The discussion revolves around the question of whether the spot of light created by a torch shining on the moon can move faster than the speed of light (c) when the torch is swung across the lunar surface. Participants explore the implications of this scenario on the nature of light, information transfer, and the behavior of photons.
Participants express differing views on whether the spot of light can be considered to move faster than c and the implications of this for information transfer. There is no consensus on the interpretation of these phenomena.
The discussion includes assumptions about the nature of light and the definition of information transfer, which may not be universally agreed upon. The implications of the travel time of photons are also noted but not resolved.
Yes, the spot can move faster than c. But as the spot moves from one side of the moon to the other, no information travels between those two points. (Astronauts on opposite sides of the moon cannot use the spot to communicate; the only potential for information transfer is between the light source and the moon, and that information would of course travel at speed c.)gonzo said:I was thinking a bit more about this, and can even the spot move faster than C? Wouldn't that imply that information can travel faster than C?
The travel time only introduces a delay in the time it takes the "spot" to reach the object; but that delay is a constant 10 years, so it doesn't affect the "sweep rate" of the spot.Think about a more extreme example. You shine a light 10 light years away in one direction, then flip around to shine on an object 10 light years away in the opposite direction. By the original example the "spot" has moved 20 lightyears in a very short time, but this neglects the travel time for the photons from the flashlight to the object.
gonzo said:I was thinking a bit more about this, and can even the spot move faster than C? Wouldn't that imply that information can travel faster than C?