The Personalized A-Theory of Time and Perspective
aa r X i v : . [ phy s i c s . h i s t - ph ] A ug The Personalized A-Theory of Time and Perspective ∗ Vincent Conitzer † Abstract
A-theorists and B-theorists debate whether the “Now” is metaphysically distinguishedfrom other time slices. Analogously, one may ask whether the “I” is metaphysically distin-guished from other perspectives. Few philosophers would answer the second question in theaffirmative. An exception is Caspar Hare, who has devoted two papers and a book to arguingfor such a positive answer. In this paper, I argue that those who answer the first question inthe affirmative – A-theorists – should also answer the second question in the affirmative. Thisis because key arguments in favor of the A-theory are more effective as arguments in favorof the resulting combined position, and key arguments against the A-theory are ineffectiveagainst the combined position.
Keywords: metaphysics, philosophy of time, philosophy of self. ∗ This paper will appear in dialectica . † Departments of Computer Science, Economics, and Philosophy, Duke University, Box 90129, Durham, NC27708, USA; Email: [email protected] Introduction
In a series of unconventional but lucid works, Caspar Hare has laid out and defended a theory of egocentric presentism (or, in his more recent work, perspectival realism ), in which a distinguishedindividual’s experiences are present in a way that the experiences of others are not (Hare, 2007,2009, 2010). Closely related ideas appear in the writings of others. One example is Valberg(2007)’s notion of the “personal horizon,” especially considering his discussion of “the truthin solipsism” and his insistence that “my” horizon is really “the” (preeminent) horizon. Merlo(2016)’s “subjectivist view of the mental” is arguably even more closely related; he argues that“one’s own mental states are metaphysically privileged vis-`a-vis the mental states of others” anddiscusses in detail the relationship of his view to Hare’s. As another example, in a review of“The Character of Consciousness” (Chalmers, 2010), Hellie (2013) argues that this work fails todo justice to the embedded point of view aspect of consciousness. He illustrates this with whathe calls a “vertiginous question”: why, of all subjects, is this subject (the one corresponding tothe human being Benj Hellie) the one whose experiences are “live”? In other work (Conitzer,2019), I explore whether the “liveness” of one particular perspective is a further fact – a factthat does not follow logically from the physical facts of the world – by considering the analogyto looking in on a simulated world through a virtual reality headset: besides the computer codethat determines the physics of the simulated world, there must be additional code that determineswhich simulated agent’s perspective to show on the headset.In any case, Hare’s exposition of these ideas is clearest for the present purpose, so I willfocus on it. In an effort, possibly with limited success, to avoid misrepresenting his position,2s well as to clarify the relation to other work, let me introduce my own terminology. Let usrefer to the theory that states that there is a metaphysically (rather than merely epistemically)distinguished I (or Self ) as the α -theory. The intent is to emphasize the analogy with how theA-theory (McTaggart, 1908) states that there is a metaphysically distinguished Now . Similarly, Iwill refer to the theory that contradicts the existence of any metaphysically distinguished I as the β -theory. Hare is thus defending the α -theory. It is not entirely clear to me whether the specificversion he defends is intended to be analogous to presentism (or actualism – I will refrain fromdiscussing modality in this paper, but the parellels between time/subjectivity and modality arewell recognized (Prior and Fine, 1977; Bergmann, 1999)), or rather to something like a spotlighttheory (or possibilism). In fact, his writing suggests different answers to this question in differentplaces, and I will not attempt to resolve this small mystery here.Others have commented on the idea of a metaphysically distinguished I – or, similarly butnot equivalently, a metaphysically distinguished Here – in the context of the philosophy of time.(While the differences between a metaphysically distinguished I and a metaphysically distin-guished Here will not matter for some of the arguments presented in this paper, it is useful tonote that, in the context where a distinguished I is combined with a distinguished Now , the com-bination of these two immediately implies a distinguished
Here as well – namely, the location ofthe distinguished individual at the distinguished time. ) However, they have usually dismissed itrather quickly, in order to move on with the case of a metaphysically distinguished Now (whetheror not they support the latter). For example, Zimmerman (2005, page 422) writes:An egocentric analogue of actualism (‘personalism’, to steal and abuse a term) is veryhard to imagine. Perhaps there is some kind of not-merely-epistemological solipsism3hat would qualify. In any case, only the maniacally egocentric could be this sort ofpersonalist.Further back, Williams (1951, page 458) writes:Perhaps there exists an intellectualistic solipsist who grants the propriety of conceiv-ing a temporal stretch of events, to wit, his own whole inner biography, while denyingthat the spatial scheme is a literal truth about anything. Most of the disparagers ofthe manifold, however, are of opposite bias. Often ready enough to take literally thespatial extension of the world, they dispute the codicil which rounds it out in thedimension of time.Fine (2005) treats the case of first-personal realism in detail, but advocates for adopting a non-standard variety of realism, either taking reality to be relative to a standpoint, or (his preferredoption) considering it to be fragmented. He notes:It has seemed evident that, of all the possible worlds, the actual world is privileged;it is the standpoint of reality, as it were, and the facts that constitute reality are thosethat obtain in this world. On the other hand, if we ask, in the first-personal casewhether we should be a nonstandard realist (given that we are going to be first-personal realists in the first place), then the answer to most philosophers has seemedto be a clear ‘yes’. It has seemed metaphysically preposterous that, of all the peoplethere are, I am somehow privileged - that my standpoint is the standpoint of realityand that no one else can properly be regarded as a source of first-personal facts. Thecase of time is perplexing in a way that these other cases are not.4 believe that there is value in exploring the α -theory more thoroughly, rather than dismissingit summarily for being repugnant in one way or another. The words “egocentrism” and “solip-sism” are both loaded with too much baggage. While “egocentric,” taken literally, aptly describesthe α -theory, the common interpretation of the word carries various negative connotations, andit is not clear to me that these are fair to apply to every possible α -theorist. Just as A-theoristscan take great interest in times other than their own (otherwise why would they bother to writepapers?), the α -theorist can presumably take great interest in people other than herself. Therelation to solipsism is also not obvious. Hare intends for his theory to be only a weak and sub-tle version of solipsism that does not deny the existence of others’ consciousness (Hare, 2009,pages 41-46), and others have granted him as much (e.g., Smith (2011), and Mark Johnston inthe introduction to Hare (2009)). Indeed, a key point is that, just as there are multiple versions of the A-theory, there are alsomultiple versions of the α -theory, and these vary in the status they accord to other individuals.Perhaps more importantly – and this is the main focus of this paper – something is lost whenattempting to study the A vs. B question separately from the α vs. β question; the two are verymuch interrelated. To illustrate this, consider a theory that allows a distinguished I that is not aliveat the time of the distinguished Now , thereby treating the two types of distinction as independent.Many of the arguments that I give in what follows would do little to support such a theory. Hence,in what follows I will not take the α A-theory – the label that I will use for a view that combinesthe α -theory with the A-theory – to allow this possibility; what I have in mind is that a single (living-)person-stage is distinguished. This interrelation is relevant to the previous point. Forexample, the α A-theorist may accord to other persons the same metaphysical status as she does5o herself in past and future time slices.After presenting, for the sake of