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The Sterile Neutrino Probably Doesn’t Exist
And other news from space and physics this week
Of the dozens of subatomic particles, one stands out as especially mysterious. The neutrino — a particle so small and elusive that we detect far less than one in every trillion — has long puzzled physicists with its strange and volatile behaviour. There is, indeed, a fair bet that new physics — when it comes — will somehow involve these odd particles.
Part of the problem lies in how neutrinos pay little heed to the atoms that make up our everyday world. They interact only through the aptly named weak nuclear force — an interaction that can only occur when a neutrino strikes the core of an atom. Since atoms are mostly empty space — the core is a tiny fraction of the overall thing — neutrinos are free to travel through the entire planet — the entire galaxy, indeed — with little trouble.
There may, however, be an even more ghostly form of neutrinos. In theory, some neutrinos — known as sterile neutrinos — should be able to ignore the weak force too, rending them all but invisible to our world. True, they should still exert a gravitational pull — and might, therefore, explain dark matter — but gravity is weak, and neutrinos are very small. No detector on Earth could ever hope to pick up that signal.
