quantum physics
This is something I wrote for another forum, and I figured I may as well actually post in my journal. It's a brief explaination of one of the most famous experiments in modern physics, Young's double slit experiment. This was written mostly off the top of my head, but I think it is correct. I should warn you, this post may be pretty damn confusing...
Um, if anyone is still reading after that...
imagine a set-up like this; a wave generator (something moving up and down regularly in a shallow container of water) sends waves at a screen with a board in between that has two slits in it. If ony one slit is open, you get a pattern like when you throw a stone in a pool of water; waves travel from the slit until they reach the far side of the pool. There is a relatively simple pattern of high and low water levels at the far wall. Switch the slits and you get the same thing, originating from the second slit.
Now open both slits... you get a much more complicated pattern. High and low water levels (peaks and troughs) combine; either increasing eachother, or canceling eachother out. The far wall now gets a pattern that consists of alternating highs and lows. This is interference of waves.
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http://img.photobucket.com/albums/v217/Dt3r/dslit.gifNow change the set-up; replace the wave generator with an "electron gun." Using electrons we get the same results; that is to say electrons interfere like waves. Now close off one of the slits... the electron begins to act differently. The electron behaves like a particle and has a large central area with maximum exposure. It behaves as if it were a ball or a bullet fired through a hole, a particle. Open both slits and it returns to acting like a wave. Even if you fire one electron at a time, it will still pass through both slits; because it is acting like a wave.
So the electron seems to act like both a wave and a particle... depending on the situation.
Now keep both slits open, but measure to see if the electron goes through one of the slits. Suddenly, the pattern of the far wall changes. We now see the pattern for a single slit, but both are open. The detectors never see the electron at more than one hole.
The very act of measuring changed the pattern.
By measuring the presence of an electron, we forced it to go through one path. Our measurement fixed it's position, and forced it to assume a particle behavior. Left on it's own, the electron would "keep it's options open" and remain a wave.
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