What happens to light in a vacuum?

Answer 1

It depends on what are you asking for. If the question is related to the speed, then nothing occurs. If it is related to absortion, then you do not have absortion and you can "see" it from far, far away.

"Light" is an electromagnetic wave. As all of them, its speed is independent of the medium in which travel. They do not need a physical medium to travel (in contrast to pressure waves, like the sound). The speed of light (defined as c = 3·108 m/s) is the same everywhere in the Universe.

Of course, any material medium cause absortion. Due to this it is impossible to see object which are far away, because the atmosphere absorbe the energy of the light. In the outer space, opposite to this, you have almost a "vacuum", so you can see star's light which comes from light-year distance. As the medium is the vacuum, the light doesn't have absortion and it travel a lot.

You have of course some regions with dust, so you do not see all the stars in the Universe.

Answer 2

Light travels through a vacuum at its maximum speed of approximately 299,792 kilometers per second, without interaction or absorption. It does not slow down or dissipate as it would in a medium such as air or water.