Lets say that you're in a car travelling at the speed of light, and no you havn't died or dissappeared or owt. What would happen if you turned on the headlights?

You can't travel at the speed of light but if you're travelling at 99.9999% of the speed of light and you switch on the headlights you observe the lights from the head lights to be travelling at the speed of light relative to you. Everyone measures the speed of light the same in all inertial (non accelerating) reference frames, that's one of the postulates of special relativity.

Sweet

You can't travel at the speed of light

Just out of curiosity, what part of nature says we can't travel at or beyond the speed of light? This, assuming we have a way to protect our bodies at such speeds.

And please no 'Einstein said so' or any variation of that.

Just out of curiosity, what part of nature says we can't travel at or beyond the speed of light? This, assuming we have a way to protect our bodies at such speeds.

And please no 'Einstein said so' or any variation of that.

Because it would take an infinite amount of energy to accelerate a particle with mass to the speed of light, since its inertial mass increases without bound(to an observer's point of view) the closer to the speed of light it goes.