What proof is there that the big bang theory actually happened? Also what is dark matter and how was it discovered?
Just in the last two months scientists have discovered major new evidence of the Big Bang. Until now, most of the evidence was less direct: if you chart the paths of the all the galaxies in the universe, they all seem to be moving away from each other...and if you follow all those paths backwards, they all seem to meet....at the Big Bang.
But here is a link even more direct proof. Physicists had predicted that if the Big Bang really happened, it would have to leave traces of gravitational waves in the universe--kind of like the ripples on a pond after a stone is thrown into it. And just two weeks ago they announced that they had found exactly that evidence:
Dark matter is part of the universe that we can't see. We know it exists because it affects the rest of the universe--it absorbs light and has a gravitational effect on the rest of matter. But we can't see it directly. It was "discovered" by physicist who added up all the observable matter in certain stars and galaxies, and realized that the stars and galaxies had more gravitation pull than they could explain...so there must be something else they that they could not observe or see...
Hope that helps
Most of this stuff is explained pretty well on any number of astronomy sites...or even Wikipedia.