sean Carroll shows the current situation. No one interpretation is massively accepted, which is of course a consequence of the lack of indicative experimental results to separate most of them. However, this is not an issue for superposition. $\endgroup$ – Wouter Mar 21 '14 at 0:37

As Hunter already remarked we can't say by no means that Quantum Mechanics is a complete theory, nevertheless a lot of experimental observations agree with QM predictions and on the other hand I don't think that there exists another theory which predicts so many phenomena in agreement with the experiments. (So that you may explain some "quantum" effects with a classical ad hoc theory, but you won't explain a lot of other "quantum" effects with it.)

Having said this, a strong experimental evidence of the existence of superposition is given by subsequential Stern-Gerlach filters. In short you filter a stream of spin 1/2 particles by measuring their spin along the z-axis and taking only the ones with positive component, then you do the same for the x-axis and you measure the z-axis spin again, you see that particles with negative component of z-axis spin reappears. If you look for a classical explanation of the measurement process (such as the measurement outcome is undeterminate because we don't know the pre-measurement state) you will have some problems in interpretating this regeneration. On the other hand the superposition explains this phenomena in a neat way: the superposition of states is a distinct state on its own, and not just an "unknown but determinate" state of the superposition.

  • $\begingroup$ Not to mention that even if you came up with a classical way of explaining most quantum effects, Bell's theorem always lurks. $\endgroup$ – Jerry Schirmer Mar 21 '14 at 0:27

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