Right after the big bang, ALL matter was superheated to a plasma state at trillions of degrees. Bodies tend to stay in the same state they are, unless they are affected by an external force. If there was no “space” or other form of cold mass to transmit heat to, why did the superheated matter start to cool down?
I’m thinking it may be related to energy released when particles started to merge/combine with others to form atoms, molecules, etc., but I’m sure someone here has a better explanation.
In: Planetary Science
It’s straightforward- it’s because the universe expanded. Things were very hot in the early universe, but there’s still a finite amount of total heat (or, if we’re talking about an infinite universe, a finite heat density). As the universe expanded the same amount of heat became spread out over greater and greater space, which naturally resulted in things cooling down. If the universe were to ever come back together again (as described in the now-considered-unlikely Big Crunch scenario) it would heat up as the galaxies come closer and start colliding with each other.
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