How to actually time travel (if you had a fast enough space craft).

[mistertrickster]

Was listening to a lecture the other day about astrophysics, and it went like this:

Einstein's Theory postulated that a denser gravitational field would slow time down relative to lighter field. This was proven true on many occasions. In fact, satellites in space have clocks that move faster than clocks on earth, so they have to calibrated to earth time.

So if you travelled to a black hole and approached the event horizon, your time would appear to move perfectly normally. However, relative to earth's gravitational field, your time would be passing much, much slower.

Then you could travel back to earth and it would be many centuries into the future.

All you need is a space craft that would take you to the center of the galaxy (where a supposed black hole is) and back.

Unfortunately, such space craft do not exist at this time.

BTW, the latest Star Trek movie was fatally flawed by this fact . . . The Enterprise was caught in the gravitational pull of a black hole, narrowly escaped, but experienced no time distortion because of it. They should have returned to an earth a couple of hundred or thousand years in the future.

[Rabrrrrrr]

1. The satellites in space actually go slower, not faster, through time

It's not gravity but velocity relative to that gravity-field that does it.

And you don't need to go to the center of galaxy - you can do it anywhere, as long as you go fast enough.

[Salviati]

4. Nope, it is the strength of the gravitational potential.

This is one of the effects due to general reletivity. The deeper you are in a gravitational well, i.e. the lower your gravitational potential, the slower your clock will run.

This is seperate from the special reletivistic effect where clocks moving with a high reletive velocity run slower.

The clocks abord GPS satalites need to take into account both effects to give out accurate signals. So if anyone ever asks what good theoretical physics is, the GPS system could not funciton without our current understanding of general and special reletivity.

[thereismore]

9. Actually, I believe the difference between using relativity for GPS and not using it is relatively

insignificant. It takes years of orbiting for the satellite to exhibit a shift of a tiny fraction of a second compared to a Earth-bound clock.

[Salviati]

13. But a tiny fraction of a second would translate to several meters of distance

if the clocks were not calibrated with the utmost precision. Both reletivistic effects combine to give a differance of rates of about 38 microseconds a day. This isn't a big number, but in order to get a feel for how it would affect the GPS readings, we need to multiply by c. This ends up giving a drift of up to about 11 km per day. So totally ignoring these effects would have a huge effect on the accuracy of the system.

http://en.wikipedia.org/wiki/Global_Positioning_System#Relativity

[mistertrickster]

11. You are partly correct as I understand it (I am far from expert in this area)

If you went very very fast, like 1/2 the speed of light, you would become more massive, hence the gravitational field would increase and time would slow down relative to earth time.

Don't think you'd gain much mass at satellite speeds though . . .

[pyoom]

14. You're referring to the Special Theory of Relativity

whereas the OP is talking about the General Theory.

[PVnRT]

2. That would work for any black hole

The larger the hole, the better chance you have of not getting spaghettified by the gravity near the event horizon.

[Ratty]

3. I think I read once

The Enterprise has "time dilation nullifiers." :rofl:

[Javaman]

7. ...

:spray:

they are right next to space calibration equalizers right?

[Birthmark]

5. You can figure out how much time dilation takes place...

...at various speeds here: http://en.wikipedia.org/wiki/Lorentz_transformation

It's a good way to kill some time. :)

[Javaman]

6. Well, if you do, just don't forget you galoshes! nt

[thereismore]

8. This has been known since 1915. You can travel through time, but only in the forward direction. nt

[Ratty]

10. Well, if there are such things as wormholes ...

Then travel backward in time might be possible. Leave one end on Earth and cart the other end around with you on a relativistic flight, say circling the solar system a couple of dozen times, then return home. One end of the wormhole will be in the past while the one you brought back with you will be in the present.

http://en.wikipedia.org/wiki/Wormhole#Time_travel

[Moochy]

15. seems like the wormhole would get tangled up around Mars and Venus

These thought experiments are fun. Especially all of these Faster than Light thought experiments... the ones that start with assumptions like you have a battery that has infinite energy capacity :)

[Statistical]

12. You don't need a blackhole just a substantially fast ship.

Einstein postulates the same thing happens to an object moving relative to an object at rest.

Moving at a substantial percentage of the speed of light would cause a magnitude more time to pass on earth relative to the craft. No need for a blackhole since any ship fast enough to reach a blackhole in our lifetime would be fast enough to suffer the effects of time dilation.

Just go in a loop to nowhere and back taking a couple years at a really high speed and when you get back to other substantially more time will have passed.

This has been partially proven with ultra accurate clocks. Taking a pair and having one remaining stationary (relative to the earth) and flying the other at very high aircraft speeds. The dialation is incredibly small (millionths of a second) but it happens.

[Silent3]

16. Forward time travel is the "easy" kind of time travel.

Simply speeding up the rate at which you go into the future has been pretty obvious since Einstein's Special Relativity.

As long as you have enough energy to propel a spaceship at very high speeds, and can withstand the acceleration (the more acceleration you endure, the more you can reduce your personal passage through time vs. the the time for everyone else), you can reduce the amount of time that passes for yourself vs. how much passes on Earth simply by flying away from the Earth, turning around, and coming back.

This is a one way ticket, however. Once you're on the future Earth, you're there to stay and aren't coming back to the present Earth, not at least without some far more exotic solution which will bring up troubling questions of causality.

[wolfgangmo]

17. geek alert

In theory, if such a term can be applies to fiction, the star trek folks do not experience for time dialation because the warp fields employed actually reach outside our universe (to a multiverse?) and thus the ships are outside our universe, sort of.

OK, so it's not a theory. Stop picking on fiction as if it should have to conform to some silly old Einstein thingy. Ahem. Snort.

[Ratty]

18. Warp drive = Alcubierre drive?

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

OK, so warp drive may not send the Enterprise back in time :) The problem with its impulse engines remain. They can propel the Enterprise at speeds approaching light. Why no time dilation?

Seriously, I'm geeked out for the day.

[HiFructosePronSyrup]

19. Welcome to the early twentieth century.