Julian Barbour is a British physicist with research interests in quantum gravity and the history of science. He rose to public prominence on the back of his 1999 book, The End of Time, which proposed the idea of timeless physics: the controversial view that time, as we perceive it, does not exist as anything other than an illusion. Since then, he has also written The Discovery of Dynamics and Absolute or Relative Motion?

We spoke to him about the structure of space, time as an illusion, and the possibility of finding an elegant description of the universe we live in.

Newton and Leibniz had conflicting ideas about the structure of space. How did they differ, and which of the two proved to be more successful in describing the universe?

Newton thought that space is like a huge block of unchanging and invisible ice with each point like every other. He felt he needed such a concept to make sense of his first law of motion, according to which a body left to itself will move forever in a straight line (the law of inertia). Leibniz did not like the invisibility of space: you could imagine moving the whole universe in some direction, but nothing visible would be changed. He therefore argued that only the distances between objects have reality.

However, he never formulated laws that would determine how the distances should change, and for two centuries Newton appeared to be the victor in the debate. However, Newton's laws were not confirmed relative to space but relative to the distant stars, as Mach pointed out, arguing that they must explain why Newton's law of inertia works so well through some as yet unknown mechanism.