Objective Becoming

In “After Reading a Child's Guide to Modern Physics,” English poet W. H. Auden laments the disconnect between the picture of reality offered by physics and our ordinary experience:Our eyes prefer to supposeThat a habitable placeHas a geocentric view,That architects encloseA quiet Euclidian space:Exploded myths—but whoCould feel at home astraddleAn ever expanding saddle? (Auden 1962, 48)Bradford Skow's Objective Becoming is therapy for those of us who, like Auden, feel alienated by the non-Euclidean space-time that modern physics offers us. Here is one way of understanding the tension. Suppose you think there is a real difference between the past, present, and future. And there is some kind of change in our world that is profoundly unlike mere spatial variation. Whatever time is, it genuinely passes. Objects in time change in profound ways as well. I will call this package the Passage Intuition. The Passage Intuition seems easiest to model if we think of time as divided up into instants, some past, some future, and exactly one present. The present one is when the action is—when you, the reader, are and when the most interesting kinds of change are occurring. These additional assumptions we might call the Unique Present Intuition.The challenge is to reconcile the Passage Intuition with the model of time offered by our best physical theories. More specifically, the theory of Special Relativity is well supported empirically and requires a Minkowski space-time geometry. Crucially, the Minkowski geometry does not identify any unique set of space-time points as absolutely simultaneous. Instead, it draws spacelike and timelike lines based on the past and future light cones surrounding particular points. Points can disagree with one another about whether a particular event is past, present, or future. So there is no unique present in Special Relativity.Special Relativity has since been supplanted with General Relativity and increasingly complex attempts to provide a unified physical theory of gravity, space-time, statistical mechanics, and quantum mechanics. A major debate in the philosophy of physics concerns which temporal structure could underwrite the final theory. But even if Special Relativity is not the final physics, the days when we could reasonably think space and time had a simple Euclidean structure are over. So where does that leave the Passage Intuition and the Unique Present Intuition?One option is to think that there is no unique past/present/future structure and this demonstrates that the other assumptions of the Passage Intuition are false as well. Temporal passage and change are just mere variations in a single eternal space-time manifold. This is the so-called “block view” of space-time.While Skow ultimately endorses the block (or, as he calls it, the “anemic”) view of passage, he thinks defenders of passage have more options. Objective Becoming is an impressively clear and thoroughly argued attempt to reconcile versions of the Passage Intuition and Special Relativity. Most work on this topic commits one of two sins. Either it is too superficial, overstating the problems that relativity poses to the Passage Intuition, or it is impenetrable to philosophers not already well steeped in the relevant physics. Skow's book is virtuous in contrast. He accomplishes three tasks, making this an important text for any serious researcher in contemporary philosophy of time:He systematically explicates the challenge that relativity poses to so-called Moving Spotlight theories of temporal passage, in the process developing more general worries for how to accommodate the Passage Intuition within Special Relativity (chaps. 1–7).He develops a new version of the Moving Spotlight Theory that can match the challenge from Special Relativity, in the process offering new options for interpreting key components of the Passage Intuition (chaps. 8–10).He argues that what's most important about our experience of passage can be accommodated even in metaphysical frameworks with more “anemic” theories of passage (chaps. 11–13).While I am unconvinced that many defenders of the Passage Intuition will be attracted to Skow's proposal, Objective Becoming indicates important new research veins for work on temporal ontology, especially in light of the resurgence of interest in eternalist A-theories of time (see Cameron 2015; Sullivan 2012; and Deasy 2015). Such theories hold that nothing comes into or out of existence—all of space-time and its constituents eternally exist, but time nevertheless passes. This book's most important contribution is developing a previously underexplored version of one such Moving Spotlight theory.Skow suggests that defenders of the Passage Intuition adopt a theory he calls MST-Spacetime. According to MST-Spacetime, reality is composed of a set of space-time points with a structure described using the Minkowski geometry. Each point is absolutely present with respect to itself. Using the Minkowski geometry, timelike, spacelike, and lightlike lines can be defined relative to every point. Objects change through time because while they are one way relative to a set of present points, they were or will be otherwise at other points in their timelike lines. Time genuinely passes because, relative to each present point, other points are past, future, or spacelike-separated. Readers familiar with Kit Fine's fragmentalism will notice parallels between Fine's view and MST-Spacetime (see Fine 2005, 261–320). On both MST-Spacetime and fragmentalism, we accept that reality (the collection of all space-time points) can disagree with respect to whether a point is absolutely present, past, future.Skow argues that MST-Spacetime has several benefits over other passage theories. It is consistent