illustration, some versions of the α A-theory (Section 2), I willargue that key arguments that have been given to support the A-theory support the α -theory justas well, and in fact support the combined α A-theory especially strongly (Section 3), placing theonus on the β A-theorist to explain why she accepts the A-theory but not the α -theory. (It wouldseem that most A-theorists, at least publicly, are β A-theorists in my terminology.) Specifically,in 3.1 I will discuss the argument from presence simpliciter , and in 3.2 the argument from theappropriateness of sentiments such as those expressed by “Thank goodness that’s over!” I willalso argue that some serious challenges that the β A-theorist faces are much less problematic forthe α A-theorist (Section 4). Specifically, in 4.1 I will discuss the argument from special relativity,in 4.2 the argument that the direction of time may be a local matter, in 4.3 the argument that asksfor the rate at which time passes, and in 4.4 the argument from time travel and G¨odelian universes.Overall, my main objective is to argue that the α A-theory is superior to the β A-theory. Iwould similarly argue that the α A-theory is superior to the α B-theory, but I do not expect manyto defend the latter view. This would leave the α A-theory and the β B-theory as the remainingcandidates. The reader might expect that my next step will be simply to argue that the α -theory isso unappealing that we should accept the β B-theory, and hence, a fortiori , the B-theory. However,I believe that that conclusion is too hasty; an effective discussion of the relative merits of the α A-theory and the β B-theory requires arguments of a different type than what I will present here. So,I will be content to let both theories stand for now.6
Some versions of the α -theory The A-theory counts among its supporters presentists, moving-spotlight theorists, and growing-block theorists. Can we conceive of similar distinctions among α -theorists? Rather than studyingthis in isolation from the A vs. B question, it seems more enlightening to ask what natural versionsof the α A-theory there are. (Common versions of the A-theory and the B-theory can straightfor-wardly be reinterpreted as versions of the β A-theory and the β B-theory.) I will present someversions in this section. My aim here is not to defend specific versions or to reach any definitiveconclusion about which version is best. I also make no claim that this list is exhaustive, thoughI believe that it includes the versions that are most natural to discuss in the context of the exist-ing literature on the A-theory. The aim of this exercise is merely to clarify some aspects of the α A-theory and prevent overly narrow interpretations of it. Moreover, it will be helpful to refer tosome of these versions in what follows. I will also contrast these versions with some scenariosfrom the literature. • Personalized presentism.
This is the most natural way to adapt presentism into an α A-theory. In this version, there is a single distinguished individual whose experience at asingle distinguished point in time is, in some sense, “present.” (I hope that the intendedmeaning of “presence” is at least somewhat clear at this point; I will discuss it in moredetail in 3.1.) Beyond this present experience, nothing exists. Or, perhaps, some part ofthe outer world can be granted some type of existence; but other experiences do not exist.However, presumably, the present experience can change (more on this below), just aspresentists typically consider it possible for the Now to change.7
Personalized moving spotlight.
As in the classical moving-spotlight theory, a spotlightmoves over the four-dimensional block universe, except now this spotlight shines on asingle individual (or that individual’s experience) at a single point in time. For the person-alized moving spotlight, it is less obvious how it moves (more on this below). • Personalized growing block.
In the classical growing block theory, time slices are addedto the block that contain all the events in the universe at that point in time. In the personal-ized growing block theory, only those parts of spacetime are added that are experienced bya distinguished individual (and, perhaps, their past light cones).Every one of these versions of the α A-theory leaves several possibilities for how the point ofpresent experiences – the “I-Now” – could change or move (if it changes or moves at all). These include the following variants: • Single individual overall.
The I-Now moves along with a single individual throughout hisor her lifetime. It is never associated with any other individual. • Changing individual ( α A-reincarnation).
At the end of the distinguished individual’slifetime, the I-Now jumps to another individual. We can consider various subvariants. Forexample: (1) the I-Now cannot jump backwards in time; (2, a relativistic subvariant) theI-Now can jump anywhere that is outside of all the past light cones of points in spacetimethat the I-Now occupied earlier; (3) the I-Now can jump anywhere it has not previouslybeen; (4) the I-Now is not constrained in where it can jump. • Rapidly changing individual.
The I-Now can jump from one individual to another even8efore the former’s demise, and then jump back to the previous individual as well. We canconsider the same subvariants as for α A-reincarnation.It is admittedly odd to propose all these different versions of the α -theory without making anyserious attempt to justify them individually or to claim to be exhaustive. Again, my goal in do-ing so is merely to illustrate some of the possibilities that the theory leaves open. The availabilityof multiple distinct interpretations should not be surprising given the analogy and interrelationwith the A-theory. It is also clear that some of these versions are much more solipsistic thanothers, or, at least, fit the negative connotations of solipsism more than others.Moreover, in earlier work on theories resembling the α -theory, scenarios are often sketchedthat fit much better with some of these versions than with others. Usually, this is done withoutmuch discussion of why the author prefers such a version or even of what the alternatives mightbe. This has the effect of opening up the theory to criticisms that another version of the α -theory might have avoided. Consider the following passage by Hare (2009, page 51) (discussinga thought he had as a child), corresponding to a single-individual-overall theory:Isn’t it amazing and weird that for millions of years, generation after generationof sentient creatures came into being and died, came into being and died, and allthe while there was this absence, and then one creature, CJH, unexceptional in allphysical and psychological respects, came into being, and POW! Suddenly therewere present things!Later on, Hare (2009, page 83) considers a type of reincarnation:9s it necessary that only one person ever have present experiences? Again, the naturalthing is to say no. Egocentric presentism gives me conceptual resources to imaginebeing one sentient creature, and then, later, being another sentient creature. So (re-call Nagel’s “fantasy of reincarnation without memory”) I can imagine that, after alifetime of oblivious egg consumption, I die a happy philosopher, then find myself ina cage eighteen inches tall by twelve inches wide, my beak clipped to its base. Thisneed not involve imagining that CJH dies a happy philosopher and then becomes abattery chicken. It may only involve imagining that after CJH’s death there are againpresent experiences, and they are the experiences of a battery chicken. Once againthis is a real, real nasty, metaphysical possibility.So “the one with present experiences” is a definite description that may be satisfiedby different things at different times. Like all such descriptions, it behaves as a temporally nonrigid referring term .Similarly, Valberg (2013, page 366) writes:We can, however, give sense to the possibility that a human being other than JV inthe past was “me,” or that a human being other JV [sic] might be “me” in the future.That is, it makes sense experientially (as a way things might be or develop fromwithin my experience) that, in the past, a human being other than JV occupied theposition at the center of my horizon, or that a human being other than JV will occupythis position in the future.Again, the main point here is to make clear how many possibilities the α -theory leaves open10nd thereby to prevent overly specific interpretations. The discussions in the remainder of thepaper generally apply to all of the above versions of the α A-theory. A reader who wants tokeep just a single version in mind might focus on, for example, personalized presentism or apersonalized moving spotlight theory, with a single individual overall.
