OK, well here is what I think. All the antiparticle and positron stuff is a theory, so theoretically, it time travel IS possible. I am sure we'll never if it is for real in our lifetime. Here's the theory that I like. As you probably (hopefully!) know, it is thought that the universe started at the big bang -- it was infinitely dense and infinitely small. Then it started expanding and we know for sure that it is in fact expanding right now. There are, what are called, three Friedmann models of the universe. They suggest three possibilities. One is that the universe started expanding at the big bang and the gravitational pull of the matter in the universe will eventually slow down the expansion process a little, so it won't be expanding very fast. Another model is that it started expanding and the gravitational pull is stronger than in the first case, and the expansion rate will reduce significantly, approaching zero, but will never actually reach zero. In the last model, the gravitational pull is so strong that the expansion stop and then the universe is pulled back into a singularity (infinitely dense + infinitely small) at the event called the Big Crunch.

Well, there are those things called the arrows of time. There are three of them: thermodynamical, psychological, and cosmological. The thermodynamical arrow is the direction of time in which entropy (disorder) increases. If you break a glass, and it breaks into small pieces, entropy or disorder increases. And there's no way to get it back in the original state before it was broken. The psychological arrow of time is the direction of time in which WE think of time. We remember past, but not the future. The cosmological arrow of time is the direction of time in which the universe is expanding. Well, it turns out that all three of them have the same direction. There's an idea that when (and IF) the universe starts contracting, the arrows will reverse their direction, and we will remember our future, but not the past, and the disorder will decrease with time! There are some inconsistensies in the idea, but it's pretty bizzare and kinda makes sense.

Some other things with time involve wormholes. I don't wanna get into that, cause I dunno this stuff that well.

Antoher thing with time has to deal with black holes. Like time is curved and stuff....

• How about causality when reversing time? - alexander - January 16, 2002 - 04:05 UTC
  • no direction? - medvedbr - January 21, 2002 - 20:55 UTC