Traveling at near-light speeds-do your headlights work?
Q: If you could drive your car in the dark of space at the speed of light what would happen if you turned your headlights on? Could you see in front
of you?
A:
I'm sorry but I can't answer that question because you can't drive at the speed of light. It's a physical impossibility. Only massless objects, like a photon,
can travel at light speed. An object with mass requires an infinite amount of energy to accelerate to light speed. Can't be done.
I can tell you what happens if you drive a car at very nearly the speed of light and turn on your lights. You can see in front of you. What's more: try looking in
the mirror. Light from your face bounces off the mirror and reflects back at light speed, even though you are traveling at nearly the same speed. You can see
yourself.
Einstein doped all this out back in 1905. His Special Theory of Relativity states:
- The rules of physics have to work in all frames of references-moving or at rest, as long as the moving frames are not accelerating. Things have to work as
usual.
- The speed of light in a vacuum is a constant.
So, the lights from your headlights have to go at light speed with respect to any reference frame. The light will go speeding forth at its constant speed, hit
objects in front of you, and bounce back to your eyes. All objects will be coming toward you at near-light speed so the reflected light will be shifted toward the
high frequencies, like the high pitch of an approaching train's whistle. The light frequencies go from visible to ultraviolet or beyond. Things outside your
window would look strange, if you could see those frequencies: length-shrunk images, distorted by aberration and bizarre time effects.
See "Relativistic Flight" in Further Surfing for a trip that shows the outlandish scene going by at near-light speeds. Hang onto your hat!
"My simulation of a relativistic flight neglects the shift of colors and brightness," says Norbert Dragon, research group leader at the Institute for Theoretical
Physics in Hannover, Germany. If headlights of a moving observer light the scene, the colors change even more surrealistically and the brightness becomes a
"complicated function of the position and the velocity."
(Answered by April Holladay, science correspondent, June 6, 2001)
Further Surfing:
Inst for Theor Physics: Relativistic Flight
How stuff works: Special Relativity
Greg Egan: Special Relativity
American Institute of Physics: Albert Einstein- the man
Further Reading:
Conceptual Physics by Paul G. Hewitt, 8th edition, Addison-Wesley, 1998.
Special Relativity by Anthony Philip French, W.W. Norton & Company, 1989.
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