Proton size measured with a better ruler ➥
In atoms, electrons normally orbit the nucleus of an atom. The nucleus can contain a mixture of protons and neutrons in most atoms although hydrogen just has a single proton, which makes it the simplest atom to study: there’s just one electron orbiting one proton.
One day a bunch of scientists wondered what would happen if they evicted the electron from a hydrogen atom and instead replaced it with a muon. A muon is part of the same family of particles as the electron — a family collectively called leptons — and it has the same charge and spin, but it’s 207 times heavier and doesn't exist for very long.
Alas, it all came down to a faulty ruler.
They thought the standard proton (with an electron orbiting it) was 0.876 femtometers and measured the muonic proton to be 0.84 femtometers.
But some clever-dick has come along and measured the standard proton with a better ruler and pegs it at 0.833 femtometers +/- 0.01, which removes the discrepancy found with the muonic proton.
I feel sorry for all those scientists who expended much brain-power coming up with new theories, although I did giggle a bit.