This is a little book of profound questions-unknowns that address the secrets of our world, our civilization, the meaning of life. Here are the deepest riddles that have fascinated, obsessed, and haunted the greatest thinkers of our time, including Nobel laureates, cosmologists, philosophers, economists, prize-winning novelists, religious scholars, and more than 250 leading scientists, artists, and theorists inlcuding Jared Diamond, Steven Pinker, Carlo Rovelli, Alison Gopnik, Lisa Randall, Ian McEwan and many more.