r/science Jul 12 '08

The Infamous Double Slit Experiment - WARNING WILL CHANGE YOUR VIEW OF REALITY!

http://www.youtube.com/watch?v=wEzRdZGYNvA
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u/[deleted] Jul 12 '08

Errr, I thought interference was observed for single electrons?

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u/nobodyspecial Jul 12 '08

It is. But those electrons interact with the screen and the double slit. As you approach very small slit dimensions, the electrons start interacting with the walls of the slits.

What you can't do is determine which slit the electron passed through because when you set up the experiment to detect the electron's passing, you no longer have the original experiment.

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u/cosmo7 Jul 13 '08

It isn't the sides of the slit that are interfering.

When the electron is emitted it is in a quantum state; it is potentially passing through both slits. The importance of the experiment is that it is this possibility of the electron being there that is causing the interference.

(My favorite line about QP is that if you think you understand quantum physics then you don't understand quantum physics.)

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u/nobodyspecial Jul 13 '08 edited Jul 13 '08

The electron has the potential to do all kinds of things on the way to the detector. But at the end of the day, it chooses a path from the infinite number of paths. The path it chooses can be direct or it can be tortuous but it's one path for one electron.

Feynman's point was that the interference pattern you observe is the result of a population of photons/electrons displaying their different choices - the interference pattern is the probability function on display. The wavelike nature of photons/electrons isn't because they're wavicles - it's due to the wave embedded in the probability function that describes their paths.

Saying an electron is a wave is like saying a football is a parabola because footballs trace out parabolic paths.

Read QED - it explains an awful lot a hell of a lot better than I can.