The cosmological constant refers to a uniform energy density that presumably could explain the accelerated expansion of the Universe. However, a straightforward calculation of this constant gives an impossibly large value. A new approach to this problem, detailed in Physical Review Letters, involves a slight reformulation of general relativity, in which the cosmological constant ends up being a historical average of the matter energy density in the Universe. Besides predicting a small cosmological constant, the theory foresees an eventual collapse of our Universe in a big crunch.

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