By Maria Coffey
304 pages. Tarcher/Penguin.
Maybe it's a spiritual addiction: the need for death-defying adventure. "It is often the hardest, most challenging experiences of our lives that crack us open," writes Maria Coffey in Explorers of the Infinite (Tarcher/Penguin), a book that probes the ecstasy of extreme sport. Her interviews with athletes and scientists yield fascinating thoughts about how risktakers experience pain and how terror can be a passport to bliss.