Universe Cooling and Formation of First Stars and Comets

[LJP07]

I read before in a Universe Book, that the Universe shortly after the Big Bang, followed a period of rapid cooling, but what was to cause this cooling of such an extremely hot region, I thought it might be due to the gases in the Universe expanding, but is this realistic to such a high temperature that the Universe was at?

Also, in that early period of the Universe, where did the first star come from, one study suggested it came from Dark Matter clumped which attracted normal matter and collapsed to form a giant star. http://www.space.com/scienceastronom...ar_011115.html

However, this is just a suggestion and I can't find any other information about it. Although would it not be like normal star formation with nebulae of gases heating up over time, part of Particle Physics that I read before said
everything came from Leptons, so the few gases needed from Nebulae could possibly of came from that, or is finding the proof the difficult part.

As regards rocky planets and everything else, from what was a Universe full of gases, how could all these rocky planets etc be possibly formed? Would I guess true that the gases cooled like I mentioned above, and over time this would create them over time, although I'm really not sure about any of this.

[C1ay]

Rapid expansion of any compressed medium will cause it to cool. This is easily demonstrated by discharging a pressurized vessel like a fire extinguisher. As this vessel becomes almost empty the valve will cover with frost. This is how refrigeration systems work.

[LJP07]

Originally Posted by C1ay

Rapid expansion of any compressed medium will cause it to cool.

If the Universe was expanding, what medium got compressed, surely something expanding would cause less compression?

[Little Bang]

Prolu, the heavier elements that make up the solar systems were created in the first stars and are still being created today in stars. The Big Bang in theory was nothing but pure energy(photons). How that energy was turned into the protons and electrons that make up the universe is anyone guess.

[C1ay]

Originally Posted by Prolu2007

If the Universe was expanding, what medium got compressed, surely something expanding would cause less compression?

The matter of the universe was already compressed in a tremendously dense, hot state and the Big Bang was the expansion of that matter....

[LJP07]

What elements existed to create the stars, hydrogen, oxygen and methane?

[LJP07]

Originally Posted by C1ay

The matter of the universe was already compressed in a tremendously dense, hot state and the Big Bang was the expansion of that matter....

In that case, did it cool the yoctosecond the Big Band started almost instantaneously, so the Universe is still cooling today, would it be possible for the cooling to continue but make conditions too bad for life to exist, at what rate is this cooling and how cold can it get in the Universe, what temperature would it be if I was to exist in space?