What Neutrinos Reveal

Oct 12, 2015

By Lawrence M. Krauss

This week the 2015 Nobel Prize in Physics was awarded jointly to Takaaki Kajita and Arthur B. McDonald for their discovery that elementary particles called neutrinos have mass. This is, remarkably, the fourth Nobel Prize associated with the experimental measurement of neutrinos. One might wonder why we should care so much about these ghostly particles, which barely interact with normal matter.

Even though the existence of neutrinos was predicted in 1930, by Wolfgang Pauli, none were experimentally observed until 1956. That’s because neutrinos almost always pass through matter without stopping. Every second of every day, more than six trillion neutrinos stream through your body, coming directly from the fiery core of the sun—but most of them go right through our bodies, and the Earth, without interacting with the particles out of which those objects are made. In fact, on average, those neutrinos would be able to traverse more than one thousand light-years of lead before interacting with it even once.

The very fact that we can detect these ephemeral particles is a testament to human ingenuity. Because the rules of quantum mechanics are probabilistic, we know that, even though almost all neutrinos will pass right through the Earth, a few will interact with it. A big enough detector can observe such an interaction. The first detector of neutrinos from the sun was built in the nineteen-sixties, deep within a mine in South Dakota. An area of the mine was filled with a hundred thousand gallons of cleaning fluid. On average, one neutrino each day would interact with an atom of chlorine in the fluid, turning it into an atom of argon. Almost unfathomably, the physicist in charge of the detector, Raymond Davis, Jr., figured out how to detect these few atoms of argon, and, four decades later, in 2002, he was awarded the Nobel Prize in Physics for this amazing technical feat.


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2 comments on “What Neutrinos Reveal

  • I didn’t notice who’d written that article originally but by the time I’d got to the end I was thinking this is way better written than the usual incomprehensible and error filled output of the average “science” journalist. Then I scrolled back up. Ha! No wonder. Fascinating stuff Lawrence.



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  • Ah, neutrinos; cheeky little buggers aren’t they.

    It’s known what electrons, neutrons and protons get up to, but this little chap keeps us guessing.

    I think it’s my favorite particle; not that I know diddly-squat of course.

    Anyway, if anyone can enlighten yours truly it’s Lawrence Krauss; he’s among the best expositors of science we can enjoy.



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