(x,y,z)

Meters of x are meters of z and meters of y. Relativity (and I'm really simplifying a lot by just saying 'relativity'), well relativity comes along as says that time is also a dimension, just with the constant of 'c' attached (the speed of light). That way you can convert seconds into meters.

(x,y,z,ct) not just (x,y,z,t).

So now the time dimension is much larger than the spatial dimensions. About 300,000,000 times larger, a third-ish of a billion. So a meter of x is ~1/3 of a billion meters of time.

Now, there is a lot more about relativity, like, just tons. And I skipped most of it. And trying to just say that time is a simple little conversion away from meters is just wrong. And how that all relates to entropy is a mess that we really haven't figured out yet.

I forget the name of the book, but it was trying to convey intuitions about relativity (first special, then general).

It’s very easy to make the mistake of trying to understand space and time first, concepts we think we intuit, but in relativity these are somewhat higher-level concepts. Instead, start with what the most fundamental part of the theory and go from there: the speed of light is constant. Accept that first. It’s the comfort zone. You can always return safely to this point.

So, when moving to space and time, the book explained it like this: everything moves at the speed of light, at all times. It’s just that instead of x,y,z – we add t, time, as well. So for an object that’s still, all it’s movement is through the time dimension. Conversely, an object that moves incredibly fast, like a photon, already “used” it’s speed in the spatial dimensions, so it doesn’t “age” in terms of time.

This is just special relativity, but I liked this approach. It’s basically embracing the theory first instead of trying to shoehorn it into the world we have so many misconceptions about.