|MadSci Network: Physics|
As you probably know already, if we ignore the effects of gravity (which are very weak except near VERY heavy objects like stars), light in a vacuum travels in straight lines. However, by using objects like lenses and mirrors, we can make a beam of light follow just about any path we want to. So if I wanted to make a light beam travel around a helix (or any other shape that doesn't bend too fast), the way I would do it is by bending a glass optical fiber into the shape that I wanted the light to follow. Then I merely have to shine the light in one end of the fiber, and it will travel along it and come out the other end. If I do this experiment of making light travel through a helix of optical fiber, something very interesting happens. The direction of the polarization of the light is rotated by the helix! This is an example of an effect called Berry's phase.
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