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In the thirties, Pauli realized: without tiny ghost-like particles, the energy of stars doesn't add up. Thus neutrinos were born — intangible wanderers that permeate everything. They must have mass, otherwise they can't transform into one another, but observations of the expansion of the Universe showed their total weight was nearly zero. Meanwhile, laboratory experiments insisted on a larger number.

A new study compares neutrinos to potatoes in a leaky sack. If half the tubers go missing along the way, weighing the remainder will leave you short. It's the same with cosmology: if neutrinos decay into completely invisible particles over a period of ten million to a billion years, today we measure only their surviving fraction. Fresh data from the DESI survey and the cosmic microwave background from the Big Bang allow a mass up to four times higher than previous estimates — enough to settle the dispute.

An unexpected twist: decay into familiar neutrino types yields almost no benefit. The sack still seems full. So nature is hiding something beyond the Standard Model inside it — particles we don't yet know about. That's where the search should go.