Anselm Kiefer: 'When I make a truly great painting, then I feel real'

Fifty years ago he outraged his fellow Germans with Nazi salutes. Now, at 74, the artist's epic canvases are exploring a different kind of darkness

I arrive at White Cube in south London just as Anselm Kiefer is writing the title of his exhibition on a gallery wall. Perched on a mini-forklift, the 74-year-old German slowly and meticulously inscribes the words "Superstrings, Runes, the Norns, Gordian Knot". It is a typically dense and allusive title for a show that merges Kiefer's now familiar preoccupations - ancient myths, astronomy, alchemy, history and arcane systems of knowledge - with a more recent obsession, string theory.

"These advanced mathematicians are attempting to find a theory of everything," he says, when we sit down for a chat in a back room of the gallery, "but each time they open a door, many other doors reveal themselves. It is all abstract mathematics, of course, so nothing is really yet proved. The more I read about it, the more I think they will never find the answer." He is not good at maths, he tells me, laughing, but nevertheless when a serious mathematician visited his studio recently, he looked at the paintings inspired by string theory and exclaimed: "That's it!"