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Time travel

(Tue Jun 23 17:01:29 2009)

Time travel is a very interesting subject - not just because of the possibilities

Time travel is a very interesting subject - not just because of the possibilities, but because of the impossibilities. I've read a lot of books, watched a lot of movies, and listened to a lot of radio shows about it; on top of that, I've written some of my own stories that feature time travel. There's a lot of theories on what may or may not happen if it were possible, and I have a few of my own.

As a note, along with the other methods of time travel, there is also "Forward-only." This is fairly easy to explain, mostly because it's what we experience every day. In addition, this includes being suspended somehow (via cryogenics, for example), or being "kicked" forward some amount of time. This is the least exciting method of time travel, and since it only involves going forward, it's not so much travel, since you never come back. There's not much to be debated with forward-only travel, so I'm just going to leave it there.

To understand even a little bit of time travel, there has to be some basics, so I'll start off with a simple list.

A "Timeline" is just what it sounds like, a line of time. Timelines contain every event that happens to a person, place, or thing; timelines can cross, interact, and otherwise affect other timelines. A good way to visualize a timeline is to picture yourself walking down a hallway full of doors, holding a ball of string. The string begins the instant you begin to exist, and ends while you die. As you go through life, you unroll the ball of string as you go, leaving a line of string everywhere you go.

A timeline is made up of a series of linked "decisions." A decision occurs when a timeline has the possibility of going in multiple directions - for example, an ant choosing between which of two identical leaves on a tree to cut - a decision is made, and the timeline follows that possible branch. Every decision is linked to more down the line, and affect other decisions made by other timelines; that is, if our hypothetical ant happens to choose the leaf that had just gotten infected by some disease, the tree won't die, where it otherwise would have been killed by the disease. The ant may not be affected either way (say it gets stepped on), but its decision would doom or save the tree.

If you happen to go back in time, the changes you inevitably make will give either an open-loop response or a closed-loop response. A closed-loop response would mean that if you make a change in the past, that change propagates through time, eventually affecting you. However, there would be no perceived change to you; because you are directly affecting your own past, you would have lived through those changes growing up. Any changes made would directly be part of your memory.

An open-loop response gives the opposite effect; going back in time and changing something simply severs your timeline. When you return to the present, there will be changes, drastic or small, but you won't "remember" it happening. If, for example, you murder yourself in the past, you can still return to the present, which will be just the same, except that everyone will think that you're dead.

When change occurs, it can happen immediately, or it can happen slowly. In the first "Back to the Future" movie, Marty McFly accidentally changed time, making his parents never meet, and thus removing himself from the future timeline. However, since the change did not occur immediately, he had time to right the wrongs and survive. Unfortunately, timelines just don't work that way. Instead, any change made in a timeline will "always have been that way" to anyone/anything later in the timeline, thus changing your own timeline will have immediate results, assuming a closed time loop.

When a change is made, it may or may not affect later timelines, depending how time itself reacts. There are three possibilities: the change brings about substantial change, affecting many other timelines in a short amount of time; the change brings almost no difference, affecting few timelines before being effectively "averaged out"; the change carries forward through time, but without affecting enough timelines to make any significant changes.

If time had an under-damped response, any minute change would have considerable effect on a timeline. A common example is that of a butterfly flapping its wings; the tiny draft of air, over time, eventually causes a hurricane. In our ant example, the disease in the leaf may mutate, eventually wiping out a huge number of trees, and causing a chain of events that eventually changes the entire world, should the ant not bite off the diseased leaf.

However, if time had an over-damped response, small changes would not affect time in the long run. In our ant example, if the tree were to be cut down to make a desk, that desk wouldn't exist if the tree died. However, if the desk owner's house caught on fire and the desk inside burned completely, the end result would be the same either way; the desk may have existed for a short time, but it didn't affect many other timelines.

The most difficult would be a critically-damped response. While an under-damped response dramatically affects time, and an under-damped response would have no effect on time in the long term (or even short term), a critically damped response would cause small, permanent changes to occur. Basically, small changes in the past will affect some timelines, and while those timelines cause long-lasting change, they don't affect many other timelines, and thus have little effect on the rest of history. In our ant example, if someone cuts down the tree and makes a desk out of it, but leaves it in an attic, the desk would exist, but would not affect timelines not directly relating to it. Another example is going back in time and depositing a few dollars in a bank account; hypothetically, this would allow you to gain a large amount of money through interest, but wouldn't affect many timelines, apart from the bank having one more account number.

Still hanging in there? Good!

