Compared to say quantum physics or relativity the big bang seems straightforward – there was a big bang, right? In fact, the idea of an expanding universe is as strange and intuition-defying as any in physics.
The strangeness of the big bang model first become clear to me when I quizzed Robin Hanson along the following lines. How can the universe be infinite (as some cosmologists think) when we know that the universe is some 14 billion years old and it is expanding? Doesn’t this mean that it must be finite?
Robin, who continues to publish papers in quantum physics as well as economics, explained that the universe is infinite and was already infinitely large when the big bang began, it’s space that has expanded. The big bang was not an expansion in space but an expansion of space. (My interpretation – think of the infinite number of points between 0 and 1 being mapped to the infinite number of points between 1 and 10.)
If that’s not clear, and I don’t suppose that it is, this month’s Scientific American has the best introduction to the big bang that I have ever read. I’ve also found this FAQ useful (see especially the answer to my question here).