TITLE: What happened to high temperatures in the universe?
QUESTION [1 upvotes]: We know that after the big bang the temperature was about 10^32 K.
But now the average temperature of the universe is about 4 K. What happened to the temperature at that time?  Where did it go?

REPLY [0 votes]: Maybe it is simplistic but look at it like this:
Think of temperature as the height of a water resevoir. The water represents is heat energy and as the resevoir base expands and becomes larger, the water level drops, whilst retaining the same amount of water (energy).
Remember temperature is a statistical measurement, and not an inrinsic quantity to matter. A single atom does not have an temperature, but an average speed which we relate to temperature. (Look up the kinetic theory of gases for more into this).
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