Today's post, Feynman Paths was originally published on 17 April 2008. A summary (taken from the LW wiki):

Instead of thinking that a photon takes a single straight path through space, we can regard it as taking all possible paths through space, and adding the amplitudes for every possible path. Nearly all the paths cancel out - unless we do clever quantum things, so that some paths add instead of canceling out. Then we can make light do funny tricks for us, like reflecting off a mirror in such a way that the angle of incidence doesn't equal the angle of reflection. But ordinarily, nearly all the paths except an extremely narrow band, cancel out - this is one of the keys to recovering the hallucination of classical physics.

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This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was The Quantum Arena, and you can use the sequence_reruns tag or rss feed to follow the rest of the series.

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