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If the force were applied in a straight line,...

How does one determing if a straight line is, indeed, a straight line?

How does one determing if a straight line is, indeed, a straight line? Ordinarily, a straight line is the shortest distance between two points. Richard Feynman wrote an excellent book called Six Easy Pieces in which he attempted to give simple explanations of some quantum theory. He used as an example the reflection of photons from a mirror surface. The Newtonian theory is that the angle of reflection is equal to the angle of incidence. However, Feynman shows (I think) that photons might follow any path to and from the mirror, but "statistically" the majority will follow the shortest path, which just happens to be that in which the angle of reflection equals the angle of incidence. (I hope I haven't botched this up too much, read his book!