I initially thought that dark energy must in some way violate conservation of ma
ID: 1378547 • Letter: I
Question
I initially thought that dark energy must in some way violate conservation of mass and energy since the component of the energy density of space that comes from dark energy is constant, and space is expanding. Therefore, as space expands the energy in the universe that comes from dark energy would increase. I presumed the source of this energy was not coming from the conversion of other types of energy to dark energy, so it must violate conservation.
I decided to Google this and came upon this article:
http://scienceblogs.com/startswithabang/2011/12/02/dark-energy-accelerated-expans/
It says that dark energy does NOT violate conservation and quotes Carroll, Press, and Turner (1992):
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Explanation / Answer
The total energy in the space does increase, precisely because of the reason you mention. Energy is not expected to be conserved, because the metric is not invariant under time translations.
What does hold is the first law of thermodynamics, dU=?PdV+?. Since the pressure in this system is negative, this is one way of seeing the origin of the extra energy as the space grows.