Three Dimensions or Four?

There are surely respects in which the notion of “space-time” as a unitary block, the view of time as
just one of its dimensions, has served a useful role in the further development of science
and technology. Insofar as it does, we might accept it pragmatically as true.  But (secondly)
broad propositions are often ambiguous, even when not obviously so, and in the case of any
ambiguity it is always open to us to say that the statement or the idea is true in one respect, false
in another.

What might tempt us even at an early blush to suspect that there are respects in which this idea
is false? There are the various ambiguities and paradoxes that come with the idea. Consider the
bicycle in the doorway as an example.

A bicycle stands in an open doorway such that the front of the bike is inside the house, the back of
the door is outside. A philosopher asks us, “Well, is the bike in the house or not?” We might well
reply, “some parts are, some parts are not.” Simple enough, one would think.

But can we do that with regard to the dimension of time? Suppose our bicycle came into existence
at T1 and ceased to exist at T100. Isn’t the bike wholly present at each of those times? At T1, at T2,
at T3, and so forth? It isn’t intuitively  plausible to say that only part of the bike, or certain parts of the
bike, are present prior to T20 and that other parts become present after T20. We can say that with
regard to space and the physical threshold of the doorway, but we don’t want to talk like that as to time.

Of course we might say that the bicycle at T21 was rusty whereas the bicycle at T3 still had
that pristine right-from-the-factory look. Then the bicycle at, say, T40 was newly cleaned and
painted and looked pristine once again. But what we want to say is that the same bike was present
at all of these times, and that different predicates were true of that subject at the different time, not
that it was a different object, or even a different part of the one object. So there is something a bit
“off” about treating time, and in such a case the age of the bicycle, as merely another dimension,
quite analogous to its length.  

It may be that the world is made up of subatomic particles that don’t rust (or do anything analogous
to rusting) over time. In such a case, we would surely want to say that a proton at its T41 is  
identical to what it was at T40 and will still be identical at T42 etc. In such a case, too, we might
also be tempted to say that the three-dimensionality of space is a more fundamental fact than the
four dimensionality of space-time.