In this section, I will revisit some well-known arguments in favor of the A-theory. 3.1 concernsthe argument from presence simpliciter and 3.2 concerns the argument from the appropriatenessof sentiments such as those expressed by “Thank goodness that’s over!” In both cases, the ar-gument will be shown to support the α A-theory more strongly than the β A-theory, because theargument supports a distinguished I just as it supports a distinguished Now . Whether these argu-ments are indeed effective against the B-theory is not the topic of this paper, so I will not reviewresponses that B-theorists may give to these arguments here. simpliciter
Arguably the most basic argument in favor of the A-theory is that of “the presence of experience.”Many have made such an argument; a good exposition of one is given by Balashov (2005). Theargument is that my current experience of writing this paper is present (or occurs ) in a way thatmy going through security at the airport yesterday is not present. This is not to be taken as arelative statement; everyone will agree that the writing experience at 5:50pm on March 18, 2019is present at 5:50pm on March 18, 2019 in a way that the airport security experience at 8:15am11n March 17, 2019 is not present at 5:50pm on March 18, 2019 . Rather, the writing experienceseems present in an absolute sense that does not require the boldface phrases, and this is referredto as presence simpliciter .I argue that, if we are to entertain such a notion, for it to be at all palatable, it must bepersonalized, for the following reason. Just as my earlier airport security experience is not present simpliciter , neither is David’s experience of eating breakfast in Australia present simpliciter , evenif this event happens to take place at the same time. Let me first attempt to explain what I meanby this, and then argue for it. In order to clarify what I mean, it is tempting to write that David’sbreakfast experience is not present simpliciter to me . But to do so would undermine the argument,in the exact same way that it would undermine the purely temporal version of the argument to saythat my airport security experience is not present simpliciter right now . In the latter sentence,“ simpliciter ” is clearly at odds with the indexical “ right now .” The exact same is true aboutthe juxtaposition of “ simpliciter ” and “ to me .” If an experience takes place simpliciter , then tocapture this we should not add any relativizing indexical phrases.Moreover, it seems that only an experience can be present simpliciter in this way. Forexample, it is not at all clear to me what it would mean for a chair to itself be present simpliciter .My experience of a chair – visual, tactile, and the result of significant cognitive processing – canbe present simpliciter . Such an experience is the kind of thing that can have the “liveness” thatpast and future experiences do not, and that others’ experiences do not. But I cannot imaginewhat it would mean for the chair to itself be “live” in this way. If we are willing to be a bit loosewith our language, in most cases it will not cause confusion to, as a shorthand, say that the chairis present simpliciter when we really mean to refer to my experience of the chair. But if we are12eing strict, the experience is not the chair itself. Moreover, it seems that an experience can onlybe had by a single person at a single time, and it does not seem that two distinct experiences,corresponding to different individuals and/or times, can be co-present simpliciter in this way. So,if anything, the argument would suggest the existence of a metaphysically distinguished (I, Now)pair.Is this argument equivocating between “presence” in the temporal sense and “presence” in theexperiential sense? Indeed both meanings of the word seem to play a role, and I believe that thisis revealing rather than misleading. Insofar as the current moment in time has a “liveness” thatother moments do not, it has it only through my own experience; the same moment elsewhere,even if experienced by someone else, lacks this liveness just as a past moment here, even ifexperienced by me, lacks it. In this way, the two meanings of the word are inextricably linked.Hare (2009, page 100) similarly argues that it is in fact advantageous that the word “present” hasmultiple readings.It is also important here not to be misled by how we use language. The sentence “David iseating breakfast” is, in a sense, simpler than “I went through airport security yesterday morning.”Both sentences explictly refer to their subject (“David” and “I”), but only the latter needs toexplicitly refer to when the event took place (“yesterday morning”) in order to place it in time.So the first sentence has a type of simplicity that the second one lacks; we could add “now” tothe former, but it is not needed. On the other hand, dropping “I” from the second sentence leavesit grammatically mangled. From this asymmetry between “I” and “now” one might be temptedto conclude that the word “simpliciter” more naturally corresponds to what is happening now –since the word “now” is usually not needed for sentences concerning the present – than it would13orrespond to what is happening to me – since a word such as “I” or “me” is usually needed fora sentence concerning the first person.However, I would argue that the significance of this asymmetry is not metaphysical, but ratherentirely linguistic. So many of our spoken sentences concern the present that, pragmatically, itwould be inefficient to require adding a word like “now” to all these sentences. On the otherhand, usually a conversation concerns multiple actors, so it is important to make it clear who isthe subject in each sentence. To make this clear, consider a different context: my planner. In myplanner, I write entries such as “attend faculty meeting at noon.” It would be an inefficient useof my time to add “I” (or “I will”) to the beginning of the sentence, because I would have to doso for almost every entry in my planner! In contrast, naturally, each of my planner entries must have a time associated with it; after all, if the event were happening right now, I would not haveto add an entry to my planner. So, in the context of my planner, the roles that subject and timeplay in the pragmatic issue at hand are reversed: the former is generally implicit but the latter isnot. This appears to confirm that the asymmetry is due to pragmatic reasons.
