Person/Erwin Schrödinger/Cat
Schrödinger's Cat
Overview
- A thought experiment Person/Erwin Schrödinger published in 1935 to show how strange the Copenhagen interpretation of quantum mechanics becomes when a Superposition reaches an everyday object.
Context
- Schrödinger worked the idea out in letters with Person/Albert Einstein after the 1935 EPR paper. Einstein had proposed a keg of gunpowder that is both exploded and unexploded; Schrödinger replaced it with a cat.
- It appears in "Die gegenwärtige Situation in der Quantenmechanik" ("The Present Situation in Quantum Mechanics"), Naturwissenschaften, 1935.
Mechanism
- A sealed box holds a cat, a flask of hydrocyanic acid, a small radioactive sample and a Geiger counter wired to a hammer.
- If an atom decays within the hour, the counter trips the hammer, the flask breaks and the cat dies. If none decays, the cat lives.
- Quantum mechanics describes the atom as a superposition of decayed and undecayed. Carried through the apparatus, the whole box, cat included, ends up in a superposition of dead and alive until someone opens it.
Interpretations
- Copenhagen — opening the box is a measurement that collapses the superposition into one outcome.
- Many-worlds — both outcomes happen, in branches of reality that no longer interact.
- Decoherence — interaction with the environment resolves the superposition into classical outcomes long before anyone looks, which is why large objects never show superposition.
Misconceptions
- Schrödinger meant the cat as a reductio ad absurdum. He called the dead-and-alive cat an absurdity of the existing view, and never offered it as a picture of how the world works.
Sources