"WHEN a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong." So runs Arthur C. Clarke's first law of prediction. Michio Kaku's latest book, "Physics of the Impossible", aims to explain exactly why some visions of the future may eventually be realised while others are likely to remain beyond the bounds of possibility. It concludes that there is little in science fiction that could not, in principle, be realised.

Recent scientific progress means that ever more imaginative scenarios have begun to look feasible. A sensor that has been implanted in the brains of paraplegics and which enables its recipients to move a wheelchair constitutes a limited form...