Another well-known argument (Prior, 1959; Zimmerman, 2007) in favor of the A-theory (andpresentism in particular) concerns the appropriateness of statements such as “Thank goodnessthat’s over!” Here, “that” might refer to something like a headache the speaker was experiencing.It is often argued that the B-theory does not provide the resources to capture the full significanceof this statement. Prior argues that the meaning of such a statement is not that it is good thatthe headache takes place at a point in spacetime earlier than the point at which the statement is14ttered; in his words, “Why should anyone thank goodness for that?” Instead, what the statementis getting at is that the headache is simply over , and the A-theory provides the resources tocapture this. But one might similarly argue in favor of the α -theory, for example appealingto the appropriateness of statements such as “Thank goodness that is not happening to me !”This is closely related to the question of whether self-bias could be metaphysically justified, asstudied by Hare (2007, 2009). The β A-theorist is likely to complain that the analogy is not apt,because the second statement merely reflects a selfish disposition rather than something morefundamental. It is not clear to me why the same could not be said of the first statement, that thestatement merely reflects the speaker’s callousness towards her past self. To avoid this criticism,perhaps one can make the first statement about someone else (“Thank goodness John’s headacheis over!”), but, and I believe this is telling, the argument seems to lose force with this move.Let us explore this in a bit more depth. Suppose all headaches last exactly one or two dayswith no ill effects afterwards, and consider the following two statements: S : Thank goodness John’s headache, which started yesterday, ended yesterday as well, ratherthan continuing into today. S : Thank goodness John’s headache, which started the day before yesterday, ended the daybefore yesterday as well, rather than continuing into yesterday.Here, we imagine caring a great deal about John and preferring him not to suffer. Under the β A-theory, one would expect S to have a significance not shared by S , as the former concernsa difference in what is happening now , whereas the latter concerns a difference that is in any caseentirely in the past. It is not clear to me that such a difference in significance is really there. Is15t not just as reasonable to appreciate that John did not suffer yesterday, as it is to appreciate thathe is not suffering today?Yet, one may have an intuition that indeed, S has a significance that S does not. I believethat the likely grounds for this intuition are not germane to the issues under discussion here, andwe can modify the scenario to remove these grounds. First, in the first situation, if John were stillhaving a headache, I might feel compelled to try to do something to alleviate his suffering. How-ever, this is easily addressed by postulating that it is common knowledge that I can do nothingof the sort. Second, if John is in my immediate environment and I see him suffering, this maycause me to suffer as well, for example due to the mirror neurons in my brain. But this is merelyreturning us to an example where I myself suffer, which is precisely what we were trying to avoidby introducing John. Hence, we should postulate that John is somewhere else entirely.To make all this concrete, suppose that John has decided to go on a two-month retreat in afaraway country. He will not communicate until he gets back. Halfway into his retreat, I realizethat around this time of year, he always gets a headache, which may last one or two days. I carefor him and so I hope that it is just a one-day headache this time. But I will not find out untilhe comes back and tells me. Imagining this scenario, I do not find myself concerned specificallyabout whether his headache happens to be taking place right now, or not. Hence, given that the scenario is set up appropriately, I remain unconvinced that there isany significant difference between S and S , and this seems to deal a blow to the β A-theory.Naturally, the β B-theory avoids this blow; but I believe the α A-theory also avoids it, in that Johntoday is just as much “outside the I-Now” as John yesterday, because I am not John. In fact,compared to the β B-theory, the α A-theory does a better job explaining why something about the16xample seems to change when I myself am brought into it. That is, if we replace “John’s” with“my” in the statements above to obtain S ′ and S ′ , then it does seem that S ′ has a significance that S ′ does not. S ′ is not an unreasonable statement – it makes sense to appreciate having sufferedless than one might have, just as it makes sense to appreciate someone else suffering less thanhe might have – but only S ′ concerns the immediate presence or absence of suffering, which isthe vivid characteristic that imbues “Thank goodness that’s over!” examples with their intendedsignificance. Indeed, both Suhler and Callender (2012) and Greene and Sullivan (2015) report on an exper-imental study by Caruso et al. (2008) in which subjects were asked what would be fair compensa-tion for a particular task. The study found that when subjects were asked to imagine themselvesdoing the task in the future, they felt that they should be compensated significantly more thanwhen they imagined themselves doing the task in the past; but this effect disappeared when theywere asked to imagine someone else doing it. Suhler and Callender (2012) take this to invalidatethe “Thank goodness that’s over” argument, and Greene and Sullivan (2015) argue for completetemporal neutrality in making decisions. (The argument for temporal neutrality is worked out indetail in Sullivan (2018). Hurka (1996, page 61) argues that temporal neutrality is appropriatefor certain non-hedonic goods, but is convinced that it is not for avoiding pain, by the examplefrom Parfit (1984, page 165) that we would prefer a more painful operation in the past to a lesspainful one in the future.) The analysis above suggests that while indeed, the results of the Carusoet al. study cast doubt on whether the “Thank goodness that’s over” argument effectively supportsthe β A-theory, they are perfectly consistent with this argument supporting the α A-theory.17
Revisiting arguments against the A-theory
In this section, I will revisit some well-known arguments against the A-theory. 4.1 concerns theargument from special relativity, 4.2 concerns the argument that the direction of time may bea local matter, 4.3 concerns the argument that asks for the rate at which time passes, and 4.4concerns the argument from time travel and G¨odelian universes. In all cases, the α A-theory willbe shown to avoid most of the bite that these arguments inflict on the β A-theory, roughly becausethe arguments hinge on the fact that the Now is global in nature – that is, it stretches across all ofspace. Because the I-Now is local in nature, the arguments are ineffective against the α A-theory.
Einstein’s theory of relativity has often been invoked to criticize the A-theory. Unlike in a Newto-nian universe, in the special theory of relativity, simultaneity is not absolute; rather, whether twoevents are simultaneous depends on the reference frame. But if there is no absolute simultaneity,then how can there be an absolute Now? Special relativity can also be used to cast doubt on spe-cific arguments in favor of the A-theory – or at least, the β A-theory. For example, let us modifythe example from 3.2 by putting John on a faraway planet, so that whether his headache is earlieror later than our own time depends on the reference frame. This seems to make it difficult to holdthe position that, in order to know how we should feel about John’s headache, it is important toknow whether it is in the past or in the future. Now, perhaps there may still be a separate, absolutesense in which John’s headache is in the past, even if this is not implied by the theory of relativity.But if there is not, this poses a problem for using the “Thank goodness that’s over!” argument in18upport of the β A-theory – but, importantly, not for using it in support of the α A-theory, because,as discussed in 3.2, in that case the argument is only made about one’s own pains rather thanthose of someone on a faraway planet. Still, we must investigate the implications of relativity forthe α A-theory more broadly.Some (e.g., Markosian (2004)) have argued that, in fact, a philosophically austere version ofthe theory of relativity could explain the empirical evidence without implying that there is noabsolute simultaneity. The relation of absolute simultaneity could be added on top of the theoryof relativity. For example, one might suppose that there exists a distinguished frame of referencethat determines which events are absolutely simultaneous. Positing such a distinguished frameseems a rather awkward and inelegant addition to the theory, one that is rather contrary to thespirit of the theory of relativity and perhaps more in line with older theories of a stationaryaether. But, Zimmerman (2007) has argued that such an addition to the physical theory is nodifferent in kind from the addition of a distinguished Now in the first place. That may be so,but it is a further addition, and it seems that, for the sake of parsimony, each addition should atleast count against the resulting theory. The analogy is also imperfect. It can at least be arguedthat we know when the Now is; in contrast, it is not clear whether and how we could ever knowwhat the distinguished frame of reference is. Zimmerman (2011) discusses and responds to allthese concerns in far more detail than I can do here, and argues well that they are not fatal to the β A-theory, but it is clear that at least they pose significant challenges.In any case, the above arguments only concern the β A-theory. In the α A-theory, there is noneed for any observer-independent simultaneity at all. While the Now in the β A-theory must beglobal – in the sense that everywhere in the universe, there are events happening Now, thereby19ntroducing an observer-independent simultaneity relation across all of space – the I-Now inthe α A-theory is local. The precise nature of this locality – for example, whether the I-Nowis spatially extended – does not matter much for the arguments at hand; what matters is thatthe I-Now is associated with an observer, and that that observer can be localized in spacetime.Specifically, this ties the I-Now to the frame of reference associated with that observer; ifso desired, simultaneity could be determined based on this frame of reference according to thetheory of relativity. For that