If you were driving your car at the speed of light and you turned on your headlights, what would happen?

Answer 1

if you have a car with that capabilities then everything would work the same if the car was going 45mph.

Answer 2

That is a great question, one that everyone asks when they learn about light speed.

Lets overlook the fact that your car can never travel at the speed of light because that wasn't what you wanted to understand, and instead lets just say your car is "close" to the speed of light when you turn on your headlights.

And lets say that there is an additional observer way out in front of your car.

OK, when you turn on your headlights while driving this fast car, light leaves your headlights at the speed of light. Even though you are traveling close to the speed of light, the headlight light still leaves your car at the speed of light.
If you measure the speed of the light leaving your headlights, you would measure the speed of light, c.

Now that observer way out in front of you, when the light gets to him, he too sees the light traveling at the speed of light, c, and it would be the same speed to him that you measured when it left your moving car.

But there is a difference: Since you were moving towards him when the light left you, it has a lot more energy for the observer due to the motion you gave it. So the light that he sees is much bluer in color than when it left you.

Because of the energy you imparted to the light, by virtue of your velocity, it has become blue-shifted. So the observer sees the light as bluer than when you emitted it.

Blue light photons have more energy than, say, red light photons. So when you add energy to white light (by adding motion to it) it shifts toward the blue end of the spectrum.
If you had been moving away from the observer then the light would have lost energy and been shifted toward the red end of the spectrum. That's called red shift.

So the key thing is that the speed of your light is the same to both you and the observer that you are moving towards, it is just of different color (because it is at different energy).
And lets say your observer held up a mirror to you: The the light would be directed back to you, and you would see it blue shifted but it would still approach you at that same speed of light, c.

Of course your car, or any other mass, cannot travel at lightspeed. Only mass-less things like photons can travel at lightspeed, so there is no possibility that your can would ever get to the observer before the light or anything like that. When traveling this fast the speeds do not exactly add algebraicaly like at low speeds.

Kinda neat, huh?

Answer 3

mina x is right. but she should have mentioned that it is impossible for your car to go that fast. It can go 0.9999999 of the speed of light or add as many 9's as you want. But it can not go at the speed light. The beams of the headlights, if you measured their speed, would still be the speed of light. That is the way the universe is set up, not much you can do about it. You might think that velocities add by, well, simple addition. V of headlights = (V of car) + (speed of light). But not so. Two velocities add like: V = (u + v)/(1 + uv/c2). So even if one of them is the speed of light (c) you get:
V = (c + v(/(1 + v/c) = c no matter what the other velocity is.

To Karl L. If you are traveling NEAR the speed of light, eveything at rest relative to you would look just the same as it always does. Now other things would look strange. The effects are the Lorentz contraction, the Doppler effect and aberration. The guy at the source below does a pretty good job of describing these things except that things far away, when you look at them, do not appear squished because of the Lorentz contraction but instead appear to be rotated. This was not actually realized until around 1959.

Answer 4

I think light is the fastest thing in the galaxy. Like nothing can travell at the speed of light.

Since this is a hypethetical question then i suppose what would happen is that the light from the headlights would probably just build up up around the bulbs.

A second idea is that you wouldnt see anyhting since the light isnt dispearsing anywhere.

Another theory is that the light would adopt a doppler effect like the way sound does on a speeding train . the light would bunch up at the front of the car and the rest of it would flow back towards you .

I have a question to add to this as well. Since humans see by way of light reflecting of objects,,,,then how do things look when your travelling at the speed of light??

Answer 5

You are in the reference frame of the car, so to you, the light would behave normally.

The light would travel out from the headlights at light speed, just like normal, and reflect off things, but if you are traveling at that speed those objects would be so distorted you might not recognize what they are.

Answer 6

You are asking a question about an impossible situation.
Therefore, the answer to your question is: you can't.

You can't drive a car at the speed of light, and you can't turn on the headlights.

Answer 7

The fundamental premise of Einstein's special theory of relativity is that everybody measures the speed of light the same. It is a constant. It is independent of the observer's speed, or reference frame.
You and your car could not move at the speed of light. But even if you could, you would measure the speed of a light beam the same as everybody else in the universe.