thermodynamics and the universe

Hi Ng
when we think about the earth to cool down and the sun to burn its fuel, there are believes that are naive (and plain wrong).
Why do you think, the inner of the earth is hot? When will it be cold? Why was it hot in the first time?
Our supposed answers to that questions are based on believes about thermodynamics, that are not appropriate to cosmology.
For some reason you may think, our universe is isolated and for that reason its an adiabatic process. Its a perfectly closed system and cannot gain or loose entropy, since there ain't no somewhere to loose that to.
So entropy in the universe is kept as sum over all. This is not our common believe. And even allmost no cosmologists think so, but: if the universe is a closed system and second law of thermodynamics is true, it can't change.
The right picture is, if you think about a balance of temperature and expansation. That is like a ideal gas being carefully expanded. That is an adiabatic process. Real expansation increases entropie and let the gas heat up a bit more than it could be and prevent that process from being reverted.
But the counter-intuitive part in this picture is, the ideal gas is something like spacetime itself. Thats kind of strange, since we apply those terms of i.e. heat only to objects or maybe gases.
As consequence of this believe we think about stars as beeing build out of dust and gases. That is the naive part.
As said above, spacetime itself is that carrier of entropie, what is quite against our believes.

Thomas Heger

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