*TroyCheers asked the Naked Scientists:*

My mate proposes that if you are in a car travelling at the speed of light with the headlights on that you could not see the light from the headlights.

First, and this has already written to you, it's impossible to travel *exactly* at the speed of light, and it's not a mere technical or formal difficulty; between 299,792,457.999 m/s (for example) and 299,792,458 m/s (which is exactly light speed) there is the same difference as from 1 and infinity. Infact you need a *finite* amount of energy to reach the first speed while you would need an infinite amount of energy to reach the second (and the entire universe's energy is finite...). You would understand this studying relativity.

Second, to travel very very close to light speed, you should do it in the void, or any tiny particle, any air molecule, any atom in the space that you would hit would became an enourmosly energetic bullet that could istantaneously disintegrate you and your spaceship.

But if you are in the void you can't see light from your headlights anyway, because there isn't any particle/molecule to scatter that light back to your eyes...

Third, if you travelled at very very close to light speed and you would illuminate some obstacle in front of you, as evan_au suggested, you would see that reflected light, yes, but with a little problem: it would have incredibly high frequency *AND* incredibly high intensity (according to relativity law of frequency and amplitude transformation between two frames of reference, in this case the light source would approach you at almost light speed).

And so you would die of your very act of switching on the headlights...