[Balgair]

To be suuuuuuper pedantic here: Relativity tells us that time is a dimension, one that is a bit unique. In that it has a constant attached to it. So, the 3 dimensions you're used to are just normal, they have no constants.

(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.

[contravariant]

That constant is immaterial, it's just the conversion constant between two different units. It just turns out that for the units we're used the time unit is a lot larger than the space unit.

The real difference has to do with the metric on spacetime, but that gets tricky to explain. Suffice it to say that a rotation involving 2 of the spatial dimensions, and the equivalent of a rotation for time and a spatial dimension are quite different.

[trenchgun]

Is it because of th minus sign?

[contravariant]

Pretty much yeah. A metric like x^2 - t^2 is quite different from one like x^2 + y^2 (and to some extent those are the only possible in 2d)

[cubefox]

The last sentence surprised me.

[kergonath]

And yet… If you want to get properly depressed, there is a lot we don’t understand about gravity, either.