What wilI I observe when travelling at almost the speed of light? If I and a group of friends are travelling at or just below the speed of light - can I see myself, can I see them, or they me? Would we see anything at all?
 A: Unless you have zero mass, you cannot reach the exact speed of light. But lets work with the hipothesis that you are just below light speed. Two things would happens:


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*Doppler effect: light coming towards you would get blue shifted. That means you would be unable to see a blue object coming towards you, since you would see it as UV radiation or, depending on how fast you are, even as a X-Ray or gamma radiation. But you would be able to see the infrared radiation of a oven flying towards you, or even the radiowaves of a cellphone tower (your cellphone would not work, although). In the other hand, light coming from behind you would get red shifted. You would not be able to see a red object behind you because, for you, it would be infrared light. And if someone fired an X-Ray machine behind you, perhaps you could see it as a blue flash.

*The other effect is a geometrical one and is caused due to a combination of the time dilatation and spatial contraction. It is called Terrel rotation and basically states that if someone at large relativistic speeds sees a cube, it would appear rotated. Wikipedia points to some references about this
http://en.wikipedia.org/wiki/Terrell_rotation
