So...if electrons and photons are both particles and they pass the two slits, why do they create an interference pattern as if they were waves? Now from what I've read, it's because of the superposition of an electron and since an electron is in every possible state until observed, it is going through both slits and interferes with itself and that's why, if not observed, the double slit experiment will show that interference pattern.

Now my question is: how can that electron propagate as a wave if it interferes with itself? Shouldn't the outcome of the experiment be the same with or without an observer? I mean...that's just so very extremely counter-intuitive that I can't grasp it...an observation changing the outcome. Why does the observation of the slits change the outcome and not the observation of the screen? Why do we get wave interference even with one slit?

Please correct me if I'm mistaken about how this double slit experiment works cause I've also seen interpretations about the wave nature of electrons and photons and it just made things more complicated for me.


It has nothing to do with an observer. The pattern is disturbed because you interfere or block the photons that make up the pattern. If you place anything (like a detector) between the slits and the detection screen you will disturb the photon distribution and the pattern.


Interference patterns of electrons or photons are due to their wave nature. It is easy to see the duality nature of fundamental particles compared to the everyday objects (where it is thought practically they have only particle nature.)

As you might guess any waves can interfere. I am attaching this nice video (intended for kids but I find it informative even for adults like myself).

Dual Nature of Fundamental Particles

Young's Double Slit Experiment in Quantum Field Theory

And finally what you really want to know is already in our website:

What is the wavefunction of the Young Double Slit experiment?

  • $\begingroup$ I've seen this video, and it's nice, but it doesn't talk about the probability distribution which I guess is a key factor in explaining the patterns? $\endgroup$ – griffinwish Mar 17 '16 at 23:54
  • $\begingroup$ The links provided by ACuriousMind are wonderful resources in regards to your concerns too if you want to be more mathematically involved. $\endgroup$ – Benjamin Mar 17 '16 at 23:57
  • $\begingroup$ You want to see the very last link. $\endgroup$ – Benjamin Mar 18 '16 at 0:04

Not the answer you're looking for? Browse other questions tagged or ask your own question.