Neutrinos are still the most mysterious particle we know of

"But as we continued to investigate the nature of reality through many different avenues: through laboratory experiments with radioactive materials, through cosmic ray experiments done first with hot air balloons and later, from space itself, through underground, well-shielded experiments surrounded with exquisite detectors, through high-energy particle physics experiments done with colliders, and through a wide array of astrophysical observatories,"

"The zoo of standard model particles and the four fundamental forces, plus the discoveries of dark matter and dark energy, all came into focus in the late 20th century, with many more details uncovered through the first quarter of the 21st. Through it all, however, the humble neutrino remains the most mysterious of all the known particles, and the only known particle with a chance to solve the three biggest mysteries in all the Universe. Here's how."

In the 21st century many discoveries revealed an expanding Universe, the Big Bang, quantum fields, and substructure of protons (quarks and gluons). Major unresolved problems include dark matter, dark energy, and the matter–antimatter asymmetry. Multiple experimental paths—laboratory radioactive experiments, cosmic ray studies (balloons and space), underground shielded detectors, high-energy colliders, and astrophysical observatories—have together refined the picture of fundamental particles and forces. The Standard Model particle zoo and four forces became clear by the late 20th century, with dark components emerging. The neutrino remains the most mysterious known particle and stands as the only known particle with potential to resolve the three biggest cosmological puzzles.

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