[da_chicken]

It's only as abstract as "meters of distance". Which is to say, not in any practical sense until we introduce general or special relativity. The fact that it's synthetic and not an natural unit doesn't mean it's abstract or variable. It means it's arbitrary. It could be any value, but it must remain static.

That's also why we don't use the kings body dimensions as the standard of measurement anymore. We don't need to recalibrate the entire nation's standard of "foot," "inch," "cubit," or whatever when the king grows. That's not useful.

Just because the inch is the width of an adult man's thumb doesn't mean the purpose of the inch is to define thumbs and should always follow from that. That is not the goal of wanting the measuring unit. It's the same for seconds.

That's why I said: Sometimes you want to know what time of day it is, and sometimes you want to know how long something took to occur. That is to say, a datetime and a timespan. Now, you could use a different unit of measurement for those to, but in practical terms it's stupid.

[fluoridation]

Meters and seconds are both abstract and arbitrary. Abstract because time and space aren't divided. A measure of length isn't concrete like a count of atoms in a cup is. Surely we can agree that those two things have different degrees of concreteness. Yes, the phrase "a second" can be translated to a real equivalent, but the "second" is human idea, unlike the atom.

[da_chicken]

Distance can absolutely be concrete. We can specify distance traveled by light in a vacuum, or, if you'd rather, a specified number of Planck units. Similarly, time can be defined by the number of wavelengths of a photon of a given energy level. Which is basically the definition of modern SI second and meter are derived. They're based on the speed of light.

In the end, all you're doing is finding different ways to dissect physical constants. But you're still using those constant. The constant itself doesn't change because the Earth revolves slower today than it did yesterday, yet the planet certainly does revolve the same distance about its axis in more time.

Which is why I say distance and time are not really variable or imprecise (better terms than abstract, which simply has to many nebulous meanings) until you start to introduce relativity.

In fact, time is a fundamental element of many physical constants. The Planck constant, the gravitational constant, and the speed of light are all fundamentally based on time and distance. And since the speed of light relates to mass and energy, whatever units you pick need to be consistent. If we say that 1 second is always 1/84,000th of a solar Earth day (instantaneously I suppose?) then you've immediately made 3 of the known physical constants depending on how quickly the Earth spins. And you could do that and recalculate all of physics every day if you wanted to. But it's kind of stupid. It would be like re-graduating a tape measure every day you build a house. In theory it's just fine. Practically it's really not.