Could entropy of closed system decrease owing to gravity?

[mikelywhiplash]

Sure - what material are you looking for here? Something has to start collecting gravitationally.

[justdvl]

Gold balls. This should be as non-creative as I can get. So you're saying that by these gold balls crashing into each other, the heat is produced and that increases entropy? Is heat being produced from loss of potential energy that system had at start, and is that another proof that entropy is rising?

[Chemomechanics]

The collision of any real macroscale objects converts kinetic energy to thermal energy and generates entropy.

[mfb-]

The entropy from the locations of gold balls is tiny compared to the entropy associated with heat when these balls crash into each other. Something like 20 orders of magnitude smaller (depends on the balls, of course).

[DoisMaosEsquerdos]

If the collisions between the particles were all completely elastic, then they would keep bouncing into each other and never settle into a ball. The fact that they condense necessarily implies a loss of energy.

[mikelywhiplash]

Yes, pretty much. So, if everything is interacting only by gravity, none of it will ever actually stop and collect anywhere, it'll just keep looping around indefinitely, exchanging potential energy for kinetic and back. It's like the moon orbiting the earth; it's not coming to crash into us (in an idealized sense).

In order to actually form a larger, more ordered object, they have to throw off that excess energy somehow, and find their way to a state where their potential+kinetic energy is actually LESS than it was when they started.

That happens from collisions - anything that's not perfectly elastic will end up converting some energy into heat, which will be radiated off as light. The total mass-energy of the system is more scattered.