TITLE: If empty space has energy, and space is expanding, is this energy equally distributed as space expands?
QUESTION [4 upvotes]: The cosmological constant (dark energy) is often described in terms of empty space having a non 0 energy value and this energy being the source of the accelerated expansion of the universe. If space is expanding, what does this imply for energy conservation? Is this energy conserved by being more thinly distributed as space expands? Does this question make any sense or am I just crazy?

REPLY [0 votes]: Dark energy due to a cosmological constant does not get diluted by metric expansion of space. However, this does not violate energy conservation as the increase in energy will be cancelled by gravitational potential energy. The problem with general relativity is (some would say arguably) not energy conservation, but energy localization:
In a rotating frame of reference, energy conservation only holds if you include the contribution of the centrifugal potential. Analogously, in general relativity, energy conservation only holds if you include the contribution of the gravitational potential. In both cases, you cannot associate a meaningful energy density with these contributions. General relativity just comes with the additional complication that you cannot transform away gravitational energy by going to a globally inertial frame of reference.
Note that there are ways to separate gravity from inertia if you go beyond general relativity (eg the teleparallel approach or bimetric theories) and get a gravitational energy density this way, but energy conservation will only hold if you include inertial effects.
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