An anonymous reader writes "Light doesn't just make things brighter; it can also push things around. Normally this "radiation pressure" force is so small you don't notice it. But if you get a really big mirror then you could use it to power a space ship to the stars. This is the idea behind solar sails. The impact of light is more obvious on small things. Scientists are thinking about levitation of a mirror that would be large enough to see with the naked eye. If this turns out to work, the motion of the floating mirror could be used to probe the physics that connects quantum theory and general relativity."