In the Sahara one day, I climbed over a dune to descend into a deep bowl of sand. Sitting at the bottom I encountered for the first time absolute silence, stillness that is indivisible. For there are two silences: a silence can be no more than the absence of noise, it can be inert; or, at the other end of the scale, there is a nothingness that is infinitely alive, and every cell of the body can be penetrated and vivified by this second silence's activity.