THE LOGIC OF
MODERN PHYSICS
BY
HOLLIS PROFESSOR OF MATHEMATICS AND NATURAL HISTORY
IN HARVARD UNIVERSITY
NEW YORKTHE MACMILLAN COMPANY
COPYRIGHT, 1927,
By THE MACMILLAN COMPANY.
PREFACE
This excursion into the field of fundamental criticism by one whoseactivities have hitherto been confined almost entirely to experiment isnot evidence of senile decay, as might be cynically assumed. I havealways, throughout all my experimental work, felt an imperative need ofa better understanding of the foundations of our physical thought andhave for a long time made more or less unsystematic attempts to reachsuch an understanding. Only now, however, has a half sabbatical yeargiven me leisure to attempt a more or less orderly exposition.
In spite of previous writings on the broad fundamentals by Clifford,Stallo, Mach, and Poincaré, to mention only a few, I believe a newessay of this critical character needs no apology. For entirely apartfrom the question of whether many of the points of view of these essayscan be maintained, the discovery of new facts in the domain ofrelativity and quantum theory has shifted the center of interest andemphasis. All the quite recent activity with the new quantum mechanicsseems to call for a new examination of fundamental matters which shallrecognize, at least by implication, the existence of the specialphenomena of the quantum domain. However, the necessity forre-examination does not mean at all that many of the results of previous[Pg v]criticism may not still be accepted; some of these results have becomeso thoroughly incorporated into physical thinking that we can assumethem without mention. Thus the fundamental attitude of this essay isempiricism, which is now justified as the attitude of the physicist inlarge part by the inquiry into the physiological origin of our conceptsof space, time, and mechanics with which the previous essays werelargely concerned.
None of the previous essays have consciously or immediately affected thedetails of this; in fact I have not read any of them within severalyears. If passages here recall passages already written, it is becausethe ideas have been assimilated and the precise origin forgotten; it isprobably worth while to let such passages stand without revision,because such ideas gain in plausibility through having been foundacceptable to independent thought.
I am much indebted to Professor R. F. Alfred Hoernlé of the Departmentof Philosophy of Johannesburg University, South Africa, for suggestingseveral modifications to make the text more acceptable to a philosopher,and slight amplifications for the benefit of readers not familiar withall the details of recent technical developments in physics.[Pg vi]
INTRODUCTION
One of the most noteworthy movements in recent physics is a change ofattitude toward what may be called the interpretative aspect of physics.It is being increasingly recognized, both in the writings and theconversation of physicists, that the world of experiment is notunderstandable without some examination of the purpose of physics and ofthe nature of its fundamental concepts. It is no ne