CRITICAL NOTICE Presentism and Relativity*

In this critical notice we argue against William Craig’s recent attempt to reconcile presentism (roughly, the view that only the present is real) with relativity theory. Craig’s defense of his position boils down to endorsing a ‘neo-Lorentzian interpretation’ of special relativity. We contend that his reconstruction of Lorentz’s theory and its historical development is fatally flawed and that his arguments for reviving this theory fail on many counts. 1 Rival theories of time 2 Relativity and the present 3 Special relativity: one theory, three interpretations 4 Theories of principle and constructive theories 5 The relativity interpretation: explanatorily deficient? 6 The relativity interpretation: ontologically fragmented? 7 The space-time interpretation: does God need a preferred frame of reference? 8 The neo-Lorentzian interpretation: at what price? 9 The neo-Lorentzian interpretation: with what payoff? 10 Why we should prefer the space-time interpretation over the neo-Lorentzian interpretation 11 What about general relativity? 12 Squaring the tenseless space-time interpretation with our tensed experience Brit. J. Phil. Sci. 54 (2003), 327–346, axg017 &British Society for the Philosophy of Science 2003 * A review essay of William Lane Craig, The Tensed Theory of Time: A Critical Examination (Dordrecht: Kluwer Academic Publishers, 2000), x + 287 pp. ISBN 0–7923–6634–4, hardback, e113.50/$123.00/£78.00; Idem, The Tenseless Theory of Time: A Critical Examination (Dordrecht: Kluwer Academic Publishers, 2000), x + 256 pp. ISBN 0–7923–6635–2, hardback, e95.50/$103.00/£65.00; Idem, Time and the Metaphysics of Relativity (Dordrecht: Kluwer Academic Publishers, 2001), xi + 279 pp. ISBN 0–7923–6635–2, hardback, e109.00/$92.00/ £62.00. 1 Rival theories of time According to the tensed theory of time, reality is characterized by objective tense determinations of being past, present, and future. On the rival tenseless theory, no such determinations are objective. Rather, they are features of a particular perspective on reality, a reality which is not itself tensed. No events or moments of time are by themselves past, present, or future. They only become so when viewed from a given vantage point in time, t*. They can then be described as being past, present, or future, but what make such descriptions true are the tenseless facts that the events in question occur, respectively, earlier than, simultaneously with, or later than t*. There is nothing special about t*. Any other moment can serve as a focal point of a perspective on other times, because all moments of time and their contents are on the same ontological footing. They tenselessly exist at their respective dates, much like different places and their occupants exist at their respective spatial locations. The issue between the two rival views—alternatively (but not always correctly, but we gloss over that) labeled the ‘Aand B-theories’ (following McTaggart), ‘dynamic’ versus ‘static time’, ‘presentism’ versus ‘eternalism’, ‘real time’ versus ‘spacelike time’—remains central in the flourishing philosophy-of-time industry. William Lane Craig’s monumental tetralogy (Craig [2000a,b], [2001a,b]) is both a state-of-the-art survey of the entire field and an uncompromising defense of (a version of) the tensed theory. The scope of Craig’s study, summarizing (but also going beyond) what he and others have done in the field in the past twenty years or so, is overwhelming and the amount of detail staggering. We venture to say that no single important argument for or against any of the two rival views of time is left unaddressed by Craig and challenge the reader to find such an argument. He traces the evolution of the B-theory from the old ‘translation thesis’ to the new ‘truth-conditions’ claim, making the motivations and pressures involved in the transition highly perspicuous. He examines in detail the experience of time and devotes a good fifty pages to McTaggart’s paradox. He literally takes the issues of temporal passage and becoming apart. In particular, Craig 328 The British Journal for the Philosophy of Science 1 However, Craig’s discussion of the related issue of persistence (Craig [2000b], Ch. 9) leaves much to be desired. First, he rejects, without a convincing argument, a combination of endurantism (the view that material objects persist over time by being wholly present at all moments at which they exist) with the tenseless theory of time. This combination is widely accepted on the basis of a predication schema known as adverbialism (see, e.g., Rea [1998], Balashov [2000] and references therein). This approach solves the problem of temporary intrinsics by insisting that objects have intrinsic properties in ways characterized by temporal modifiers. Craig complains that this requires taking ‘[t]he apparently complex