Time Travel and the Space Time Continuum
 

So, since another thread kind of deviated into this, I thought it best to start a proper topic devoted to travel forwards, backwards and sideways through time, and the effects on the space time continuum and causality.
I can't be bothered posting what I said earlier, but any/everybody who wants this kind of discussion, post away!

I have no knowledge of timetravel other then what I see in movies, TV shows and games. And that subject has been done to death so many times, so many different ways, one even more stupid then the other, that I wouldn't have a clue as to what's possible or not.

I guess I like the theory about an infinite number of universes that have different outcomes for every choice every made. It would kinda eliminate the 'fucking up a timeline by traveling back in time' theory.

Anyway I always get a headache when thinking to much about timetravel so I'll just leave it at that for now.

something = something else

But if we will time travel, then haven't we already time travelled?

Yeah, that is kind of one of the eternal problems with time travel. One argument is that once it has been invented, it has already been invented/existed at every point in history.

Or, if that isn't the case, then once it is invented, the furthest back you can travel is to the point it was invented. So, if it was invented in 2010, then suppose in the year 2034, you could only travel back as a far as 2010.

I think that's only with the wormhole model.

time travel=PARADOXES

Not necessarily. If you killed your grandmother in the past for she had your mother, for instance, then obviously she wasn't your real grandmother.

It would probably be impossible to complete such a bizarre and murderous mission, because history says you failed.

If causality does no wrong, then any trips to the past before the invention of time travel were well concealed and thus did not interfere with what we call our history, and the dreaded butterfly effect was really a crucial part of history as well, and couldn't have happened any other way.

I really don't know the half of the subject I'm getting into, but this is based on what I've collected over the years. My interpretation on "causality" being all of the actions that have occurred and will occur based on the arrangement of particles at the beginning of the universe, and "butterfly effect" being the notion that the slightest change depending on how far back you go can throw off history. If this is totally wrong and I've just made myself look foolish, please point it out so that I may not look foolish in the future.

You can dwell into plenty of paradoxes related to time travel - but wouldn't it be more interesting to look at that which is actually possible? Theoretically, it is possible to accelerate time due to time dilation, both velocity based and gravitational. So in essence, we're quite good at traveling into the future, whereas the whole going-back-in-time-scenario seems to fail pretty hard right off the bat.

Unless of course, regardless of the possibility of time travel, events conspire to prevent the invention of your time-travelling machine. I'm no theoretical physicist, which renders my musings technically moot, but I have envisioned a "tree of time," an image of the time line that splits every time a quantum event occurs, and both/all outcomes of that event play out, meaning that there is an exponential growth in the number of parallel universes (this is the "many worlds" interpretation of quantum theory).

A time machine would essentially mean that an element of this tree, a twig, has been bent backwards and grows back into the time line. If you imagine the way a tree grows, which I think models this idea of a time line rather well, you can see why the time line would never have "grown" that way in the first place.

Particularly since events are affected after the twig fuses again, essentially meaning that events in the future are affecting the events in the past that lead to them in the first place (I am aware that this is a re-imagining of all the same paradoxes and problems of time travel, but I think a visual model is very helpful).

So there is a loop through which events are played over and over, different each time. It is not unreasonable to suggest that, unless all events line up perfectly (which they probably wouldn't, given the quantum events making new universes during this process, leading to new futures with the same loops. The whole period would be incredibly tangled) eventually events will occur whereby the loop never occurred at all. It has been "pruned" from existence.

This would of course be fertile ground for the first loop to occur, so it is no more stable than the loops ever were. What effect this would have on history (time is in flux? Thank you Doctor Who, very informative) I can't say. I would conclude that there must one of two outcomes:

1: Events conspire so that the time machine was never invented.
2: Events conspire so that the time machine is never used.

Another possibility that come to mind is that the invention or activation of a time machine would cause your universe to be pruned from the rest of the tree of time. It would continue to growth naturally, but you could not go further back in time. If it is the invention that causes this, there won't be any paradoxes about inventing time machines, but others may become available as the tree grows and matures. If activation causes this, then despite your fully functional time machine, there is no past you can get back to.

The future, it it exists yet (and there is no reason to suggest that it does not), is actually an infinite number of possible futures, each created every time there is a quantum event in one of them. The effect on the human-scale world is inestimable, but going to the future would not be as enlightening as one would hope. Who knows which one you will get to, whether or not that branch of the future will be ruined by your arrival, and if you do not return to your own time at the moment you left, no doubt more quantum events would have occured during your brief absence, leaving a number of time lines/universe devoid of your presence. Although you would never notice it, your family in those universes would suffer emotional distress from our disappearance.

Then again, if human affairs are affected by or are quantum in nature, there are a large number of universes where you went missing anyway, or have died, were never borne, the human race never evolved etc, assuming that there were a sequence of quantum events that could have led up to such incidents.

I've thought of it like that before too, BM. I'm just thinking in terms of there being only one time that is consistent and any "changes" in the past from interference from the future were meant to happen. With probability and all I can see why your interpretation is valid. I sort of like to think of it in a notion I had while watching Samurai Jack once. Say Aku really did exist and all of those events in the show transpired. We all know Jack inevitably beats Aku and sets the time line right, so perhaps we are living in the correct timeline. But for that to happen, an alternate history had to take place first so that events would transpire and lead setting the timeline straight, so in the end, everything turned out the way we see it, so any sort of time travel was meant to happen and so paradoxes are theoretically impossible. Oy vey, we need a physicist on board.

There would have to be something that allowed for and caused the problem in the first place, assuming anyone other than the inhabitants found it to be a problem. It is almost as if a time machine causes a distortion in time, like a lensing effect in our visual representation that creates the loop.

Or maybe, something else causes the distortion, and time machines inevitably appear inside them. What could cause such a thing would be extra-universal, and therefore beyond all supposition. Interesting, but one of the more pointless hypotheses.

I don't see why specifically a time machine would appear out of the space-time distortion, and if something is extra-universal, that means it's out of our own space-time, right? So how could it interact with our universe in the first place?

Ehh, I'd just like to think all alternate realities are safely kept in boxes.

Time is just change. Once something is changed, it can't go back on that. It would have to change to what is was before.

Time travel into the "future", is theoretically possible; it would just be skipping some of the change, no paradox.

But traveling back in time is different. If anything could travel back in time, it would cause a paradox. Anything that is involved in a paradox is eliminated from the beginning of change. Thus, with the whole idea that anything affects everything, it's very likely that the entire universe would be erased before it even existed.

Though, you could change everything back, and then it would change to how it was/ would be. Or you could travel to another dimension.

But then that gets into pocket dimensions, and alternate universes, and Bullet Magnet's tree idea (But a little differently), and the whirlpool theory.

I just say that time travel is theoretically implausible as there are just so many problems involved with it that it gets fairly ridiculous quite quickly.

So just because you don't understand it means it's not possible?

I think I now get why you're the But that was an excellent post, BM. I think more or less the same along the tree thing, but can't articulate it that well. I believe though that rather than entering a loop, the tree sheds a branch, and the time flow that would be a paradox due to time travel instead is separated from the central tree and becomes a composite universe, with no sky-tearing paradoxes. The only way to get back on to the normal track from there would be to go back in time to when you changed history, and this time do nothnig. Events would be re-played out as they were in the original tree, but in this separate universe, and then afterthey have been successfully replayed by you going back in time again, the branch snaps back on to the central tree. Do you see what I'm getting at?

Yeah, but your very presence will alter things. It is all about quantum events. Such as the radioactive decay of a Carbon-14 atom inside your very body.

The short story A Sound of Thunder explains it very well.