Time and Relativity: Some Philosophical Considerations

TIME AND RELATIVITY: SOME PHILOSOPHICAL CONSIDERATIONS N OT ONLY WAS Newton an outstanding mathematician , he was also an astute physicist who clearly saw the difficulties of formulating a solid foundation for the laws of motion. To resolve these difficulties he postulated the existence of absolute time and absolute space-concepts upon which his entire theory of physics rests.1 Not until the second half of the 19th century, when the principles of electrodynamics became known, was his theory shaken. Plainly, the laws of electrodynamics could not be incorporated satisfactorily into the Newtonian system. Further criticism of the Newtonian world by Mach and Poincare helped open the door to a new concept of mechanics, and through Einstein's publication in 1905 a new vision of the universe emerged-the special theory of relativity. Relativity establishes a new system of definitions for the reckoning of space and time. Since definitions of physical theories are of course arbitrary, a variety of definitions may give rise to various systems which represent equivalent descriptions of the same physical reality.2 For example, the same physical space can be described by several geometries resulting simply from a change in the definition of congruence. " All these descriptions," Reichenbach says, " represent different languages saying the same thing; equivalent descriptions therefore express the same physical content. The theory of equivalent description is also applicable to other :fields of physics; but 1 Sir Isaac Newton, Mathematical Principles (Berkeley, 1960), trans., F. Cajori. For the concepts of absolute space and absolute time see: pp. 6-8. Cf. Albert Einstein , Essays in Science (New York, 1934), trans., Alan Harris, p. 34. 2 Hans Reichenbach," The Philosophical Significance of the Theory of Relativity", in Albert Einstein: Philosopher-Scientist (New York, 1951), edited by Paul A. Schilpp, pp. ~94 ff. 62 TIME AND RELATIVITY 68 the domain of space and time has become the model case of this theory." 3 Since different definitions for the description of the same physical reality are possible, this paper will first analyze the definitions and concepts concerning time in Einstein's theory of special relativity. Second, these definitions and concepts will be compared with the philosophical definitions and descriptions of the same physical reality, namely time, in the thought of Aristotle and Aquinas. Relativity Theory and Objective Time Einstein's concept of time poses an important philosophical problem. Before relativity, it had always been assumed that the statements of time had an absolute ·significance; that is, the uniform flow of time was independent of the state of motion of the body of reference. This assumption seems to be incompatible with the relativistic idea of simultaneity, for, as Einstein illustrates, the time of a coordinate system is different from the time of any other coordinate system imparted with different velocity: " Every reference-body (coordinate system) has its own particular time; unless we are told the reference-body to which the statement refers, there is no meaning in the statement of the time of an event." 4 Thus, an observer in motion may have a:s many clocks as there are different bodies in motion with respect to the observer . Which is the clock which corresponds to our planet? There is no such clock-but there ought to be one with respect to the sun, another for those who look at the moon, and so· forth. This seems to destroy the possibility of something we have always taken for granted: the existence of an objective and universal time, valid for all coordinate systems. Bachelard describes the problem in vivid terms: This operational definition of simultaneity dissolves the notion of absolute time. Since simultaneity is linked to physical experiments •Ibid., p. ~95. 4 Albert Einstein, Relativity, the Special and the General Theory (New York, 1931), trans., Robert W. Lawson, pp. 3~-33. 64 ANTONIO MORENO which occur in space, the temporal contexture is one with spatial contexture. Since there is no absolute space, there is no absolute time ... Therefore from the standpoint of philosophy, it is evident that scientific thought requires a rebuilding of the notions of space and time in terms of their solidarity.5 Physicists have tried to solve the problem in various ways, and several have suggested solutions...