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Double slit experiment - no interference in the vicinity of light

  1. Feb 20, 2013 #1

    I'm reading N. Zettili Quantum mechanics. In the "double slit experiment", when the beam of the electrons pass the the two slits, they present an interference pattern on the screen. But when we have a light source there to trace the electrons, we see what we have expected to see of the particles in classical physics.

    Ok, we say that this goes back to Heisenberg uncertainty principle and light photons will affect the pattern of electrons.

    My questions is: why does the electrons show particle like behaviour when they are being observed by the light source? (esp concerned with the shape of the pattern on the screen) I mean why they choose the classical pattern? should we consider sth like compton scattering? Then why it is guaranteed that they show classical pattern on the screen? why don't we see a different pattern other than interference and classical?
  2. jcsd
  3. Feb 20, 2013 #2


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    Could you give the argument of the book? What should the Heisenberg uncertainty principle have to do with it? It refers to the preparation of particles and not, as is falsely written often even over 80 years after Bohr's correction of Heisenberg's first but wrong interpretation, to the unavoidable disturbance of observables by the interaction with the measurement apparatus?
  4. Feb 20, 2013 #3
    In the book that I am reading, in section 1.4 "Particles versus Waves" it has described the double slit experiment in both classical and quantum realm and it has concluded that "observation" causes the micro-physical systems to show a different behaviour. (Referring to the dual behaviour wave/ particle of such micro systems) and it has implied a little about the indeterministic nature of the micro-physical systems.

    When we are observing the electrons passing through the double slit by a light source, they are showing classical pattern. Why is it so? I mean, the observation by the light causes the electrons to present classical wave-like behaviour or at least the pattern shows like this. But why like "classical waves" why not in a different shape ("waves", but different from classical waves)?

    what are the formulations behind it
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