Through this site and others, I have learned that light waves do not have a charge, and that a light wave is a field with probabilities of where photons, are likely to be. My question is: When two coherent waves (fields) become "out of phase" what cancels to produce the dark fringes in interference patterns. There no charge to cancel. There's no physical wave to cancel. What is there to cancel? Do probabilities cancel? In my old classical view, interference made sense, but not in this new view of light. There must be some explanation as to how interference works in the quantum world.

  • $\begingroup$ the probability cancels out? Is this a helpful way of thinking about it... $\endgroup$
    – tom
    Feb 11, 2017 at 1:06
  • $\begingroup$ Thanks for you quick response. I guess I could just accept it, but how would that work a p=.99 next to a p=0. The average would be about p=.5 $\endgroup$
    – Lambda
    Feb 11, 2017 at 1:14
  • $\begingroup$ I dont' know if it's useful to think of light waves as "where photons are likely to be". For one thing, the thing that is quantized is the vector potential, not the $E$ and $B$ fields, and for another thing, mapping quantum fields onto wavefunctions is problematic in and of itself. $\endgroup$ Feb 11, 2017 at 1:28
  • $\begingroup$ Thinking in terms of where a photon is likely to be is sketchy, IMHO. $\endgroup$
    – DanielSank
    Feb 11, 2017 at 1:56

1 Answer 1


Wavefuctions cancel out ,as the name suggest wavefuctions are solutions to a wave equation (The Schrödinger equation) so like any other solutions of a wave equation they can interfere. Wavefuction of a photon passes through the slits and interfere with itself and cancel out in some regions on the screen and add up in some regions .The regions where the wavefuctions cancel are very unlikely(even impossible if the wavefuction cancels out completely) to get hit by the photon. Now if you send so many photons like this ,a dark fringe will appear in the regions where wavefuction cancels and bright fringe will appear where the wavefunction get added


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