The Ultimate Quantum Reality Questionnaire

(Which interpretation of quantum physics are you?)

In everyday physics, we track solid things — baseballs, planets, coffee cups — by giving their positions and speeds. Down in the quantum realm, that picture breaks — an electron, photon, or atom doesn’t have one sharp location or momentum until we measure it. Instead, the system is described by a mathematical object called the wave function, written ∣ψ⟩ (“psi”).

Think of ∣ψ⟩ as a recipe for possibilities. At each point in space, it provides a complex number whose squared magnitude tells us how likely we are to find the system there when we look.

Because those numbers can be positive, negative, or even purely imaginary, different parts of the recipe can add or cancel like ripples on water. That’s why electrons form interference patterns and why a quantum coin can be described with states like “heads + tails” until observed.

When we do measure, we always see one definite outcome, and the recipe updates so future predictions reflect that fact. What, if anything, “really” exists between preparations and measurements — and what exactly the update means — is the deep puzzle which an “interpretation of quantum physics” is meant to resolve.