notion of having a property tly [. . .] as semantically primitive, which to all appearances it is not’ ([2000b], p. 191, note 37). But should a correct semantics be a matter of ‘appearances’? This is hardly a reasonable requirement (recall the semantical quandaries of descriptions and propositional attitudes). Craig’s critique thus begs the question. Starting with the basic expression ‘O ist j’, presents, in the second volume, a series of arguments against the minddependence interpretation of becoming and the ‘spatializing’ of time. In that volume he also explores the connections between the nature of time and the ontology of persistence. Last but not least, he attempts to undermine the B-theorist’s reliance on relativity theory by undertaking a comprehensive philosophical study of this theory. We are sure many readers will find most of Craig’s central claims controversial, and some of his tactics (e.g., ample use of theological considerations in philosophical argumentation) questionable. But he succeeds, we think, in challenging his opponents. In any event, we feel challenged and are aware of other critical responses, some in print, some still brewing in the works, to various strands in Craig’s extended defense of the tensed theory and his assault on its tenseless rival. Needless to say, it is not possible to do Craig’s work full justice here. To make the subsequent discussion focused, we have chosen to concentrate on what seems to us most provocative and most misguided: Craig’s attempt to reconcile the presentist version of the tensed theory with relativity. 2 Relativity and the present Presentism is, roughly, the view that only the present exists. The advocate of this doctrine is therefore committed to there being a fact to the matter of what events on Pluto are present (hence real) when John snaps his fingers here on Earth. Special relativity (SR) denies that there are any such facts. Craig contends that facts about absolute simultaneity and the absolute present have a place in SR after all, provided this theory is given a suitable, ‘neoLorentzian’ re-interpretation, and argues that this re-interpretation is physically acceptable, as well as metaphysically preferable to the standard formulation. Unlike some other A-theorists who tend to ignore, evade, or Critical Notice: Presentism and Relativity 329 where t modifies the copula, we can then analyze ‘O is j’ along the lines of ‘9t (O istj)’, just as we can analyze running in terms of running somehow (e.g., slowly or quickly). Cf. Rea ([1998]), p. 245. Second, Craig’s (unavailing, in our opinion) attack on adverbialism is part of his chapterlong attempt to favor the presentist endurantism solution to the problem of temporary intrinsics over all other candidates. Unfortunately, his discussion does not take into account important recent developments in the 3D/4D debate. In particular, it overlooks a distinction that has emerged within the perdurantism camp, one between the worm theory and the stage theory. The advocates of the latter (see, in particular, Sider [2001] and Hawley [2001]) have argued that, among other advantages, their theory offers the best unified solution to the paradoxes of material constitution and coincident entities and to the problem of vagueness. Craig’s discussion barely touches on the first and practically ignores the second. Since both are now big metaphysical industries, this makes Craig’s arguments in the chapter on persistence and his final verdict far from being up-to-date in yet another respect. 2 This is the main subject matter of the third volume (Craig [2001a]) and of a good portion of the second (Craig [2000b]). The reader should be warned that there is considerable overlap between these two expositions. In fact, the entire material on relativity contained in Craig ([2000b]), pp. 11–126, is reproduced verbatim in Craig ([2001a]). Hence the reader specifically interested in relativity can safely confine her/himself to Craig ([2001a]). table the relativistic objection, Craig confronts it head-on. We believe his arguments all fail, but it is not entirely trivial to see why they fail. Craig’s volume-long defense of the neo-Lorentzian interpretation touches on many issues ranging from the history of relativity to scientific methodology to the foundations of spacetime theories. Responding in detail to what Craig has to say on all of these topics would probably require another volume of comparable length. We want to focus on what we think is the central issue. Because of his metaphysical and theological predilections, Craig wants to resurrect the notion of a preferred frame of reference in physics. We want to show—no more and no less—how forcefully the physical evidence militates against such a return to the days before Einstein. We claim (see Section 10 below) that the argument from physics against Craig’s metaphysically-motivated