WARPED: Cosmic microwave background radiation collected by telescopes on the earth and in space has been subtly distorted by dark matter. By tracing the distortions, physicists can chart the dark matter's structure, which has been shaped by neutrinos and can, in turn, place strict limits on neutrino mass. Image: George Retseck
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Measuring the minuscule mass of neutrinos has so far proved impossible—and not for lack of trying. Numerous laboratory experiments over the past few decades have succeeded only in placing loose limits on the three neutrino masses.
We have very compelling reasons to expect that the best way to measure the mass of these tiny particles is, surprisingly, to look for their influence at the largest scales of the universe. For although neutrinos are virtually massless and nearly invisible, their sheer numbers—some 1089 in the universe—make them very consequential players in the cosmos.
This article was originally published with the title The Neutrino's Secrets, Written on the Sky.