Help please? Physics question.?

Question

An airplane generates soundwaves. When it flies at the speed of sound, it catches up with the waves, producing a sonic boom. Would an object radiating light ever catch up with its wave? Explain.

This has to do with Einstein's 2 postulates of relativity. I think the answer is it won't, but why?

Answer 1

As an object grains speed it also gains mass, but the relationship is non-linear, since at the speed of light an object would have infinite mass and therefore infinite energy. Obviously this is not possible since there is only a finite amount of energy in the universe.

However, when not passing through empty space, (ie: when travelling though a medium) the speed of light is slowed. If a particle is then fired through such a medium faster than the speed of light in that medium, you can get a "light boom". That is the cause of Čerenkov radiation:

http://en.wikipedia.org/wiki/Cherenkov_r...

However this is a distincly different effect to that of a sonic boom.

Answer 2

no.

If an object is traveling at 99% of the speed of light (or 99.999%) and emits a beam of light forward, that beam would still move at the speed of light relative to the object.

And the new beam of light measured by a stationary observer would be moving at the speed of light.

.

Answer 3

Sound and light are very different kinds of waves. Sound waves are vibrations of molecules. In the case of an airplane, the air molecules are vibrating and the plane is moving through the air. So as the sound causes molecules of air in front of the plane to vibrate, the plan can catch up to those molecules.

But in the case of light, there is no medium for the object to catch up to. There is nothing that is vibrating except the light itself.