matter, no notion of simultaneity across space is even required for thetheory to make sense. While the β A-theory necessitates such a notion – whatever is happeningNow across space must be simultaneous, in an objective sense – it does not seem to pose anyproblem for the α A-theorist to hold that there is no absolute notion of simultaneity. As far as the α A-theorist is concerned, we can define a notion of simultaneity for convenience, for examplethe one based on the theory of relativity and the distinguished frame of reference correspondingto the I-Now as just suggested, but none is truly needed. In fact, the problems that the theoryof relativity poses for the A-theory have already led to at least one proposal similar to the α A-theory, namely Skow (2009)’s relativistic spotlight theory, in which the spotlight shines locally,not globally. For any version of the β A-theory in which time flows, there needs to be an objective direction inwhich time flows. Presumably, it flows from what we perceive as the past to what we perceiveas the future. But if the laws of physics are invariant to time reversal, then these laws do notnaturally provide such a direction. It is commonly held that what we perceive as the direction of20ime is tied to the entropy gradient, and that this entropy gradient may well be reversed in otherparts of spacetime. If so, we may imagine a Doppelg¨anger being that is otherwise very much likeourselves, living its life in such a part, backwards in time from our perspective (Williams, 1951;Maudlin, 2002). The Doppelg¨anger would presumably think that we have it backwards, that thedirection of time’s flow is opposite from what we think it is. So what gives us reason to believethat we are the ones to have it right? A key issue here is that presumably, the β A-theory requirestime to flow in the same direction everywhere; the direction should be globally consistent. Ithas been argued that we have no reason to believe that the Doppelg¨anger even has mental states atall, by virtue of the fact that the way its life proceeds is so unlike the way ours proceeds (Maudlin,2002). But this seems a rather odd conclusion, since we have supposed that, mutatis mutandis for the difference in direction, the Doppelg¨anger’s life is entirely like ours. For a more detaileddiscussion of this point and these issues more generally, see Price (2011) and references citedtherein.In contrast, the putative existence of persons living in parts of spacetime with a reversedentropy gradient, living their life backwards in time (from our perspective), poses no problem forthe α A-theory. This is because the I-Now is inherently local (in both a spatial and a temporalsense), so it does not matter if the entropy gradient is reversed elsewhere; all that matters is whatthe entropy gradient is here (and now ), because that is what determines the direction in whichthe I-Now moves. If the I-Now actually tracks a Doppelg¨anger at some point, it does not appearto pose any problem for the theory for it to then move in the opposite direction. (This may poseproblems for some of the specific illustrative versions presented earlier in Section 2, but it posesno problem for the other versions.) We can view external time as nothing more than a dimension21hrough which the I-Now travels.Taking this to an extreme, we may even imagine a machine that transports you to anotherregion of space where the entropy gradient is reversed relative to ours, and that transforms youinto a Doppelg¨anger there. You will, in some sense, continue your life there uninterrupted, exceptmoving in the opposite temporal direction. Of course being transported to another region of spaceis likely to be a bit shocking; but, if such scenarios are possible at all, there seems to be no reasonto believe that your experiences will be any different than they would have been if you had beentransported instead to a region of space that happens to have the same entropy gradient (andnot been transformed into a Doppelg¨anger). Accommodating this intuition is easy under the α A-theory; for example, the I-Now could simply jump along with you and then start movingbackwards (from our initial perspective). On the other hand, this example appears problematicfor versions of the β A-theory that require a globally defined direction of time, because such atheory would have to conclude that one of the two halves of your life is lived, in an absolute sense, backward. If we believe Maudlin (2002)’s argument, we would then conclude that youhad real mental states in only half of your life. This seems to be an odd conclusion. If near theend of your life you were transported back to the original spacetime region, the suggestion thatyou had not had any real mental states since the original transportation event would seem utterlybizarre to you!
Opponents of the A-theory (or β A-theory) have also criticized it as follows: if the Now moves,what is the rate at which it moves? It has been argued that if one says that it moves at second22er second, this poses a problem for the theory, because one can cancel the units of seconds andconclude that the rate is simply , and (supposedly) is not a rate (e.g., Olson (2009)). Now,the idea that a unitless rate is not a rate is simply nonsense. This has been convincingly arguedelsewhere: Skow (2011) uses the example of sociologists tracking what the “most common birthyear” in the population is. One would expect the most common birth year to generally increaseby roughly year every year, though the rate may be higher or lower than depending on de-mographic phenomena. In any case, the rate is unitless (one might just as well say the rate isapproximately decade per decade). The example is convincing to me, and clearly many otherexamples of sensible unitless rates can be provided. One such example is particularly relevanthere: due to relativity, satellites and astronauts on the International Space Station age at a slightlydifferent rate than objects and people on the surface of the Earth. The amount of time that such asatellite or astronaut experiences per unit of Earth surface time is a unitless rate. This exampleactually seems to pose a more serious problem for the answer that time moves at “ second persecond” – if the idea is to think of time as moving globally rather than just locally, then in just whose seconds are we measuring this rate? In any case, a weaker version of the original criticismseems to hold up: the question only allows uninformative answers. The answer that it moves at“ second per second” seems tautological. We could instead introduce the concept of supertime to track the Now’s motion through time, so that at different points in supertime, the Now is at adifferent time. (For a detailed discussion of the metaphor of supertime, see Skow (2012).) Then,we can ask how many seconds pass per supersecond. However, there seems to be every reasonto simply define the supersecond so that the answer becomes “ second per supersecond,” whichremains uninformative. 23n the α A-theory – or, at least, in versions of it where the I-Now moves along with a personthrough time (see Section 2) – the question of how fast the I-Now moves does not pose suchproblems. First, the fact that on a space station, a different amount of time is experienced to passno longer poses any problem, because the I-Now is local, so there is no requirement that timepasses at the same rate everywhere. Moreover, the question of how fast the I-Now moves canhave more interesting answers. In the relativistic example above, it is natural to respond that theI-Now moves at a different rate when it is associated with an astronaut in orbit than it does whenit is associated with a person on the surface. Alternatively, let us put relativity aside for a momentand focus on the I-Now’s experiential aspect instead. One might reasonably hold that the I-Nowmoves through external (i.e., clock) time at a different rate when it is associated with a personwho is under anesthesia than it does when it is associated with someone who is highly alert.If we allow ourselves to speculate, a computational theory might be used to unify these twoexamples: consider a person’s “clock speed” – the number of mental operations, according tosome suitable definition, per (Earth surface) second – and take this to determine the rate at whichthe I-Now moves. Specifically, let us define a supersecond so that there is always exactly onemental operation per supersecond. Then, the number of (Earth surface) seconds per supersec-ond – which is just the reciprocal of the clock speed defined above – will vary in the differentscenarios above, in a way that conforms with our intuitions. Focusing on Earth surface secondsper supersecond (regardless of the location of the person) simultaneously addresses both the rel-ativistic and the experiential components of the scenarios, and also allows us to handle mixedcases, such as a space station inhabitant who is under anesthesia. In such a case, the number ofmental operations per Earth surface second can be written as the number of mental operations per24pace station second, multiplied by the number of space station seconds per Earth surface second,thereby separating out the experiential and relativistic components, respectively. This shows thatthese two components are compatible. Per the theory of relativity, there is nothing special aboutEarth surface seconds, as opposed to space station seconds or Mars surface seconds; they are justdifferent ways to measure external time.Supertime, so defined, perhaps more naturally corresponds to our sense of passage, leavingregular time (as tracked by clocks) in the more modest role of a dimension through which wehappen to pass, as noted earlier. That is, this notion of supertime would allow us to give meta-physical meaning to the idea of time passing more or less quickly from a subjective viewpoint.Of course, this view may conflict with other intuitions that we have developed. In our ordinaryexperience of time, relativistic issues do not come into play, and our waking experience of howfast time passes is usually fairly stable. Given this, we tend to conceive of time as objective, andtreat any variance in how we perceive its passage as a mere error in estimation. For the currentpurpose, I believe such intuitions are misleading. The following two examples are intended toillustrate that it is in fact quite natural to assign primary importance to the notion of supertimeas defined here. In each of them, we will imagine a choice between two alternatives that resultin you having different amounts of time but equal amounts of supertime left in your life. I arguethat you should be (close to) indifferent between the options in both scenarios. Example 1.
