View Full Version : Does light that has been reflected still travel at the speed of light?

2010-Jun-20, 12:46 PM
I was wondering if a beam of light that was directed at a mirror would still travel at the speed of light after being redircted? Say a beam of light was aimed at a mirror on the moons surface and directed to return back to earth. Would the travel time for the beam be the same in both directions?

Thanks in advance!

grant hutchison
2010-Jun-20, 01:23 PM
It would still travel at the same speed. Light always travels at the same speed, no matter what the state of movement of the emitter or reflector. That observation (among other things) is what led to the Theory of Relativity.

Travel time wouldn't necessarily be exactly the same in both directions in the scenario you describe: the Earth and Moon would have time to move a little closer or a little farther apart during the round trip, changing the travel time by a tiny amount.

Grant Hutchison