- There are two different though related ways of indicating time distinctions. On the one hand there is the machinery of tenses associated with the notions of past, present, and future; and on the other the temporal ordering of events effected by the earlier-later relation. Different metaphysical pictures result according to which mode of time indication is taken to be fundamental. The debate between thinkers who take tenses to be the basic mode of time indication and those who are opposed to this approach - who I shall call 'tensers' and 'detensers' respectively - has been conducted on a wide variety of grounds. There is one ground, however, which many detensers regard as decisively favouring their approach, and this is what we might call the argument from the special theory of relativity. Special relativity is widely thought to provide a knock-down argument against tense because, it is claimed, it undermines the notion of the present on which tenses ultimately depend. In this paper I shall argue that while special relativity is at odds with our 'classical' or 'Newtonian' notion of the present, which I think must be rejected, there is a modified account of the present, which I call the 'causal theory', which reconciles the present with special relativity.
- The argument from special relativity rests on the claim that the notion of the present depends upon that of simultaneity, which the theory indermines1. I shall argue, however, that although the implications of special relativity for 'distant individuals' are surprising, they do not render the present incoherent. Despite the scare stories, the present is all right. The particular problems for the present which allegedly arise from special relativity are brought out most clearly when we attempt to settle the temporal status of distant events. The problems, however, can be raised for any spatially separated - that is, distinct - events; but they are more readily grasped in connection with events which are reasonably remote. Special relativity introduces an element of conventionality into the dating of distant events, but the stress on distance just dramatises the problem. The exact ordering of proximate events, if they are of short enough duration, is subject to exactly the same difficulties.
- According to tensers like Arthur Prior, to ask what is happening now is simply to ask what is happening. On this view the present is characterized as a vacuous modifier which attaches to all our judgements. Prior's notion of the present is explicitly associated with a tensed ontology, according to which the difference between the present and the past and future is 'but one facet of the great gulf which separates the real from the unreal'. But according to special relativity there is no unambiguous answer to a question about what is going on at some remote place now. The answer will depend on the location and inertial frame occupied by the observer who raises the question. Though we are at liberty to date distant events, there is an indefinitely great number of ways, all equally valid, in which this may be carried out. The present, which Prior wished to treat as a vacuous qualification of any statement, seems merely to reflect the parochialism of a particular observer.
- Prior's notion of the present appears quite compatible with the classical Newtonian view of time as a succession of instantaneous world-wide configurations of objects. But special relativity denies that there can be any such thing as a unique class of simultaneous events which are common to all inertial frames. Hence Prior's idea of the present appears to be deprived of all objective significance. The primitive idea of the present is that class of events simultaneously perceived by an observer. But if which events are regarded as simultaneous depends on a conventional choice of an inertial frame, then it seems that what is present is a matter of convention. And if what is present is a matter of convention then the past and future are also to that extent matters of convention. It seems to follow that any enterprise such as a logic of tenses, which seeks to draw an absolute distinction between what is present and what is merely past or future, is in jeopardy. The alternative to a logic of tenses, in which it is claimed that temporal distinctions should be treated through the first-order logic of the earlier-later relation, is claimed to be better equipped to accommodate the facts of special relativity.
- It is curiously overlooked by most detensers that the special relativity problem which produces a conventionality about what is present leads to an exactly similar problem for a logic of tenseless dated propositions. One alleged advantage of the latter approach is that the resulting propositions are not subject to the exigencies of changing temporal reference. Tenseless dated propositions are claimed to have the merit of being freely repeatable. But 'It is raining in Canberra', transformed into its tenseless counterpart 'It rains (tenseless) in Canberra at t', is going to face comparable relativistic problems; not to mention other well-known difficulties. For what the date t is going to be will depend on the location and inertial frame chosen from which the description is to be framed. According to special relativity the suggested tenseless translation will not be freely repeatable. Any system of dating depends on correlating events with one another, and which events are correlated with a time t depends on the frame of reference chosen. Relativistic problems about time therefore arise for our dating systems as well as for tensed notions, and indeed I will argue that here they are even more pressing. This only makes it all the more urgent to unravel the implications which special relativity has for our temporal notions.
- What? “Undermines”?
- But simultaneity is important to SR – just not “universal simultaneity”.
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