306 INTRODUCTION TO PHILOSOPHY OF SCIENCE 



For the relativity theory, the important thing about the 

 observer is that he is located in a certain frame of reference. 

 Space and time are therefore plural in the sense that they 

 are determined by systems of reference; "length and duration 

 are not things inherent in the external world; they are rela- 

 tions of things in the external world to some specified ob- 

 server." 1 "A length is . . . but the expression of a rela- 

 tionship between the observer and the observed, and the 

 two partners of the relationship must be specified before the 

 length can have any meaning. . . . Duration and time 

 are mere relatives, mere expressions of relationships, and 

 have no absolute significance per se" 2 Hence there are as 

 many values assignable to any given length and to any given 

 duration as there are possible systems of reference. In this 

 sense space-time may be separated into space and time in 

 an infinite number of ways. Yet in a more abstract sense 

 space-time may still be said to be one, for there is a constant 

 manner in which measuring devices are affected by changes 

 in systems of reference. Though space and time are relative 

 in their measured aspects, the law of the change of measuring 

 devices is absolute. The old absolute of the Newtonian- 

 Euclidean system of a space and a time has merely been 

 transferred to the relation between space-time and measur- 

 ing devices. 



Continuity and infinity. Nothing in the operational 

 derivation of classical space and time suggests that the 

 assumptions of continuity and infinitude are illegitimate. 

 Both of these have to do with the serial properties of space 

 and time, and these are essentially irrelevant to considera- 

 tions of relativity. Hence space-time of the relativity theory 

 is continuous in the three senses discussed earlier in the 

 chapter. It is amorphous, i.e., it exhibits no metric. It is 

 describable in terms of the linear continuum, the most im- 

 portant feature of which is the absence of adjacency with 



1 A. S. Eddington, Space. Time, Gravitation (Cambridge: Cambridge University, 

 1920), p. 34. 



2 A. d'Abro, Evolution of Scientific Thought (New York: Boni and Liveright, 1927), 

 p. 151. 



