In the double slit experiment we see that light waves can interfere with themselves to create interference patterns made of constructive and destructive interference. However, when we observe light before the slits, the wave function collapses and light acts as a particle, generating columns of light instead of the interference pattern.

There is also a phenomenon of pure destructive interference where a light wave can completely cancel itself out.

Does this phenomena mean it might be possible to filter collapsed photon particles vs light waves. If such a shape/mechanism was designed that would only let particles through and not waves, and we attached a camera to the output, what would we see?

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    $\begingroup$ I think there may be more than one concept that you misunderstand, but It's hard for me to untangle them. One stands out though. You said, "pure destructive interference where a light wave can completely cancel itself out." Sounds like you might be thinking that light is destroyed by that process, but that is not the case at all. If there's a place where the amplitude of the wave is zero (total cancellation), then that just means that the energy (photons) can't go there. There will always be some other place where the energy can go, even if it's just reflected back to the source. $\endgroup$ Sep 12, 2020 at 14:36
  • $\begingroup$ If the wave function were to collapse before entering the slits, there would be no interference pattern beyond the slits. There are no “columns of light” before the light enters the slits; only plane waves, most of which are absorbed by the material in which the slits are cut. $\endgroup$
    – R.W. Bird
    Sep 12, 2020 at 14:47
  • $\begingroup$ look at this double slit experiment one photon at a time google.gr/… $\endgroup$
    – anna v
    Sep 12, 2020 at 15:08

2 Answers 2


Firstly I think with you about radio waves and how it is possible to get an interfrence of them and after only we think about the double slits intensity distribution.

Destructive interference is possible for radio waves. Two radio sources of the same frequency and a receiving antenna at a point where the two signals have opposite amplitudes let half of the involved electrons in the rod move down and half of them move up. This is the only case one may talk about destructive interference.

If one put two measuring instruments behind two crossing radio waves (in the crossing point perfectly I with opposite amplitudes), one get the full signal on both instruments. The reason is the following. Radio waves consist of photons. They do not interact and cross each over indisturbed.

Interference in the double slit experiment is a method to calculate the intensity distribution behind the slits. There are single photon experiments. A real destructive interference for the dark areas (destruction of the photon) implies that two photons should arrive in the case of the constructive interference. That is impossible of course.

To me it is unsatisfying that the transition through slits doesn’t involve the slit’s surface electrons as part of the process. A quantized redirection of the photons towards the screen is the less mysterious explanation. It let be the photon be a indivisible quanta, oscillating with its E- and B-field component from the emission until the absorption.


When an incoming resonant photon stimulates an excited atom, the atom emits another identical photon which is in line with and in phase with the one coming in. One might postulate that if the incoming photon is absorbed by a non-excited atom, that atom emits an identical photon which is in line with but out of phase with the incoming photon; producing total destructive interference.


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