Alternatively, Presentists could take an atomistic, rather than holistic, approach. There would have to be a system of acceleration vectors possessed by some particles at each moment of time. If a particle has had an acceleration vector throughout some period of time, then it must be assigned a continuous path, and if it has had a zero-valued acceleration vector throughout that period, then it must be assigned an un-accelerated path. This enables Presentists to acknowledge the metaphysical possibility of a miracle in which a particle's atomistic acceleration vector doesn't conform to the forces acting on it.
Now, what is supposed to be wrong with this? The greatest problem for the atomistic approach is to explain the connection between acceleration vectors and the actual changes in relative positions of particles. As Tooley (1988) suggests, we could use a kind of Ramsification strategy (see Chapter 6 for more on Ramsification). Atomistic acceleration properties of particles are those properties that play a specified causal role with respect to the effects of the force laws and the causes of the changes in relative position over time.
Sider argues that Presentists face some sort of vicious circularity here, since they cannot merely help themselves to a function relating position in the affine structure to time. However, Presentists do have full access to the set of facts about the configuration of forces and to the set of facts about changes in relative positions of particles over time. We don't see why these two sets of facts aren't sufficient to provide a Ramsified definition of acceleration properties. The change in relative velocity between two particles should be a function of the vector sum of the two particles' acceleration vectors, and the acceleration vectors should, together with the intrinsic forces, satisfy Newton's F = ma force law. It seems, in fact, that Eternalists are in much the same boat. How else do we gain cognitive access to the affine structure of the physical world except as the product of forces and as the explanation for changes in relative position?
Once again, however, the possibility of miracles seems to be a persistent problem for Presentists. It seems possible for a set of particles to change their relative positions over a period of time in a way that diverges from the atomistic vectors possessed by the particles at each moment. Presentists must invoke some kind of metaphysical necessity linking the intrinsic acceleration vectors and changes in relative position over time, a necessity so strict as to rule out all miraculous deviations. Eternalists need no such necessary connections. This is a clear advantage for Eternalism.
21.2.7 Truthmaker problems: Other cross-temporal relations between past entities
Presentists also face problems to do with quantification and existence. It seems that there are things that once existed but no longer do so, and Presentists have no truthmakers for such truths, since there aren't things that exist wholly in the past. We focus first on an example from Lewis (2004b):
(3) There have been two English kings named ‘James’.
James I and James II had non-overlapping lifetimes. Thus, Presentists' analysis of this sentence must take this form:
(3*) WAS(∃x)(x is an English king named ‘James’ & WAS (∃y)(y is an English king named ‘James’ & x ≠ y))
The difficulty arises in giving the truth-conditions for the final clause, ‘x ≠ y’. Since James II (our ‘x’) did not exist at the same time as James I (our ‘y’), he does not belong within the domain of quantification associated with the second, embedded ‘WAS’ operator. Yet (3*) seems to entail that James II did exist then, so that we can meaningfully assert, within the double embedding, that James I ≠ James II.
Lewis argues that there is a solution available to Presentists. They can make use of not only past-tensed sentences, but also past-tensed predications. In other words, we can suppose that James II had, while he was alive, the past-tensed property of having been distinct from James I (or, more precisely, the property of having been distinct from an English king names ‘James’). This solution has two puzzling consequences. First, it entails that people can have properties that predate their own existence. When RCK came into existence, he immediately acquired a host of past-tensed properties, namely the properties of not having existed at any previous point in time (and, consequently, the properties of not being identical to any of things existing then). But there seems to be something paradoxical about saying that RCK has any property (even the property of not having existed) indexed to any time before his existence commenced. Serious Presentists (it would seem) should deny that RCK has any property indexed to any time before he began to exist. But this would make it impossible to provide an adequate interpretation of (3).
Second, Lewis's solution entails that the past changes with the generation or annihilation of things. When RCK began to exist, his existence added a new layer of fact to each past moment, namely, the fact that he did not exist then. Analogously, when RCK ceases to exist, these layers of fact are scrubbed away, leaving behind only the purely general fact that there once existed a person like RCK who didn't exist then. This seems to conflict with a pretty strong intuition of the absolute fixity of the past.
Presentists have two possible alternatives. The first embraces Anti-Actualism (12.1A), whether Possibilism (12.1A.1T) or Meinongianism (12.1A.1A); that is, it appeals to something like Possibilistic Presentism (20.2T.4.1). The second invokes surrogates of past things, like haecceities, bare particulars, or some kind of abstracta.
POSSIBILISTIC PRESENTISM Anti-Actualism gives Presentists non-existent things to which present things can stand in cross-temporal relations. All the while, one can maintain the claim that merely past or merely future things do not exist. The drawbacks are just those of Anti-Actualism generally. We discuss those in Chapter 12, and do not repeat that discussion here.
SURROGATE PRESENTISM Surrogate Presentism appeals to haecceities, bare particulars, or some kind of abstracta as surrogates for wholly past or future objects. The idea is that present things stand in cross-temporal relations to past or future things by standing in present relations to their surrogates. There are at least three versions of surrogate Presentism.
