Time Travel

[Big Stupid]

OK, I'm guessing that none of you folks have taken Physics past the college Freshman level. I guess I'm being condescending, but I would encourage deeper study on the matter, because most of what I've read on this thread is kind of misinformed. Or even just read "The Physics of Star Trek." It's pretty good.

That said, if you want to read some good time-travel based science fiction, I suggest Robert Heinlein's short story "All You Zombies" (you can find the full text online) and his novel "The Door Into Summer." They're both fun reads.

I am not aware of any current theory in Physics that would allow for stationary time travel, but I really don't know the really complicated stuff, or even much of the senior-level undergrad stuff, since that wasn't my major. However, if I could travel back in time and remain on Earth, I would probably assume a pseudonym and live my life. I kind of like the name "Warren Buffett".

Speaking as someone who never took physics, time travel may never be physically possible as reaching the speed of light would require more mass then the universe has, unless of course we invent an hyperefficient way of space travel.

However, I hold it to be LOGICALLY possible the same way that a cow jumping over the moon is logically possible because it doesn't contradict itself in anyway although cow physiology would make it PHYSICALLY impossible. This holds true to the double jumps you see in many platformers. Also me beating Battletoads is still logically possible, unlikely as it may be. Heck it might even be physically possible with enough coffee, and gumption.

I don't actual believe that human beings will ever be able to achieve time travel. However, I just believe that each and everyone of you should exercise extreme caution in using the word impossible to describe anything.

As long as we're listing our favorite time travel tales I'd like to plug Michael Crichton's Timeline.

[RyaNtheSlayA]

As long as we're listing our favorite time travel tales I'd like to plug Michael Crichton's Timeline.

Same here

[Mod_Man_Extreme]

OK, I'm guessing that none of you folks have taken Physics past the college Freshman level. I guess I'm being condescending, but I would encourage deeper study on the matter, because most of what I've read on this thread is kind of misinformed. Or even just read "The Physics of Star Trek." It's pretty good.

That said, if you want to read some good time-travel based science fiction, I suggest Robert Heinlein's short story "All You Zombies" (you can find the full text online) and his novel "The Door Into Summer." They're both fun reads.

I am not aware of any current theory in Physics that would allow for stationary time travel, but I really don't know the really complicated stuff, or even much of the senior-level undergrad stuff, since that wasn't my major. However, if I could travel back in time and remain on Earth, I would probably assume a pseudonym and live my life. I kind of like the name "Warren Buffett".

Speaking as someone who never took physics, time travel may never be physically possible as reaching the speed of light would require more mass then the universe has, unless of course we invent an hyperefficient way of space travel.

However, I hold it to be LOGICALLY possible the same way that a cow jumping over the moon is logically possible because it doesn't contradict itself in anyway although cow physiology would make it PHYSICALLY impossible. This holds true to the double jumps you see in many platformers. Also me beating Battletoads is still logically possible, unlikely as it may be. Heck it might even be physically possible with enough coffee, and gumption.

I don't actual believe that human beings will ever be able to achieve time travel. However, I just believe that each and everyone of you should exercise extreme caution in using the word impossible to describe anything.

As long as we're listing our favorite time travel tales I'd like to plug Michael Crichton's Timeline.

True, I'll agree that unless we've managed to make a light speed or near light speed mode of transportation, or find a way to cross into a different dimension in which the past is actually the present then there is no possible way to travel through time at the present moment.

Here's some very basic info from the wiki page on Time Travel:
http://en.wikipedia.org/wiki/Time_travel

It's pretty crazy stuff and is tricky as hell to get down pat, but best left to Sci-Fi writers and TV shows for the meantime.

[d123456]

Even if I were to build a ship that would travel twice the speed of light. (Which is theoretically possible!) No time change/travel/slow down/speed up would occur. (I would just loose my ballz.)
Why?
That is not the question. The question is why would anything happen.
And writing down a theory and publicizing it does not make it theoretically possible at all.
Theoretically means proven to certain extent, but never executed. Time travel does not fall into that category.
Still, I love to argue about it.

Not logically possible either, forget it!
Still we need more time travel movies.

If you really want to time travel. Do it like Michael. Freeze yourself and maybe in the future.....they can revive you.

[Limewater]

And writing down a theory and publicizing it does not make it theoretically possible at all.
Theoretically means proven to certain extent, but never executed. Time travel does not fall into that category.

