# Speed of light vs standing still

I’m having a hard time with relativity, please help me out. If I was traveling at 9.999…% the SOL and I passed you and you are standing stationary and turned on a laser beam running parallel to me, would I be able to see the very tip of you laser while looking back and would it be receding away from me?

Your description of the set-up is a little confusing, so I’m going to restate what I think you’re asking:

You’re traveling at nearly the speed of light relative to me. As you zip past me, I turn on a laser pointed in the same direction you’re traveling. Your question is, what do you see?

It will appear to you that the laser beam is shooting out ahead of you at the speed of light. Of course, the only way you can “see” this is if the beam hits something that bounces some of the light back to your eye, but any observations you make will be consistent with the beam traveling at the speed of light relative to YOU. Of course, from your perspective it seems like the beam is traveling at almost twice the speed of light relative to ME, since I’m quickly receding in the distance behind you at 99.9999… % of the speed of light.

It will NOT appear to you as though you’re “keeping pace” with the laser beam. (Although that’s what it will look like to me … .)

Right. Just to elaborate one point, since nobody’s speeding up or slowing down or changing direction, there’s no way to say which one of us is standing still and which one is moving.

So, from your point of view, you’re just sitting there and I come whizzing past at 99.999% lightspeed. Then I turn on a laser just as we go past. The light takes off at light speed in whatever direction the laser was pointing, while I continue on my merry way at 99.999% lightspeed.

Things would actually appear much stranger due to relativistic effects. You travelling at 0.99c and I would not agree about the time the laser was turned on. I would think I turned it on just as you passed, but you would not think so.

Moreover, your view of me and the “stationary” world would be oddly distorted, compared to what I saw:

http://www.fourmilab.ch/cship/aberration.html