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Presentism is the position in the philosophy of time that maintains that nothing exists that is not present. In other words, only present events and objects exist, but no past or future events or objects do. Furthermore, it usually assumes that there is a succession of presents, i.e. a moving Now. The appeal of presentism derives from our intuition that past things have existed, but no longer do, and that future events have yet to occur. Presentism seems to be capable of accounting, quite naturally, for our sense that the future is open, that time passes, and that past events irretrievably slip away from us. Presentism thus claims that there is a fundamental difference between time and space: while we all happily concede that other spatial locations, such as New York or Paris, exist and are equally real as San Diego, presentists deny that temporal instances other than the present moment exist.

There are a number of metaphysical objections against presentism in the literature. And some authors have denied that it presents the only, or even the best, way to account for our intuitions about the phenomenology of temporality. But a much more powerful challenge arises from modern physics: Einstein's special theory of relativity provides strong, and perhaps conclusive, reason to view space and time not as two separable and quite distinct animals, but much rather as entangled aspects of the same underlying four-dimensional manifold that fuses the two into a "spacetime." In pre-relativistic physics, the notion of simultaneity of spatially distant events was unproblematic. In special relativity, however, it turned out that the requisite four-dimensional spacetime had a radically different structure: whether or not two spatially distant events are simultaneous or not was no longer an objectively and universally determinable fact of the matter. Two inertial observers at some relative velocity with respect to one another do not agree whether two events are simultaneous or not. The relation of simultaneity is thus relativized to observers. In a technical language, this means that there is no preferred foliation of spacetime into slices of three-dimensional spaces representing classes of simultaneous events. If we define "the present" as consisting of all those events which occur simultaneous with the point in spacetime representing the here and now, then the relativity of simultaneity seems to imply that the presentist is committed to relativize existence analogously: if we are two inertial observers moving at some relative speed, we take different distant events to be real!

Although special relativity does not apodictically rule out presentism, it constrains it in a way that renders whatever presentism survives the relativistic revolution a metaphysically rather unattractive cripple. One might have expected that this would do it. But presentism dies hard, very hard. In fact, presentism enjoys something of a renaissance in the philosophy of time. What is striking about this renaissance is that many of the hold-out (or born-again) presentists attempt to support their position by arguments of the kind that have traditionally been the weapon of choice for many of their opponents: arguments drawing on results from the physical sciences.

Apart from the unpalatable rejection of special relativity as unintuitive, incoherent, or empirically inadequate, I discern at least eleven presentist defences, some involving rather technical material, most of which have actually been undertaken in the literature:

  1. Special relativity is empirically adequate, but has been misinterpreted; in particular, it is suggested, a Lorentzian interpretation that avoids vesting the relativity of simultaneity with ontological implications ought to be pursued.
  2. It is argued along similar lines that although it is not empirically accessible, absolute simultaneity still exists at the ontic level.
  3. Another argument claims that only absolute simultaneity will ascertain that the velocity of light relative to inertial frames agrees with the "zero acceleration limit" of the velocity of light relative to rotating (and thus non-inertial) frames.
  4. Cosmological models in general relativity permit the re-introduction of a preferred foliation of spacetime into space and time, thereby re-establishing absolute simultaneity.
  5. (Not yet for public eyes).
  6. Julian Barbour offers an approach to relativistic mechanics that denies the reality of time and operates merely with three-dimensional systems spanning physical space. It has been argued that this view lends itself naturally to a presentist reading of these three-spaces as sets of simultaneous events ("presents").
  7. Group averaging techniques of quantization effectively yield a preferred foliation.
  8. Collapse interpretations of quantum mechanics require absolute simultaneity of spatially distant events.
  9. Bohmian quantum mechanics, an alternative interpretation of quantum mechanics, violates special relativity; in particular, it also seems to rely on absolute simultaneity.
  10. Special relativity is only a kinematic theory underwriting electrodynamics, and not all or even most of physics.
  11. (Not yet for public eyes).

Critics of presentism have responded to some of these arguments in print, but definitely not to all. In fact, I believe that the presentist strategies (v) and (xi) and entirely novel. Furthermore, I am not aware of any responses to (iii), (v), (vi), (vii), (x), and (xi). My suspicion is that all of these purported salvations of the presentist doctrine will ultimately turn out to be unsuccessful.

The first objective of this research project will be to survey the landscape and to collect presentist arguments based on results from physics and responses to them. It is almost certain that there are more potential or actual arguments in favour of presentism than those listed above. Once we have gained a systematic overview, the task would then be to subject each of these arguments as well as their reponses--if they exist--to detailed scrutiny.


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