🌀 Hardy's Paradox
Three facts that hold every time rule out one outcome — which happens anyway.
Opens a free Jupyter session on mybinder.org (via QuBins) — starting it can take a few minutes
git clone the repository, create the conda environment from environment.yml, and open Hardys-Paradox.ipynb.Two cars leave a factory; far apart, two inspectors each check a car’s color or its engine. Three facts hold every single time, and by simple logic they rule out two diesel cars. Any classical spec sheets — even random ones — obey that logic: two diesels 0% of the time.
Quantum cars, two entangled qubits, keep all three facts. Yet when both inspectors check the engine, both cars are diesel 1 time in 12 — and up to (5√5 − 11)/2 ≈ 9% with the best measurement angle, the most quantum mechanics allows. The notebook lets you try every spec sheet, builds the quantum factory in Qiskit, shows the faulty step in the logic (“unperformed experiments have no results”) and finds the 9% maximum.