What happens if you would ride on top of a light stream and you would look into a mirror that is in front of you, could you actually see your own face? I am asking this because I heard that nothing can be faster than light--shouldn't this be the case here as well?
migrated from skeptics.stackexchange.com Apr 6 '11 at 19:55
This question has a great pedigree! Supposedly it's what Einstein asked himself when he was first thinking about relativity.
The answer is that you can't "ride on top of a light stream" -- that is, you can't go as fast as the speed of light.
The speed of light is invariant -- same for all observers. So at any sub-light speed you can see yourself in a mirror just fine. No matter how fast you're going, a beam of light going past you still moves at the speed of light, relative to you. No matter how hard you fire your rocket engines, you never catch up with it.