# Running real fast while holding a mirror

1. Jun 5, 2005

### Moneer81

Hello

if you're running and looking at your own imagine in a mirror you're holding in your hand, how would the image look like? what if you were running at .99c ? and why?

2. Jun 5, 2005

### εllipse

It would simply look like you. Although you're running, if you're keeping a constant velocity, then according to the special principle of relativity, you're perfectly justified in calling yourself "at rest". Therefore, the image you will see in the mirror will be identical to the image you will see if you are not running.

3. Jun 5, 2005

### pmb_phy

It would be the exact same thing as if you were at rest since in that frame you are. This was one of the thought experiments used by Einstein. He used to wonder what he'd see in his bicycle mirror if he was moving at the speed of light.

Pete

4. Jun 5, 2005

### Chronos

Yep, to 'stationary' observers you might look like a funhouse mirror as you run by, but your mirror will never lie to you.

5. Jan 22, 2009

### Underdoped

What if you were running at a stationary mirror? I know the rest of the world would appear shrunk by a factor of 1/$$\gamma$$ in a direction parallel to your motion but what about the image in the mirror?

6. Jan 22, 2009

### Staff: Mentor

Sweaty, because it is really hard to run that fast.

7. Jan 22, 2009

### A.T.

Your picture in the mirror approaching you at almost c would be extremely blue shifted beyond visible range. And you would "see" your actions delayed by a time offset but executed much faster. So that just before you collide with the mirror, the picture in it almost catches up with your actions.

http://www.spacetimetravel.org has a lot of such simulations.

Also note that the effects I describe above are not really "relativistic". It is simple Doppler-effect and signal delay.

Last edited: Jan 22, 2009
8. Jan 22, 2009