 General relativity is the currently favourable model of space and time. Whereas quantum mechanics deals with the stuff matter, if you like, which appears in space and time. Quantum theory is really quite an extraordinary subject because it does have a very profoundly challenging conceptual background. Yet also it's incredibly useful. I mean the whole modern world works because of quantum mechanics. Every electronic device we have around the house and the lab everywhere is based on quantum theory. So it's amazing actually that there's a subject that is so profoundly mystical. It's also so useful. At the school at the physics master he lent me a book. I just opened it at random and I saw an equation. It was written down and this equation some are very fundamental. Describe how things were. And I was astonished. It was just a string of Greek symbols and some I didn't recognise at all. There was a letter H with a bar through it. It was sort of very mystical. There were hats over things like that. The whole thing looked extraordinary. It suddenly hit me. How can it be that you can describe the world in some depth with strings of letters? It absolutely fascinated me with that idea. And that's when the idea of actually becoming a theoretical physicist first started in my mind. The second thing that happened that really triggered me to do in theoretical physics was when I was in my gap year with the GPO. And one lunch I had nothing much to do. I wandered up into the library and booked a book off the shelf at random. It turned out to be a book by David Bohm, a very well-known physicist on quantum physics. I opened the book and I realised that it was the same strings of letters and things that I'd seen and much more developed in this previous book. And that's when I really finally decided that I've got to do this. I've got to understand this. It's just so profound. The fascination in theoretical physics is always the same really. It's this strange business that mathematics can describe the world and that you can make predictions with mathematics about how things are going to happen and actually it works. The universe works. It's out there for you. It works. That's incredible, I think. I used to think from time to time about why did we use the mathematics that we did to talk about space and time? And basically we used real numbers. But why do we do that? In ordinary mathematics, a statement is either true or false and also the things I've existed that don't exist. But apparently in Topos theory, which is the case, you can have statements that are partly true and what's even more extraordinary are mathematical entities that can partially exist and partially not exist. And that degree of partial existence is actually specified in a very precise logical mathematical way. And it suddenly hit me, wow, that's quantum theory. I thought, there's got to be a way you can use Topos theory in quantum physics. I was so excited I couldn't sleep that night at all. One of the reasons for doing this Topos theory wasn't just to do quantum theory in general relativity. It was to try and find out a different way of doing theoretical physics altogether. And it does actually give you that. It does give you a different framework, a bigger framework for discussing or applying math to physics than existed before. You have mathematics which takes you, as you were, from one type of experiment to another and it predicts a relation between the two experiments. But in between there's like a path, a mathematical path that goes from one to the other. If you ask, what does that path mean? You can't possibly, there's no answer. It's just it's there in the mathematics. It's where mathematics gets to places that human reasoning can't. And that's one of the fascinations of theoretical physics actually, is that mathematics has this extraordinary ability. It's not just to describe the world, but to take you beyond the current understanding and suggest new ideas which turn out to be correct. As far as my best work is concerned, I think it's the stuff on top of theory. I think I had a genuinely original idea. And I can tell you original ideas are very rare actually in science. It's a very abstract way of earning a living, I have to say.