It is based on the fact that radioactive decay is a statistical process and that unless an observation is attempted a quantum event cannot be said to have occurred or not occurred -- the mathematics which is QM allows the event to remain in a superposition of possible states. Schrodinger proposed locking a cat in an air-tight box with an apparatus containing a radioactive substance, a vial of poison gas and a means of breaking the vial when a radioactive decay occurs such as a hammer released by a Geiger counter. Enough of the radioactive substance is placed in the box so that there is only a 50/50 chance of a single decay in one hour. The box is then closed for 1 hour.
At the end of the hour we can observe that the decay either has or has not occurred by opening the box. The cat will be either dead or alive. But the standard interpretation of QM says that it is meaningless to ask if the decay event occurred before we open the box to make our observation. The decay event remains in a superposition of states until the observation. So also argued Schrodinger must the cat whose life depends on the event. It seems as though the standard interpretation of QM requires the cat to be neither alive nor dead until we open the box!
.Return to Tom Jonard's Quantum Mechanics page.