Neutrinos have about as little influence as a particle can have. They have essentially no heft, no electric charge, and no “color” charge. As a result, the neutrino has no connection with most of nature’s forces; it can slip through whole planets and stars without striking a single atom.
But neutrinos have proven more than capable of bending the life path of a scientist.
In the late 1990s, when physicists unexpectedly discovered that neutrinos have mass, Thierry Lasserre abandoned cosmology to go all in on the particles. “It was so exciting I just couldn’t resist,” said Lasserre (opens a new tab), now a physicist at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. And Mark Ross-Lonergan was planning to be a meteorologist until a chance encounter with particle physics in 2010 inspired him to switch fields. Lassere and Ross-Lonergan, along with thousands of others, have devoted their careers to investigating this tiny and almost perfectly inert speck.
For more than a decade, their investigations seemed to be closing in on a breakthrough. Experiments reported strange acts of neutrinos appearing and disappearing. These results, along with neutrinos’ mysterious mass, all pointed to a single potential explanation: A particular “sterile” type of neutrino, of a particular mass, seemed to lurk undiscovered behind the scenes.
Researchers spent years running increasingly sophisticated experiments to pin down the interloper. However, in the face of an increasing number of null results, most notably in studies published in late 2025, most physicists now agree that this sterile neutrino doesn’t exist. “This is, in my opinion, the death knell for sterile neutrinos,” said Ross-Lonergan (opens a new tab), a physicist at Columbia University and co-author of one of the latest studies.
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