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wundayatta's avatar

A question about time travel (theoretical physics)...

Asked by wundayatta (58599points) September 9th, 2008

So I know that mathematecally, the universe could just as easily run backwards, as forwards. But in our reality, it only runs forwards.

Suppose we could break the light speed barrier. It seems to me that we could travel backwards in time (catching up to and passing light that was emitted in the past, thus experiencing those things again. But how could we move forward in time? If time only moves forward, those events have not yet occurred, and we can’t catch them, even if we can go faster than light. Due to chaos, there is an infinite possibility of future events.

This is why I don’t like multiple worlds theories: every second can be divided into an infinite number of parts, and in every one of those parts there is an infinite number of possibilities, so after one second, it seems to me the universe would have been multiplied an infinity of infinities and where would the space for all that be?

So how could we travel into the future? Seems to me we can only travel into the past (theoretically), assuming the light speed barrier is broken, and of course, that is theoretically impossible. Ergo, no time travel. Ever. Period.

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21 Answers

sacaver's avatar

See, but I have always wondered if we could only travel into the future, based on laws of conservation of energy. Think about it this way, if you travel into the past, are you not then duplicating the mass present in your body/clothing/gear to the existing mass of the universe at that point in the past? It would seem to me that going to the past would not be possible because you would be “creating” energy.

Going to the future, on the other hand, could be possible since the mass represented by your body/clothing/gear would be removed from the current stream. It’s not duplicating mass within the universe. You’ve just temporarily taken it to the “side” and then you are going to deposit it at some point in the future.

Do we have any theoretical physicists on this site?

girlofscience's avatar

If anything goes wrong, Desmond Hume will be my Constant.

sacaver's avatar

^LOL. Where’s a good TARDIS when you need one?

Poser's avatar

I don’t know, but I have to follow this thread. I came to my own conclusions about God based on this very idea (basically, He’s just really, really, really fast).

qualitycontrol's avatar

time is an illusion created by people to control other people. if you want to travel through time all you have to do is let go of the fact that there is time. then you can free yourself. it’s merely a matter of being where, not when.

sacaver's avatar

Here’s another question for you, based on the issue of time.

Just prior to the Big Bang (or whatever creative element you wish to use), there was nothing. Correct? Then the Big Bang happens and the entire Universe gets created. The clock starts running on time since the Big Bang. But what about time BEFORE the Big Bang? Does that not also get created instantly after the BB?

robmandu's avatar

Actually, according to the Twin Paradox, traveling forward in time is certainly the more likely way to go.

To the person on the rocketship traveling really, really fast, time outside his perception would appear to go by faster because when he returned to Earth, more time would’ve passed here than what he experienced.

As far as catching up to light so you can “re-experience” it… well, I don’t think I would consider that to be time travel to the past.

JackAdams's avatar

At last, it has happened.

Someone has posted a question here, to which s/he already knows the answer, and has even stated it.

lapilofu's avatar

Robmandu is right, and to expand on that idea, every time you move, you are actually traveling into the future slightly faster than if you were staying still. As someone approaches the speed of light, everything around them will appear to be moving more rapidly. Or to an outside observer, they would appear to be moving more slowly.

So, in short, time travel into the future is not simply possible, but it is already happening to you constantly.

Relatedly.

wundayatta's avatar

@jackadams: it’s just the sf approach. You get to break one law of physics, but all the rest stay the same. Of course, in reality, we can’t break the laws of physics. That’s all I was trying to acknowledge.

@robmandu: but is that really travel to the future? More time passes on earth than on the spaceship. So, I guess you’re skipping time a bit.

However, it’s a one-way trip. Another way to look at it is that the time traveller is really aging more slowly than others as they move into the future. In that sense, we’re all one-way time travellers moving at approximately the same speed, but some of us might go slower. We’re just talking about when the relative difference in aging speed becomes obvious, or significant.

Interesting point by lapilofu. It means that astronauts and airplane pilots are aging more slowly as they move into the future than the rest of us. Anyway, since it’s a one-way trip for all of us, it somehow doesn’t seem like a journey, because what we really want to do is to be able to take the trip and return home.

