Whatever time may be, it seems to involve duration and simultaneity, neither of which are arbitrary ramblings, but would have to be accounted for by (or included in) any theory of time:

• duration: it takes time to get to work in the morning
• simultaneity: we get to work about the same time in the morning, as agreed prior

People sure have come up with a few ideas about time over the years (pun intended):

• Zeno: motion is illusory
• Aristotle, Hume: no change implies no time (an empirical perspective)
• Kant: time and space are a priori (pre)conditions for all experience
• McTaggart: bah, smoke and mirrors, nothing but illusion and humbug
• Robb: time is a causal dimension of the world
• Shoemaker: time without change is conceivable (and logically consistent)
• A scientific approach: time is a (measurable) quantity of any kind of change

An aggregate of duration and simultaneity, an entropy gradient, an irreducible or basic aspect of the universe, that we wish to quantify with clocks, subject to relativity, …? Whether time is fundamental or not, duration and simultaneity will have to be taken into account.

For context, let’s just briefly examine non-spatiotemporality (like abstracts perhaps):

• Suppose x is defined as not spatial, “outside of space”. Well, then obviously x is nowhere to be found. And x cannot have any extent, volume, area, length, or the likes, not even zero-dimensional (like a mathematical singularity).
• Suppose x is defined as atemporal, “outside of time”. Well, then there can be no time at which x exists. And there can be no duration involved, x cannot change, or be subject to causation, cannot interact, and would be rather inert.

Causation is roughly uni-directional interaction, or uni-directional aspects thereof — what we find as related, temporally ordered events. Causes and effects are events, and events are subsets of changes — they occur (in context).

Suppose we were to reduce time/temporality to something else, then how do we account for that something else? There’s an analogy to be found in the diallelus, regarding ontological reduction. Can there be answers that do not admit further questions, even in principle? Doesn’t really seem like it, in which case we just find ourselves on some indefinite path of inquiry. ^{wikipedia, iep}

It may be possible to argue that “time does not pass” for a free photon, or that a photon does not age, in some sense, by moving at light speed. Indeed, photons are thought to not decay. They can still interact, however, which can be a drastic change in reference frame. Does this lend credence to Shoemaker’s odd thought experiment?

There’s also a linguistic oddity related to time. Time versus existence: Did/does time exist or was/is existence temporal? Expressing temporality in tensed language can be challenging. The term “to exist” also has past tense — our language can express things existing tensed — did exist, do exist, may yet come to exist. What, then, about time itself? Something’s fishy. Well, at least some things exist for some duration only, like processes, like dawn to dusk. But time itself would perhaps have to be referenced, or characterized, tense-less. Either way, we shouldn’t let our linguistic practices bewitch us (cf Wittgenstein). We have (possibly confusing) double-temporal proposition like “it is true now, that it rained the other day”. Contemporary cosmology supposes that time is an aspect of the universe, among others. The past was, the present is, and a future may yet come to be. The past already “solidified”, the future has not, and the present divides them.



Presentism and the A-series may lead to, or express, a form of idealism (philosophical, not political), and seems kind of inadequate. Process philosophy has more going for it.

On the other hand, eternalism and the B-theory seem to lack what we experience indexically, and so is incomplete in some sense. There’s no privileged “right now” included, at least not without adding it to the model. But once I’m gone, I could be characterized, in part, as a 4 dimensional “blob” (in lack of a better term), my connected spatiotemporal locales.

The growing block universe has a kind of intuitive appeal, and is a move from the block universe towards accounting more closely for a privileged now, albeit subject to some critique (like much else). Does the growing block already presuppose time, and hence cannot be used for setting out a model or definition thereof? Maybe, maybe not.

Relativity is apparently compatible with eternalism and the B-theory, which may be inherent in how such theories are formed. It’s intended that no particular “now” is all that’s modeled; the descriptive power is exactly the independence of a special “now”. Relativity is commonly said to describe a non-Euclidean geometry of 4 dimensional spacetime, and operates on something akin to a block universe, but that seems inherent in how no particular “location” (like the indexical “here-now”) has a special status.

(An odd but seldom noticed consequence of McTaggart's characterization of the A series and the B series is that, on that characterization, the A series is identical to the B series. For the items that make up the B series (namely, moments of time) are the same items that make up the A series, and the order of the items in the B series is the same as the order of the items in the A series; but there is nothing more to a series than some specific items in a particular order.) — https://plato.stanford.edu/entries/time/#McTArg

Sometimes there’s a (possibly subtle) misunderstanding of eternalism, or a block universe, in that the universe is said to be frozen, static, something like that. This is inaccurate, however, since change already is modeled along the temporal axis. On eternalism, or the block universe, there “is” still time (— by the way, notice the present tense “is” here — it’s misleading due to our language). Claiming that the past exists now is incoherent. Should a future come to pass, then that’s what the block model is supposed to have (thereby also separating ontology and epistemology). Time is one of the dimensions, and the (rest of the) universe is not static, since it changes along the temporal axis. The part that’s “incomplete” (in lack of a better word) is just that no particular “now” is privileged. Rather, the model includes any “now” on equal footing, if you will, and so does not privilege our current, indexical, experienced, present now (without the quotes). And that makes perfect sense for models like relativity, where we want descriptions that hold for any “now”.

Time is the fire in which we burn. — Delmore Schwartz, Calmly We Walk Through This April’s Day (1938)

They say time is the fire in which we burn. — Tolian Soran, Star Trek: Generations (1994)

________

• Heraclitus (Wikipedia article), “panta rhei”, “no one ever steps in the same river twice”
• Parmenides (Wikipedia article), timeless existence
• Time (Wikipedia article)
• Time (Internet Encyclopedia of Philosophy article)
• Time (Stanford Encyclopedia of Philosophy article)
• Temporal logic (Wikipedia article)
• Arrow of time (Wikipedia article)