It is the year 2400, and you are part of a group of people on a lifelong spacevoyage. The group is about to split up into two subgroups that will take separate spacecraft. Itis common knowledge that the two subgroups will never communicate again, either with eachother or with the people left on Earth. You get to choose in which subgroup you will be. They25re indistinguishable, except the two spacecraft will move to orbits around different massivebodies, with different relativistic time dilations. If you choose to be on spacecraft 1, your lifewill therefore be shorter in Earth time than it would be on spacecraft 2. As a result, your firstreaction may be that you would prefer to be on spacecraft 2. But, I argue, upon closer inspectionthere is little reason for this. This is because, to make up for the shorter amount of Earth timein your life on spacecraft 1, correspondingly more events will happen per unit of Earth time onspacecraft 1. You would experience entirely similar lives on the two spacecraft, with equallymany interesting events taking place on both. If it were possible to communicate from Earth tothe spacecraft, you might prefer being on spacecraft 2 because (for example) more papers, books,and movies would be produced on Earth and sent to spacecraft 2 for your consumption duringyour life. But we have assumed that such communication is impossible. As far as I can see, theredoes not seem to be any compelling reason to have a preference about on which spacecraft youcontinue your voyage.
Example 2.
It is again the year 2400, but this time we will stay on the surface of the Earth.After a long and happy life, you have regrettably contracted an incurable disease that, if leftuntreated, will kill you almost immediately. Unfortunately, the only possible treatments will putyou in a type of comatose state until your death. You will, however, have wonderful dreamsin this state. Due to secrecy issues, your friends and family will never be made aware of yourpredicament. There is no chance at all that any new treatment will become available during theremainder of your life. You have a choice between medications M and M . Compared to M , M would keep you alive for twice as long, but would allow your brain to process at only halfthe rate. Your first reaction may be that you would prefer to receive M . But again, I argue, upon26loser inspection there is little reason for this. Because of the difference in brain processing rates,you would have equally many wonderful dreams under the two medications. If your friends andfamily could visit you in your comatose state, you might prefer for them to have that option for alonger or shorter period of time, but we have ruled this out. If you had hopes that scientists coulddevelop a cure, you would prefer M to give the scientists more time, but we have also ruled thisout. As far as I can see, there does not seem to be any compelling reason to have a preferenceabout which medication you receive.In summary, to the extent that the question about the rate at which the Now moves poses aproblem for the β A-theory, it does not pose this problem for the α A-theory, since for the latterthe answer to the question need not be tautological.
A final criticism of the ( β )A-theory is that it does not make much sense of time travel scenar-ios. Following Lewis (1976), it seems natural to distinguish between external time and the timetraveler’s personal time. But if one takes external time seriously in the metaphysical sense, aswould be expected of a β A-theorist, it would appear one cannot simultaneously do the same forpersonal time. This, in turn, necessitates unintuitive attitudes towards time travel. The followingpassage by Sider (2005, page 333) illustrates this perfectly.But if personal time bears little similarity to external time then “personal time” ismerely an invented quantity, and is misleadingly named at that. That I will viewa dinosaur in my personal future amounts merely to the fact that I once viewed a27inosaur, and moreover that this is caused by my entry into a time machine. Sincethis fact bears little resemblance to the facts that constitute a normal person’s genuinefuture, I could not enter the time machine with anticipation and excitement at thethought of seeing a dinosaur, for it is not true that I am about to see a dinosaur, noris the truth much like being about to see a dinosaur. If anything, I should feel fear atthe thought of being annihilated by a device misleadingly called a “time machine”.The device causes it to be the case that I once viewed a dinosaur, but does not makeit the case in any real sense that I will view dinosaurs.Perhaps there is a way out of this conclusion for the β A-theorist, but I cannot see it. Or perhapsshe is willing to bite the bullet and accept the conclusion that (at least backward) time travel isto be avoided at all cost. In any case, the α A-theorist avoids this issue. For her, personal time iswhat is taken seriously, and she can legitimately look forward to – if this is in fact something tolook forward to – her encounter with a dinosaur. Closely related to the issue of time travel is that of G¨odelian universes that cannot be givena global temporal ordering. The theoretical possibility of such universes perhaps poses a prob-lem for some versions of the β A-theory. The α A-theory, however, does not require any globaltemporal ordering. For versions of the α A-theory with a moving I-Now, one may yet worry ifsuch universes do not create different problems. For example, Dieks (2006) discusses an exam-ple by Reichenbach (1958, pages 141-142) in which a person loops around to meet his earlierself again at a particular point in spacetime. Dieks, who argues for a B-theoretic notion of localbecoming, argues that this example illustrates that even a local type of spotlight is problematic.He argues that when the spotlight shines on the region in spacetime where the younger and older28ersions of the person meet, there must in fact be two distinct spotlights, one that will travel withthe younger version and one that will travel with the older version. Then, the spotlight associ-ated with the younger version loops around as that version becomes the older version, eventuallyreaching the same region again. By the same reasoning as before, we will again need two spot-lights at this point. But the other spotlight, the one that was initially associated with the olderversion, is not available for the task, being meanwhile associated with an even older version. Sowe will need a third spotlight, and so on ad infinitum, which seems problematic.But it is easy to find an escape from Dieks’ argument. The fact that the two versions ofthe person are (roughly) at the same point in spacetime does not imply that the spotlight shineson them simultaneously in the supertime sense . That is, the “same” spotlight might earlier (insupertime) light up the younger version only (i.e., that version’s experience at that point) and later(in supertime) the older version only. Hence, there is no need to introduce additional spotlightswhen the meeting point is reached. This illustrates one advantage of associating the spotlight withperson-stages (I-Now) rather than with small regions of spacetime (Here-Now): even though theyounger and the older version are both in (roughly) the same location at the same time, theycorrespond to different person-stages. This requires, of course, that in this type of scenario weassociate the I-Now with a person-stage (where a younger and an older version of the same personat the same time are still considered separate person-stages), rather than with a pair of a personand a time, which in this case might pick out both person-stages. This interpretation of the I-Nowin any case aligns better with the other arguments presented in this paper. For example, it seemshard to imagine the (simultaneous) presence simpliciter of the combination of both person-stages.Also, the older person-stage may think, looking at the younger person-stage, “Thank goodness I29m no longer that immature!” The idea that the spotlight was previously (in the supertime sense)associated with the younger person-stage and now with the older person-stage seems to capturethe significance of this statement well. Finally (and more speculatively), if we imagine the brainof the older stage to have slowed down and no longer to be processing at the rate of his youngerself, associating the I-Now with person-stages would allow us to say that the I-Now moves at adifferent rate with respect to external time when associated with each of these two person-stages.
