“It’s ironic: in order to observe the Sun, you need to go kilometers underground.” -Art McDonald
Imagine you finally thought you understood how the Sun worked: how light elements fused into heavier ones, emitting energy in the process. And when you finally completed your calculations, you got nuclear physics results that matched what you observed exactly, energy outputs that fit, and a prediction for the emission of neutrinos.
Yet when you built the detector to see them, you only saw a third of what you anticipated! What would you do? Well, this was a mystery that took nearly 40 years to solve, but it turned out that neutrinos aren’t massless, but have a small, non-zero mass that allows them to flavor change from one type into another: neutrinos oscillate. It was finally confirmed in the 2000s by the Sudbury Neutrino Observatory, and for that, Art McDonald won the 2015 Nobel Prize in physics.