proposal is on a par with the argument against proposals to return to the days before Darwin in biology or the days before Copernicus in astronomy. We want to preface our discussion with a cautionary note on the genre of Craig 2001a. This volume should be looked upon not so much as a ‘philosophically-informed introduction to relativity theory’ (p. ix; unless otherwise indicated, page references below are to Craig 2001a) but as an exposition of a highly controversial view of this theory by a philosopher who has an active agenda (and much at stake). For this reason, we would not recommend it to a philosophically-minded beginner wanting to learn SR. Such a reader is much better off reading, for instance, Geroch ([1978]) or Sartori ([1996]). 3 Special relativity: one theory, three interpretations Craig distinguishes three interpretations of SR: (1) the ‘Relativity Interpretation’, which is essentially the form in which Einstein ([1905]) originally presented his theory; (2) the ‘Space-Time Interpretation’, which is essentially the geometrical interpretation that Minkowski ([1909]) gave to Einstein’s new kinematics; (3) the ‘Neo-Lorentzian Interpretation’, which is a modernized version of (the relevant parts) of the classical theory of Lorentz ([1915]) in its final form. We can take the theory itself to be the requirement that all physical laws—or at least all laws effectively governing observable phenomena—be Lorentz invariant. A historian of relativity will have to be more careful, but for our philosophical purposes, as well as for all practical purposes of modern physics, this characterization is perfectly adequate. We also have no trouble with Craig’s taxonomy of the theory’s interpretations, 330 The British Journal for the Philosophy of Science 3 We should warn the reader, however, that Sartori ([1996], pp. 123–8) fails to do justice to Lorentz’s theory (see Janssen [2002] for a concise characterization of Lorentz’s theory and its development). even though many physicists and philosophers would exclude the neoLorentzian interpretation since it runs counter to the spirit if not the letter of SR by retaining a preferred frame of reference and absolute simultaneity. For us it is Craig’s analysis of these three interpretations, and the relation among them, that is problematic. 4 Theories of principle and constructive theories What Einstein presented in his 1905 paper is basically—the reason for the qualification will become clear below—what he would later call a ‘theory of principle’ as opposed to a ‘constructive theory’ (Einstein [1919]). Here is our understanding of the distinction. In a theory of principle, one starts from some general, well-confirmed empirical regularities that are raised to the status of postulates (e.g., the impossibility of perpetual motion of the first and the second kind, which became the first and second laws of thermodynamics). With such a theory, one explains the phenomena by showing that they necessarily occur in a world in accordance with the postulates. Whereas theories of principle are about the phenomena, constructive theories aim to get at the underlying reality. In a constructive theory one proposes a (set of) model(s) for some part of physical reality (e.g., the kinetic theory modeling a gas as a swarm of tiny billiard balls bouncing around in a box). One explains the phenomena by showing that the theory provides a model that gives an empirically adequate description of the salient features of reality. Consider the phenomenon of length contraction. Understood purely as a theory of principle, SR explains this phenomenon if it can be shown that the phenomenon necessarily occurs in any world that is in accordance with the relativity postulate and the light postulate. By its very nature such a theoryof-principle explanation will have nothing to say about the reality behind the phenomenon. A constructive version of the theory, by contrast, explains length contraction if the theory provides an empirically adequate model of the relevant features of a world in accordance with the two postulates. Such constructive-theory explanations do tell us how to conceive of the reality behind the phenomenon. Both the space-time interpretation and the neo-Lorentzian interpretation provide constructive-theory explanations. In the space-time interpretation, the model is Minkowski space-time and length contraction is explained by showing that two observers who are in relative motion to one another and therefore use different sets of space-time axes disagree about which crosssections of the ‘world-tube’ of a physical system give the length of the system. In the neo-Lorentzian interpretation, length contraction is explained as a combination of dynamical effects and artifacts of measurement. We shall examine this explanation in more detail below. Critical Notice: Presentism and Relativity 331