Zalta-Williamson mutationism. Merely past and future objects exist but only as abstracta (Zalta 1988, Williamson 1998). George Washington was once an abstract object, then he became concrete (a human being), and then upon death, he went back to being an abstract object (setting aside for simplicity's sake the possibility of an afterlife as a soul).
Bare particulars. Past and future objects exist, but they lack all qualities and relations, other than the minimal logical and metaphysical properties, such as self-identity and particularity. This may be equivalent to (1), depending on our conception of abstract objects.
Thisnesses or haecceities. The property of being George Washington may have existed before George Washington himself and may have continued to exist after he ceased to do so. If so, the fact that George Washington was a great President could consist in the fact that the property of being George Washington was once co-instantiated with the property of being a great President. Suppose we accept the existence of uninstantiated haecceities corresponding to no-longer or not-yet existing things. We can use haecceities to provide truthmakers for the non-existence or distinctness of things. Consider (4) and (5):
(4) James II no longer exists.
(5) James I ≠ James II.
(4) is made true by the fact that the haecceity of James II is uninstantiated but has the property of having been instantiated. (5), is made true by the fact that the haecceity of James I is possibly instantiated without being co-instantiated with the haecceity of James II, and vice versa. Similarly, we could suppose that both James I and James II exist eternally but are concrete or thick particulars only for limited periods. Contrast this with mutationism, according to which (5) receives its usual interpretation, and (4) is interpreted as the claim that James II is no longer concrete (alive, causally active, spatially located, having occurrent physical or mental properties).
Here is another example of a cross-time relation:
(
6) Some American philosophers admire some ancient Greek philosophers.
The trouble is that there is no time at which both American and ancient Greek philosophers are both alive. The haecceity account would have to introduce a new kind of relation, that of admiration*, which holds between someone and the haecceity of someone whom the first person admires. (6) becomes (6*):
(6*) Some American philosophers admire* some haecceities that were in ancient times co-instantiated with the properties of being Greek and of being a philosopher.
21.2.8 A final truthmaker problem for Presentism: Open-ended generalizations
Presentists have at least one more difficult phenomenon to deal with, namely, universal quantification over all of time involving accidental generalization. Consider (7):
(7) There will never be a golden mountain.
(7) seems possibly true. But it cannot be true at any time. Of necessity, there never will come a time at which (7) has a truthmaker. This is because there will necessarily always be still later times lying in the future, and so there may always come a time when there are golden mountains. (We assume that the future existence of a golden mountain is never ruled out by the laws of nature. If this assumption is false, merely modify the example, or consider an indeterministic world in which (7) is true but in which a golden mountain is never nomologically excluded.) This seems to put considerable pressure on the combination of Presentism and Truthmaker Theory. However, most Truthmaker Theorists reject the strong position of Truthmaker Maximalism (2.1T.1), which requires every truth, even negative ones, to have a truthmaker. (7) is clearly a negative statement, so it may be enough for its truth that it never has a falsity-maker.
Still, there's something paradoxical about saying that (7) is possibly true. At least, it seems paradoxical for Presentists to say this, since they identify true at the present with true simpliciter. How can (7) be possibly true if it is impossible for it ever to be true simpliciter?
Perhaps Presentists can add a real omega-moment, at the infinite horizon of time. This would have to be a moment (or quasi-moment) without successor or immediate predecessor. Such generalizations as (7) will have truthmakers then (namely, the totality of all time-indexed facts that will ever obtain). The greatest problem with such a proposal is the necessary lack of moments later than the omega-moment. Why and how would time freeze then? The answer might lie in the fact that the omega-moment consists entirely of past-tensed facts, all of which are intrinsically static.
21.3 The Theory of Relativity
The standard interpretation of Einstein's special theory of relativity makes trouble for Tensism because it challenges the idea that there is a unique present moment. Tensism, in all of its forms, is committed to the claim that there is a unique present moment. But according to the standard interpretation, physical reality contains nothing that corresponds to a relation of absolute simultaneity. There is no fact of the matter as to whether two space-like separated events (events such that no light signal or other direct causal chain could possibly connect one to the other) are or are not simultaneous in an absolute sense. Questions of simultaneity between such events have real answers only relative to an inertial frame of reference. That is, whether one such event is earlier than, later than or simultaneous with another varies, depending on one's point of view, where each velocity-vector corresponds to a different point of view or reference frame.
The conflict between Tensism and special relativity is pretty straightforward, since the standard interpretation of special relativity deprives us of a unique present moment. Two events belong to the same moment of time just in case they are simultaneous. Hence, according to special relativity (by which we mean the standard interpretation of special relativity), whether two events do or do not belong to the same moment is relative to one's reference frame. If there is no metaphysical fact of the matter as to whether any set of events constitutes a single moment at all, there could hardly be a metaphysical fact of the matter that one such moment is uniquely present. As simple as this argument is, it seems decisive.
