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

I thought of something, if time travelling can be done, then we are all doomed. Ok let me explain myself, this is what I was thinking. If time travelling ( backwards in time ) can be done we should probably see a lot of people from the future walking the streets OR humanity don't survive to build time machines. Since there is no people from the future around that leaves me two options, eiter they can't be built, or mankind will die before we build them. Personally I don't think they ever could be built.

Actually I am from the future. It is possible. Or will be. Or something. I was born in 2216. There are many others like me, but we're sworn to secrecy. One of us, a chap called Einstein (friend of mine from college year 2237) came back to the first part of the 20th century and blew his cover. Took back a page from an encylopedia about light speed and special relativity. He didn't actually know jock-all about the subject, but he managed to bluff that he'd thought it all up. He was not allowed back to his time.

We are all travellers back and forth through time ... we just haven't learned to appreciate it yet.

We are all refugees fleeing from the terror within us, too

By the 28th century, they will have set up a time police whose job is to ensure this sort of thing doesn't happen. But you do get the occasional traveller from the 26th or 27th century dropping back to see how their ancestors are doing. They usually come in strange saucer-shaped space ships and sometimes abduct people.

I remember having a long long and complicated conversation on this subject some months ago on H2G2. It went under the subject of Jane Austen or something totally irrelavent so it will be very difficult to find. Hold with me and I might find it and post the link in a couple of days!!!

PS - don't go looking for Austen, that was only an EXAMPLE. If I knew what the subject was, I could post it now

I wish that someone would start up a conversation about time travelling.

OKOKOKOK I'll make a concentrated effort to find it. No point in saying everything over is there?

Look at the conversation Anything About Time Travel.

Well, I did a search, and not only is there Anything About Time Travel, but the words "time travel" crop up anywhere and everywhere. So have a read around, some is relevant stuff, some only brush on the subject.

Time Travel can be very confusing - you start thinking about space time continuums and how did thing that was caused by the person travelling back in time happen in the first place to enable them to go back when they couldn't have gone back first unless it happened in the first place - and then you go boss eyed and make a sound like "duuuuuurrrrrrrrr"

I think the Back To The Future is the coolest movie made about time travel. I really like how they managed to link all three movies together like that. But seriously, to me it doesn´t seem there is any solution to the time travel paradoxes, unless everything is predestined.

What about the 'many worlds' idea? If I understand correctly, this basically states that anything that can happen *will* happen, in one of a number of universes, and therefore there isn't necessarily any contradiction involved in people travelling between the present and the future / past. Or something like that.

If this is so, presumably it would discount the idea that everything has to be predestined for time travel to work - not that I'm saying it will work, mind...

Well, look at it this way. If we can travel into the past, then it must still exist. But if it does, how do we know we are not also past. So there is a future out there, already predestined, with people visiting the past, which is our present. And besides, the more worlds thing isn´t time travel in the strictes sense of the word is it?

Many worlds is not time travel, but it allows time travel to occur without any paradox. If you go back in time and change things, then come forward, you just come forward into a different world, so there is no contradiction between what you knew before you went back and what now has happened.

That's kind of what I was trying to say. Thanks Gnomon...

The lack of visitors from the future is suspicious; if time travel exists then we should see vast numbers of them, even if only a very small percentage reveal themselves or are revealed by accident. However, there is a convenient theory that might explain why we don't see time travellers even though it is possible.

The suggestion is that you can only use a time machine to travel between times when the machine was in existence; i.e. if a machine was built in 3000 AD and destroyed in 3245 AD then you could only use it to travel backwards and forwards during that 245 year period. Thus we don't see time travellers because there are no mchines yet and so they cannot travel back this far. They would be seen in the future once such a machine was built (and then the World would be REALLY weird!).

Of course, this doesn't mean that a more advanced alien civilisation haven't built one millennia ago.....but that's a different line of thought!

To go back to the 'many worlds' view of things, the (apparent) non-appearance of visitors from the future can be explained away without too many problems. You see, if they're travelling back into the past from their own time, they are actually *creating* that possible past as they're travelling. So there is no way that we here would ever see them - they wouldn't get back to *us* in *this* particular possible universe. Do you see? The point is that, if the 'many worlds' theory applies (potentially) in one direction of time travel - ie, the conventional direction, what we call 'forwards' - then there is no reason why it shouldn't also apply to any other possible directions.

Assuming that it's actually possible to go in any other direction, of course.

Also assuming, for that matter, that we agree with the 'many worlds' theory. I'm not a scientist, but I understand that it's not without its critics...

shame. It would be lovely to be able to remodel your past to your own design. Like Groundhog day, sort of.

Well, trilian, most of the world has been remodelling the past to suit themselves, (what do you think the academic persuit of History has always been) why not you and me?

If I went into the future and "borrowed" some absolutely fantastic gizmo - say a machine which cured cancer - then brought it back to today and claimed I had invented it, then the "actual" inventor who may have invented it in, say, 2070, wouldn't bother inventing it because it would already have been available for 70 years. Therefore a hugely advanced and complicated piece of machinery would exist without anyone actually having had to work out how to build one. Where has the idea then come from???