Quantum Cat Tricks

Erwin Schrödinger, the brilliant Austrian physicist who was among the founders of quantum mechanics, once dreamed up a paradoxical thought experiment to highlight one of the stranger aspects of quantum theory. Put a cat in a box, he proposed, along with a vial of poison and a lump of some radioactive element. After a certain period of time, depending on the element used, there’s a fifty-fifty chance that an atom will decay and emit a particle, triggering a device that smashes the vial, releases the poison, and kills the cat. There is, of course, an equal chance that the atom will not decay, thus sparing the cat. But during the entire time, according to quantum mechanics, the atom is simultaneously in the decayed and undecayed states. Not until someone makes a measurement of the atom is it forced into one mode or the other. And the cat? Schrödinger said that one would have to express this situation by having the living and the dead cat mixed, or smeared out (pardon the expression) into equal parts, living and dead.