Alan Guth is a big name in astrophysics. He solved a problem to do with the Big Bang Theory. The problem was that the time since the Big Bang (roughly 15,000 million years) is not long enough for galaxies to form and for space to seem flat. Stars form when the gravitational forces between hydrogen atoms start to pull them inwards into large balls. Think about it - the gravitational attraction between atoms in piddly small so it should take forever. Then the stars have to be attracted together to form galaxies. What Guth proposed is called inflation. Early in its life, there was a massive expansion of the universe. That magnified the clumps of matter and let them pull in faster. It also stretched out the curved up ball of space-time so that it appeared flat.
Alan Guth has done this year's Isaac Newton lecture for the Institute of Physics. They have put the lecture up on the internet. I haven't had time to watch it yet, so of course it might boring but there's only one way to find out:
http://www.iop.org/activity/awards/International%20Award/newton09/page_37514.html
