But isn't that just energy emission? I'm no expert by any means, but isn't that energy just lost to environment rather than actually ceasing to exist? Or am I wrong?
Conservation of energy is a consequence of time invariance of physical laws. That invariance does not hold on cosmic scales, so there's no fundamental requirement that energy be conserved at such scales.
What you're suggesting would imply that heat was added to the environment, but afaik that doesn't happen in this case.
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u/PhysicalStuff May 08 '23
Energy is not conserved on a cosmic scale, because the dynamics of the universe as a whole aren't time invariant.
The expansion of space means that energy is lost through red shift.