Book review: What makes time special?

What makes time special?
by Craig Callender (2017)

This book was a joy to read.  Its question can be formulated as follows.  All peoples share a conceptualization of time (as distinguished from our direct sensory experience) that Callender calls “manifest time”–of time “flowing” with a special time “now”, etc.  None of these features appear in physics–Aristotelian, Newtonian, relativistic, or quantum–so where does our sense of manifest time come from?  This question is broken down into parts.

  1. Since “now” would be a special spacelike hypersurface of spacetime, it is established that the laws of physics do not justify singling out any particular foliation of spacetime.  This might seem obvious, but Callender wants to show that proposals to inject features of manifest time into physics fail in their goal.  One example is causal set theory.  Callender argues against the theory’s own founder–and I found the argument entirely convincing–that the flowing now in causal set theory is a gauge freedom with no physical significance.  Callender actually gives slightly  more credit that I do to arguments from quantum nonlocality.  He does show that there is only an issue here if one adopts the Copenhagen interpretation and insist within it that there must be some some fact of the matter about which of two spacelike observesrs collapses a wavefunction.  I would not be inclined to grant either premiss.  Even if one does and makes of it an argument for Lorentz’s interpretation of relativity as opposed to Einstein’s, Callender makes an important point.  Lorentz’s preferred frame is completely unobservable and so can’t have anything to do with our experience of time.
  2. Physics does indeed give a reason to favor foliations of spacetime into spacelike hypersurfaces, a reason of “narrative”:  the world is more intelligible when cut up this way.  From other hypersurfaces (e.g. a plane extending in t, y, and z representing a “moment” of x), one could constrain the rest of spacetime, but only spacelike hypersurfaces provide initial data for a well-posed Cauchy problem:  the data on the initial slice is unconstrained, and the subsequent (and past) evolution is a continuous function of the initial data.  Ultimately, this comes down to the spacetime metric, which I would say expresses the causal structure of spacetime.  Callender mostly agrees, but his empiricism sometimes leads him to formulate things in (what seems to me) odd ways–that what’s real is observable events, which data can be compressed by fundamental laws of physics which happen to be hyperbolic equations with the same characteristic speeds, which makes it handy to speak of a causal structure of spacetime.
  3. The explanation of manifest time must therefore be sought in human psychology.  There is a brief discursion into the argument over indexicals which all philosophy of time works address:  that our statements no more prove that there is metaphysically privileged “now” than that there is a privileged “here” or “me”.  I am skeptical of attempts to tease out metaphysics from grammar, but since it keeps coming up, I guess Callender had to address it.  More substantially, Callender argues against the intuitive belief that we have a direct experience of the present.  We are used to similar arguments from empiricists, e.g. “I have no particular experience of myself; therefore selves don’t exist.”  This argument isn’t quite that bad.  Callender has already given independent arguments that the now of manifest time is an illusion, so all he needs to do here is neutralize the counter-argument that we directly experience this putatively non-existent thing.  One might wonder (although the book doesn’t do so explicitly) if “now” is like the self in that, while not directly experienced, it must be posited to explain a perceived unity of experiences.  In fact, what is needed for this is just an experience of simultaneity, which seems to me rather unthreatening from a physicist’s point of view.  Nevertheless, Callender recounts experiments showing a degree of haziness in perceived simultaneity.  Some of it is interesting–I learned that we process sound faster than sight and that it’s possible to recognize that two stimuli are slightly non-simultaneous without being able to say which came first–but I don’t think it’s necessary for the main argument, which doesn’t hinge on how sharp our sense of simultaneity is.  There follows discussions of IGUS and evolutionary pressures to explain our experience of motion and greater concern over future vs. past pains.  In some ways, this is the most important part of the book, because it is here that manifest time is supposed to actually appear, but given my lack of interest in psychology I didn’t give it as much attention as the rest of the book.

Callender concludes with a criticism of what he sees as the philosophy of time’s disengagement from science and retreat into metaphysics.  In some ways, this complements my criticism of neo-Thomism’s retreat into metaphysics, but Callender drives home a point specific to the philosophy of time.  The point of this branch of philosophy is to explain our experience of time, but it is hard to see how metaphysical constructs that leave no trace on physics could be much use to phenomenology.  For example, even if there is an unobservable preferred frame, how could this have anything to do with how we experience time?

2 Responses

  1. […] Whenever I read a philosopher arguing that the theory of relativity has not made presentism untenable, I come away more convinced than ever that relativity has indeed made presentism untenable. One must posit a preferred foliation of spacetime that has left no trace on the laws of physics or human experience, or one must hold out hope that some future physics will provide such a trace, or one must define the “now” counterintuitively using arbitrarily selected special events. Additionally, I think the truthmaker objection to presentism is stronger than Feser gives it credit for, but as a traditionalist I may be too sentimentally attached to the reality of the past. Feser’s mostly grammatical arguments didn’t convince me, but he does make one very strong point. Namely, that it won’t do to say that change as common sense would recognize it is not real but exists only in the mind, because if it exists in the mind, then it exists. The eternalist absolutely must establish that change as he understands it is sufficient to explain everything about the human experience of the distinctive character of time. For a recent attempt by the eternalist side to do this, I recommend Craig Callender’s book. […]

  2. […] Whenever I read a philosopher arguing that the theory of relativity has not made presentism untenable, I come away more convinced than ever that relativity has indeed made presentism untenable. One must posit a preferred foliation of spacetime that has left no trace on the laws of physics or human experience, or one must hold out hope that some future physics will provide such a trace, or one must define the “now” counterintuitively using arbitrarily selected special events. Additionally, I think the truthmaker objection to presentism is stronger than Feser gives it credit for, but as a traditionalist I may be too sentimentally attached to the reality of the past. Feser’s mostly grammatical arguments didn’t convince me, but he does make one very strong point. Namely, that it won’t do to say that change as common sense would recognize it is not real but exists only in the mind, because if it exists in the mind, then it exists. The eternalist absolutely must establish that change as he understands it is sufficient to explain everything about the human experience of the distinctive character of time. For a recent attempt by the eternalist side to do this, I recommend Craig Callender’s book. […]

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