Hi, I'm super new (registered one minute ago) because I tried yahoo answers, but realized no one there cares. So I came here (I've read a few random questions on my trek through the "internets") So, I'm just a kid, well I'm a sophomore in high school, but same thing. I have a pretty basic understanding of physics, I've read Hyperspace and I'm halfway through The Elegant Universe, but thats basically it. As a kid who naturally believes (or wants to) in the fantastical, I've (I'm embarassed to say it) googled time machines... and from reading the Elegant Universe I figured if you just stick a guy in a car and go like 99.99% the speed of light, then it's basically like a forwards time machine (well, cheating, but sure.) But I want a backwards time machine. And I posed this to my physics teacher (physics honors, you know, heh) and he stared me down and told me that our universe is based on "cause and effect", and that if we made a time machine that goes backwards, it would destroy everything we know about the universe and based all our conclusions on. I'm not quite sure what to make of that... but I feel a little bit beat: all I can figure is that, to go back in time, you have to go negative lightspeed, which I know, is ridiculous. I thought for a second that if you went faster than light, somehow that would work, but that was pretty stupid because then... well, that upsets the whole reasoning (p.s. I don't understand why we CAN'T go faster than C) Basically, is it completely hopeless like it seems to be? Or do you have any good arguments I can use to thwart my physics teacher's plans to abolish all my hopes and dreams of backwards time travel? (Even on a theoretical note). And... WHY is C the defining object of all? How do we know we go through time at the speed of light? I understand why time goes slower as you approach C, but not why, or how we know, that we rocket through time at lightspeed. Any comments would be nice, just please don't make fun of me for not really knowing what I'm talking about here. :D Thanks!