why did the universe cool when it expanded ?
it is said everywhere "as the universe expanded, it cooled and so........" whats the physics behind why the universe cools when it expands?
many say that it does so the same way a hot gas cools when it expands
if this is so, why does the gas cool when it expands?
- Anonymous1 decade agoFavorite Answer
Nearly everything cools when it expands. Hartley mentioned lava expanding when it's ejected from a volcano, but something that you've more likely noticed is what happens when you pump air into a bicycle tire. When you compress air it gets warmer, so the pump heats up....and , although it's more difficult to notice, when you let air out of the tire, it cools.
Basically, when anything expands, the molecules just have more room to move around in, and the same amount of energy is spread over a larger volume.
- 1 decade ago
when the universe was very compact in a primeveal atom, it was ultradense. so, the kinetic energy with the particles were too high. the more the kinetic energy, the more is the temperature. When the temperature and density got too high, the atom exploded into big bang. then, the entire universe started expanding. because of this expansion, the kinetic energy with the particles decreased, which caused the universe to cool down.
- Anonymous1 decade ago
Because time passes, particles expand outward and they begin to cool over time. Just as bits of hot lava and fire began cooling even as they are ejected from the volcano.
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- Chandramohan P.RLv 71 decade ago
That is what the laws of heat or thermodynamics says.
Little heat is shared by more volume,so heat per volume becomes less by lowering the temperature.