1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The double slit experiment the same old

  1. Jan 26, 2015 #1
    A question...
    Perhaps a dumb question...
    A simple question... or maybe not...

    In the experiment, why are the slits needed in the first place?
    If one shoots electrons, then the edges of the slit must therefore do something with them in order to make them act the way the do: the seem to interfere to each other. If the edges have nothing to with it, the shooting electrons without the slits should produce the same phenomena... The edges themselves contain electrons at their outermost "shell"...

    So... the dumb question is: what do the edges do ?
    In case of water waves, it is rather clear, what happens (hopefully) because of the edges...

    But no so clear to dumb old me...
    Haven't come to any good explanation in the textbooks...


    Is it so obvious that a person with brains should be able to deduce that like 2+2 just by looking at it?

    Any ideas?

    Thank you all kindly for the previous discussions at this forum!
  2. jcsd
  3. Jan 26, 2015 #2


    User Avatar
    Gold Member

    If you just shoot a stream of electrons there would be no reason for any interference. If there were, cathode ray TV sets would be all fuzzy.
  4. Jan 26, 2015 #3


    User Avatar
    Gold Member
    2017 Award

    Hi Ott,
    the slits (openings) provide different possible paths for the particles (and the barrier(s) exclude some paths), see e.g this picture:

    And in the following case a single barrier ("filament") is used, and you can again see that there are different possible paths for the particles (the arrows in the picture):

    http://www.hitachi.com/rd/portal/image/fig1.gif [Broken]
    (picture taken from this page: http://www.hitachi.com/rd/portal/research/em/doubleslit.html)
    Last edited by a moderator: May 7, 2017
  5. Jan 26, 2015 #4


    User Avatar

    Staff: Mentor

    The edges of the slits form a barrier that the electrons can't pass through. This restricts the possible paths they can take to just the slits, which is why the interference pattern is different with two slits than with no slits. With no slits the possible paths the electron can take are restricted based on where/what it was emitted from instead of being restricted by the slits.
  6. Jan 26, 2015 #5


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    There are (at least) two steps involved here. Firstly one needs to understand how the geometry of a situation involving waves can affect the diffraction pattern. That is fairly straightforward to do for simple cases and involves a bit of Maths.
    Then one needs to understand - or accept that the statistics of where a 'particle' arrives (the probability density function) is a diffraction pattern, if the particles can be assigned with a particular wavelength (always - even when you can't spot haw that applies to a particular situation). It is then a reasonable jump / step to see how a large number of particles will eventually form a recognisable diffraction pattern.
    There can be a certain amount of 'faith' involved in this until you realise that it has been demonstrated very many times by experiment that this particular model works very well. Personally, I don't have a great problem with this sort of thing because I don't find it necessary to believe in any particular 'ultimate truth' about what is 'really happening'. I am quite prepared to accept that a good enough model is good enough - within the limits that it applies. This model actually works well down into the higher orders of difficulty so it gets my vote.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook