Philisophical question.

[Loké]

Time travel. There are three theories I know about it. (For the sake of argument you've gone 100 years into the past.)

 

1. 'Butterfly theory'-the very fact you've travelled back in time has altered the furure somehow, so when you return your future will be different somehow. May be big, may be small, but a difference there will be.

 

2. 'Fragmented theory' as above, except that your furure is uneffected. Essentially the past you have visited is now an alternate reality.

 

3. 'Pretzel/fixed theory'-when you were born, you'd already travelled into the past. So if you didn't travel into the past, the world as you know it in your 'real' time would not exist.

Or in laymen's terms, anything you did in the past has already happened before you were born. So you actually need to travel back in time for your world to exist!

 

Discuss and/or come up with your own theories.

[Andyr]

I'd go with Hawking et al on this. Relativity permits time travel in universes of certain geometries. However, I don't think there's a feasible way to jump back/forward in time at will. Modern theories say it may be possible but highly unstable, or requiring massive amounts of energy.

 

You could, of course, say that you're always travelling into the future at a rate of 1 second per second...

 

Travelling at high speeds is one way to go into the future, though very expensive and you can't get back. I am ill and others can probably explain it better than me, so I Googled: http://www.phys.unsw.edu.au/~jw/twin.html

[jester]

I thought there were connections between black holes constituting a way to travel in time named Einstein-Rosen-bridges IIRC, but other than Andyr I choose to go with Marty McFly on that issue.

[Andyr]

Yeah, black holes are one of the theories of possibility. But it is thought that perhaps the hole might close after use, or crush you in the process, or something.

[CamDawg]

The best explanation I've seen is the infinite parallel universe theory--in such a system, time travel paradoxes cease being paradoxes. The closest would be #2 in the initial post. I've also seen it trotted out to explain light particle/wave duality.

 

Every time there are multiple possible outcomes to an action, all of them occur in parallel. An analogy would be the idea that your universe is a road, and any action with multiple possible outcomes is a fork in the road. To push the analogy, going back in time would mean traveling back to a point on your particular road. However, you would proceed forward along a different branch, making it impossible to affect "your" future. Hence, the common what-if of eliminating your ancestor no longer contains a paradox.

[Loké]

Yea, sounds like II.

[jester]

@Cam: Would that be something like the Heisenberg theory?

[jastey]

I don't know about the existing theories, but what I find logical is: Past already happened, so if you'd travel into the past - it already happened, so you won't change "your" future, because you being in the past is part of it.

[CamDawg]

Jes: Do you mean the Heisenberg Uncertainty principle? It's a different beast and essentially says you can never have exact measurements of momentum and position of a particle simultaneously--i.e. if you know the exact momentum, you have infinite uncertainty in the position, or vice-versa. It an also be expressed as "if you measure something, you change the results."

[Domi]

I am with alternative realities simply because it is the simplest one to comprehend, I guess.

[jester]

Jes: Do you mean the Heisenberg Uncertainty principle? It's a different beast and essentially says you can never have exact measurements of momentum and position of a particle simultaneously--i.e. if you know the exact momentum, you have infinite uncertainty in the position, or vice-versa. It an also be expressed as "if you measure something, you change the results."

Yes, but I thought together with Schroedinger's cat example it is quite good at explaining alternate realities. I wish I had been more attentive in class.

[Hendryk]

Actually, it is a moot point. The World-as-we-know-it was created five minutes ago, including all memories and records of a past that never existed. It is a part of an anchovy-pizza induced nightmare, happening to a guy named Fred. In ten seconds, he will belch, switch dreams and that will be it for us.

[jester]

I like that idea. It reminds me of that butterfly story with the dream.

[Galactygon]

Yeah, black holes are one of the theories of possibility. But it is thought that perhaps the hole might close after use, or crush you in the process, or something.

 

I believe you would never reach the center of a black hole beacause time would slow down infinetly as gravity would become infinite. Einstein's Theory of Relativity claims as gravity increases, time slows down.

 

You would just float forever going infinitely nearer and nearer to the center, but you would never make it.

 

-Galactygon

[CamDawg]

You would just float forever going infinitely nearer and nearer to the center, but you would never make it.

 

Your feet stretching to an infinite distance from your head would pose a significantly more immediate problem.

 

Yes, but I thought together with Schroedinger's cat example it is quite good at explaining alternate realities. I wish I had been more attentive in class.

Well, yes and no. Schrodinger's cat is an excellent example of how quantum mechanics is based upon probability which in turn leads nicely to the parallel universe theory. I happen to think the classic dual-slit experiment is a simpler, more concrete example. The gist is that in our universe, light does indeed behave as a particle and pass through one slit. The observed interference pattern is due to the effect of parallel universes. I really get lost in the mathematics and theory (been a long time since my Quantum Mechanics courses at Berkeley) but that's the idea. I also don't know if this is something that's being embraced by the mainline physics community or some of the theorists floating ideas.