[floatrock]

The part that was new to me was the bit about how a space full of life tends toward more entropy faster than the same amount of space without life.

Like the best ideas, it’s simple and makes sense if you think about it, but it’s still a really interesting framing that the complex machinery of life is really just the most efficient “entropy converter”.

If there’s something about the arrow of time that speeds towards the heat death of the universe, we’re just helping it go a tiny bit faster here on our floating speck of dust.

[quickthrower2]

Does Einstein’s model of time care about entropy. In other words if there are 2 regions, one where entropy is increasing at that time and one where it isn’t as much, does it affect time?

[semi-extrinsic]

No. Entropy can be used to explain the direction of time, as a kind of symmetry breaking of all the microscopic laws that are symmetric in time. But it does not say anything about the "speed of time". Relativity does tell us the speed of time - it's the speed of light.

[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.

[klabb3]

> Relativity does tell us the speed of time - it's the speed of light.

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.

[danq__]

Entropy is an orthogonal to Einstein's laws of physics.

Both newtons and Einstein's description of the universe are time reversable. The physics are valid independent of the direction of time.

Entropy is literally a separate observable phenomenon with it's own set of axioms.

[Piezoid]

There is a video by PBS Space Time on that subject: https://youtu.be/GcfLZSL7YGw

[Timon3]

> Like the best ideas, it’s simple and makes sense if you think about it, but it’s still a really interesting framing that the complex machinery of life is really just the most efficient “entropy converter”.

Right? I think this could be a really interesting basis for a sci-fi novel - the first space-faring civilization in the entire universe trying to force every form of life to keep "entropy usage" to a minimum, so they can prolong their own life span.

[hunter-gatherer]

Isaac Asmiov's short story "The Last Question" isn't super inline with your suggestion but is a short discourse on humanity's struggle against entropy.

[ineptech]

Not exactly what you're describing, but this is along those lines: https://slatestarcodex.com/2015/06/02/and-i-show-you-how-dee... It's pretty silly but the ending is both satisfying and relevant.

[franky47]

> a space full of life tends toward more entropy faster than the same amount of space without life.

And a space full of children is exponentially faster at increasing entropy.

[tgv]

Isn't there a theorem that says that the overall rate is constant in a closed system? If you look at the universe as a whole, it would be closed, and we wouldn't have any impact. However, I learnt about entropy decades ago, and never applied it, so don't take my word for it.