# if you are in a car and traveling the speed of light..what would happen if you turn on the headlights?

somebody asked me this..and it's been killing me..so if you \have any idea..please tell me=D

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What you say to them is, "A car can't go the speed of light." According to the theory of relativity, NOTHING that has mass can go as fast as light.

If you were in a car travelling at 99.999999% of the speed of light, and you turned on your headlights, the light from your headlights would shine out in front of you, and it would light up the landscape, and you would be able to see it.

From the point of view of a hitchhiker standing on the side of the road, the light from your headlights would be 'blue shifted' because of the doppler effect. Actually, 'blue' is a bit of a misnomer here, because at that speed, the 'light' from your headlights would appear to the hitchhiker to be a beam of extreme, high-energy X-Rays.

I'm not 100% sure, but I think that the light that you see, reflected off the hitchhiker's shirt and other objects in the road would be blue-shifted by exactly the same amount. (Wear your sun-glasses. :-)

The light from the headlight will still travel at the speed of light and not at twice the speed of light as you might expect. In Einstein's theory of relativity, the addition of velocity takes the form,

s = (v + u)/(1 + (vu/c^2))

where v and u are the two velocities to be added and c is the speed of

light.

At velocities we normally associate with our daily experience, a car's speed for example, say 76mi/hr and 90 mi/hr, the equation for s essentially boils down to

s = u + v --> since the denominator is approximately equal to 1

Once you approach relativistic velocities, the denominator becomes significant.

In your question both v and u equals c, and so the denominator term is equal to 2

s = (c+c)/2

= 2c/2

s = c

• Anonymous

Neither you nor the car could be traveling at the speed of light in the first place. According to Einstein:

E = γmc^2

This means that it would take an infinite amount of energy to accelerate the car to the speed of light. At today's gas prices, that would cost a pretty penny ;-)

• Anonymous

According to relativity, you're in the same frame of reference as the headlights, and not moving with respect to them, so that's look normal. (Light travels at the speed of light, regardless of how fast the source is traveling - that was the brilliance of Einstein's thought experiment.)

The question doesn't make any sense. Massive objects cannot travel at the speed of light.

• bonobo
Lv 7

(guessing) Well the headlights will work, I mean it will light up and all. But you wont see if the light will reach the road, you won't be able to see it in front of you.

You would not believe this, but last night I dreamed this last night.

Wow, to come across a question like this, also I had barely any brakes and had to save them, my sister was in the passenger seat?

Wonder if this is really meant to mean something?