tronvillain

sophie:
My name is tronvillain: if I wanted it spelled "TronVillain" I would have spelled it that way myself. Now, what the hell is "logical plausibility"? I have only spoken of "physical possibility" and "logical possibility." Time travel may or may not be physically impossible given the structure of reality, but it is not logically impossible. Of course, all that means is that there are hypothetical structures for reality that would permit time travel, so I do not have to use "a BIG IF" because the "BIG IF" should be obvious to anyone reading the words "logically possible."

sophie

tronvillain, I deeply apologise for spelling your name incorrectly, I am truly sorry for any inconvenience that may have caused you.

Logical plausability means at least your premises should be correct based on some reality or at least plausable.

I hope I am communicating some sense to you. I realise I am not always clear to everyone, but I try my best and acknowledge my mistakes.

nermal

Two points, not very deep (deep thinking about time travel makes me crave sugar.)

1. The H.G. Wells idea of time travel, ie. a guy jumps into a machine in Boston and travels back to prehistoric Boston or forward to post-apocolyptic Boston is absurd. Consider the consequence if he traveled back or forward only 6 months. The earth has moved halfway around its orbit, and the solar system has traveled thousands of miles on its track. Our traveler would arrive in interplanetary space.

2. I always get a chuckle when people talk about possibilities of traveling forward in time, as if it were a great future endeavor. I myself traveled forward in time more than three minutes while writing this post.

Ed

Jesse

Well, relativity says there's no such thing as "absolute space", so if you're saying the time traveler would remain "at rest" while the earth and solar system are moving around, the question is, "at rest" relative to what?

Anyway, the whole "teleportation" idea of time travel, where you disappear from one time and place and reappear in another, has no scientific plausibility. Any real time travel would involve some sort of continuous path through space and time, like taking a journey through space that for you lasts five years but finding that 1000 years have passed when you return to earth, or taking a journey through a wormhole and finding that the mouth you exit lies in the past of the mouth you entered.

crocodile deathroll

I have no problems travelling into the future, as you have already achieved that in spectacular fashion when you skipped though an estimated time scale of 14 billion years and Alas! you were born. I you happened to be born a little earlier. By a little I mean just a few hundred thousand years which is barely significant on any cosmic timescale, you may well be observing a world as Homo Augustus 600,000 BC. So the world of 600,000 BC and the world of 2003 AD are both equally real.

Travelling back into the past may also be possible because when you ultimately die, the events of this life will be totally irrelevant to you and all states of your potential existence in the universe are restored to an equiprobable state. The event of your death and the event of your birth are both equally real, so you could just as easily replay your life all over again like it is a first life experience, as there is nothing in nature to remind you that you have already lived your life.

rfwu

What about that quantum leap type time travel? I don't mean the type where you takes someone else's place, but with the other guy. Imagine time traveling back in time (and only to the past) as a non-corporeal. That would be perfect, because nobody can see you, and you can't interact with anything in that time period. Absolutely no change is made, so continuity remains the same. It's perfectly safe and people can learn a lot of stuff, like what really happened in a crime, or who really shot JFK, or what really happened during the crucifixion.

nermal

At rest relative to the curved path they earth and solar system take, of course. I suspect you would still travel through space at whatever velocity you were traveling when you stepped into the capsule, but would no longer be accelerating as the earth and solar system are, therefore you would travel off on some kind of tangent line, and arrive in empty space (most likely).

The wormhole stuff, well, that's a different kettle of fish altogether.

(In unison: "That's a different kettle of fish.")

Ed

Jesse

But when you say it'll follow a tangent line, aren't you failing to take into account the fact that spacetime is curved? The closest to a "straight line" in curved spacetime is a geodesic, but if your capsule followed a geodesic it'd still be responding to the "force" of gravity (which in general relativity is really just a consequence of the fact that mass/energy bends spacetime, and objects always follow geodesics in the absence of other forces). If it didn't respond to the electromagnetic or strong or weak forces, I guess this'd mean that your capsule would fall right down to the center of the earth and then its inertia would carry it up through the other side, at which point it would fall again and repeat the cycle over and over. You'd have to time the moment of your reappearance very carefully so you didn't materialize deep within the earth somewhere.

But asking what would "really" happen is a bit meaningless, since as I said the whole "disappear in one time and place and reappear in another" idea of time travel is totally implausible and has no scientific justification.