Relational and substantival theories of time
The issue here is: what's the nature of time? Is it a reality independent
of the universe, or just a feature of it?
1. Substantival theory:
-
a moment is a real entity in its own right.
-
time is the series of all moments ordered by relations of “earlier” and
“later”.
NOTE: hence, time does not presuppose events.
NOTE: the above account needn't take time as a totum syntheticum
(i.e.
a totality composed of its parts, that is, such that the parts are ontologically
prior to the whole, as bricks to a house).
2. Relational theory:
-
Start with an actual event e (if constructing actual time) and the
tenseless (or tensed) temporal relation R of “being earlier (or in the
past) at a temporal distance d.”
-
A moment is the collection of all (possible) events having the relation
R to e.
-
Time is the series of all moments, i.e. these collections of events, ordered
by relation R.
NOTE: hence, time presupposes events. So, no events, no time.
In other words, time presupposes change.
NOTE: temporal relations are prior to time (time is constructed out
of them).
Hence the bone of contention between the two theories is whether moments
are parasitic on events or not.
3. Criticism of the relational theory.
The relational theory has the important advantage of leading to ontological
simplification. However, there are some criticisms which have been raised
against the relational theory of time:
-
The awareness of time passing in the absence of any awareness of change
in events shows that time doesn't depend on change.
Replies:
-
passing moments are not observable, and the alleged awareness of time passing
without awareness of change in events questionable.
-
At any rate, the argument makes a questionable move from epistemology to
metaphysics.
-
Two counterfactual-arguments:
-
“Nothing might have happened now” is true. Hence, the moment identified
by “now” cannot be a collection of events.
Reply: Three possible replies:
-
“nothing might have happened now” is false.
-
“nothing might have happened now” must be understood as “the present time
might not have existed”.
-
“nothing might have happened now” must be understood as referring to
the empty collection of events.
NOTE: this requires that merely possible events be admitted in
the construction of moments.
-
“Now Joe is asleep, but might have been awake” could be true. But if Joe's
being asleep is a member of the collection constituting “now”, then Joe's
being awake could not be a member of the collection constituting “now”,
i.e. the identical moment at which he is asleep.
NOTE: if this is right, then there are interesting consequences for
possible worlds. A possible world is a complete way in which
things might have been. Possible worlds are useful in dealing with
counterfactuals. For example, I'm now typing, but I could
have been walking. Then, there's a possible world W at which
now I'm walking. Individuals are world-bound if they
can exist in only one possible world. If individuals are world bound,
then the person walking at W is someone very similar to me but not numericallly
identical to me (he isn't me). If the world I am at is the only possible
world, then there's no other way things could have been, and all that happens
happens necessarily.
If criticism (2) is right, then relational time entails world bound
individuals (individuals exists only in one possible world) or necessitarianism
(the actual world is the only possible one)
-
The 'Time without change argument':
Imagine a world in which many things cease and restart to exist at
regular intervals gradually turning white before they cease, and gradually
regaining their color after they restart existence. Suppose that we can
calculate that at 4 each object in our world ceases for 20 minutes. Then,
suppose that today at 4 everything is white. The next thing everybody
notices is lots of white things gradually regaining their color. One could
reasonably conclude that between 4 and 4:20 no event took place but time
went by. Hence, time doesn't presuppose change, and the relational
theory is wrong.
Replies:
-
Is the story coherent?
-
Assuming that the argument is good, all it shows is that empty time preceded
and followed by non-empty time is possible. But this can be accounted
for in two ways:
-
by a relational theory allowing the events out of which moments are constructed
to be merely (metaphysically or physically) possible.
-
by holding that time is substantival in some worlds but not in the
actual world.
Reply: But if relational theory true, it would give the nature
of time, which would be the same in all possible worlds.
4. Criticisms of the substantival theory of time
-
Moments, which go by in time, are unobservable. Hence, it's possible for
a change to occur in the sense that all events speed up with respect to
the rate of passage of moments. This speeding up, however, would be unobservable
and unknowable. But a change which is in principle unobservable and unknowable
is no change at all. By contrast, if relational theory is true, then
no such speeding up is possible.
-
If an event occurs now, there must be an explanation why,
even if we might not know it. But if absolute time exists and it stretches
beyond the existence of the universe, then there's no possible explanation
why the universe occupies this stretch of time because each
stretch of time is indiscernible from any other. Hence, there's no absolute
time (Leibniz).
Reply: Is the global question of why the universe exists when
it does a proper one?
-
Two internally identical possible worlds occurring at different dates would
be indiscernible. Hence, if one accepts the principle of the Identity
of Indiscernibles (if two things are qualitatively identical, then they
are numerically identical), then the two world would not be two.
So, the principle of the Identity of Indiscernibles entails that there
is no absolute time (Leibniz).
Reply: deny the principle of the Identity of Indiscernibles,
or that at any rate it's applicable to the case.
Appendix: A relational modal view of time
1. Construction from an event e plus a metrication given by the
distance relation R and a number n:
(Et) [Rn (t, e)] <-> Possible (Ex)[ Event x & Rn (x, e)], that
is,
[there is a time t with a temporal distance relation Rn to a given
event e if and only if there is a possible event x which has the temporal
distance relation Rn to e].
So, a time t located at n units from an event e is a collection (or
alternatively the set) of actual or possible events located n units from
e.
2. by varying “R”, “n”, “e”, “possible”, one gets different topologies.
a. Varying R:
-
R = “before”, then time one-dimensional.
-
R globally asymmetric, then no closed time (no loop).
-
R globally symmetric, then closed time (every event “before” and “after”
any other).
b. Varying n:
-
n ranging on integers, rational or real, then time discrete, dense, or
continuous.
-
n ranging over a closed interval, then first and last moment.
-
n ranging over a semiclosed (open) interval, then no first or last (neither
first nor last) moment.
c. Varying e (allowing closed variables in place of e), then possibility
of branching time.
d. Varying range of “possible” (actual, physically possible,
metaphysically possible), then possibility of differently structured times.