eli5: does redshift disobey the first law of thermodynamics
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Cosmological redshift does not violate conservation of energy because in an expanding universe (which causes cosmological redshift) there is no global conservation of energy.
Noether’s theorem states that any symmetry of a physical system corresponds to a conserved quantity. Time symmetry (i.e. it doesn’t matter when you conduct an experiment, everything else equal, it will always give the same result), which would normally cause conservation of energy, does not exist when the universe is expanding.
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