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[–]Hel 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (4 children)

ELI5 why The Laws of Thermodynamics require the heat death of the universe.

[–][deleted] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (3 children)

Only in a closed universe where energy is conserved. If it a closed physical system eventually it would reach thermodynamic equilibrium no matter how many times it goes bang, or whether it doesn’t go bang. It can be eternal if it is an open system.

[–]Hel 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (2 children)

At the moment the observable universe is expanding and thus cooling. However the observable universe is uniform, so if said uniformity continues sufficiently outside of the observable universe then the observable universe is necessarily contained in an event horizon. Thus eventually everything will move back towards the origin which will cause warming. Since energy is conserved this cycle of expansion and contraction can be eternal.

[–][deleted] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (1 child)

If we imagine it like an simple harmonic device where there is no friction I suppose it could work.

So the universe for all eternity is not in equilibrium and continues to oscillate to reach equilibrium?

[–]Hel 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (0 children)

It’s not that there is no friction, but rather that the friction just generates heat which is then “absorbed” into the singularity/ringularity, along with all the other energy/mass, until it reaches “critical mass”.