Does dark energy change over time? An alternative model of the as yet undetected entity that is thought to be accelerating the universe's expansion could explain some puzzling observations of galaxy clusters. But it will have to jump many more hurdles to compete with the simplest and so far most successful model of the elusive entity. That model, called the cosmological constant, holds that there is a certain amount of repulsive energy in every cubic centimetre of space, and that amount stays the same over time. As the universe expands, more space exists, and so the expansion accelerates.
Now Edoardo Carlesi of the Autonomous University in Madrid, Spain, and his colleagues have simulated a universe where the amount of repulsive energy per unit of volume changes with time."
News coverage: http://www.newscientist.com/article/dn21315-variable-dark-energy-could-explain-old-galaxy-clusters.html
Journal Article: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2966.2011.19660.x/full
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