Upon inspection, key criticisms of the A-theory are only effective as criticisms of the β A-theory,and key arguments in favor of the A-theory are much more convincing as arguments for the α A-theory. To the extent I have succeeded in showing that A-theorists are rationally compelled to be α -theorists as well, surely many will interpret this as a significant blow to the A-theory becausethey consider the α -theory implausible. Nevertheless, some philosophers may well be willingto adopt some version of the α A-theory (Hare being an obvious example). As I emphasizedearlier, a detailed discussion of the relative merits of the α A-theory and the β B-theory is outsidethe scope of this paper. Such a discussion is sure to revisit many familiar arguments in thephilosophy of time and modality (and mind), and is unlikely to reach a swift conclusion. I dohope to have convinced the reader that the α A-theory will fare better in such a comparison thanthe β A-theory. The former has an internal consistency that allows it to escape some of the moredamaging criticisms to which the latter has fallen prey.30 cknowledgments
I am thankful to anonymous referees who provided especially thorough and helpful comments,which significantly improved the paper.
Notes Throughout the paper, I will be deliberately noncommittal about the exact nature of such metaphysical distinc-tion. The reason is that the arguments presented here do not depend on what this distinction consists in. In theanalogous case of a metaphysically distinguished time (rather than a metaphysically distinguished subject), by notcommitting to any particular interpretation, I can simultaneously address all varieties of A-theorists – presentists,moving-spotlight theorists, growing-block theorists, etc. – even though they disagree about the exact nature of theNow’s metaphysical distinction. Of course, there is disagreement even about how to define the individual varieties.Deasy (2017) discusses this at length, and proposes to define each of the main varieties as the conjunction of theA-theory (which he takes to mean “There is an absolute, objective present instant”) and a proposition about whetherthings begin and/or cease to exist. For example, for the growing-block theorist, that proposition is “Sometimes,something begins to exist and nothing ever ceases to exist.” While the distinctions between the various definitionsare significant, again, my aim is to steer clear of this debate here and stick to arguments that work for any of thesedefinitions. The same is true for the case of a metaphysically distinguished subject. Again, what exactly the distinguished entity is – a human being, a brain, an experience – is not essential to myarguments, so I will remain deliberately noncommittal. Is a commitment to a distinguished
Now what defines the A-theory, or is it a commitment to tensed facts? (Andin the latter case, should the α -theory’s defining commitment instead be to first-personal facts?) To the extent thatthese commitments are not equivalent, in this paper, I will stick with the commitment to a distinguished Now (or I ), as others have done – e.g., Cameron (2015, page 89). For what it is worth, while a detailed analysis is outside he scope of this paper, I believe that they are in fact equivalent. I believe that a distinguished Now implies tensedfacts, such as the fact that today is July 3, 2019. The other direction is perhaps more controversial, but I believe itholds as well: tensed facts such as the fact that today is July 3, 2019 distinguish a specific time, to which we mayrefer as the
Now . A theory such as fragmentalism (Fine, 2005) might be used to dispute the second direction: ifwe consider all tensed facts, including those for other times, then no specific time is distinguished. But, of course,the set of all tensed facts taken together is full of contradictions, as it also contains, for example, the fact that todayis not July 3, 2019. Avoiding such contradictions means restricting attention to a consistent fragment – but this inturn distinguishes a specific time. For further discussion of problems that fragmentalism faces, see Cameron (2015,pages 86-102). For a discussion of the differences and their implications, in the related context of the Lewisian and Quineanaccounts of centered worlds, see Liao (2012). The combination similarly implies a distinguished observational frame of reference corresponding to the distin-guished individual’s state of motion. All of this does, of course, require the distinguished individual to be spatiallylocated and to move through time and space, rather than, say, an immaterial soul or something existing for only aninstant. Lipman (2015) discusses fragmentalism in more detail. It should be noted here that, on the face of it, Hare (2007, 2009) does introduce his theory to justify placinggreater weight on oneself than on others in making decisions. However, he also points out that the (distinguished)presence of an experience is only one factor in making decisions (“It is better that there be present suffering from ahangnail than absent suffering of leg-crushing.”). Perhaps more importantly, key examples that Hare uses in theseworks to support his theory are preferential in nature, such as an example where one knows that CJH (Hare) andJoe Bloggs have been in a train crash, CJH is about to have a painful operation, the subject knows he is one ofthese two but cannot remember which one, and so the subject hopes to not be CJH (Hare, 2007). Such preferentialexamples are quite helpful to illustrate and motivate these types of theories – similar ones can be given to motivatethe A-theory, as Hare does and others have done before him – even if one does not wish to normatively endorse the references used in the example. I will also discuss such examples later in this paper. Others have tried to distinguish between more and less defensible versions of solipsism along similar lines; aparticularly notable example is Valberg (2007). Similar ideas also appear in Johnston (2010). Of course, to accept this conclusion, it is not necessary to agree with every single argument presented here. In fact, Hare (2009, page 48) writes that “If you think that theories that dignify a slice of history do not survivesustained critical inspection, then you can still be a four-dimensionalist egocentric presentist. Indeed, I find thatan attractive position.” This may appear to put him in the α B-camp. However, on the whole in this section on therelationship to positions in the philosophy of time (Hare, 2009, pages 46-50), he is clear that egocentric presentismdoes not commit one to a particular view on time, while also stating that the moving-spotlight theory is the mostanalogous one. Elsewhere (Hare, 2010), he writes “If you find yourself sympathetic to [the central tense realist idea]then I recommend that you consider going the whole hog , and becoming a perspectival realist” (emphasis in boldmine), which might be interpreted to imply that perspectival realism is a stronger position than tense realism. In anycase, as I hope will become clear from this paper, the α A-theory does not at all require a dignified slice of history. The word “I-Now” sounds more mystical than I would like, but we will need such a word. The word “spotlight,”when interpreted as shining on a single individual’s experience at a single point in time, would give the right idea,except it seems to commit the discussion to a view that all of the four-dimensional spacetime block exists, but notall of it is illuminated. While I do not want to dismiss such a view, in