The Asymmetric Nature of Time

Front matter

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NATIONAL JOURNAL Vincent Grandjean OT

Contents

TiO WEA: gos os RS Rhee eae nade endudadetopeees Ses 1.2 A Temporal Asymmetry: The Open Future and the Fixed Past... .

How Is the Asymmetry Between the Open Future

Chapter 1 A Introduction Geek for

Abstract In this introduction, my aim is threefold. First, I situate the present book in the vast landscape of the philosophy of time. Against powerful traditions of thought, I argue that a perspicuous philosophical account of time can only be obtained through the reconciliation of the manifest image of the world and contemporary science. Second, I introduce the book’s primary objective, namely to account for the intuitive asymmetry between the ‘open future’ and the ‘fixed past’, and contrast it with some current forms of skepticism brought by science. Third, I outline the three-phase structure of the book — characterization, modeling, reconciliation — and expose the main expected results.

When we think of time, no accurate definition comes to mind. As Augustine famously puts it: “[w]hat then is time? If no one asks me, I know; if I want to explain it to a questioner, I do not know” (2006: 242). However, some features of time some are experienced quite vividly. First, time flows uniformly and universally. It indeed seems that time passes at the same speed everywhere, i.e. no matter where we are located. For example, if two friends separate — one starts living in the Swiss Alps, the other in Paris — and they meet up again years after, we think that time will not have elapsed more for one than for the other; one will not have lived longer than the other. Second, it seems that ‘our present’ extends throughout the whole universe. In particular, it makes perfect sense for us to call a friend who is visiting New York to ask him what he is doing now. Regardless of the jet lag issue, we assume that our friend and ourselves can have simultaneous activities. For example, while I am writing this introduction, he is visiting the Guggenheim Museum. Third, and perhaps most importantly, it seems that there is a difference between the future and the past: the former is open while the latter is fixed (or closed). For example, whereas we think that there are things we can do to affect how the future will unfold (e.g., making a significant donation to an NGO, acting in an environmentally responsible manner), we think that the past is beyond our control (‘what is done is done’).

© The Author(s) 2022 1 V. Grandjean, The Asymmetric Nature of Time, Synthese Library 468, https://doi.org/10.1007/978-3-031-09763-8_1

Although these features of time play roles of varying levels of importance in our epistemic life, they are all pieces of the ‘manifest image of the world’, where by ‘manifest’ one should understand ‘the world as it appears to us’ (cf. Sellars, 1962: 37-38). This is supported by various empirical works (cf., for instance, Latham et al., 2020a, b, 202 1a, b).

The problem is that science, especially contemporary physics, contests these features of time, and hence contradicts our intuitions. First, Albert Einstein understood — a century before we had clocks precise enough to measure it — that time passes more slowly in some places, more rapidly in others.! To use the previous example, if two friends separate — one starts living in the Swiss Alps, the other in Paris — and they meet up again years after, the one who has stayed in Paris will have had a shorter life than the one who has stayed in the Alps. This is a consequence of General Relativity (GR), which posits that a large mass — such as the Earth — warps spacetime and thus slows down time in its vicinity. This so-called ‘time-dilation’ effect is more important in the plains than in the mountains, because the plains are closer to the center of the gravitational field.? Second, as Special Relativity (SR) has stated, there is no unique present, for there is no absolute relation of objective simultaneity: two spatially separated events may be simultaneous for one observer, and temporally distant for another observer. It therefore makes no sense to call a friend who is visiting New York to ask him what he is doing now (or while I am writing this introduction), for there is no privileged moment that constitutes the present. Third, since the ‘block universe’ view of time (which seems implied by SR) is isotropic (spacetime has no intrinsic direction) and the fundamental laws of physics are time-reversal invariant (they do not distinguish the future-direction from the past-direction), it appears that any intuitive asymmetry in time is at best a non-fundamental phenomenon (that plausibly results from how matter is contingently distributed through spacetime), and at worst an illusion (due to the peculiar way our brains interact with the world). This leads us to think that our intuition that the future is open while the past is fixed is not physically grounded, at least at the fundamental level.

