The present book contains an expansion of the Rede Lecture delivered before the University of Cambridge in November 1930.

There is a widespread conviction that the new teachings of astronomy and physical science are destined to produce an immense change on our outlook on the universe as a whole, and on our views as to the significance of human life. The question at issue is ultimately one for philosophic discussion, but before the philosophers have a right to speak, science ought first to be asked to tell all she can as to ascertained facts and provisional hypotheses. Then, and then only, may discussion legitimately pass into the realms of philosophy.

With some such thoughts as these in my mind, I wrote the present book, obsessed by frequent doubts as to whether I could justify an addition to the great amount which has already been written on the subject. I can claim no special qualifications beyond the proverbially advantageous position of the mere onlooker; I am not a philosopher either by training or inclination, and for many years my scientific work has lain outside the arena of contending physical theories.

The first four chapters, which form the main part of the book, contain brief discussions, on very broad lines, of such scientific questions as seem to me to be of interest, and to provide useful material, for the discussion of the ultimate philosophical problem.