INTRODUCTION

‘We go about our daily lives understanding almost nothing of the world. We give litle thought to the machinery that generate the sunlight that makes life posible, to che gravity that gles us to an Earth that would otherwise send us spining off into space, or t0 the atoms of which we are made and on whose stability we fundamentally epend. Except for chikren (who Jon't now enough ‘not to ask the important questions, few of ws spend much time wondering why nature ithe way is; where the cosmos came from, ‘or whether it was always here if ime will oe day flow backward and effects precede causes; ot whether there are ultimate limits to what humans can know. There are even children, and I have met some of them, who want to know what a black hole loks lke; what isthe smallest piece of matter; why we remember the past and not the future; how iti if there was chaos ety, that there i apparent, ‘ode today; and why there i a universe, In ou society it is sill customary for parents and teachers to answer most of these question witha shrug, oF with an appeal to ‘vaguely recalled religious precepts. Some are uncomfortable with fasues lke these, Because they so vividly expose the limitations of ‘human understanding.