Given this, it seems that any philosopher who aims at providing a perspicuous account of time has to deal with at least two conflicting concepts of time: on the one hand, phenomenal time, of which we possess direct knowledge through mental awareness and, on the other hand, physical time, of which we have indirect knowledge. Whereas phenomenal time is embedded in the perspective of a particular encounter with the world, physical time is inferred from important results obtained in contemporary physics (especially SR and GR). Once the conflict between these two

' Of course, this terminology is metaphorical: in Relativity, velocity is not absolute. A more accurate way to introduce this idea would be to say that the geometry of spacetime is influenced by the distribution of matter.

Besides gravitational potential differences between locations, Special Relativity (SR) indicates that time dilation may be due to two clocks having a velocity relative to each other. For example, if, instead of sending two friends to the mountains and the plains respectively, we ask one of them to stay still while the other walks around, time will pass more slowly for the one who keeps moving (cf. Rovelli, 2018: 31).

concepts of time has been properly identified, the issue that arises for philosophers is ‘How to manage this conflict?’. Roughly, in recent history of philosophy, two rival options have been privileged, though they both issue from a ‘conflict-avoidance’ strategy: subjectivism and scientism. Subjectivism consists in being exclusively concerned with intuitions to the detriment of science; scientism in abandoning intuitions for the benefit of science. Although these two options have taken on a variety of forms, for our purpose it will suffice to briefly describe each of their two most famous manifestations: phenomenology and the philosophy of inner life (or Bergsonism) on the one hand, and empiricism and naturalized metaphysics on the other.

First of all, many twentieth-century philosophers have been interested in the phenomenology of temporal awareness. Maurice Merleau-Ponty, for example, was highly critical of scientific conceptions of time. He famously put forward a view of time that agrees more with “[...] the descriptions given by literary men and artists than that given by physicists” (Mays, 1972 : 355). As Merleau-Ponty puts it: “[t]here is more truth in mythical personifications of time than in the notion of time considered, in the scientific manner, as a variable of nature itself, or, in the Kantian manner, as a form ideally separable from its matter” (1962: 422). Although “[...] his remarks apply specifically to the human cultural situation rather than to the scientific context [...]” (Mays, id) (“mythical personifications of time” would be regarded as a gross anthropomorphism by physicists), they still inform us about the role that philosophy is, in his view, meant to play. According to Merleau-Ponty, philosophy must concentrate on describing time as it is reflected in human experience, i.e. as the ultimate subjectivity, which “[...] reveals the subject and the object as two abstract moments of a unique structure, namely, presence” (1962: 474).

Of course, Merleau-Ponty’s view may, in some respects, appear to be caricatural. But the fact remains that phenomenology has, from its earliest beginnings, excluded physical time from philosophy’s primary concerns. Edmund Husserl, for example, with his watch-word ‘back to the things’ argues that philosophy must begin with the phenomena themselves: philosophers must concentrate on describing the authentically given — the contribution of empirical sciences is relegated to the background, even within transcendental phenomenology, which reproaches science for not questioning the foundations of the objectivation of the world. As a result, physical time, which is not adequate to the task of explaining how consciousness experiences temporal objects, is neglected in philosophical inquiry, understood as an epistemological analysis of temporal lived experience. For example, whereas Newtonian time (conceived as an empty container of discrete, atomistic nows) can explain the separation of moments in time (e.g., separated tones), it cannot explain the continuity of these moments (e.g., a melody). Such a quantitative view of time must therefore be supplanted by a phenomenological attempt to articulate how flowing objects are experienced. As Husserl (1964: 26) makes clear, a perspicuous account of time must explain how temporal objects, though composed of distinguishable moments (which can be measured by clocks), are apprehended as a unity (rather than as a convoluted patchwork).

Second, some philosophers have been interested in the notion of duration as being a qualitative multiplicity, i.e. a temporal heterogeneity in which “[...] several conscious states are organized into a whole, permeate one another, [and] gradually gain a richer content [...]” (Bergson, 2010: 122). This approach is heir to Henri

