Time travel is a little tricky...
Does anyone know that silly little hand-shape you make in electronics to figure outwhat way currents and magnetic fields are going? The one that looks like a gang symbol? And how you can flip this around if you change the polarity of the connections?
(A shit explaination, but I am utterly shite at electronics, as I spend too much time asking questions about whether electrons actually flow as per the model, and asking why they didn't change round the words 'positive' and 'negative', and the postulated idea of elctron flow when they found it they'd got it the wrong way originally).
Essentially, as SYN says, time is a dimension, but one that is rather one way... UNLESS you do something so magnificently huge you manage to 'flip' the arrow of time, as in the example of reversing polarity of an electric circle.
From memory, a 1000 mile-long structure, rotating 40,000 times a second, would generate such massive forces it could travel in time, as it would 'flip' the dimensional arangement so that time became a direction (with the rather disturbing side-effect, according to my understanding, that one of our nice and cuddly three dimensions would become a one-way street like time).
Unfortunately, the time travellers in such a device would look like steam-rollered pizza. No... worse than that.
Obviously, there might be more subtle ways, but if there are, people are keeping quiet.
As for time paradox... well, it depends on how the Universe is made.
One could argue if one went back in time and killed one's grandfather one would not go back in time and kill one's grandfather, as one would not be.
This is true. But what would happen when you pulled the trigger? Would the bullet fire, your grandfather die, and you go 'poof'? Would going 'poof' be unbeingness, or finding yourself a little further back in your subjective time-stream (i.e. before you pulled the trigger). Would you miss, or the gun misfire, on some kind of 'conservation of reality principle' as yet undiscovered? If, as some speculate, reality is a infinate set of possibilities, constantly expanding at every possibility, then you could kill your grandfather, and you would cease to exist in one Universe, but would still kill your grandfather dead and be alive yourself, as by killing your grandfather you created an entire Universe where your grandfather died, which wouldn't effect you as you'd come from a Universe where he hadn't. How elastic is reality? If Hitler had died in infancy, would someone have filled his little nazi boots regardless?
I personally dislike the idea of infinate realities. It's messy, confusing, and I'm sure it violates the conservation of energy. Me turning right instead of left cannot logically create enough energy for a whole Universe. Therefore you're left with something like ultimate causality, which means shit happens, and once it's happened, it's happened... in other words, if you killed your grandfather, he'd die and you'd live, even if you killed him as a child, as you would still have your own seperate time-frame and mass, even if your actions meant that you couldn't have.
But, for obvious reasons, no one is entirely sure... but it makes for great bullshit conversations, especially with a few bottles of good wine and some pot.
