There is a contradiction in Professor Michio Kaku's appearance, as if he had been drawn by a composite artist, based on the memories of an unreliable witness. It is to do with the smoothness of his skin being at odds with the silver hair that flows down to his shoulders. The latter reflects his age, 61; the former suggests he is a teenager.

That answer would have been true to form. Prof Kaku has a gift for communicating complex scientific ideas in a way that lay people can understand. He argues, moreover, that good physics should be simple, so simple that it can be understood as an image. I'll let him explain. 'A good physicist is driven by a childlike fascination and imagination. If we find ourselves getting jaded or bored we have to try to recapture that childishness. Einstein used to do that. He could be quite childish. He wanted to get access to that feeling of wonderment.