Bergson’s philosophy of inner life, which famously criticizes the scientific spatialization of time: scientists conceptualize time as an ordered arrangement of defined events, rather than as an unceasing flux impressed upon consciousness.’ Specifically, in the Bergsonian view, space is fundamentally unlike time: space is homogenous (in space, things exist separate from alongside each other), divisible, and infinite, whereas time is heterogenous (in time, things interpenetrate and are never completely independent), indivisible and finite. Space is a homogenous medium, whereas time is a process that emerges continuously in the absolute new.‘ For example, while one often draws a parallel between the ticks of a clock and time itself, Bergson argues that there is ‘no point of contact’ (other than conventional)° between these things: the clock’s hands move through space, not time. According to Bergson, duration (or ‘real time’) is ineffable and can only be grasped through a simple intuition of the imagination; attempts to intellectualize or measure duration are doomed to failure, at least if one seeks to understand reality in its deepest nature. The Bergsonian intuition is, however, not merely a pre-theoretic experience of the world (as described above), but a method that consists in entering into the things (rather than going around them from the outside) to get absolute knowledge. As a result, the common representation of time as a one-dimensional line (on which the present is a point) is, according to Bergson, a pure abstraction: time is mobile and incomplete, and the present consists in the consciousness of our body experiences. Moreover, a scientific concept such as ‘spacetime’, according to which time is just as much a dimension as any of the spatial ones, is quite alien to Bergson: “[b]Jasically space and time play opposite roles in his philosophy, which might even be regarded as a dualism of space and time” (Lacey, 1999: 17). Crucially, Bergson’s approach should not be confused with phenomenology: whereas phenomenology takes the multiplicity of phenomena to be always related to a unified consciousness, Bergsonism takes the immediate data of consciousness to be a multiplicity.

An immediate objection that could be raised against this first ‘subjectivist’ option of managing the conflict between intuitions and science is to observe that the world existed in time before human beings and human consciousness ever appeared on the Earth.° For example, it appears that the emergence of the first living organisms

3Bergson’s criticism of the spatialization of time culminated in his debates with Einstein, and in the book that tentatively grappled with relativistic physics, Duration and Simultaneity (1922).

“The differences between space and time are detailed in Bergson (1972: 515). It is worth noting that the idea of infinite space is abandoned in Matter and Memory (1896).

5As Bergson puts it: “[w]e substitute [...] for the qualitative impression received by our consciousness, the quantitative interpretation given by our understanding” (Bergson, 2010: 51). Interestingly, Bergson describes the spatialization of time as a social convention, which results from our pragmatistic look at the world — we look at the world from the point of view of action, while philosophy’s role is precisely to discard this point of view.

ĉThis objection has been taken up by Merleau-Ponty. One reply to it might be, he says, that “[...] every equation in physics, presupposes our pre-scientific experience of the world” (1962: 422). In that sense, no physical concept is independent of man and the cultural environment in which he finds himself. However, this reply seems to fail, since one can perfectly conceive things, e.g., possible worlds, without being able to have sense-awareness of them.

temporally follows ocean formation, which implies that time was already passing, say 4 billion years ago. It therefore seems simply wrong to claim that time has no reality beyond our subjectivity. Moreover, philosophers (especially metaphysicians of time) may have more ambition than merely describing phenomena. They may want, for instance, to contribute (together with physicists) to the exploration of the fundamental structure of reality and, therefore, to the exploration of physical time. For example, philosophers may aim to account for the notion of ‘the passage of time’, not conceived as a subjective phenomenon, but rather as a central aspect of the scientific picture of the world. Tim Maudlin, for instance, argues that “[t]he passage of time is an intrinsic asymmetry in the temporal structure of the world, an asymmetry that has no spatial counterpart” (2007: 108-109). Of course, such a revisionary (as opposed to descriptive)! way of undertaking metaphysics must be scientifically well informed. After all, assuming that philosophers and physicists can both investigate physical time, they cannot deliver contradictory truths about it. For these reasons, it seems that dismissing scientific resources from philosophical inquiry is methodologically doubtful.

