Uncertainty

Quantum mechanics -- the arcane branch of physics that governs the atomic and subatomic realms -- means something. It must: It led us to transistors, solar cells, quantum cryptography, and lots of other wondrous stuff . But what it means has been a matter of debate for almost a century.

My ages-ago QM classes were taught by professors of the "shut up and calculate" school. As in: Don't ask what it all means. Just know that it works. That, alas, never worked for me.

It's not like I have the answer, but I do read about QM from time to time. I've just finished an outstanding book on the subject. It's Uncertainty: Einstein, Heisenberg, Bohr, and the Struggle for the Soul of Science, written by physicist David Lindley.

To take just one thing the book makes wonderfully clear, it is why such giants of modern physics would fight over an increasingly successfully mathematical description: its implications. To embrace the math at face value was to accept a change from determinacy (that whatever scientists observe follows from a knowable -- if not necessarily known -- cause) to probability (that events at the atomic level have a chance of happening, but when they will, and why they will, are unknowable). As in: Why does a particular electron change energy states now? Why not, say, a second from now? Or equivalently: Why does a particular uranium atom decay now, and not in a thousand years?

Without determinacy, we lose -- or at the least, we redefine -- cause and effect. That's a large implication normally glossed over by abstruse mathematics -- and certainly glossed over when QM is taught by the "shut up and calculate" method.

Highly recommended.