What Schrödinger's cat actually meant

Schrödinger invented his famous cat to make quantum mechanics look ridiculous. He was on the side of the cat.

In 1935, Erwin Schrödinger proposed sealing a cat in a box with a vial of poison wired to a single radioactive atom. If the atom decayed, the vial shattered. According to the prevailing Copenhagen interpretation of quantum physics, the atom existed in a superposition — both decayed and undecayed — until someone looked. Followed to its logical end, that meant the cat was simultaneously alive and dead until the box was opened.

The thought experiment was a reductio ad absurdum. Schrödinger wanted to expose what he saw as a flaw: it was one thing to talk about a particle in two states at once, quite another to talk about a mammal. He expected his colleagues to laugh and revise the theory.

They did not. Quantum superposition has since been demonstrated in molecules of thousands of atoms, and physicists still argue about where the line between the quantum and the everyday is drawn. The cat was meant to be a joke. It became the most famous unresolved question in modern physics.