"Peebles is one of the outstanding physicists and cosmologists of our time. His account of the practice of physics will be of interest to physicists and to anyone curious about what physicists do."-- Edward Witten, Institute for Advanced Study "You can't do physics without committing to certain philosophical stances, but often those commitments remain hidden in the background. In this book, one of our leading scientists offers a careful and thorough examination of what working physicists actually think as they go about their business. It is intellectually important and hopefully the beginning of a fruitful dialogue between practitioners in both fields."-- Sean Carroll, author of The Biggest Ideas in the Universe series "Over a remarkable career, Peebles has helped to expand our understanding of the cosmos. Here he reflects on how physicists build reliable knowledge of the natural world from imperfect data and evolving hypotheses. Thoughtful and engaging.

"-- David Kaiser, Massachusetts Institute of Technology "Peebles, a uniquely respected leader in the field and friendly mentor to generations of cosmologists, offers a distinctive, fascinating, and personal distillation of physics--not just its history, but its special philosophical standing among the sciences. His thoughts will enlighten both specialists and general readers."-- Martin Rees, author of On the Future: Prospects for Humanity.