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This is my understanding regarding electron waves. What is seen as an electron wave is just the probability distribution of an electron, the electron always remains a particle. In interference and diffraction patterns, we just observe the probability distribution, which is interpreted as the square of a wavefunction.

If the above understanding is correct, then I have the following questions:

  1. In electron interference, the interference patterns do not appear if the electrons are seen [I mean observed with a light source]. Why does this happen? The interaction should just change the wavefunction and some sort of interference pattern should be seen, because it has some probability density associated.

  2. If all particles can be interpreted as waves by probability distributions, then why is light still considered sometimes as an EM wave. [I read in the book by Arthur Beiser that light apparently travels as waves but exhibits particle behaviour when exchanging energy].

Thanks for the help.

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    $\begingroup$ Required reading: Is the wave-particle duality a real duality? Your statement What is seen as an electron wave is just the probability distribution of an electron, the electron always remains a particle is incorrect. $\endgroup$ – John Rennie Mar 2 '17 at 18:04
  • $\begingroup$ Thank you. From the above suggested answer I understand that wave and particle natures are complementary. Could you please explain the physical meaning of saying electron can behave like a wave? Does electron wave mean that electron gets smeared out in space? $\endgroup$ – Tejas P Mar 2 '17 at 18:46
  • $\begingroup$ @TEJASP The electron never gets smeared. It is the probability which is smeared. Either you find a 100% electron at x=1 or none. There is no such thing as 30% electron here n there $\endgroup$ – Shashaank Mar 2 '17 at 19:03
  • $\begingroup$ @Shashaank, my initial understanding was that , the probability of an electron is what is smeared. Could you please give me a physical interpretation of saying that electron behaves like a wave? $\endgroup$ – Tejas P Mar 3 '17 at 4:48
  • $\begingroup$ @TEJASP Sorry, I don't think I will be able to give you the correct intuition ( because I don't think that a very good intuition is possible).And There is no point in giving the wrong intuition. I think you should ask professors here or Sir John Rennie . They are the best who can help you ! $\endgroup$ – Shashaank Mar 3 '17 at 6:29
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These are quantum effects, and as @John Rennie said, we are not observing a probability density function when we observe the interference pattern. If the electrons are not observed, there exist a superposition of multiple quantum states, in which the electron can be in. Observation causes decoherence, which leads to the collapse of a wave function. They start behaving like particles, and the interference pattern vanishes. This phenomenon has to do with the quantum interaction of electrons and matter in its environment. I suggest you study QED for further details.

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