THE MEANING OF
RELATIVITY
FOUR LECTURES DELIVERED ATPRINCETON UNIVERSITY, MAY, 1921
BY
WITH FOUR DIAGRAMS
PRINCETON
PRINCETON UNIVERSITY PRESS
1923
Copyright 1922Princeton University PressPublished 1922
NOTE.—The translation of these lectures into Englishwas made by EDWIN PLIMPTON ADAMS, Professorof Physics in Princeton University
CONTENTS
LECTURE I
SPACE AND TIME IN PRE-RELATIVITY PHYSICS
LECTURE II
THE THEORY OF SPECIAL RELATIVITY
LECTURE III
THE GENERAL THEORY OF RELATIVITY
LECTURE IV
THE GENERAL THEORY OF RELATIVITY (continued)
INDEX
THE MEANING OF RELATIVITY
LECTURE I
SPACE AND TIME IN PRE-RELATIVITYPHYSICS
THE theory of relativity is intimately connected with the theoryof space and time. I shall therefore begin with a brief investigationof the origin of our ideas of space and time, although indoing so I know that I introduce a controversial subject. Theobject of all science, whether natural science or psychology, isto co-ordinate our experiences and to bring them into a logicalsystem. How are our customary ideas of space and time relatedto the character of our experiences?
The experiences of an individual appear to us arranged in aseries of events; in this series the single events which we rememberappear to be ordered according to the criterion of "earlier"and "later," which cannot be analysed further. There exists,therefore, for the individual, an I-time, or subjective time. Thisin itself is not measurable. I can, indeed, associate numbers withthe events, in such a way that a greater number is associatedwith the later event than with an earlier one; but the nature ofthis association may be quite arbitrary. This association I candefine by means of a clock by comparing the order of events furnishedby the clock with the order of the given series of events.We understand by a clock something which provides a series ofevents which can be counted, and which has other properties ofwhich we shall speak later.[Pg 1]
By the aid of speech different individuals can, to a certainextent, compare their experiences. In this way it is shown thatcertain sense perceptions of different individuals correspond toeach other, while for other sense perceptions no such correspondencecan be established. We are accustomed to regard as realthose sense perceptions which are common to different individuals,and which therefore are, in a measure, impersonal. The naturalsciences, and in particular, the most fundamental of them,physics, deal with such sense perceptions. The conception ofphysical bodies, in particular of rigid bodies, is a relatively constantcomplex of such sense perceptions.