The state of a quantum thing, before you look
A quantum particle isn't just probabilistically located — it's described by a wave function, a mathematical object that contains all the probabilities at once. The wave function is real in the sense that it evolves predictably according to the Schrödinger equation. It tells you the probability of finding the particle in any state if you were to measure.
Then you measure. Something strange happens. The wave function collapses to one specific state. Before measurement, the particle was "smeared" across many possible positions/momenta/spins. After measurement, it's at one. The collapse is sudden, irreversible, and (in standard quantum mechanics) probabilistically determined. You can predict the odds; you can't predict the specific outcome.
Schrödinger's cat — a teaching prank that worked too well
Schrödinger proposed in 1935 a thought experiment to highlight how weird quantum mechanics gets if you take it literally. Put a cat in a sealed box with a quantum-triggered poison vial. The poison is released only if a radioactive atom decays — a quantum event with 50/50 probability over a fixed time. According to a literal reading of the wave function, before you open the box, the cat is in a superposition of alive and dead. Open the box, the wave function collapses, the cat is one or the other.
Schrödinger meant this as a reductio — this is silly, so the literal reading must be wrong. But the experiment, in spirit, has been done with smaller objects (atoms, then molecules, then small biological systems), and the superposition is real up to surprisingly large scales. The cat itself is too big and too noisy to maintain superposition for long, but the principle is genuine.
What "observation" means here
A common confusion: does observation require a conscious observer? No. "Measurement" in quantum mechanics is any interaction with a sufficiently large system that the result gets recorded. An electron hitting a photographic plate counts. A photon scattering off an atom counts. No human needs to look. Once the quantum system entangles with a large enough environment, the superposition decoheres into one outcome.
This is why the world doesn't look quantum at our scale — we're too big and too entangled with our environment to maintain quantum superposition. The wave function is technically describing us too, but decoherence collapses our state continuously, faster than we can notice.
The connection to the everyday
Think of every choice as a kind of measurement. Before you decide, multiple futures are weighted by their amplitudes (probabilities, roughly speaking). When you decide, one becomes actual. The other amplitudes don't disappear in the literal quantum sense — for that you'd need many-worlds — but in your local lived experience, one branch becomes "what happened" and the others fade. The structure of choice and the structure of measurement share a shape. The next two lessons make this concrete with Feynman's path integral and a D20 rolled across a tabletop.