[Donald piniach]

Donald piniach asked the Naked Scientists:
   In a perfect elastic collision, there is conservation of momentum and energy. A ball dropped would return exactly to the height it was dropped from. Gases exhibit this. I can see how one can go from Jupiter size to the sun by accretion.  My problem is getting from one helium atom or hydrogen molecule to a football, then to earth mass sized.  It would seem that the perfect elastic collisions would frustrate it sticking together! Both  hydrogen and helium being gases and rarefied in those cosmic conditions. How is the density achieve? It can't be just gravity! Kinetic energy has to be lost! How?
What do you think?

[Mike Gale]

Solid objects like rocks and crystals are held together by valence electrons, which mediate the electric field between adjacent nuclei. Vaporous objects like suns and gas giants are held together by gravity. The idea that they condensed out of diffuse clouds of gas is highly speculative, but the alternative is primordial black holes, which are equally inexplicable.

[sceptic-eng]

It must either be due to some sort of surface tension/casimir effect or more probably because the magnetic field force is stronger than the repulsion force.   

[Bored chemist]

Donald piniach asked the Naked Scientists:
   In a perfect elastic collision, there is conservation of momentum and energy. A ball dropped would return exactly to the height it was dropped from. Gases exhibit this. I can see how one can go from Jupiter size to the sun by accretion.  My problem is getting from one helium atom or hydrogen molecule to a football, then to earth mass sized.  It would seem that the perfect elastic collisions would frustrate it sticking together! Both  hydrogen and helium being gases and rarefied in those cosmic conditions. How is the density achieve? It can't be just gravity! Kinetic energy has to be lost! How?
What do you think?

Most collisions are not perfectly elastic.

[jeffreyH]

Temperature, that is, kinetic energy, is important in the solidification of matter. So part of the answer lies in a reduction of kinetic energy. Opposite charges on electrons and protons will help achieve this via electron capture. Once atoms start to form the charge is neutralised. This gives the gravitational field an advantage. Due to the weakness of the gravitational field this will be a slow process. Also as Bored Chemist said most collisions are not perfectly elastic.

[Kryptid]

Donald Piniach already asked this question before and it was answered: https://www.thenakedscientists.com/forum/index.php?topic=70125.0

Why is he asking a second time?

[Colin2B]

Donald Piniach already asked this question before and it was answered: https://www.thenakedscientists.com/forum/index.php?topic=70125.0

Why is he asking a second time?

Probably because there was no answer to this first question. Reply #1 is more recent than the link you found, which appears to give an in depth answer.