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Comment by sklivvz1971 | Hacker News Reader

sklivvz1971

Well, think about a star shining, that's a hell of a lot of gravitational energy being turned in to radiation...

Stars aren't powered by gravitational energy - that would only give a lifetime 20 million years for the sun (Kelvin Helmholtz timescale). Fusion is what powers the sun.

Eh, the fusion wouldn't happen without gravity so it's more correct to say that fusion provides extra energy, but the basic process is indeed gravitational collapse.

I don't think so - it's deeply misleading to say it's powered by gravitational collapse, which is tiny in the energy budget. They are formed by gravitation collapse and gravity is necessary for their function. A fire wouldn't start without a match, but you wouldn't say they are powered by matches or the air.

I don't think saying stars are essentially about gravitational collapse is misleading, certainly not compared to saying fusion is the dominating part of the story while leaving out opacity.

In the story of the match, who lights the fire is far more interesting, to me, than what brand of match is. Honestly stellar evolution is far too much chemistry for me, just give me a well calibrated redshift and I'm happy.

I think we have to disagree there. Of course the details about what brings matter together, the opacity, etc, are important, just like anode/cathode design and casing are important in batteries. Gravity's decisively not where the energy is coming from. Without fusion, stars would be cold, slowly cooling lumps of matter (or black holes, if there were no initial stars).

But it also creates stable long living structures called atoms. Without gravity there will be no elements.

Same can be said about the strong force and electromagnetic interaction. So why gravity would be the one that's weird in the context of the second law?

Do you think gravity is what keeps subatomic particles bound into atoms? Perhaps I am too much of an amateur but to my knowledge that is a gross misunderstanding... that would be the strong nuclear force and electromagnetic force that hold atoms together. Gravity is much too weak at such a small scale

It is the weak force, strong is what keeps quarks together in subatomic particles like protons/neutrons. But yes, gravity is way too weak at that scale.

Again I could be wrong, however I thought the strong force holds protons/neutrons together but is also responsible for protons and neutrons being attracted to each other

You are correct! I learned something again today. There is no thing the weak force keeps together, the strong force does both subatomic particles and quarks.

Perhaps the GP means fusion within the star and upon its collapse caused by gravity creates new heavier elements that wouldn't exist otherwise.

That’s how I read @novaRom’s comment.

That makes some sense, however even the primordial universe was capable of producing hydrogen and helium

I said you need gravity to create elements. Stars do that.

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