Evidence for Electron Interference
Okay, that's a very nice computer simulation, but how do I know it represents
anything real? Have experiments like this actually been done?
Well, it's not really possible to set up the experiment just the way we've shown it here, with
electrons being shot at a screen through a pair of slits. The two slit
experiment with light has been done many times--originally by Thomas Young in
1801--but it's just not practical to do exactly the same experiment with
electrons. The equipment would have to be made on an impossibly small scale
to show the effects we've been discussing. So the applet you saw is what's
known as a thought experiment. It shows the results that would
be obtained, according to quantum theory, if a hypothetical experiment like
this could be performed.
Sounds like you're basically just making up this whole thing. I knew all that
stuff about the electrons interfering with each other was too weird to be
true!
Hold on--I didn't say there was no experimental evidence for the effects I
showed you. Electrons have been observed to interfere with one
another. In the late 1920's, Clinton J. Davisson, Lester H. Germer, and
George P. Thomson observed beams of electrons scattering off of various
metals. The electrons produced interference patterns that could be measured
and even photographed. For more information about these experiments, take a
look at the following links:
And those interference patterns must mean that the electrons were somehow
behaving like waves, with crests and troughs that could cancel or reinforce
each other.
That's right; those experiments showed that electrons sometimes act as if they
were waves, just as quantum theorists, like Schrödinger and de Broglie,
had predicted. So we know that if the two slit experiment could be done with
electrons the way it's done with laser light, an interference pattern like the
one you saw would show up on the screen.
