THE NATURE OF THE PHYSICAL WORLD BY A. S. EDDINGTON M.A., LL.D., D.SC., F.R.S. Plumian Professor of Astronomy in the University of Cambridge THE GIFFORD LECTURES 1927 NEW YORK: THE MACMILLAN COMPANY CAMBRIDGE, ENGLAND: AT THE UNIVERSITY PRESS 1929 All rights reserved COPYRIGHT, 1928, By THE MACMILLAN COMPANY. Set up and electrotyped. Published November, 1928. Reprinted February, 1929. Twice. March, 1929. Reprinted April, 1929. SET UP BY BROWN BROTHERS LINOTYPERS PRINTED IN THE UNITED STATES OF AMERICA BY THE FERRIS PRINTING COMPANY [Pg v] PREFACE This book is substantially the course of Gifford Lectures which I delivered in the University of Edinburgh in January to March 1927. It treats of the philosophical outcome of the great changes of scientific thought which have recently come about. The theory of relativity and the quantum theory have led to strange new conceptions of the physical world; the progress of the principles of thermodynamics has wrought more gradual but no less profound change. The first eleven chapters are for the most part occupied with the new physical theories, with the reasons which have led to their adoption, and especially with the conceptions which seem to underlie them. The aim is to make clear the scientific view of the world as it stands at the present day, and, where it is incomplete, to judge the direction in which modern ideas appear to be tending. In the last four chapters I consider the position which this scientific view should occupy in relation to the wider aspects of human experience, including religion. The general spirit of the inquiry followed in the lectures is stated in the concluding paragraph of the Introduction (p. xvii). I hope that the scientific chapters may be read with interest apart from the later applications in the book; but they are not written quite on the lines that would have been adopted had they been wholly independent. It would not serve my purpose to give an easy introduction to the rudiments of the relativity and quantum theories; it was essential to reach the later and more recondite developments in which the conceptions of greatest philosophical significance are to be found. Whilst much of the book should prove fairly easy reading, arguments of [Pg vi] considerable difficulty have to be taken in their turn.