A swarm of fireflies rarely collides, yet they synchronously change color by exchanging signals. This is how neutrinos behave in dense streams from collapsing stars: they collectively transform from one type to another, even though individually they interact extremely weakly. Bardeen, Cooper, and Schrieffer once showed that electrons in a metal can form pairs and flow without resistance: this is superconductivity. Could neutrinos, following similar laws, create such stable duets?

In the new work, physicists proved that under ordinary weak interactions, neutrino pairs do not form. This requires a sharp cutoff in the particle momentum distribution, like electrons at the Fermi surface in a metal (the level above which all states are empty). It's like a tram where all seats are taken and standing places are empty, with an absolutely clear boundary between them. In a real neutrino cloud, such a boundary does not exist: particles fill states smoothly, without jumps. But if the energy is artificially broken into discrete levels, as in computer simulations, false cutoffs appear, and the model predicts pairing. This is like replacing a hill with steps: you can trip on each step, although the real slope is smooth.

The authors warn: discretizing the spectrum in numerical calculations can deceive, giving rise to non-existent neutrino superfluidity. In the continuous limit, as in real physics, pair instabilities disappear. Thus nature avoids a 'neutrino wedding'—at least within the Standard Model.