Anonymous Caller I MUST KNOW THE ANSWER!!! If you were in a car, traveling at the speed of light, and you flipped your headlights on, what would happen? O.O Otakon I'm not all that great when it comes to quantum physics or anything like that. My specialty is more along the lines of nuclear physics and robotics. If I had to take a stab at it, I'd say by the nature of energy, if you were travelling at the speed of light, you would _be_ light, and there would be no car or headlights. That's just my guess though. I'm sure someone else here has more expertise than me. Ritsuko? Akagi Ritsuko According to General Relativity, matter cannot travel at the speed of light, therefore the question is moot. It all stems from time-space distortion that you get at relativistic speeds, but the short-short version is that it would take an infinite amount of energy to accellerate matter (that which has mass) to the speed of light. Those things that do not have mass (i.e. light) do not have this problem, and, in free (i.e. completely empty) space, cannot propagate at any speed other than that of light. Now there are all sorts of parallel and sundry concepts for getting from point A to point B faster than light could through the free space between them, but all of them involve loopholes in Relativity. For one, you could create a zone around you were the local speed of light was faster than that of normal free space (i.e. warp-drive). The other involves cutting a hole in space that allows you to skip the intervening distance (i.e. Stargates). In both these cases, since the effect would be around you and your car, your headlights would function just as they would when you are driving down the street. So, the boring, but accurate, answer is: nothing much. Akagi Ritsuko Now the more interesting question would be: If you were in a car approaching the speed of light, and you flipped your heatlights on, what would happen? This, of course, is at least theoretically possible, if horribly expensive, energy-wise. As one approached the speed of light, things in your headlights would appear compressionally distorted (like tunnel vision) and increasingly blue-shifted in spectra (the wavelength being compressed due to your added velocity). (Both effects are a biproduct of your travelling through the photons they are producing while you are running towards the ones that you are emitting--to put it in lay terms.) From your point of view, the objects are approaching you at high speed and their velocity toward you is causing the reflected light to be blue-shifted upon reflection. From theirs, they are standing still and your headlights are moving at them at high speed, so the light comes-out blue shifted and you would be as stretched as they would appear compressed. And so, everything would look increasingly blue/violet and compressed until the light shifted out of your visual spectrum, and then you'd be quite blind to anything in front of you. Meanwhile, everything behind you would increasingly red-shift until it was in the infrared and you couldn't see it either. (And that's not just due to your tail-lights.)