Mysteries of the Universe : First Law of Thermodynamics (Conservation of Energy) DOES NOT APPLY to Expanding Universe.

Mysteries of the Universe
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First Law of Thermodynamics (Conservation of Energy) DOES NOT APPLY to Expanding Universe.

Posted by DFM on September 10, 2020, 6:52 am, in reply to "Looking for plausible alternatives to Big Bang Theory"

https://en.wikipedia.org/wiki/Noether%27s_theorem#Time_invariance

Briefly, momentum is conserved if and only if the system as a whole is invariant with respect to spacial translation. If the system is unchanged if it is displaced in space, then momentum is conserved in that system.

Similarly, energy is conserved in a system if and only if the system is invariant with respect to time translation. If the system is unchanged if and only if it is displaced in time, then energy is conserved.

BUT, the Universe is NOT the same if it is displaced in time because it is expanding. Hence, energy is NOT conserved in the Universe as a whole.

Gravitation has rather unique thermodynamic consequences that are not found from other forces.