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# time travel possible? watch

1. (Original post by Kebmo)
Sorry for my ignorance, but is the speed of light a constant? could you not slow down light so that you could travel faster than it?
When people talk about the speed of light, they mean the constant value 3x10^8 ms^-1. The important part is the numerical value, rather than the fact that light travels at that speed in free space. Hence when light is slowed down under certain conditions, it doesn't affect the value, c still = 3x10^8. Even if the light photons in question are going slower than this.

Time travel is possible to a limited extent. If you were to travel really fast say on a spaceship for a few years, when you come back to land on earth time will have gone much faster on earth than it did for you. You could have a twin on earth and when you got back he'd be older than you. Wierd eh ? This effect happens every time you take a plane somewhere, and is due to the effect of relativity. Incidentally with planes and super precise clocks was how relativity was experimentally verified.
2. (Original post by DeanK2)
Infact, we all time travel on the quantum level.
no we don't- QM is non-local but it is still causal.

(Original post by wizz_kid)
This is how you could possibly travel back in time.

However, travelling faster than the speed of light violates the laws of physics and hence it is not possible.
(a) even if you travel faster than light, proper time is never negative. it is a parameter independant of the metric of spacetime.

(b) It doesn't actually violate the laws of physics as I know them. All governing equations that I've met are time-reversal invariant. There is nothing, on a fundemental level, "preferred" about forwards time.
3. (Original post by john !!)
no we don't- QM is non-local but it is still causal.

(a) even if you travel faster than light, proper time is never negative. it is a parameter independant of the metric of spacetime.

(b) It doesn't actually violate the laws of physics as I know them. All governing equations that I've met are time-reversal invariant. There is nothing, on a fundemental level, "preferred" about forwards time.
hhhhmmmmm.....

It is well known fact that subatomic regualry travel back in time. Of course, we observe them as their own antiparticle when they do this.
4. Fact or theory?
5. (Original post by teachercol)
Fact or theory?
Everything in science is a theory - I seemed a bit hard and faast with the use of the word 'fact'.
6. you cannot go faster then the speed of light, energy becomes infinite. however theoretically you could get very close, without energy becoming near infinite, but alas, i think individual research needs to be done on your part, as these are quite complex things we are talkign about.

The only thing I know of that has sub particles travelling faster than the speed of light is cerenkov radiation.
7. (Original post by A_Fictitious)
The only thing I know of that has sub particles travelling faster than the speed of light is cerenkov radiation.
Except it doesn't travel faster than c. That is impossible. It travels faster than light in the same medium because the light is slowed down.
8. Quite, but for the none "knowers" here, you could of left them to dream
9. I prefer to crush dreams.

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