"We go about our daily lives understanding almost nothing of the world. We give little thought to the machinery that generates the sun light that makes life possible, to the gravity that glues us to an Earth that would otherwise send us spinning off into space, or to the atoms of which we are made and on whose stability we fundamentally depend. Few of us spend much time wondering why nature is the way it is; where the cosmos came from, or whether it was always there, if time will one day flow backwards or whether there are ultimate limits to what humans can know. What is the smallest piece of matter; why do we remember the past and not the future; and why there is a universe."