The second option of managing the conflict between phenomenal and physical time is to ignore our intuitions and to concentrate solely on science. This scientistic option has taken on a variety of forms, but we will focus on two of them: empiricism and naturalized metaphysics. First, many philosophers of physics tend to think that it is solely empirical science that provides access to the fundamental structure of reality. For instance, Otto Neurath writes that “[t]here is no such thing as philosophy as a basic or universal science alongside or above the various fields of the one empirical science; there is no way to genuine knowledge other than the way of experience; there is no realm of ideas that stands over or beyond experience” (1973: 136). This thought is historically based on some ‘verificationist principle’, according to which every synthetic statement must be empirically verifiable.? As a result, most metaphysical statements are meaningless. For example, empiricists typically believe that a true picture of time could only be arrived at by a study of such things as atomic clocks and physical processes. In this perspective, the way the world is pre-theoretically grasped has no relevance. Against the rationalist tradition, empiricists do not see intuitions as cognitive tools designed to produce guidance toward the truth, but rather as a misleading product of our immediate environment, which

The expression ‘descriptive metaphysics’ was first coined by Peter Strawson in his book Individuals to capture his task to “[...] describe the actual structure of our thought about the world” (2003: 9).

8 ‘Naturalized metaphysics’ should be contrasted with ‘moderately naturalized metaphysics’, as it is defended by Matteo Morganti and Tuomas Tahko (2017), the latter of which seems to partly legitimate the use of intuitions.

° This formulation of the verificationist principle is obviously too stringent. For example, it renders all universal generalizations (which are empirically unverifiable) meaningless and, therefore, undermines vast domains of science and reason. That is why some logical positivists (Rudolf Carnap, Otto Neurath, Hans Hahn and Philipp Frank) tried to make the verificationist principle more inclusive (this movement is known as the ‘liberalization of empiricism’ ) (cf. Sarkar & Pfeifer, 2006: 83).

must in turn be studied by the precise methods of empirical science.!° According to empiricism, the role of philosophy is merely to react to scientific discoveries by reshaping traditional concepts, such as time and reality. But, while (at least some) philosophers make use of intuitions, their work is of no value when it comes to discerning the fundamental structure of reality. Of course, this is not to say that there are no difficulties in the scientific theories, but rather that training in philosophy or discussing these difficulties with subjectivist philosophers would not help to solve them. Their work is fundamentally misguided, after all."

Another, though less radical, way of dismissing intuitions is promoted by some metaphysicians of science, who assume that the main role of philosophy is to unify hypotheses and theories that are taken seriously by contemporary science. As James Ladyman and Don Ross famously claim: “[n]aturalized metaphysics must go beyond mere consistency with current science; it must be directly motivated by and in the service of science” (2013: 109). Here the starting point is clearly science; metaphysics comes second and builds upon scientific results. For example, when statistical mechanics was extended to the quantum realm, it was found that in order to obtain empirically adequate statistics, particles of the same kind (e.g., fermions) must be indistinguishable, though they can be counted. This induces a metaphysical response, namely that the Leibnizian Principle of Identity of Indiscernibles is false. Here again, although philosophy contributes to the inquiry into the nature of reality (e.g., in terms of theoretical unification), the use of intuitions is strictly limited. In particular, naturalized metaphysics explicitly excludes any reasoning based on intuitions and a priori considerations, for “[...] there is no reason to imagine that our habitual intuitions [...] are well designed for science” (Ladyman & Ross, 2007: 2). Such a metaphysical stance should be contrasted with “Lewisian-style’ metaphysics. In short, whereas Lewis takes for granted that abandoning intuitions (e.g., the intuition that causes occur prior to their effects) should be regarded as a cost associated with accepting a metaphysical thesis, naturalists, such as Ladyman and Ross, are not concerned with preserving intuitions at all; they are merely concerned with serving science.

An first objection that could be raised against this scientistic option of managing the conflict is that it rests on a caricature of science. It is wrong to claim that scientists exclusively rely on empirical data and rational methods, at least in the context of discovery. As Jonathan Tallant (2013, 2014) has highlighted, the term ‘intuition’ is frequently applied by scientists to explanations, pictures, and results. This can be illustrated by an ethnographic study, carried out by Ference Marton and Peter Fensham (1993), which is based on data collected from 83 Nobel Prize-winners, drawn from physics, chemistry, and medicine. This study reveals that most of the

10 Some studies (e.g., Morris et al., 1995) tend indeed to show that intuitions depend on our ontogenetic makeup and partly on culturally specific learning.

''This ‘empiricist’ view is part of the heritage of logical positivistic work against metaphysics, which aims to show that “[...] all meaningful discourse can be reduced to, or at least rigorously justified by reference to, reports of observations regimented for communication and inference by formal linguistic conventions [...]” (Quine, 1966: 151), see also Carnap, 1931.

