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Historians usually divide the history of mankind into three epochs: Antiquity , Middle Ages, and Modern Times. In a similar manner, philosophers distinguish between ancient, medieval, and modern philosophy; physicists speak of ancient, classical (Newtonian), and modern physics. Because the concept of simultaneity, as shown in preceding chapters, is a subject of both philosophical and physical studies, it is tempting to apply a similar chronological trisection to the history of this notion even though it denotes only a (temporal ) relation. This is feasible because, in the history of this notion, there were precisely two temporally separated major conceptual developments that radically revolutionized the meaning of this concept. Consequently each of them defines the end of an epoch and the beginning of a consecutive one. The first of these two critical events was Roemer’s discovery of the finite velocity of light in 1676, a decade before the publication of Newton’s Principia . This discovery changed fundamentally the ancient conception of simultaneity , for it abolished what was called “the visual simultaneity thesis” (see chapter 4) by implying that events seen simultaneously have in reality not occurred simultaneously unless they had been equidistant from the obEpilogue 296 Concepts of Simultaneity server when observed. In other words, and strictly speaking, the world as we see it is an optical illusion. The first period would then end in the late seventeenth century and be followed by an epoch that lasts until the beginning of the twentieth century, an epoch during which the concept of simultaneity was recognized to raise important problems for philosophical and physical inquiry (Leibniz, Kant, and Poincaré). The third and last epoch begins in 1905 with the publication of Einstein’s ground-breaking paper on the special theory of relativity, which offered an operational definition of the notion of simultaneity, proved that it is a relative (frame-dependent) concept, and initiated the conventionality thesis that is still a matter of dispute. Philosophers and physicists date the beginnings of their disciplines from the day when Thales of Miletus and his school, or the physicists, as Aristotle called them, relegated the Greek mythological gods to the domain of fable and instead explained nature by principles and causes. In contrast to the history of (Western) philosophy and physics, in the history of the notion of simultaneity it is impossible to determine a precise beginning of the first epoch. For long before the beginning of Greek (or Oriental ) philosophy primitive man had an intuitive, albeit imprecise, idea of a global “present” or “now” and thereby of a worldwide simultaneity.1 It has been even contended that this kind of simultaneity is the prototype of the real simultaneity for it is, as Bergson2 called it, “perceived and lived” (perçu et vécu). In contrast, it is claimed, the simultaneity defined by modern relativists is based merely on mathematical symbols, is relative, and not experienced by anyone. In a similar vein a noted philosopher of modern physics claimed that “the classical idea of world-wide instants, containing simultaneously spatially separated events, still haunts the subconscious even of relativistic physicists; though verbally rejected, it manifests itself, like a Freudian symbol, in a certain conservation of language.”3 In any case, in agreement with the metalinguistic remarks made in the earlier sections in chapter 2, we have to conclude that the beginning of the first epoch of the trisection under discussion is not precisely determinable. 1See chapter 1, note 26. 2 See chapter 8, note 21. 3 M. Čapec, The Philosophical Impact of Contemporary Physics (Princeton: Van Nostrand, 1961), pp. 190–191. That the third epoch in the history of the concept of simultaneity also is not yet a closed chapter follows already from the fact that the controversy about the conventionality thesis of distant simultaneity has not yet abated and that, from time to time, new ideas and new methods are proposed to tackle outstanding problems. A typical example is Hans C. Ohanian’s recent suggestion that the conventionality thesis has so far been widely discussed by physicists and philosophers only in the context of kinematics and that an appropriate application of the laws of dynamics could resolve all ambiguities in synchronization and thus, in particular, the conventionality problem. A nonstandard synchronization, he contended, “introduces pseudoforces into the equations of motion, and these pseudoforces are fingerprints of the nonstandard synchronization, just as the centrifugal and Coriolis pseudoforces are fingerprints of a rotating reference frame.” He concluded, therefore, that “in an inertial frame, the nonstandard...


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