Indeed, if we combine the standard interpretation of relativity theory with Presentism, we would be forced to embrace the uncomfortable (maybe absurd) conclusion that existence itself is frame-dependent. Presentism, after all, is the view that all that there is exists at the present moment.
If there is an incompatibility between special relativity and Tensism, then Tensers are forced to reject either special relativity itself or at least the standard interpretation of the theory. Sider (2001) considers either of these options to be equally revisionary of scientific theory and practice. But this is not obviously true. There is clearly a gap between the claim that special relativity requires no relation of absolute simultaneity and the claim that it excludes the existence of such a relation. Put another way, there is a gap between the fact that it is impossible to identify any privileged frame of reference and the hypothesis that there is no such privileged frame. Only if we assume the sort of verificationism that was (due to the physicist Ernst Mach) quite common among physicists when Einstein formulated his theory do these gaps disappear. Since verificationism is now almost universally thought to be indefensible, it behooves us to reconsider the matter carefully.
Both Michael Tooley (1997: 340–370) and William Lane Craig (2008) have argued for a non-standard interpretation of special relativity that is compatible with the existence of absolute simultaneity. Tooley's approach, in particular, seems defensible. To get a privileged frame of reference by which one can measure absolute simultaneity, one needs something like absolute space. (This requires Spatial Substantivalism 17.1T.) It is hard to see how one can get absolute space, especially assuming Presentism, without supposing that space is a kind of substance. That is, one must reify the points (or regions) of space. One can then assume either that points of space endure eternally throughout time or that, as Tooley assumes, each point in spacetime causally generates a unique spatial successor at the next moment of time. (It's a good question whether Tooley's model requires discrete time. This will depend on how Tensers handle diachronic causation, a matter we take up in Chapter 28.)
If absolute space exists, then moments can be defined as those sets of events that are simultaneous relative to a privileged frame, namely, the frame that is at rest with respect to absolute space. On such an interpretation, special relativity poses no problems for Tensism.
Tooley describes how to reach the non-standard interpretation in Time, Tense and Causation (Tooley 1997: 341ff.). (What follows assumes some knowledge of relativity theory.) First, we replace the Lorentz transformations with a more general scheme of e-Lorentz transformations, which were first described by Hans Reichenbach and used by John Winnie in his formulation of special relativity (Winnie 1970). In this formulation, we don't assume (as Einstein did) that the speed of light is the same in all directions in all frames of reference, but only that the average round-trip speed of light is the same in all directions in all frames of reference. We allow that the one-way speed of light in one direction might differ (in some frames) from its speed in the opposite direction. The e parameter, which takes values between 0 and 1, allows us to express a weaker assumption: if the speed of light in one direction is c/2e, then its speed in the opposite direction must be c/(2-2e). If e is always assumed to be 1/2, which was Einstein's assumption or convention, then the one-way direction of time in any direction and in any frame is always c. However, in the e-Lorentz transformation, we make no such assumption. Second, we add the assumption that absolute space exists, which gives a privileged frame of reference. The result is consistent with the experimental results of special relativity, since it can be proved that the e-Lorentz transformations guarantee that the round-trip average velocity of light is always c in every frame of reference.
It's not clear that this involves a substantial revision of current scientific theory, as opposed to an alternative interpretation of it. It clearly involves metaphysical assumptions that differ from the usual interpretation, lik
e the existence of substantival space, but this does not require a change in scientific theory or practice.
Tooley argues that his account has several advantages. First, it can account for the continued existence of spatial relations by way of a causal mechanism, since on this view each momentary spatial point causes the existence of its location-successor. This is a fact that Spatial Relationists (17.1A) have to treat as a brute fact. This putative advantage is hard to evaluate. One might argue that the spatial relatedness of the new points generated at each moment remains an unexplained brute fact on Tooley's account, just as the continued spatial relatedness of things is unexplained on the standard account. Tooley's account explains the continued existence of the substance of space, but this involves an explanandum that simply doesn't exist on Relationism.
The second putative advantage Tooley cites involves the compatibility of his account with wave-collapse interpretations of quantum mechanics. On wave-collapse interpretations, a measurement somehow precipitates the collapse of a quantum wave into a set of discrete eigenvalues. If the quantum system involves mutually “entangled” particles that are, at the time of measurement, space-like separated, then the measurement of one particle has an instantaneous and therefore superluminal influence on the other particle. Such collapses can, from a God's-eye point of view, be used to synchronize distant events. This requires frame-independent, absolute simultaneity relations.
The question of how to interpret quantum mechanics and how, if at all, to make relativity and quantum mechanics mutually compatible, is a thorny and deeply contested ones. There are no-collapse versions of quantum mechanics, such as the Everett many-worlds or Albers many-minds interpretations, that may not require superluminal influences. In addition, the minimalist reinterpretation of special relativity described below shares this advantage with Tooley's postulation of absolute space.
The Atlas of Reality Page 76