Laureates (72) say they use scientific intuitions to guide the shape of their inquiries. For example, as Michael Brown” declares, “[...] we almost felt at times that there was almost a hand guiding us. Because we would go from one step to the next, and somehow we would know which was the right way to go. And I really can’t tell how we knew that, how we knew that it was necessary to move ahead” (cf. Tallant 2014: 295). Of course, one might reply that the use of intuitions by scientists is not the same as that of metaphysicians. For example, one might argue that scientists, unlike metaphysicians, never use intuitions to justify their claims. But, even if one grants this difference, it is does not follow that metaphysicians always use mere intuitions to this end, nor that they cannot but do so. In particular, although the term ‘intuition’ is notoriously vague, one should agree that both scientists and metaphysicians may use intuitions at least “[...] in the sense of background assumptions influencing how they interpret (empirical) data [...]” (Morganti & Takho, 2017: 2570).

This more realistic picture of science seems to match with how Arthur Eddington and John Wheeler introduce physical knowledge. Contrary to Albert Einstein (1936), who claims that “[w]e can view only as miraculous that our sense-experience can be unified by our freely created concepts”, Eddington and Wheeler do not believe in miracles. In particular, they do not believe that scientific concepts are freely created by pure thought alone divorced from our actual intuitions. They both emphasize the role of inferences from ‘data’, ‘pointer readings’ or ‘information’ to phenomena and knowledge of physical reality. As Eddington points out, all physical knowledge is “hypothetico-observational knowledge’, which means that science is an inference from good observations (cf. 1939: 49).'* This view can even be pushed further if we consider, as Alfred North Whitehead does, that some important scientific concepts — such as velocity, acceleration, momentum, and kinetic energy — are unintelligible when disconnected from temporal experience. For example, it seems impossible to define ‘velocity’ without some reference to the past and the future, which makes essential the importation of this distinction into the physical picture of time. As Whitehead puts it, “[t]his conclusion is destructive of the fundamental assumption that the ultimate facts for science are to be found at durationless instants of time” (1919: 2).

A second objection against the scientistic option is that if our intuitions are indeed a misleading product of our immediate environment, then it should be explained why it is so. There is a need to explain why people across the countries and the centuries are systematically deceived by their intuitions when apprehending time. Such a ‘massive error hypothesis’ cannot be put forward without providing any proportionate explanation. For example, given the ‘block universe’ view of time (which seems implied by SR), the spacetime geometry must have been fixed and settled all at once in some single act of creation. Accordingly, you and I did not

12 Nobel Prize-winner for Medicine in 1985. 13 The quote is from Palter (1960: 4).

!4For more details on the ‘hypothetico-observational’ conception of physical knowledge, see Weinert, 2017.

come into existence later than dinosaurs or the Big Bang. Rather, if the universe were created at all, then “[...] you and I and all its parts, and all the associated events in which these parts are involved, were created together” (Brogaard, 2000: 345). But if everything is in existence (in some sense of ‘is’ that is both tenseless and timeless), then the advocate of such a model is faced with the problem of accounting for the common fact that “[...] new perceptions enter and exit our minds in successive fashion at what appear to be always later and later times” (Brogaard id.). How does one explain that our cognitive abilities are limited in such a way that we have no access to the future, if there is no difference between the present, the past and the future? And why is it that the times at which we perceive the world appear to be ordered successively? It is not clear that the advocate of the ‘block universe’ view can account for these facts. Of course, one could reply that potential solutions to these issues are to be found outside the philosophical field (e.g., in psychology). But these kinds of buck-passing answers are clearly unsatisfying: one cannot skip the question as to why everybody is mistaken in apprehending time, under the pretense that this could hypothetically be answered by other scientists. Worse still, as Mauro Dorato argues: “[...] the ontology posited by a physical theory should in principle be capable of establishing connections with the world of our experience, for the latter world is the source of the empirical tests of the theory” (2008: 54).

A last objection is that, although it should be acknowledged that many things that have seemed obviously true have turned out, upon inspection, to be false (e.g., that the sun rotates around the Earth), it seems that appealing to rational intuitions is epistemically justified. Two arguments can be invoked in favor of this claim.

