Lyston writes:
Dip a balloon in liquid nitrogen. You will notice it shrinks as it gets colder. Dip a balloon in a pot of water and heat it up. The balloon will expand as it gets hotter.
Looking at the Big Bang in reverse, matter is being forced into a smaller volume (because there is less volume to go around), which brings with it a huge increase in pressure. This will cause the temperature to go up. Your example above is a constant pressure example.
The mismatch between what you are saying and what Rahvin is saying is that in any given thermodynamics process, you have two independent thermodynamic quantities and the third is expressed as function of the other two. Rahvin is correct in that increasing volume will decrease temperature. Here volume is the controlled quantity and temperature is the result. In your balloon case, you have control over temperature. Basically one is a PV diagram process and the other a TP diagram process. Plot the dependence using the equation PV = T (nR set to 1, in case anybody is wondering). You'll see that you are both right, but you are talking about two completely different situations.
The matter at the Big Bang wouldn't have been in a Bose-Einstein condensate as the temperature wasn't right for one to exist. Also a Bose-Einstein condensate would lead to a very different current universe, which we don't observe.
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