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JB: Did you ever get to talk to Dirac?

BARBOUR: I tried. I was studying in Munich when I read the article about him. I got so hooked on the issue of time that I went back to England try and see Dirac in Cambridge. I actually spoke to him on the phone, but he wasn't a very talkative person and he wasn't all that interested in meeting somebody who'd got half — thought — out ideas about time. I can certainly understand that.

JB: Are the ideas full — baked now?

BARBOUR: They're certainly not as half — baked as they were. They've definitely taken quite a shape. I hope some at least will have a place in the new picture of the universe for which so many physicists are groping, one that is completely quantum — mechanical and not half quantum and half classical. What my Italian collaborator Bruno Bertotti and I managed to show is that the world is strongly relational according to the physics as we know it now, but this hasn't been properly recognized. The people like Leibniz and Ernst Mach who criticized Newton really were right. Einstein somehow or other put this into his theory without anyone, including Einstein himself, properly appreciating it. The world is relational. It is about how real things relate to real things. This is potentially important for how we try to picture the quantum universe.

JB: How do you fit into the leading edge of today's research — string theorists, quantum gravity people?

BARBOUR: My work has little direct connection to what the string theorists do. There are two main approaches to quantum gravity, and one of them is definitely much more popular than the other, that's the string theory line. I'm following a line that is at least twice as old but followed by far fewer people. It is closely related to basic questions — what is time, what is space, what is motion? Science has its fashions. String theorists are a bit like a pack of hounds following an extremely promising scent. But it is a particular scent. If they lose the trail, nothing will come of the great chase. In contrast, those basic questions will never go away. In fact, if string theory is successful, it will be very interesting to see how it does answer them.

JB: What is distinctive about your approach?

BARBOUR: My basic idea is that time as such does not exist. There is no invisible river of time. But there are things that you could call instants of time, or 'Nows'. As we live, we seem to move through a succession of Nows, and the question is, what are they? They are arrangements of everything in the universe relative to each other in any moment, for example, now.

We have the strong impression that you and I are sitting opposite each other, that there's a bunch of flowers on the table, that there's a chair there and things like that — they are there in definite positions relative to each other. I aim to abstract away everything we cannot see (directly or indirectly) and simply keep this idea of many different things coexisting at once in a definite mutual relationship. The interconnected totality becomes my basic thing, a Now. There are many such Nows, all different from each other. That's my ontology of the universe — there are Nows, nothing more, nothing less.

JB: But where does our experience of the flow of time come from?