On Fri, Aug 05, 2016 at 08:58:52AM +0000, jim bell wrote:
If you aimed a laser beam to one edgeof the moon, and then quickly (0.01 second) moved the beam to the other edge,the spot would look like it's travelling at 216,900 miles per second, well beyond 'c'.(ignoring the fact that the moon is a spheroid, not a flat surface, of course.)
What about this though experiment. Assume that the dark side of the Moon is covered by white photosensitive layer. If the layer is hit by light, it burns to black in $A$ seconds ($A$ is as low as possible). You have very large budget and current technologies (lasers, spaceships, etc.). Your goal is to burn a black line on the dark side of the Moon as long as possible in as low time as possible in Moon time. This is very close to speed of fire. In this scenario, can you violate 'c'? Feel free to assume whatever you want about $A>=0$ and your distance to moon. The "line" need not be entirely straight.