If we traveled at almost light speed with a mirror in hand [duplicate]

What would we see if we hold the mirror in front of us and behind us.

• a complete lack of ether. (Google around for what I seem to remember as being Einstein's thought experiment) – Carl Witthoft Nov 17 '14 at 13:23
• This might be interesting for you: youtube.com/watch?v=IgAII_crHHc – Luka Milic Nov 17 '14 at 13:23
• @coteyr: At relativistic speeds, you can no longer add up or subtract speeds as if they're simple numbers. Light coming from the mirror behind you, being light, travels with speed c towards you. Your own speed is irrelevant, it can be 99% of c or 0.00001% of c. Results are identical. – MSalters Nov 17 '14 at 16:51
• @coteyr: Time too behaves non-linear at those speeds. Light does travel at light speeds from the mirror to your eyes. We've measured it. Look up the Michelson Morley experiment, which famously killed Ether theory (hence Carl Witthoft's comment). If the speed of the source would matter, the earth moving around the sun should matter too. It didn't. – MSalters Nov 17 '14 at 17:10
• I'm also voting to reopen, because the "duplicate" question has been closed as off-topic on the grounds that it's "non-mainstream" physics. As Rod Vance says, this one avoids that by asking about being near rather than at the speed of light. – Nathaniel Nov 18 '14 at 2:13

So if you emit light toward any of the mirrors, and measure its speed upon the return of the beam, you will always measure $c$.