JackAdams's avatar

I know. Just giving you a good-natured “hard time,” so others won’t be tempted to give you a vicious one, as some in here are known to do.

robmandu's avatar

in reply to, “but is that really travel to the future?”

What’s the diff? You jump in a spaceship for an hour (assuming instant, harmless accelearation to near the speed of light), then disembark to find 80 years have passed.

And yah, today we don’t know how to travel back in time… but if you were able to continue bouncing forward, maybe some future generation would.

And then you’d likely discover the secret to global conspiracy theories… that the puppet leaders and organizations are really being controlled from the future in an attempt to bring about the utopia they didn’t have.

Oh. But wait. Then the time line would schism. And then how could they (in non-utopian future) be able to successfully direct us to a different future?

Ugh.

JackAdams's avatar

@daloon: I know. Just giving you a good-natured “hard time,” as a kind of “pre-emptive first strike,” so other folks in here would see it and misinterpret it and maybe think, “Oh good, he’s already being ‘attacked,’ so there’s no need for me to do that.”

It’s not a bad idea at all, to sometimes “run interference” for someone you admire, right?

Lightlyseared's avatar

@daloon How do you know its running forwards? It could just as easily be running backwards and we just think it’s running forwards. For example we can see whats behind us but not whats in front of us so maybe we’re going through time in the wrong direction.

I need another drink now

qualitycontrol's avatar

but wouldn’t moving faster (at the speed of light) than everything else around only allow you to move a greater distance? Like if you get in a car and drive at the speed of light. You wouldn’t transcend time would you? You would just get from point A to point B faster. Traveling at the speed of light doesn’t make sense. It has nothing to do with speed. That isn’t even a valid theory. We are all in a constant time line continually growing and aging if we were to go backwards in time we would die instantly. You couldn’t possibly exist.

wundayatta's avatar

@lightlyseared: forwards; backwards; it doesn’t matter what you call it. It’s that it runs consistently in a direction we call “forwards.” It can’t be the “wrong” direction. It is merely the direction it is. The only alternative would be in random, non-causal directions. Causality seems to work, mostly. Enough for most people, anyway.

If you’re travelling at the speed of light, then you aren’t changing direction with respect to photons and you wouldn’t be able to see anything behind you and time would essentially stand still, I think. Now, if you were travelling faster than light, you would be gaining on photons and passing them, and essentially re-seeing things that had already happened once before.

But, since you’d be beyond lightspeed, all bets are off about what would be perceivable. Perhaps there would be a kind of reverse relativity. I don’t know if you could actually travel in any direction at hyperluminal speeds. But it’s hardly worth speculating about, since it is physically impossible to achieve such speeds, or even the speed of light. Maybe even not very much of a portion of speed of light. I don’t know.

Still, it’s kind of fun to speculate about. Then again, I find I get stuck at certain points, because we’re really making up new laws of physics, and once we do that, we can make anything possible. It’s all garbage.

On the other hand, from a fictional point of view, it would be interesting if you could make it sound convincing.

damien's avatar

I’m really, really, really out of my depth the minute I mention this, but doesn’t this link in with sting theory somewhat? In that, if you could bend a dimension, you could go both forwards and backwards in time.

http://www.tenthdimension.com/medialinks.php

@lightly, I need a drink now, too

paulc's avatar

Of course, there’s always the possibility that time is total nonsense that we’ve fabricated to see things in a way that suits us. In that case, travelling in “it” isn’t an issue because “it” simply isn’t.

JackAdams's avatar

PaulC, that’s a most interesting observation.

It’s similar to the one that reads, “If a tree falls in the forest and no one SEES it fall, then it did NOT FALL!

mrswho's avatar

@sacaver I’ve never thought of time travel as having to do with the conservation of matter and energy! Great point! The main issue I have with the universe being able to move backwards is that it would screw with the laws of entropy. If fallen glasses could reassemble themselves then entropy would be lost and I’ve heard that order generally decreases. That’s my understanding of why we see time as moving forward and I think that I read somewhere that entropy is conducive to life.

intro24's avatar

Dare I say that I believe that any and all laws of physics can be broken (or “twisted”) in certain situations. The man tells you in kindergarten that time is one universal measurement of sorts. Then along comes the theory of relativity and all the sudden that’s not quite the case anymore. That sort of thing.

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