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Philosophy of Time. Time is a great teacher; unfortunately it kills all of its students (Berlioz). I. The Problem.

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Philosophy of time
Philosophy of Time

  • Time is a great teacher; unfortunately it kills all of its students (Berlioz)

I the problem
I. The Problem

The manifest image is teaming with activity. Objects are booming and buzzing by, changing their locations and properties, vivid perceptions are replaced, and we seem to be inexorably slipping into the future. Time—or at least our experience in time—seems a very busy and complicated sort of thing.

By contrast, time in the scientist image is very peaceful. The ‘t’ in the fundamental equations of physics doesn’t differentiate between past and future, nor does it speed up or slow down, nor does it pick out which time is now.

We seem to have, to echo another debate, an “explanatory gap” between time as we find it in experience and time as we find it in science.


Time in physics is (at best) a non-unique 1-dimensional parameter that partially orders 3-dimensional spatial slices.

Is physics incomplete or inaccurate? Has it missed the properties of time that cause these experiences? Or is the time of physics all the objective time needed, where the rest can be explained with psychology, environmental facts, and complicated interactions among them? I.e., is the tensed or tenseless view of time is correct?

Tenseless time
Tenseless Time

  • The past, present and future ‘equally’ exist.

  • The categories past, present and future are not the fundamental temporal properties for the detenser. The fundamental temporal properties are the famous “B-relations” of McTaggart: before, after, and being simultaneous with. ‘Past’ and ‘future’ are understood like ‘right’ and ‘left’, i.e., relationally.

  • The present according to the tenseless view is not at all metaphysically special, since the present for some event is merely those events simultaneous with it (or something more complicated along these lines).

  • Russell, D.C. Williams, Grunbaum, …

H g wells the time traveler
H.G. Wells, The Time Traveler


Your death

Earlier than

Today’s lecture


Earlier than

Your birth


Your death

Today’s lecture



Your birth


Right is a relational property or predicate



To the right of

To the left of

To the north of

To the south of



Earlier than

Later than

Simultaneous with


Monadic properties






Present, Now


Monadic Properties


The tenseless theory of time
The Tenseless Theory of Time

  • The fundamental temporal properties are the temporal relations of earlier than, later than, and simultaneous with. (The monadic predicates are just loose shorthand ways of speaking.)

  • Events earlier and later than current events ‘equally’ exist.

  • No flow, no becoming, no Now

You 4 d version
You? 4-D Version

Enter phil grad school




Tensed time
Tensed Time

  • There are many tensed theories: presentism, becoming, …

  • In all, the present is special: it may be the only time that exists, or the cusp of the moving Now, or the point at which branches fall off, etc.

  • The present in all these theories is not something that can be read off from the set of all temporal relations in the world. The present is ontologically special, something extra not captured by physical theory. Tensers often speak of absolute fundamental monadic properties of presentness, pastness and futurity.


Your death

Today’s lecture



Your birth



Mom’s memories

of your birth

Nuclear objections to tense
“Nuclear” Objections to Tense

  • McTaggart’s Paradox

    • Presentism escapes; maybe argument invalid (Savitt 2001)

  • Smart/Broad’s “how fast…?”

    • Perhaps not so damaging (Maudlin 2002)

  • Special Relativity “No-go” theorem (Putnam 1967; Callender 2000)

    • Depends on “Einsteinian” rather than Lorentzian interpretation of relativity (Callender 2000; Craig 2001)

Mctaggart the ideality of time
McTaggart, “The Ideality of Time”

  • Master Argument

    • If there is time, it must be tensed time (because only tensed time makes sense of change)

    • But time is not tensed (because that leads to contradiction).

    • Hence, time does not exist

Mctaggart on the ideality of time
McTaggart “On the Ideality of Time”

  • First Part

    • Real change requires temporal becoming

    • Temporal becoming requires the tensed theory of time (i.e., changing monadic properties of time—pastness, etc.)

    • Real change exists

    • Time is tensed


  • Second Part: tensed theory is incoherent

    • Past, present and future are incompatible properties

      Why? Well, if an event is past it can’t be present

    • But every event has all three of these properties, e.g., Socrates’ death was once future, then present and is now past.

      Claims 1 and 2 are both true according to the tensed theory, but they are logically incompatible.


  • If event e is future, then it is not past, i.e,. Fe  ~Pe

  • But for all e, Fe, Ne, Pe.

  • From 2, Fe

  • From 2, Pe

  • From 1 and 3, ~Pe

  • From 4, 5, Pe & ~Pe – contradiction!

Natural reply
Natural Reply

  • 2 is not true! Events aren’t simultaneously past present and future…that’s stupid!

  • McTaggart: HA! What do you mean when you say that?

  • One possibility: in 2004 AD Socrates’ death is past, in 3000 BC it’s future…

  • But that’s a tenseless B-relation! You’ve extracted yourself from the paradox by adopting your opponent’s theory!

Or stick tensed
Or stick tensed…

  • In the past, Socrates death is future; in the Now it’s present; in the future it’s past…

  • McTaggart: rerun my argument

    {PPe, FFe, NNe, PNe, FNe, NFe, PFe, FPe, NPe}

    Every e must have each of these, yet they’re incompatible: e.g., NNe  ~PNe

    Reply: no, not simultaneously NNe and PNe!

    Reply: Rerun with NNNe and NPNe…

    Reply: no, not simultaneously NNNe and NPNe!

    Reply: I’m getting tired…it’s an infinite regress

    Reply: not all infinite regresses are bad

    Reply: they ain’t all good either…

How fast does time fly
How Fast Does Time Fly?

  • J.J.C. Smart:

    “If time flows…this would be a motion with respect to a hypertime. For motion in space is motion with respect to time, and motion of time or in time could hardly be a motion in time with respect to time…If motion in space is feet per second, at what speed is the flow of time? Seconds per what? Moreover, if passage is the essence of time, it is presumably the essence of hypertime, too which would lead us to postulate a hyper-hypertime and so on ad infinitum.”





  • 1sec/1sec

  • 1sec/1SEC and 1SEC/1sec

  • Accept infinity

  • Ditch passage

Epistemic objection williams price
Epistemic Objection (Williams, Price)

  • “how would things seem if time didn’t flow? If we suppose for the moment that there is an objective flow of time, we seem to be able to imagine a world which would be just like ours, except that it would be a four-dimensional block universe rather than a three-dimensional one. It is easy to see how to map events-at-times in the dynamic universe onto events-at-temporal locations in the block universe. Among other things, our individual mental states get mapped over, moment by moment. But then surely our copies in the block universe would have the same experiences we do…Things would seem this way, even if we ourselves were elements of a block universe” (Price)

Dainton s overdetermination arg
Dainton’s Overdetermination Arg Occam’s razor would cut it away.

  • Do in section

Arguments for tenses
Arguments for Tenses Occam’s razor would cut it away.

  • Temporal ‘Knowledge’ Argument

    • My lecture is now

    • My lecture is 5.30pm March 1, 2004

      I can know 1 without 2, and vv. Think of the spatial versions of each… Compare with Mary argument and qualia

      2. Experience

      privileged present

      asymmetry of past and future: headache argument


How might detensers respond
How Might Detensers Respond? Occam’s razor would cut it away.

  • Temporal asymmetry:

    • Radiation asymmetry

    • Thermodynamic asymmetry

    • Memory asymmetry

    • Etc

      Imply the behavioral asymmetry

How might detensers respond1
How Might Detensers Respond? Occam’s razor would cut it away.

  • Specialness of the Present

    • Explain why we might be tempted to posit a global objective present even when there isn’t one, really. Use various facts about the world to do so.

      (Everything that follows is not testable.)

Do we experience an objective present
Do We Experience an Objective Present? Occam’s razor would cut it away.

  • Like Hume searching in vain for his self, I don’t perceive any stamp of present on my experiences…

  • Whether something is past, present or future doesn’t change the way it looks. The light from a lighthouse 1 mile away and from Jupiter look the same, even though one image is of an hour in the past and the other is of 0.000005 seconds past.

  • We cannot, as Mellor writes, “refute someone who claims to see the future in a crystal ball by pointing to the visible pastness of the image: there is no such thing” (1998, 16).

Lag times and the present
Lag Times and the Present Occam’s razor would cut it away.

  • Butterfield (1984): typically macro-objects in our local environment change much more slowly than the rate at which light and sound travels to us, plus time to form beliefs.

  • Consider looking at a chair nearby: visual lag of roughly 0.5s. At t* I form a belief about an object at t. Thanks to rapidity of light/processing and fact that macro-objects change their properties comparatively slowly, the result of this process is a belief at t* that the object 1m away at t is chair-shaped, etc.—and at t* it still is chair-shaped, etc.! The lag t-t* typically does not make the belief about local macroscopic objects false.

t*: Object is chair-shaped



t-t* doesn’t affect truth value!

Lag times and the present1
Lag Times and the Present Occam’s razor would cut it away.

  • Same goes for communication, say, by signing; same goes for some other sensory modalities (by contrast, consider mail and smell).

  • All of this makes good sense from an evolutionary perspective. Evol pressure to make t-t* small… And it makes sense to update rapidly…

  • These circumstances allow for great inter-subjective agreement about what happens “now”, agreement that can be used to explain why we’re tempted to restrict existence to the present and say that we share a now but not a here.

  • Now’s as local patches that we ‘glue’ together to form a global Now—explains alleged objectivity of the Present…

Subjective simultaneity
Subjective Simultaneity Occam’s razor would cut it away.

Subjective Simultaneity

Compensation of

Subjective Simultaneity

Subjective Time

Put headphones on a subject and let her listen to tones lasting for 1ms. If the left and right ears are stimulated simultaneously, then the subject hears not two tones but one fused tone. Hirsh and Sherrick 1961, Poppell 1988; Euler 1997

Visual simultaneity

If Occam’s razor would cut it away.






Visual Simultaneity


Not Simultaneous


Different sensory modalities
Different sensory modalities Occam’s razor would cut it away.

Different resolutions:

  • Vision: > 20 ms

  • Tactile: > 10 ms

  • Audition: > 2 ms

Event Fusion Thresholds

Temporal order

If Occam’s razor would cut it away.






Temporal order


Not Simultaneous but no reliable temporal order

Reliable Temporal Order

Simultaneity windows
Simultaneity Windows Occam’s razor would cut it away.

In all the sensory modalities, the simultaneity window varies from person to person. (In hearing, for instance, from 2ms to 5 ms.) It also varies with age, older people fusing more events than younger people, and many other factors. In each person the minimum threshold of simultaneity cannot be shrunk.

Whose simultaneity window coincides with the Present?

Stone et al 2003
Stone et al 2003 Occam’s razor would cut it away.

  • Recent experiments by Stone et al 2003 bolster the earlier experiments. In 1000 trials Stone et al presented 23 subjects with light-sound pairs of stimuli separated from -250ms (sound first) to +250ms. In each trial subjects were asked to indicate if the pair occurred simultaneously or not. These responses picked out a time t between -250ms and 250ms as the point of subjective simultaneity. Stone et al found two items of particular interest about PSS.

    (1) PSS is observer specific. The points varied greatly, from -21ms to 150ms, among subjects. Remarkably, the difference between each subject was statistically significant.

    (2) But—revealed in another experiment—the PSS is remarkably stable for each individual.

  • Given the mind-dependence theory, we might expect (1). But the second item is also one we should expect. Navigating about the world is not merely a question of aligning the visual with the auditory; it is also a question of calibrating that alignment with motor control. However your PSS differs from that of your friends, it had better be the case that it remains stable over time if you are to play table tennis at all well.

Subjective Time Occam’s razor would cut it away.

Compensation of

Subjective Simultaneity

Subjective Time

Multisensory Simultaneity

Time Course of

Neural Events

Neural Processing


Subjective Simultaneity

Poppel: at 10m “horizon of simultaneity”


Slide borrowed from Fujisaki et al,VSS 3rd Annual Meeting 5/10/03

Sound and simultaneity
Sound and Simultaneity Occam’s razor would cut it away.

  • Sugita and Suzuki “Implicit Estimation of Sound-Arrival Time” Nature 27 Feb 2003

  • Subjects were presented through headphones bursts of white noise (10ms duration) to simulate external sound from frontal direction. Brief light flashes were produced by an array of 5 green LEDs at different distances (1-50m). Intensity of light altered so as to produce consistent intensity at the eye.

  • Subjects were told to imagine that the LEDs were the source of the light and sound, while listening to sound directly from source.

  • To estimate subjective simultaneity, observers judged what came first, light or sound.

  • Subjective simultaneity increased by about 3 ms with each 1 m increase in distance up to about 40m. Sound travels 1m/3ms at sea level and room temp.

  • “Our results show that the brain probably takes sound velocity into account when judging simultaneity” (911)