DARK energy, the mysterious stuff invoked to explain why the expansion of the universe is accelerating, could have a simple explanation. The energy may be coming from neutrinos that were created in copious quantities just after the big bang. The leading candidate for dark energy is Einstein’s “cosmological constant”, which proposes that the vacuum of space has an inherent energy that counters gravity. But if you calculate the density of this energy using quantum theory, it works out at nearly 120 orders of magnitude greater than what would fit with cosmological observations. So physicists have proposed ever more exotic explanations for dark energy that require, for instance, the existence of extra dimensions.
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