Tails of Schrödinger’s Cat

Abstract

IN HIS FAMOUS THOUGHT EXPERIMENT, Schrödinger (1935) imagined a cat that measures the value of a quantum mechanical observable with its life. Adapted to the measurement of x-spin of an electron, the experiment is this. If at the start of the measurement interaction the state of the cat is |R〉 (the ready to measure state), and the state of the electron is |↑〉 (the electron’s x-spin is up), then at the conclusion of the measurement the state of the cat and electron is |↑〉|Alive〉. And if at the start of the measurement interaction the state of the cat is |R〉 and the state of the electron is |↓〉 (the x-spin of the electron is down) then at the conclusion of the measurement the state of the cat and electron is |↓〉|Dead〉 The cat records the x-spin of the electron in its state of aliveness.

When bodies are borne downwards sheer through the void by their own weights, at quite uncertain times and uncertain spots they push themselves a little from their course: you just and only just can call it a change of inclination. If they were not used to swerve, they would all fall down, like drops of rain, through the deep void, and no clashing would have been begotten nor blow produced among the first-beginnings: thus nature would never have produced aught.

Lucretius, De Rerum Natura