Out of curiosity I wanted to ask what people think about this idea. I understand that when we do the double slit experiment and observe the particle, we get a wave collapse because of the observed certainty, do you think the exact same thing would happen if instead of detecting where the particle is, we detect all of the places it isn't?

  • $\begingroup$ What looks like a wave is actually billions of individual coherent photons. If you measure any of those photons before they make it to the screen then they will not contribute to the pattern. There is no such thing as a light wave without individual photons. $\endgroup$ – Bill Alsept May 13 '19 at 16:07
  • $\begingroup$ I can't think of any way to do this measurement. It sounds fundamentally impossible. If so, the question doesn't make sense. What is the result of an experiment that can't be done? $\endgroup$ – garyp May 13 '19 at 16:43

The wave function collapses because you obtain the information where the particle is located. The same holds true if you identify all the places where the particle is not. Because then, you know where the particle has to be located.

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    $\begingroup$ Thanks, this backs up what I was thinking myself. :) $\endgroup$ – George Simister May 13 '19 at 11:53

The generally accepted view in quantum theory is that information about which way the quantum system travelled, and interference fringe visibility is complimentary.

The wavelike property of light (or in general matter) is documented by well-visible interference fringes, whereas the particle-like property is evident if one can tell along which way the interferometer has been traversed by photons (particles).

There are many ways to retrieve path information. Some of them include:

  • Placing a detector near the slit.

  • By measuring the atom's recoil in Young-type optical experiments.

  • From the spontaneously emitted photon in atom optics.

  • From the idler photon with a photon pair being involved.

No matter how, any attempt to gain the complete information of which-way will eventually destroy the visibility of fringes. Quantum mechanics dictates that if one is performing any sort of measurement on a photon, its wave function collapses. The photon then acts like a particle thereby destroying the previously observed interference pattern.

  • $\begingroup$ Thank you very much on this detailed explanation. I did think this myself, however I do know quantum is quite strange and do not have the means or money to experiment myself. :) $\endgroup$ – George Simister May 13 '19 at 19:23

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