I was holding [my four-year-old daughter] and I said, 'Sophia, I love you more than anything in the universe.' And she turned to me and said, 'Daddy, universe or multiverse?'

When general relativity was first put forward in 1915, the math was very unfamiliar to most physicists. Now we teach general relativity to advanced high school students.

Science is the process that takes us from confusion to understanding.

String theory envisions a multiverse in which our universe is one slice of bread in a big cosmic loaf. The other slices would be displaced from ours in some extra dimension of space.

Einstein comes along and says, space and time can warp and curve, that's what gravity is. Now string theory comes along and says, yes, gravity, quantum mechanics, electromagnetism - all together in one package, but only if the universe has more dimensions than the ones that we see.

Our eyes only see the big dimensions, but beyond those there are others that escape detection because they are so small.

The main challenge that television presents is that I have a tendency to say things with a great deal of precision and accuracy. Often a description of that sort, which will work in a book because people can read it slowly - they can turn the pages back and so on - doesn't really work on TV because it interrupts the flow of the moving image.