what follows we will not require this as anassumption. In contrast, the awkward word “I-Now” does not seem to rule out any of the possibilities. (Similarly,Hellie (2013) uses “me-now.”) The last two subvariants seem more difficult to reconcile with the personalized growing block theory, and mightalso have negative implications for free will. For example, perhaps it is not even necessary for the I-Now to change only in a sequential manner as in thesevariants; perhaps it can change along multiple dimensions, corresponding to changes across time and changes acrossspace or individuals. Skow (2009)’s relativistic moving-spotlight theory, in which individual points in spacetime are“lit up” from the perspective of points in superspacetime , seems very much in line with such a view. This also raises mportant qestions about how these dimensions interact: Is temporal change objective or subjective? Is subjectivityeternal or temporary? For related questions on the interaction of time and modality, see Dorr and Goodman (2019). Balashov (2005) uses “presence” and “occurrence” to refer to different concepts, but it seems to me that othershave used “presence” to refer to a concept that is closer to Balashov’s “occurrence”. In any case, this latter conceptis what I am after, and I hope that the use of “ simpliciter ” makes this clear. There is, of course, the question of what “at the same time” even really means given that in special relativity,simultaneity depends on the frame of reference. I will discuss relativity later; for the purpose of the current argument,we may assume a Newtonian universe. Merlo (2016, pages 326-327) makes a similar point. I use “person” here, and throughout, in a broad sense; presumably animals and perhaps artificial intelligencecan similarly have experiences. Also, in common parlance, of course two people can “share an experience,” but Iuse “experience” here more narrowly in its phenomenological sense. Along the same lines, Hare (2009, page 49) describes the distinguished nature of his current experience andemphasizes that it is an easy-to-make “big mistake” to extend this to other current experiences. Hare (2010) presentsan argument with strong similarities to the one presented here. Finally, at the end of his paper, Skow (2009) alsodiscusses the vivid nature of present experiences and argues that a local spotlight shining on a single individualexplains this just as well as a global one (though he does not argue that it actually explains it better ). For additional discussion of the linguistic asymmetry between time and space, and how this asymmetry is drivenby pragmatic concerns in communication, see Butterfield (1984). In this example, there is nothing to synchronize John’s experience with mine; his life is unfolding in parallel tomine and it is hard to see why it would matter which events are contemporaneous. As we will discuss in 4.1, we canmake the example even more extreme by having John fly far off into space somewhere, so that, as far as the theory ofrelativity is concerned, there really is no absolute answer to the question whether his headache is taking place at thesame time as my current experience. If so, caring about simultaneity seems to require a very strong commitment tothe β A-theory, as it requires that there be an additional fact about simultaneity over and above the theory of relativity hat is important for what we should care about, even though no physical measurement could ever tell us whethertwo events actually were or were not simultaneous in this sense. Some of this is reminiscent of Turri (2013)’s “That’s outrageous!” example. Turri argues that just as the appro-priateness of statements such as “Thank goodness that’s over” can be used to support presentism, the appropriatenessof statements such as “That’s outrageous!” can be used to attack it, because it seems perfectly legitimate to be out-raged by, say, a past genocide. I consider it telling that “Thank goodness that’s over!” examples typically involveoneself and “That’s outrageous!” examples typically involve others; this may well be what is driving the differencein conclusions from these examples. The definition of what constitutes a frame of reference varies. Here, we consider a frame of reference to bedetermined purely by its state of motion, rather than to also include a coordinate system. In earlier work, Stein (1968, page 18) hints at a similar theory when he contemplates what would result froman argument by Putnam (1967) if one tried to preserve a different intuition about the relationship between what ispresent and what is real. It is not clear whether he intends at all to defend such a theory. Hare (2010) and Hare (2009, page 48) also make some of the points that I made in this subsection. Fine(2005, 2006) similarly gives a detailed discussion of what, for the realist, should replace the role of times whenwe take into account special relativity, and concludes that most plausibly frame-time pairs should take their role,in combination with a nonstandard type of realism in which either realities are indexed to different frame-times orreality is fragmented. The Now is not localized under the β A-theory, so that there is a single Now across space; but if it moves inone direction in one location and in the opposite direction elsewhere, it is hard to imagine that after moving in theseopposite directions it remains the same
Now across these locations. One might counter that these conditions in fact correspond to different units, namely Earth surface seconds andISS seconds, so that we in fact do not obtain a unitless rate. But this misses the point that a second denotes thesame amount of aging for the people in each condition. The unitless rate indicates how much faster people in onecondition age than those in the other, and for this comparison no units are needed. Similarly, we need no units to ay that one person is 1.2 times as tall as another. That the rate being unitless is meaningful is further illustrated bythe fact that it can be both above and below 1, because of the opposing effects of relative velocity time dilation andgravitational time dilation; there is an orbit, about half the radius of the Earth above the surface, at which the rate is1 (Ashby, 2002). The rate being 1 at this orbit is not just a meaningless consequence of how we defined the units; itis the orbit at which astronauts age equally fast as those on the surface. It is important to hold a sufficiently broad view of “computation” here; such broad views are common amongthose working on the theory of computation. Alternatively, and less ambitiously, the reader may just view this as asuggestive analogy to the clock speed of a computer. Well, she may still hesitate, to the extent that it is not obvious that the presence of experience, the I-Now, willfollow her through the time machine rather than go somewhere else. As an example that illustrates this ambiguity, itmay be one of these unmarketable time machines that also leave behind a badly burned body, apparently alive for afew more seconds, where the traveler entered the time machine. (See Hare (2009, page 58) for a similar example.)But at least her believing that it will follow her back in time (rather than transitioning to a different person at thesame time, or staying with a burnt body) would not cause any inconsistency with her other beliefs. This seems all the less likely given that the problem connects to other challenging problems, such as the SleepingBeauty problem – see, e.g., Conitzer (2015).
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