Actually it has been explained. My teacher told us about how the planets, debris in space and everything else that exists is moving away from eachother. For ex:
<----Earth_______________________Some other planet on the other side of the Universe ----->
The arrows show the direction they are both moving; away from each other. Which means that there was a force that has pushed them away; they gained the momentum/energy to go that way FROM the Big Bang. This means the effect of it happening so many billions/trillions of years ago are still affecting us. There was something else my teacher said, that eventually when everything hits the edge of the universe (or something to that effect @___@) they will all start to head back to the centre again and everything will come together and again create another massive implosion; being another Big Bang; resseting everything that happened. Yes, that means in the long future when everything is repeated, there will be another PC (That is if any of us surive the Big Bang ;D).
Yah. <.<;
The hypothezation that the universe is expanding is just that: a hypothezation. Although I personally believe the Universe is forever expanding, I cannot declare it to be truth. The thing about it hitting the edge of the universe is interesting, because then he must believe in the parallel universe thing, which means he must essentially not believe in determinalism -- and determinalism (in other words: fate) is something that many people say, is supported by the big bang - in other words, everything since the big bang has been inevitable. If a being who knew all the "laws" of the universe and every past and present event, they would be able to predict the future.
However, opponents of determinalism believe the Universe is probabilistic - like quantum mechanics - a theory that explains the idea of a "mind" - obviously thoughts are chemical reactions, but what causes the things that cause
that chemical reaction at that time? Only chance could explain this idea of a "mind".
To tie it into the parallel universes - this theory says that, every probability of every event is happening, but each one in another universe that are physically closed off to eachother. That your teacher thought the universe would hit and edge, leads me to believe he buys into the "parallel universes"
What do I believe? I am on the probablistic, quantum mechanic side of things - but I do not believe in the oppiste parallel universes. I do believe the universe is expanding, but because of this probability, which I feel explains the totally random chemical reactions that take place in the mind ( which I really do not know enough about, to be honest), I do not feel that each event to happen is inevitable.
One of my favorite movies, Star Wars, I feel supports my view. Chancellor Palpatine, a master of the force, with immense knowledge, foresees Luke going to the dark side. Does this happen? No, Luke's mental conviction that he is to stay a Jedi overrides the other chemical reaction that was also likely to happen in his mind - that he would go over to the dark side.