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| quote: | ok, but think. say you do go back and kill hitler, then return to the present.
a)there is now two of you?
b)hitler is dead in that reality?
c)possibly 6-8 million new people have been alive for 50 years.. what else could have happened?
but then, think, if you do go back and kill hitler, that means that the past still exists. is there still a past being lived somewhere in the universe? has the future already been realized? i think this is where we get into multi-universes and realities.. which goes far beyond my very basic knowledge of thermodynamics |
God, now we're getting into it. 
You have to be careful when talking about time, because like I said before, it's not like it's just a straight line that can be moved up and down, it is a conecpt that's as bound to the laws of physics just like everything else. Firstly, it can be proven that time can be played around with: travelling in space for ten years at close to the speed of light and then returning to Earth will see you come back at the year 3000, even though you've only aged by ten years. So it's possible to slow time down, but only relatively remember: it may have only been 10 years to the people in the space ship, but to everyone on Earth 1000 had passed. There is no absolute time either: every single entity is bound to its own single clock. There is no giant clock in the universe that everything runs by. So to say that you can go "back in time" is a relative thing. Perhaps it is possible to go away for 5 years and come back before you came, but wherever you left from technically wouldn't have come into existence just yet: each event has it's own time-space position, and, depending on how you want to measure it, each object is technically being reborn every second. Nothing is static, and each 0.000000001 seconds that goes by the universe becomes an essentially different universe. You may be able to go back in time, but it's not like you'd just be able to land on Earth circa 1997 - because, of course, you'd be turning up in a universe completely different from the one you left originally (which bring us to the concept of parellel universes, and I'm not going there).
Then of course there's the theory that time, like matter, is prone to decay, and that the process can only be slowed down, not reversed. So, for instance, you can burn a piece of wood (increase entropy) but once you've burnt it, you can't put all the smoke and charcoal back together to form a piece of wood (which would decrease entropy). And perhaps it's the same thing with time: once time has elapsed it cannot be regained. Time may, perhaps, decay irreperably, in which case the year 1997 is lost forever and can never be regained by space travel. That piece of time has been destroyed, as have the entire 3 minutes it's taken you to read this post. In fact, for every word you read in this sentence, a few microseconds are destroyed and consigned to the unreachable annuls of history. Bet you wish you'd done something more useful with your Thursday evening now eh?
But of course, the most damning criticism against time-travel is that we've never had anyone from the future visit us yet. Then again, perhaps the future generations have discovered time-travel yet don't want to use it for fear of irreperably detroying the past and thus their present....
Sod it, I need a bed.
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i was so baked when i read that stuff; then i got all my friends to read it.
