[SamAdams76]

The big question for me is if we go faster than the speed of light won't we be overdriving our headlights?

Good question. Let's take an example here on earth. Let's say we put Roger Clemens with his 90mph fastball on the back of a pickup truck traveling 60mph. When he hurls one of his fastballs, then is not his fastball traveling at 150mph relative to a person standing on the roadside? So then, if a spaceship traveling at the speed of light turns on its headlights, doesn't the beams of the headlights move at twice the speed of light relative to a stationary object and at the speed of light relative to the spaceship? Then again, maybe it doesn't work that way in space due to zero gravity. One thing for sure, I'd make a lousy physicist with this kind of logic!

[JRandomFreeper]

I just want to know why the government moves at the speed of dark.

/john

[edwin hubble]

Your example works at 'normal' speeds.
"..doesn't the beam of the headlights move at twice the speed of light relative to a stationary object "

This works pretty well for normal relative speeds. Like the Concorde. When you get to 1/10 of the speed of light things have begun to change.

Light is always measured at 'the speed of light' no matter how fast the relative speed of the source.

But... the 'color' or wavelength of the light changes very precisely with the relative speed of the source. The headlights of an oncoming car are bluer than those of a car backing away.

[ffusco]

I think the paradox of your example is that light doesn't always behave like a particle ,i.e. a baseball, sometimes behaves as a wave.

[Charles H. (The_r0nin)]

So then, if a spaceship traveling at the speed of light turns on its headlights, doesn't the beams of the headlights move at twice the speed of light relative to a stationary object and at the speed of light relative to the spaceship?

Your explanation is exactly what Einstein's Theory of Relativity was developed in order to refute. Because, if you measure the speed of light from any frame of reference (and this has been experimentally verified) it always moves at the same speed (ie. ~300,000Km/s) relative to you. Even if you are moving very fast yourself.

This is because, as you speed up, your perception of time slows down. Let's imagine that Observer A is stationary and Observer B is moving at 1/3 the speed of light. IF Observer B was to suddenly turn on his headlights, then Observer A would see the light from them moving away from Observer B at the speed of light. But Observer B would ALSO see his headlights moving away from him at the speed of light, because time would have slowed down for him enough that the light would have moved 300,000Km away in front of him in what he perceived as one second. So the speed of light (in a vacuum) NEVER changes to any observer; only each observer's perception of the passage of time changes as his speed increases (though it's not only the perception... time actually slows down!). This has also been verified with atomic clocks and in particle decay, so it is real.

In fact, because of Einstein's Theories, a new definition of gravity can be proposed: An object moves in a gravitational field in such a manner as to take the longest time between two points. Weird, huh?

Check out Richard Feynman's Six Not-So-Easy Pieces for a great explanation of the details behind the theory...