with Special Relativity. It allows us to uphold a version of fundamentalism about tense—there are truths about how reality presently is that are irreducible to tenseless facts about a static manifold. And, it describes passage without substantially modifying Minkowski geometry. Some philosophers attempt to reconcile the Passage Intuition with Special Relativity by overwriting it: they argue that while Minkowski geometry does not specify a unique foliation of space-time into past/present/future, it does not entail that there is no unique past/present/future foliation of space-time. The metaphysician might add the assumption that there is a unique foliation, thereby saving both the Passage Intuition and Unique Present Intuition.However, Skow describes defects in this overwrite strategy. First, it violates an assumption that physical/metaphysical laws should not treat regions of space-time differently if they are geometrically the same (148). Second, it is impossible to know which foliation of space-time is the correct one (157). For Skow (and the fragmentalists before him), the problem with the overwrite option is it tries to add a unique foliation back to relativity when what we should have done is distribute the past/present/future distinction across all of the space-time points. Metaphors are typically helpful in grasping these theories. The old Moving Spotlight theorists wanted to shine a single, dynamic light of “presentness” on the space-time manifold. MST-Spacetimers instead give us a manifold that looks like a filled Lite Brite—every point glowing with its own presentness.While I am no fan of the overwrite approach to reconciling Special Relativity and the Passage Intuition, I think it deserves more sustained consideration than Skow offers here. It is not clear why the laws of metaphysics cannot make distinctions that are arbitrary from the standpoint of the physical geometry of space-time. To think otherwise is just to beg the question against the overwrite option, which depends on resisting a thoroughgoing physicalist ontology. Moreover, given an appropriately externalist epistemology, it is possible for someone to be in a position to know that he or she is present (and therefore know some facts about the unique foliation). This latter epistemic issue is a subject of important recent work on eternalist passage.1Of course, we can grant Skow that it would be better for the metaphysician to not posit any extra structure to space-time that plays no role in our best physical theories. Nobody wants to be on the wrong side of physics. But we have to ask at what cost. MST-Spacetime entails some odd consequences for macrophysical objects in space-time. For instance, my body occupies many space-time points. There is no single space-time point at which my body as a whole is absolutely present. So there is no single present that my body occupies. If defenders of the Passage Intuition want to save the appearance that the present is an instant that you, the reader, occupy, MST-Spacetime is no help. The intuitions about passage we want to recover are not intuitions about points of space-time, they are intuitions about the macrophysical world. So while Skow has developed a new version of the Moving Spotlight Theory, it is unclear whether it will convert anyone who wanted a habitable past, present, and future distinction.MST-Spacetime nevertheless suggests a way forward for developing relativistically acceptable theories of passage—defenders of passage should jettison or radically reinterpret the Unique Present Intuition. Here is another proposal in this spirit. We've assumed until now that there is robust change in the world only if time itself flows (there is change in the regions that compose space-time) or objects change with respect to which times they exist in. What if there is a space-time manifold with a Minkowski geometry, every object and every point of space-time exists eternally, but macrophysical objects in regions of space-time instantiate properties like concreteness, causal efficacy, et cetera, only relative to a frame? On this approach, “presentness” will be understood as a feature of objects, namely their manifesting these interesting properties relative to an observer's frame of reference. This proposal has the benefit of “expanding” presentness outside of a particular point. It does not require any overwrites to the physical geometry, because it is a theory not of time itself but of the dynamic properties of objects in time. It defines passage by how objects change properties. I am partial to a strategy like this, and there are further options for how to implement it (see Emery 2017, sec. 6.3).Every ontology of time eventually faces the Auden test: can we reconcile the structure of time offered by our best physical theories with the phenomenon of time that we intimately experience, that structures our reasoning about cause and effect, that structures our rational planning, and that has profound consequences for our freedom? Objective Becoming works hard (and innovatively) to recover the letter of the Passage Intuition, but in the process misses the spirit that animates it. Still, Skow is on to something, and we should expect more theories to be developed along this model

Aesthetics · Epistemology · Euclidean geometry · Geometry · Intuition · Minkowski space · Physics · Spacetime · Theoretical physics · Mathematics · Philosophy · Philosophy and Theoretical Science · Quantum Mechanics and Applications · Space Science and Extraterrestrial Life

• The Moving Spotlight

  Ross P Cameron•Moving Spotlight•2015

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• Temporal ersatzism

  Open Access•Nina Emery•Philosophy Compass•2017

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