Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Uncertainty and The Double Slit Experiment

  1. Jul 21, 2011 #1
    While reading Feynman's 6 Easy Pieces, I see he talks about bouncing photons off of the electrons that are passing through two slits. According to Feynman, when a photon strikes an electron near one of the slits, it bounces (sometimes back at the observer) and registered as a sharp point of light for the observer. In the process, the electrons momentum is disturbed to a degree that is inversely proportional to the wavelength of the light used.

    In the next experiment, light of a much longer wavelength is used (in order to strike the electrons with a minimal change in electron momentum). Feynman describes how the photon will bounce to the observer, but will cause a blurry area of light for the observer, rather than a well defined point of light.

    My questions:

    Why do longer wavelengths have this effect of blurring/uncertainty?

    And what are we finding out when we use longer wavelengths? The momentum of the electron? How do we find the momentum of an electron simply from bouncing blurry light off of it?
    Last edited: Jul 21, 2011
  2. jcsd
  3. Jul 22, 2011 #2
    I'm a bit new to QM too, but I'll try to explain. When we use longer wavelenghts we get a blurry area, meaning the electron could have been anywhere in that area. And when we're using shorter wavelenghts we get a point, a certain position, but an unknown momentum because we can't know the amount of momentum transferred to the electron when they bounced off.
  4. Jul 31, 2011 #3
    The bold bit,isn't that in reference to the (HUP) ?

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook