Philosophy of Time

Philosophy of Time

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

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.

Problem…

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?

Time in Physics

No present No asymmetry No flow

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

http://www.marxists.org/reference/archive/hgwells/works/1890s/time/ch01.htm

http://www.math.union.edu/~dpvc/math/4D/basics/welcome.html

http://www.math.union.edu/~dpvc/math/4D/sphere-slice/welcome.html

http://www.geom.uiuc.edu/docs/outreach/oi/moregraphics.html

Time

Space

Your death

Today’s lecture

Your birth

Earli

er th

an

Earlier than

Time

Space

Your death

Past

Your birth

Today’s lecture

Right?

Right is a relational property or predicate

Space

• Relational– To the right of– To the left of– To the north of– To the south of

Time

• Relational– Earlier than – Later than– Simultaneous with

“B-properties”

Monadic Properties

• Space

– Here– There

• Time

– Past– Present, Now– Future

“A-properties”

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

birth

lecture

alcoholic

Enter phil grad school

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.

Time

Space

Your death

Past

Your birth

Today’s lecture

Presentism

NOW

Mom’s memories

of your birth

“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”

• 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”

• 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

McTaggart

• Second Part: tensed theory is incoherent

1. Past, present and future are incompatible properties

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

2. 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.

Formally…

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

2. But for all e, Fe, Ne, Pe.3. From 2, Fe4. From 2, Pe5. From 1 and 3, ~Pe6. From 4, 5, Pe & ~Pe –

contradiction!

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…• 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 regressReply: not all infinite regresses are badReply: they ain’t all good either…

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.”

TIME

time

space

Replies

• 1sec/1sec

• 1sec/1SEC and 1SEC/1sec

• Accept infinity

• Ditch passage

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)

• Williams’ idea is that the flow or whoosh is extra. Occam’s razor would cut it away.

• Does this argument beg the question?

Dainton’s Overdetermination Arg

• Do in section

Arguments for Tenses

1. 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 presentasymmetry of past and future: headache headache argumentargumentbecoming

How Might Detensers Respond?

• Temporal asymmetry:

– Radiation asymmetry

– Thermodynamic asymmetry

– Memory asymmetry– Etc

Imply the behavioral asymmetry

How Might Detensers Respond?

• 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?• 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).

300,000,000m/s

t

t*: Object is chair-shaped

Lag Times and the Present

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-t* doesn’t affect truth value!

Lag Times and the Present

• 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…

Compensation of Subjective Simultaneity

Subjective Time

Subjective Simultaneity

Subjective Simultaneity

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

+

t

If

<20ms

Simultaneoust

If

>20ms

Not Simultaneous

Different sensory modalities

Different resolutions:

•Vision: > 20 ms

• Tactile: > 10 ms

• Audition: > 2 ms

Event Fusion Thresholds

Temporal order

+

t

If

20-40ms

Not Simultaneous but no reliable temporal order

t

If

>40ms

Reliable Temporal Order

Simultaneity Windows

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• 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.

Input Neural Processing

Multisensory Simultaneity

Time Course of Neural Events

Subjective Simultaneity

Subjective Time

Compensation of Subjective Simultaneity

Subjective Time

-2-Slide borrowed from Fujisaki et al,VSS 3rd Annual Meeting 5/10/03

Poppel: at 10m “horizon of simultaneity”

Sound and Simultaneity

• 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)