A failed Deep Thought

I was going to post the following as Deep Thoughts XLIII, in a series of posts meant to be largely tautologous or at least trivial statements:

1. Everyone older than you was once your age.

And then I realized that this is not actually a tautology. It might not even be true.

Suppose time is discrete in an Aristotelian way, so that the intervals between successive times are not always the same. Basically, the idea is that times are aligned with the endpoints of change, and these can happen at all sorts of seemingly random times, rather than at multiples of some interval. But in that case, (1) is likely false. For it is unlikely that the random-length intervals of time in someone else’s life are so coordinated with yours that the exact length of time that you have lived equals the sum of the lengths of intervals from the beginning to some point in the life of a specific other person.

Of course, on any version of the Aristotelian theory that fits with our observations, the intervals between times are very short, and so everyone older than you was once approximately your age.

One might try to replace (1) by:

2. Everyone older than you was once younger than you are now.

But while (2) is nearly certainly true, it is still not a tautology. For if Alice has lived forever, then she’s older than you, but she was never younger than you are now! And while there probably are no individuals who are infinitely old (God is timelessly eternal), this fact is far from trivial.

Plato and teaching philosophy to the young

In the Republic, Plato says philosophy education shouldn’t start until age 30. I’ve long worried about Plato’s concern about providing young people with tools that, absent intellectual and moral maturity, can just as well be used for sophistry.

Exegetically, however, I think I was missing an important point: Plato is talking about his utopian society, where one can (supposedly) count on society raising the young person to practice the virtues and live by the truth (except for the noble lie). We do not live in such a society. It could well be the case that in our society, young people need the tools.

We might make a judgment like this. Absent the tools of a philosophical education, an intelligent young person set afloat on the currents of our society maybe is 50% likely to be led astray by these currents. The tools are unreliable especially in the hands of the young: perhaps the tools have a 65% chance of leading to the right and 35% of leading to ill. That’s still better than letting the young person navigate society without the tools. But if our society were better—as Plato thinks is the case in his Republic—then the unreliable tools might be worse than just letting society form one.

Beginnings

An obvious definition of having a beginning is:

1. x has a beginning provided that x exists at some time but there is an earlier time at which x does not exist.

But this doesn't seem right. After all, it may well be that (a) the universe has a beginning (about 14 billion years ago) but (b) there is no time before the universe. In light of this, I've tended to say something like:

2. x has a beginning provided that x exists at some time at which it has finite age.

There is a somewhat recondite potential counterexample to (2). Suppose that the universe has an infinite past, and object x has a temporally gappy existence, such that last year x existed only for half a year (the other half is the gap), the year before x existed only for a quarter of a year, and you see where that's going. So x's current age is something like 1/2+1/4+1/8+... = 1 year. So x is one year old. By definition (2), x has a beginning. But it doesn't seem like x has a beginning.

But perhaps this case is not fatal to (2). Maybe we should agree that x has a beginning. For the relevant time sequence for saying whether something does or does not have a beginning is internal time. And x has a finite internal time past. If we say this, then we will also say that a person y that has a slowed-down past of the following sort also has a beginning: over the last year, y functioned (in all respects, mental and physical) at half of the speed of a normal person; the year before, at a quarter of the speed of a normal person; the year before, at an eighth. Thus, y experienced 1/2+1/4+1/8+... = 1 years of internal time. Yet y has always existed. While I might tolerate saying that x has a beginning, to say that y has a beginning is very awkward. (Maybe it's true, though? It's worth exploring. But for now I shall dismiss this.)

The above cases show that age in (2) must be reckoned in an external manner. To be more precise we should revise (2) to read:

3. x has a beginning provided that x exists at some time T and there is a number N of years (or other units) of time such that x did not exist more than N years (or other units) before T, where the times are reckoned externally.

Note that this is very much an extrinsic characterization of x's having a beginning. We could imagine two objects whose intrinsic careers are exactly alike, one of which has a beginning and the other does not. Take, for instance, our slowed down y from the last counterexample, and then a person who lives through y's past in one ordinary external year. The slowed down y has no beginning, but the other person does, even though their internal lives could be exactly alike. This seems unsatisfactory.

Also, intuitively, having a beginning is more about the order properties of time rather than metric properties of time. But (3) (as well as (2)) makes it be a feature of the metric properties of time.

I am not quite sure what to do with these thoughts. Maybe this: The notion of a beginning isn't actually all that natural a notion. Perhaps the natural notion in the vicinity is the notion of having a cause?

Why does time fly by as you get older?

Here is a hypothesis.

Age and time

Say that an entity E has age T at t if and only if E began to exist exactly at t-T[note 1] Observe that the age of an entity can be positive, zero, or negative. What kind of property of E is the having of a particular age?

Here is the problem. An entity continues to change in respect of age even when it no longer exists. But when an entity does not exist, the only change it can engage in is pure Cambridge change—the sort of "change" that Napoleon "experiences" when he changes from not being thought about by the Duke of Wellington or Bill Clinton to being thought about. I will assume that the age is the same kind of property during a substance's lifetime as afterwards.[note 2]

Now, Cambridge change is in the end grounded in something else undergoing non-Cambridge change. The Duke of Wellington or Bill Clinton change from not thinking to thinking about Napoleon, and thus Napoleon "changes" from being not thought about by them to being thought about by them. So the change in the age of an entity must be grounded in an something else's undergoing a genuine, non-Cambridge change. But what is that something else? And what does that something else change in respect of?

One intuitive thing to say is that "the time changes". E comes to have age T when the time changes from not being equal to t₀+T, where t₀ is the time E first came to exist, to being equal to t₀+T. But what kind of a change is that? Time surely isn't literally some enduring entity that has a succession of temporal properties like "being noon", "being 3pm", etc. Maybe what we want to say is that reality itself or the cosmos changes in respect of time: it changes from being such that it is not t₀+T to its being such that it is t₀+T.

Suppose that our ontology includes moments of time, and that if t is a moment of time, then t exists at t and only at t. We can then say that the age of E changes to T precisely when reality changes so as to include the moment t₀+T. If our ontology does not include moments of time, but, say, is relational, we may need to do some more work, but I do not see any obvious in-principle bar to defining the time.

We now have a seemingly well-defined property of age, defined in terms of reality's inclusion of a particular moment of time. Now, here is an oddity. This property of age can be equally well defined on a B-theory as on an A-theory. Indeed, I alluded to nothing A-theoretical in the account. A first consequence—Dean Zimmerman has a paper that among many other interesting things says something like this—is that it won't do to define the difference between the A- and B-theories in terms of the objective futurity, presentness and pastness of events, since such properties can be defined in terms of age, and both the A- and B-theories can define the property of age, and the definition seems mind-independent. Nor will it do to define the distinction between the A-theory and the B-theory in terms of an A-theorist's being committed to age being a non-Cambridge property. For the above argument shows that age is a Cambridge property (and by the same token, so are futurity, presentness and pastness), so it would be grossly unfair to the A-theorist thus to define the A-theory. A third consequence is that a reductio, like McTaggart's, of the very idea of futurity, presentness and pastness properties is apt to equally attack the B-theory as the A-theory, since both the B-theory and the A-theory can define such properties.

How, then, to define the A-theory, if not in terms of objective futurity, presentness and pastness of events? I see only one way at present: in terms of the idea that propositions change in truth value. The A-theorist, then, is one who gives up on the eternity of truth: p can be true at t₀ but false at t₁. This Aristotelian theory of propositions is, I think, false (on this theory, tomorrow I will no longer believe the same things as I believed today about my actions from today, even in cases where I have not forgotten these actions), but it is not clearly absurd.