This is incorrect. A theory is a system that explains observations. A theory can never be "proven" to any extent. If it could, it would be a "theorem". Some modes of "time travel" are consistent with and deducible from current theories regarding the nature of the universe. In that sense they are "theoretically possible".

You could say pretty confidently that these theories are flawed and/or inadequate, and you would be right. However, even if the last 100 years of Physics and Astronomy were thrown out of the window tomorrow, that would not make any dent in a claim that time travel is not theoretically possible.

Still, I love to argue about it.

Not logically possible either, forget it!
Still we need more time travel movies.

And you present such convincing arguments!

If you are trying to speak from a purely logical perspective, can you formulate a proof showing that time travel is not logically possible?

[Ivo]

If you are trying to speak from a purely logical perspective, can you formulate a proof showing that time travel is not logically possible?

Violation of causality is the problem. How can an effect precede the cause? In any case, it seems to me possible to idealize internally consistent time travel - most works of fiction don't do it, but as I posted earlier the Phoenix Gate examples in Gargoyles don't violate internal consistence (unlike what happens in Back to the Future, Terminator, etc.)

[Limewater]

Violation of causality is the problem. How can an effect precede the cause? In any case, it seems to me possible to idealize internally consistent time travel - most works of fiction don't do it, but as I posted earlier the Phoenix Gate examples in Gargoyles don't violate internal consistence (unlike what happens in Back to the Future, Terminator, etc.)

Exactly. Just because Back to the Future violates causality, that does not mean that it necessarily has to violate causality.

[Ivo]

Exactly. Just because Back to the Future violates causality, that does not mean that it necessarily has to violate causality.

I like to give an example of a simple classical system. Imagine a "Portal" pair of circular gates displaced in space, that are also a time travel gate. In your own time that just goes forward, send a billiard ball in a well defined direction so that it would NOT enter the "back to the past" gate. Then at some time on your clock, the "same" ball comes out of the "coming from the future" gate in a second well defined direction, hits the ball you launched and sends it into the "back to the past" gate exactly such that when it comes from the "coming from the future" gate it comes out in precisely the second well defined direction. During a small interval in your time, there are 2 balls (the same ball, but one is a bit "aged"). If you want, have the ball you send actually contain a clock.

That simple scenario is entirely self-consistent as far as I can see. The ball only goes through it "once", it is just a bit confusing. In the ball timeline, what happens is: get sent by you, get hit by something (itself, later), go into portal, travel back in time, hit something else (itself, earlier), stop due to friction (without entering any more portals), get checked for elapsed time of it's internal clock by you.

Ivo.

[d123456]

can you formulate a proof showing that time travel is not logically possible?

Time travel is not possible. Time is something that keeps on going. Time has nothing to do with speed. I know about the tests with planes flying around the world and the clock showing some differences. I just don´t believe in that. Those tests are flawed.
The next minute is really the next minute.

Even if the entire galalxy would be frozen for 1 hour that would not mean that time was stopped. it would simply mean that the galaxy was frozen for 1 hour.

Formulating proof against the possibilty of time travel is ludicrous. I know it is not possible.
why is not possible you ask? Simple.
Matter/energy can not dissappear. traveling into or back into the future would mean matter/energie would dissappear. That´s impossible.

[Limewater]

I like to give an example of a simple classical system. Imagine a "Portal" pair of circular gates displaced in space, that are also a time travel gate. In your own time that just goes forward, send a billiard ball in a well defined direction so that it would NOT enter the "back to the past" gate. Then at some time on your clock, the "same" ball comes out of the "coming from the future" gate in a second well defined direction, hits the ball you launched and sends it into the "back to the past" gate exactly such that when it comes from the "coming from the future" gate it comes out in precisely the second well defined direction. During a small interval in your time, there are 2 balls (the same ball, but one is a bit "aged"). If you want, have the ball you send actually contain a clock.

I do not think this example *actually* violates causality. It only appears to do so from your frame of reference. As you acknowledge, from the ball's perspective, there is no causality violation.

That said, I don't see the big deal with causality. On the quantum level, causality appears to be violated all the time.

That also being said, I do not actually believe such a system as you describe to be possible. I do believe there is a good chance that time travel is possible, but that time is also likely tied to space and is therefore kid of rendered useless. You could travel through time, but you'd end up on the other side of the universe, and when you got back it would be after you had initially left. But I could be totally wrong on that, too.