What is the thing you are best at that nobody watching can see?

I was very, very thorough, making sure I really understood how that telescope worked, and that it was working properly. I was quite convinced that I wasn't clever enough to be in Cambridge and would be thrown out at some stage. My policy was to work as hard as I could so that I'd know I'd done my best. We now label this as impostor syndrome, but we didn't recognise, and certainly didn't name it, back then.

Well, yes, no, I certainly visualise … it was really … I had to have a very good idea of the geometry – that was crucial. Spacetime geometry so it's not three dimensions, you have to think of the whole four dimensional spacetime, and I get sort of used to thinking about four dimensions and using various tricks to get the picture properly. I do most of my thinking in visual terms, and I'm a very visual thinker rather than writing down equations.