宇宙简史

In this series of lectures I shall try to give an outline of what we think is the history of the universe from the bigbang to black holes. In the first lecture I shall briefly review past ideas about the universe and how we got to our present picture. One might call this the history of the history of the universe.

In the second lecture I shall describe how both Newton''sand Einstein''s theories of gravity led to the conclusion that the universe could not be static; it had to be either expanding or contracting. This, in turn, implied that theremust have been a time between ten and twenty billion years ago when the density of the universe was infinite. This is called the big bang. It would have been the beginning of the universe.

In the third lecture I shall talk about black holes.

These are formed when a massive star or an even larger body collapses in on itself under its own gravitational pull.

According to Einstein's general theory of relativity, anyone foolish enough to fall into a black hole will be lost forever. They will not be able to come out of the black hole again. Instead, history, as far as they are concerned, willcome to a sticky end at a singularity. However, general relativity is a classical theory-that is, it doesn''t takeinto account the uncertainty principle of quantum mechanics.

In the fourth lecture I shall describe how quantummechanics allows energy to leak out of black holes. Blackholes aren't as black as they are painted.

In the fifth lecture I shall apply quantum mechanical ideas to the big bang and the origin of the universe. This leads to the idea that space-time may be finite in extent but without boundary or edge. It would be like the surface of the Earth but with two more dimensions.

In the sixth lecture I shall show how this new boundary proposal could explain why the past is so different from the future, even though the laws of physics are time symmetric.

Finally, in the seventh lecture I shall describe how weare trying to find a unified theory that will include quantum mechanics, gravity, and all the other interactions of physics. If we achieve this, we shall really understand the universe and our position in it.