Learn more physics!
Hey, If a short burst of energy is used to create light, lets say out in space, and it just so happens that nothing is in the path of the light for eternity (so its just traveling through nothingness, towards nothingness) will the light (and the energy the light is made out of) ever cease to exist?
- Jeffrey Twomey (age 15)
At the risk of sounding like a politician, that depends on what you mean by ’exist’. It also depends on whether the future of the universe takes any unanticipated twists. Right now it looks like the expansion of the universe will keep accelerating. Then after a while as the light gets far away, that expansion will carry it outside our horizon, so that no signals or other effects from anything it hits could ever return to us. If you want to take an Earth-centered view of existence, you could say that the light will cease to exist at that point. Of couse it's possible that the universe won't always behave that way, in which case all bets are off.
By the way, I wouldn't say that light is 'made out of' energy. You could just as easily say that energy is made out of light and other things. Energy is one property of light.
Tom points out: Of course the light will continue to exist for any observer who happens to be in the way when it strikes. And there's also the conservation of linear and angular momentum from its emitter -- anyone keeping track of these at the source will know that they were carried away by light, so at least as that sort of record, the light will continue to "exist" at the source.
(published on 10/20/06)
Follow-up on this answer.