I've discussed a few simple ways that time travel is shown, but there is much more to it. In an immediate-propagation, closed-loop time travel universe, any change in the past will suddenly and irreversibly change the present, including the time traveler's own timeline. If, for example, a time traveler were to go back in time and kill himself, he wouldn't be alive to go back in time in the first place, which means he wouldn't die, which means he would be able to go kill himself... and so on, ultimately leading to some sort of recursive time loop that, in most literature, causes time to destroy itself. This leads to two effects: first, that the universe comes to a complete and total end; second, that the universe is destroyed and re-created, or at least changed. The first means that any time travel is incredibly dangerous, in that making the wrong change could bring the immediate end of the universe. The second poses some interesting problems, usually involving hand-waving the universe into something more stable.

Because of the instability, most time travel is either closed-loop slow-propagation or open-loop immediate-propagation. This allows time travelers to change the past, without affecting themselves, at least not in any immediate sense. However, slow-propagation change does not make much logical sense. If a change were to happen 50 years in my past, it would indeed take some time - 50 years, to be exact - but to my perception, it would take no time at all. In fact, less than no time, since it would have, from my perception, "always been that way." Thus, slow-propagation may make for an interesting plot, but it would be difficult to explain logically.

This only leaves immediate-propagation, either open or closed loop, with some level of damping.

Predestination is a frequently used plot device. If you go back in time to stop an event, your actions will, unknowingly, actually be the cause of said event - a "predestination paradox." In short, nothing you can do will change time; it is forever set in stone.

"Destiny" is similar, but with a slightly different way of going about it. Going back in time and making changes will affect time, but the fate of whatever you are trying to change will stay the same. Thus, going back in time to save your sweetheart from being hit by a car may work, but she will shortly be shot, run over by a train, or otherwise die. Timelines may be changed completely, but the basic end result will not be different; the people, places, and things you try to save from destruction will, ultimately, be destroyed. This is a form of over-damped response, though more of an emotional method than physical, as timelines very well may be different.

"Self-healing Time," on the other hand, is a true over-damped response. If you go back in time and make a change, that change will have little effect on the rest of time. This is a step beyond a simple over-damped response, however, in that timelines would "fix" themselves, like a rubber band that's been stretched. Any change may affect the immediate point of change, and a short time afterwards, but events will reshape themselves to cause the least amount of damage in the future. The longer time has to fix itself (the father between the present and the time the change occurred), the less noticeable that change will be.

There are some very close resemblances between open-loop time travel and parallel universe/alternate dimension theories, in that being able to safely travel back in time and make changes doesn't affect you personally. The only difference is that if and when you return to your own time, the changes you made will have affected your own time, while changing things in an alternate dimension would have no effect of your own.

I've decided there are three possible type of alternate dimensions, as far as "similar to time travel" in concerned:

Alternate Universe 1: Infinite Possibilities
In this collection of universes, there are truly an infinite number of possibilities. Therefore, it is possible to find a world that is identical to this one, only a thousand years in the past. If you traveled there, it would seem as if you had traveled into the past, however, changes you make won't propagate to your own timeline. However, since every universe's timeline is in parallel, so while it may seem you've gone back in time by going to an alternate universe, there is no way to move backwards and forwards in time once you've arrived, without finding another universe. However, since there are an infinite number of universes, it is hypothetically possible to find a universe where an alternate universe version of yourself visited some time in the past and made the same change you had made.

Alternate Universe 2: Infinite Decision
Remember our ant example? For each decision that is made, a new alternate universe is formed. If you had the option of turning left or turning right, in one universe, you would turn left, and in a new universe, you would turn right. However, these universe's are synchronized, so time travel per se is not possible. However, you may be able to find a universe where many important discoveries had not been made, so the world would appear to be stuck in the past. Or, if you simply wanted to influence decisions, you could jump to a universe where the ant had chosen the leaf you wanted it to choose.

Alternate Universe 3: Tangled time
These universes exist in a tangled knot; while each has its own, independent, finite timeline, that timeline "touches" other alternate timelines, such that certain dates are linked. Thus, it would be possible to move from one dimension to another that happens to be flowing backward, with respect to the original dimension, and "ride" that timeline until it touches again, where you jump back, effectively looping back in time. However, since there are only a finite number of touching points, you cannot move backwards and forwards to any time you please; you may have to wait years in an alternate dimension before you can get back.

So, what's my preferred theory? I don't really have one, honestly. I've thought about it a lot; I know that a closed-loop, immediate propagation time system, especially one that is critically- or under-damped, would be a very dangerous system indeed; the possibility of destroying the universe would be enormous. I think, however, that it might be my favorite system, possibly because of the danger. If the system is over-damped, the danger would be less, but still present. Perhaps I could write a few short stories, and pick my favorite from there.

Well, I've rambled on for an amazingly long time; what are your ideas on time travel?

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This blag is tagged: Thoughts, Timeline, Timetravel, All