Expert: Steve Nelson - 2/9/2012

Question
Some of the kids in my calculus class that are also in physics asked the whole class a seemingly dumb question that turned into a class discussion. They asked, "If you're in a car that's traveling at the speed of light (hypothetically of course) and you turn on your headlights, would you be able to see them?" I think that yes you should be able to see them, because you're traveling at the same speed... What do you think?

Answer
You're invoking impossibility, traveling at the speed of light when you have mass and that would take an infinite amount of energy.  So the question is just wrong to start with.  If you could, as some kind of massless ghost, you would just observe static electric of magnetic fields instead of electromagnetic waves because you'd be traveling at the same speed as the wave...kind of like in a boat moving at the same speed as an ocean wave, you wouldn't see it waving up and down or moving relative to yourself, it would just have some height above the water's surface (which would represent the energy in the wave).  So since your eyes respond to waves and not static fields you would not "see" anything from the headlights.