Rightly or wrongly, nuclear weapons are regarded, in their threat role at least, as effective guardians of national security. Yet nothing is more menacing to the survival of our planet than the credibly communicated threat to use nuclear weapons if and when sufficiently provoked. Ergo, to escape the mind-boggling risks posed by nuclear deterrence, thinking about how to ensure world security without relying upon nuclear weapons, either extensively or at all, is as much a political as it is a moral imperative- in truth, a matter of physical survival. Without an effective alternative to nuclear deterrence, there is no letting go of the nuclear option, and without letting go of the nuclear option the world never can be free of the possibility o...