Space can vibrate, space can fluctuate, space can be quantum mechanical, but what the devil is it? And, you know, everybody has their own idea about what it is, but there's no coherent final consensus on why there is space.

You have to say now that space is something. Space can vibrate, space can fluctuate, space can be quantum mechanical, but what the devil is it?

Why is there space rather than no space? Why is space three-dimensional? Why is space big? We have a lot of room to move around in. How come it's not tiny? We have no consensus about these things. We're still exploring them.

The most important single thing about string theory is that it's a highly mathematical theory, and the mathematics holds together in a very tight and consistent way. It contains in its basic structure both quantum mechanics and the theory of gravity. That's big news.

You are a victim of your own neural architecture which doesn't permit you to imagine anything outside of three dimensions. Even two dimensions. People know they can't visualise four or five dimensions, but they think they can close their eyes and see two dimensions. But they can't.

I'm a great believer in our ability to come up with the ideas necessary to solve the big questions. I have less confidence that we'll be able to find a consensus about which ones are right without experiment.