For neutrinos created recently, the ranges they can exist in are very, very small. But over the roughly 13.7-billion-year lifetime of the cosmos, "relic" neutrinos have been stretched out by the expansion of the universe, enlarging the range in which each neutrino can exist.

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Cosmologists don't usually take their lead from the animal kingdom. But a model that postulates the existence of a 'chameleon' particle — which would change its mass depending on its surroundings — is gaining attention. More Articles

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Whatever dark energy is, explanations for it have less wiggle room following a Hubble Space Telescope observation that has refined the measurement of the universe's present expansion rate to a precision where the error is smaller than five percent. More Articles

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