AMA | October 2024

2931.578 - 2954.673 Sean Carroll

It can't be a probability, right? So you might already guess that's something you should square to get a non-negative, non-imaginary number. And indeed, it turns out there's a theorem, Gleason's theorem, that, you know, among other things, it reminds you that The set of numbers given by the wave function squared for different measurement outcomes is a set of numbers that are between 0 and 1.