More Science See Inside Astrophysicists Turn to the Skies to Measure the Mass of the Neutrino How an almost massless particle has shaped the large-scale structure of the universe By Sudeep Das and Tristan L. Smith George Retseck 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 is only a preview. Get the rest of this article now! Select an option below: Buy Digital Issue Customer Sign In *You must have purchased this issue or have a qualifying subscription to access this content It has been identified that the institution you are trying to access this article from has institutional site license access to Scientific American on nature.com. Click here to access this article in its entirety through site license access. ADVERTISEMENT Scientific American is a trademark of Scientific American, Inc., used with permission © 2013 Scientific American, a Division of Nature America, Inc. All Rights Reserved.