Time travel

[Mangetout]

*Originally posted by Czarcasm *
**Of course, time travel in and of itself is only half of the problem that needs to be addressed. The other half? Staying put!
Let’s say you manage to travel back or forward in time a mere five minutes. In that five minutes the Earth has spun on it’s axis, the Earth has continued to revolve around our sun, our solar system has moved within our galaxy, the galaxy has both expanded and moved outward, and so on and so on. So you tell me where exactly you will end up if you travel in time a mere five minutes? **

Interestingly, this would enable you establish an absolute reference frame.

[samarm]

*Originally posted by MC Master of Cermonies *
**O, it’s dependant on huge amounts of negative energy, which can be produced on a tiny scale but it requires the discovery of ‘exotic matter’ to produce it before it becomes in anyway plausible. **

What is exotic matter?

Originally posted by Mangetout
Interestingly, this would enable you establish an absolute reference frame.

What exactly would enable you to establish a reference frame?

[MC_Master_of_Ceremonies]

We’re moving into an area which I can’t claim much expertise on, but from what I understand exotic matter is hypothetical matter that produces negative energy.

[BioHazard]

Do a search, this topic has been talked to death here in the forums.

[Jonathan_Chance]

*Originally posted by Czarcasm *
**Topless Black Holes!! No Cover Charge!! **

No, no, no…

You’ve got it all wrong.

Singularities all have tops…

The just don’t have any bottoms.

Shameless, I tell you. Shameless.

[SPOOFE]

Time travel is possible. I can prove it.

…

There. You have now travelled a second into the future. Oops, there you go again… ah, and agai- whoa, stay put, would you?

[Liberal]

In the 1980s, women will have robots to do their ironing.

[smiling_bandit]

I think one physics nut proved to the best of our scientific ability (and in physics that isn’t much in this case), that by making two hollow spheres the size of the orbit of pluto and rotating them in opposite directions, one could time travel back to its creation by flying through a hole cut straight through.

[Pythagras]

There was this book on the plausability of time travel, lots of Chopin in it, lemme see if I can find it:

http://www.amazon.com/exec/obidos/ASIN/0618257357/qid=1040043461/sr=2-1/ref=sr_2_1/103-7271354-5982234

Maybe thats it

[Mastema]

Kip Thorne was the one who did the most research into using wormholes as time machines, most of it in response to a query from Carl Sagan who called asking for technical help with his (then) upcoming book Contact.
Thorne and Stephen Hawking have jointly stated that time travel via wormhole is possible, but that we haven’t got the means to locate a naturally occuring wormhole and reach it, or the energy to create one ourselves; however, they did give a rough idea of how you would go about forming one if you had the resources.

See the video “Time Travel” by Kip Thorne 1999.

[SPOOFE]

I think one physics nut proved to the best of our scientific ability (and in physics that isn’t much in this case), that by making two hollow spheres the size of the orbit of pluto and rotating them in opposite directions, one could time travel back to its creation by flying through a hole cut straight through.

Sounds interesting. Anybody got anything more specific on this? I’d love to read that theory.

[tracer]

Larry Niven’s argument as to why we will never have time-travel capability:

If someone invented a way to travel through time, then, given the enormous span of future years still to come, the odds approach certainty that someone will eventually travel back through time and prevent time travel’s invention.

[TVAA]

It isn’t possible for a universal configuration to exist such that its own causality can be violated. If time travel is possible, changing the “flow” of time is not.

[tracer]

*Originally posted by The Vorlon Ambassador’s Aide *
It isn’t possible for a universal configuration to exist such that its own causality can be violated.

Who says?

[MC_Master_of_Ceremonies]

*Originally posted by tracer *
**Larry Niven’s argument as to why we will never have time-travel capability:

If someone invented a way to travel through time, then, given the enormous span of future years still to come, the odds approach certainty that someone will eventually travel back through time and prevent time travel’s invention. **

But most time machines cannot travel further back in time than the creation of the machine, and even then the older the time machine gets the less far back in time you will be able to go.

[MC_Master_of_Ceremonies]

Also Niven is making big assumptions about the future.

btw, I think time machines are almost certainly impossible but not by Nivens logic.

[MC_Master_of_Ceremonies]

*Originally posted by The Vorlon Ambassador’s Aide *
**It isn’t possible for a universal configuration to exist such that its own causality can be violated. If time travel is possible, changing the “flow” of time is not. **

That’s making a huge assumption about the ‘universal configuration’. Remember because of quantum physics there is no true universal configuration. The flow of time can often be meaniless in extreme situations.

[ElJeffe]

I’ve heard that another problem with wormholes in general is the tremendous amount of energy needed to withstain them, and the larger they are, the more energy you need (or rather, the more force you need, as they become increasingly prone to collapsing). Tiny, useless ones require a huge amount in and of themselves. Anything large enough to be of any use would require so much as to be nigh impossible.

MC Master, could you explain, in a nutshell, why any time machine couldn’t travel back in time to before it was created? I understand that it helps prevent violations of causality, and I could see the logic in that for, say, the wormhole variety, but is there some concrete reason why any time machine of any sort would necessarily be unable to send the user back in time to before its creation?

Jeff

[TVAA]

Consider the following:

In order to seriously think about the nature of time, we must place ourselves outside of it, in a metatime.

Some time during the history of the universe, a form of energy is generated that can travel “backward” through time. This leads to two possibilities: 1) causality is preserved, or 2) causality is not preserved. In the first case, there is no paradox. In the second, since history is altered, the energy isn’t generated in exactly the same way in the “future”. From a metatime perspective, the configuration of the universe cycles through unstable historical paths, with each alteration destroying the configuration that spawned it, until a stable configuration is reached.

In that final, stable configuration, there are two possibilities: 1) By “chance”, at no point in that universe’s history will time travel occur, or 2) time travel occurs, but merely creates an Oroboros Paradox, preserving causality.

Therefore, time travel either does not exist, or cannot be used to change history.

[MC_Master_of_Ceremonies]

Well, I say this for three reasons

1. Stephen Hawking says so.

2. Everytime ‘plausible’ time machine conceived chas had this limitation

3. A time machine is basically a physical link between the past and the present, if no such acessible ‘doorway’ existed at the point in time you wanted to travel to, you couldn’t exactly go back in time and make one.