First, what we have learnt from early modern attempts to find absolute certainties is that, unless we are willing to become extreme skeptics, we must allow that “[...] it is reasonable to believe things that seem obviously true, in the absence of special reasons to doubt them; and we must allow this even if the beliefs are admittedly not certainties, and cannot be ‘proven’ in any interesting sense of the word” (Zimmerman, 2008: 222). This leads to a methodological principle, sometimes referred to as ‘the principle of credulity’ (cf. Broad, 1939; Swinburne, 1979), that seems reasonable to accept: intuitions must be preserved as long as they are not proven wrong. In that sense, intuitions are ‘innocent until proven guilty’ and their relinquishing should only be envisaged as a last resort, when our best science leaves no hope of preserving the manifest image of the world.

Second, intuitions have demonstrated success in the past. In particular, there are many examples in which a philosophical theory was found flawed because it contradicted an intuition (especially in specific thought experiments). For example, in epistemology, the ‘classical’ theory of knowledge was abandoned because, in Gettier cases (1963), we share the intuition that one can have the justified true belief that p without knowing that p. Moreover, in the philosophy of language, the descriptivist theory of proper names was rejected because, in Kripke cases (1980), we share the modal intuition that, although someone other than the U.S. President in 1970 might have been the U.S. President (e.g., Humphrey might have), no one other than Nixon might have been Nixon. Finally, in applied ethics, the naive utilitarian theory was rejected because, in Thomson cases (1976), we share the intuition that it is not morally permissible to take five organs of a healthy person in order to prevent five people from imminent death, though this action would maximize well-being. These three examples — but there are many more — show that intuitions decisively contribute to philosophical progresses in a great variety of fields and, without further arguments, it is hard to see why it would not be the case in the metaphysics of time. Of course, one might emphasize that these intuitions crucially differ from the intuitions we have about the nature of time, as they are not in tension with important scientific results. But, this does not answer the question as to why, whereas intuitions seem reliable in such various fields as epistemology, philosophy of language, and applied ethics, they would not be so in the metaphysics of time.

A further criticism could be that the three former cases (Gettier, Kripke, Thomson) are not relevant, as they do not involve any reasoning about the metaphysical structure of the world from our intuitions about the world. For example, the knowledge case differs from metaphysical theorizing in that it crucially rests on some concept that we commonly use: knowledge. Assuming that we are competent with that concept, we can elucidate its content by asking about the conditions under which we would employ it. In brief, we ask people if they would employ it in Gettier case, and we find they would not. So, that provides a reason to suppose that our concept of knowledge (as we commonly use it) is not just justified true belief. Yet, this does not seem like a very robust sense of an appeal to intuition in settling how things are with the world: we merely investigate how we are disposed to use some concept (viz. knowledge), to determine what we mean by it. It therefore seems that there is no analogy with metaphysical theorizing. In reply, two things can be said. First, the three former cases were not intended to provide an analogy, but merely to illustrate the fact that intuitions are widely and successfully used in various domains of philosophy. Second, one can easily think of cases where intuitions have played a decisive role in metaphysical theorizing. Consider, for example, Kit Fine’s influential rejection of modal conceptions of essence, according to which “[...] an object [has] a property essentially just in case it is necessary that the object has the property” (1994: 3). The rejection is based on five properties (e.g., ‘being a member of singleton Socrates’, “being distinct form the Eiffel Tower’) that necessarily belong to Socrates, but that are intuitively not essential to Socrates. The five properties thus function as five counterexamples to the classical, modal conception of essence, which is thus explicitly rejected by Fine on the sole basis of intuitions. The above arguments against scientism provide as many reasons to think that our intuitions must not only be explained but also vindicated.

Now, while none of the two ‘conflict-avoidance’ strategies (subjectivism vs scientism) is fully satisfying, one may wonder whether all hope of solving the conflict between intuitions and science is gone. In that respect, the situation is not altogether desperate, as a third way — perhaps more demanding, but also more interesting — of managing this conflict can be imagined: the way of reconciliation. As Craig Callender puts it: “[w]e seem to have, to echo another debate, an ‘explanatory gap’ between time as we find it in experience and as we find it in science. Reconciling these two images of the world is the principal goal of philosophy of time” (2008: