Big Bang Theory

One of the most amazing things that's happened even in my lifetime is the prediction of cosmology. When I started out forty-odd years ago, we thought we knew that the universe began in a Big Bang, although some people doubted that theory even then. We thought the universe was about ten or twenty billion years old. But now for really very sound scientific reasons, we can say that the universe started in a Big Bang over 13.8 billion years ago. So it's not 14, not 13, because of the decimal point in there, and it's a stunning achievement to know that. And we also know that the laws of physics that apply to tiny particles inside atoms can explain what happened in the Big Bang - you can't have one without the other. A very neat example of this is that when you apply nuclear physics, the kind of physics to understand how stars work, you find out that the oldest star in the universe is about 13 billion years old. So their universe is just a little bit older than the stars. Fantastic, if we've done it and counted in the other way around and said that the stars were older than the universe, we would say science were in deep trouble. But it's not, everything fits together and we know how the universe began, we have come to understand the way it is. We don't know quite so well what will happen in the future, but we have some ideas, which are as good as those ideas we had 40 years ago about how the Big Bang happened.