h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

In the future ...no one will invent time travel. If they had we would already know about it, and time as a linear event would cease to exist. Perhaps.

Perhaps there has been time travel. Perhaps in the future someone will figure out a way to transfer your soul, but not your body, to the past. As merely a soul you could move places and see things. But they didn't count on certain souls being visible or on certain people (or animals) being able to see souls wandering around. People would think these souls are ghosts. These "ghosts" might not always be able to (or want to) return home. These ghosts might become angry or lonely after a while of wandering the world without true interaction. After time some of these ghosts might learn to actually interact with the physical world. Hence, you would have poltergueists. This theory would explain the mystery of ghosts and the paradox of time travel except that there still is an issue. Since some ghosts do seem to learn to interact with the world, these time travellers have influenced and changed the past and therefore buggered up the future. I imagine that this sort of time travel would be rare, hard to do, and/or expensive. Normally it would be used for documentation or recovery of the past events. Certain souls might abuse it.

A very likely result of time travel is that it almost always destroys itself or the universe/dimension it was in through some sort of paradox. Look at your own experience. If you had created a time machine, what would you do with it? Probably go back in time to save yourself some previous pain in your past. The act of doing so would change your entire life from that point on. Most likely, you would never invent your time machine because everything was changed. Results of such a change would likely either be that the new timeline happens OR the universe refuses the change OR the universe simply gives up and explodes/implodes OR you don't actually change our universe but you do change a different one and always come back home to the same timeline. That last one would be a neat (if still dangerous) side effect. You could "time travel" (in this case it would be more aptly named universe/dimension jumping) to anytime feeling safe with the knowledge that you wouldn't actually be changing anything in our universe. You could use it to document history or to live in a time you feel better suited in. You could likely travel to future timelines of our universe to predict our future. Simply the act of doing so and especially telling people might change, destroy, or nullify that event, though. But think of all the damage (or at least differences) you would cause to other universes. Perhaps aliens are us from our same timeline just many many years from now.

-Destroy

hmmm ....non physical time travel. I don't know if that is a different matter or not. Regardless of whether I agree or not ..it did make me think. If a time traveller was, in some form, 'pasted' into the past then their appearance would be adjusted to match that specific era. This might not be something you could change once in place, and if for whatever reason you were stuck, you would have an appearance which would become out of date, by however long you were stuck for. Ghosts in medieval costume ...the grey lady of every National Trust property, etc. HMMMMMMMM.

Still ...I don't think it would work. If you were conscious of being from the future you would need some basis in physical matter to base that in ...this matter would be doing something else at the time and might not be available to make yourself out of.

The best way to see the past is memory; to see the future just hang around and wait for it...

The "multiple parallel universes" theory would make time travel theoretically possible, but fairly useless, since it is unlikely that the parallel universe you end up in will have developed sufficiently similar to your own to make your experiences of any practical value.

Notice, for example, that in the movie of HG Wells' "Time Machine" that the machine stayed located in the house, even though as time progressed the Earth was moving around the Sun... The chances of reappearing on the planet were minimal, let alone on the same spot...! (Plus with expansion/contraction of the Universe, the Sun was moving too!)

There is one theory that there is a universe for every different choice ever made. If you could actually find a duplicate universe of ours and go to it's past, you could change it's past and then go to it's "present time" and there would be no paradoxes because you changed the past of a different universe than your own and still therefore have your memories and reasons to have done what you did. There is one problem though. There are probably two of you on the same planet now. But you could still fix that problem by perhaps changing the history while you're still in the past so that you never get born in this universe. Who knows, you might do that accidentally when you're in the past anyways. Imagine a company that did this for a living. They would change a universe for you and then transport you to it. They could call it "A Universe for Everyone!" Imagine the abuse this could bring. Imagine some real rich guy asks this company (lets call them Universes R' Us) to change a universe so that all the males have died off on the planet. The interesting thing about this theory is that, although improbable, this kind of thing is possible. It's even possible that our universe has been changed already for the benefit some universe travellers. Perhaps another explanation for the ufos some have seen. Although I imagine that if there has been some work done on us, that they would have made it undetectable. Then again, this world might be so bad off that no one even wants to touch it.
-Destroy