No Presentism in Quantum Gravity1 Introduction2 Minkowski Spacetime and the Pressure from Special Relativity3 Monton's Incompatibilist Defence of Presentism4 The CMC Foliation Approach: A New Homefor Presentism?5 ConclusionReferencesNo Presentism in Quantum GravityChristian W¨uthrichAbstract This essay offers a reaction to the recent resurgence of presentism in thephilosophy of time. What is of particular interest in this renaissance is that a numberof recent arguments supporting presentism are crafted in an untypically naturalisticvein, breathing new life into a metaphysics of time with a bad track record of co-habitation with modern physics. Against this trend, the present essay argues that thepressure on presentism exerted by special relativity and its core lesson of Lorentzsymmetry cannot easily be shirked. A categorization of presentist responses to thispressure is offered. As a case in point, I analyze a recent argument by Monton (Pre-sentism and quantum gravity, 263–280, 2006) presenting a case for the compatibilityof presentism with quantum gravity. Monton claims that this compatibility arisesbecause there are quantum theories of gravity that use fixed foliations of spacetimeand that such fixed foliations provide a natural home for a metaphysically robustnotion of the present. A careful analysis leaves Monton’s argument wanting. In sum,the prospects of presentism to be alleviated from the stress applied by fundamentalphysics are faint.1 IntroductionPresentism is the position in the philosophy of time that maintains that nothingexists that is not present. In other words, only present events and objects exist, butno past or future events or objects do. Furthermore, it usually assumes that there isa succession of presents, i.e. a moving Now. Although logically independent fromthe thesis that defines the position, most presentists thus take change, or becoming,to be a fundamental aspect of reality. Bradley Monton (2006, 264) has appropri-ately dubbed the package of presentism-cum-becoming “Heraclitean presentism”.In logical space, as he rightly notes, there could also be a presentist metaphysicswhich holds that the spatially extended sum total of existence is completely static inthat fundamentally, it does not involve change at all. Such a “Parmenidean” versionV. Petkov (ed.), Space, Time, and Spacetime, Fundamental Theories of Physics 167,DOI 10.1007/978-3-642-13538-512,c Springer-Verlag Berlin Heidelberg 2010257258 C. W¨uthrichof presentism, however, has rarely, if ever, been entertained.1What is of relevanceto my present purposes is simply the core thesis of presentism according to whichonly present events and objects exist, and not whether this core is adorned withHeraclitean or Parmenidean plumes.2There are a number of metaphysical objections against presentism in the liter-ature, and they shall not be surveyed here. Moreover, some authors have deniedthat it presents the only, or even best, way to account for our intuitions aboutthe phenomenology of temporality–traditionally considered the strong suit of pre-sentism. But a much more powerful, and potentially devastating, challenge arisesfrom modern physics: Einstein’s special relativity (SR) provides strong, and perhapsconclusive, reason to view space and time not as two separable and quite distinct ani-mals, but much rather as entangled aspects of the same underlying four-dimensionalmanifold that fuses the two into a “spacetime”. It was Hermann Minkowski’sgreat achievement to recognize the inseparability of space and time resulting fromEinstein’s theory when he solemnly declared at the Assembly of German Natu-ral Scientists and Physicians in Cologne in September 1908: “The views of spaceand time which I wish to lay before you have sprung from the soil of experimen-tal physics, and therein lies their strength. They are radical. Henceforth space byitself, and time by itself, are doomed to fade away into mere shadows, and only akind of union of the two will preserve an independent reality.” Minkowski was alsothe first to correctly describe the geometrical properties of this fused “space-time”structure that today we call Minkowski spacetime. Section 2 explicates how SR andits attendant Minkowski spacetime exert significant pressure on presentist positionsand thus revisits the issue of compatibility of SR and presentism.Although SR does not apodictically rule out presentism, it constrains it in a waythat renders whatever presentism survives the relativistic revolution a metaphysi-cally rather unattractive cripple. One might have expected that this would do it.But presentism dies hard, very hard. In fact, after a period of relative tranquility, itenjoys something of a renaissance in the philosophy of time. What is striking aboutthis renaissance is that many of the hold-out (or born-again) presentists attemptto support their position by arguments of the kind that have traditionally been theweapon of choice for many of their opponents: arguments drawing on results fromthe physical sciences. Section 3 analyzes in some detail a particularly interestingcase recently offered by Monton (op. cit.). His proposal is important in that itpromises to breathe new, scientifically sophisticated life into the otherwise moribund1Barbour (1999) can be read as offering a Parmenidean presentist view. Of course, there is lotsmore logical space available, e.g. containing a presentist position which subscribes to a movingNow without there being any change whatever. Furthermore, the basic presentist claim can be readas obtaining by necessity or merely contingently, which opens logical space for necessitarian andHumean brands of presentism. All these further varieties and distinctions, however, do not affectthe present argument. I shall thus ignore them here.2I understand that there is real worry about whether the debate between presentism and eternalismis well-formed and metaphysically substantive, cf. Callender (2000), Dorato (2006), and Savitt(2006a). As I argue in an unpublished essay, however, I believe that these worries can ultimatelybe dispelled. I wish to thank Steve Savitt for taking me to task on this issue.No Presentism in Quantum Gravity 259idea of presentism. Section 4 then investigates the prospects of presentism in theso-called constant-mean-curvature (CMC) foliation approach to quantizing grav-ity, which Monton finds particularly amenable to his presentist inclinations. It willillustrate the many