Physics 2000 The Atomic Lab Interference Experiments

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.

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