The three major theories of temporal reality are presentism (reality
includes only the present), growing block (reality includes the present
and past) and eternalism (reality includes past, present and
future).
A recent option that has
been considered is thick presentism on which reality
includes a short segment of time including the present. This lets one
have some of the intuitive advantages of presentism (dinosaurs and
Martian settlements don’t exist) while at the same time neatly solving
the problem of diachronic causation. Moreover, it raises an interesting
explanatory problem: why does our world have the kind of temporal
reality it does.
I think that if thick presentism is metaphysically possible, likely
so are a number of other views:
Very thick presentism
Time-variable thickness thick presentism
Growing block
Space-variable thickness thick presentism
Swiss-cheese temporal reality.
On very thick presentism, the band of reality in thick presentism
becomes extremely thick, say a million years. For there seems to be no
compelling reason why the band of reality posited by thick presentists
would have to be thin.
On the time-variable thick presentism, we have a thick presentism
where the thickness varies with time. This is likely something that the
thick presentist has to countenance. For, plausibly, some
moment within the thick present has to be distinguished as “very
present” to avoid violating the law of non-contradictions (since objects
will have contradictory properties within the thick present). Suppose
that that moment happens to be at the middle of the thick present. Then
when the very present gets closer and closer to the beginning or end of
time, the band of reality must get thinner and thinner. Or suppose the
moment happens to be at the end of the thick present (I think that may
be the better theory). Then when the very present gets closer to the
beginning of time, the band of reality gets thinner and thinner. We also
get time-variable thick presentism by applying patchwork principles to
recombine worlds with thick presentisms of different thicknesses.
Growing-block with a finite past is just a time-variable thickness
thick presentism where the very present is at the end of the thick
present and the thickness of the thick present at t is equal to the duration from the
beginning of time to t. And if
we allow it with a finite past, why not with an infinite one—assuming an
infinite past is possible?
Applying patchwork principles to thick presentisms with different
thicknesses, we can get a space-variable thick presentism—here, the
present may be ten minutes thick, but there it may be ten years
thick.
Once we allow that, why not go all the way and allow a swiss-cheese
temporal reality, where at any given time various chunks of the
four-dimensional manifold are included or left out in a pretty arbitrary
fashion (perhaps subject to some restrictions to make causation
work)?
Now, here’s a fun theological speculation. Some thinkers are worried
about eternalism and growing block on theological grounds: they worry
that these theories imply that horrendously evil events like the
Holocaust will eternally be a part of reality, and that this is
inappropriate. But once we have expanded the range of options as we
have, we can have some interesting theological theories.
For instance, perhaps, growing block is true between now and the
Second Coming. Then at the Second Coming the band of reality gets very
thin, so that after the Second Coming, the band of reality includes only
the times from the Second Coming to the then-present. We can think of
this as giving a surprising reading of the “Behond, I make all things
new” of Revelation 21:5—the past events and object suddenly get wiped
out of reality. Or, as a variant, perhaps partial eternalism becomes
true after the Second Coming: reality now includes all times from the
Second Coming on.
But one may worry that that wipes out too much—for instance, it wipes
out the glory of the Cross (I am grateful to a graduate student for this
worry). Very well. Then we go for a swiss cheese version where we have
selective removal from reality—the Holocaust goes but the Cross stays,
say.
All this has a certain resemblance to Hud Hudson’s hypertime story.
But it’s different in two ways. First, it doesn’t need hypertime.
Second, I am assuming here a variant of a standard presentist picture on
which there are tensed truths, and the tensed truths function according
to standard temporal logics. Thus, if it is true that p, it will always be true that it
was true that p. What changes
is what events and substances fall within the domain of restricted
quantifiers—quantifiers do not commute with “at t” and other temporal operators.
For instance, on the “I make all things new” theories, right now all
three of these are true:
There exists an x such
that at 327 BC: x is a horse
named “Bucephalus”
At 327 BC: there exists an x such that x is a horse named
“Bucephalus”.
At 2000 AD: there exists an x such that at 327 BC: x is a horse named
“Bucephalus”.
After the second coming, when the past objects and events are wiped
out, we still have (b) and (c) holding, but (a) does not hold.
On a hypertime variant of “I make all things new”, once the past was
wiped out, we would have none of (a)–(c).
I do not endorse any of these odd possibilities, because I am a
die-hard B-theorist.