"A CAT is penned up in a steel chamber, along with the
following diabolical device (which must be secured against direct interference by the
cat): in a Geiger counter there is a tiny bit of
radioactive substance, so small that perhaps in the course of one hour one of the atoms
decays, but also, with equal probability, perhaps none; if it happens, the counter tube
discharges and through a relay releases a hammer which shatters a small flask of
hydrocyanic acid.
If one has left this entire system to itself for an hour, one would say that the cat still
lives if meanwhile no atom has decayed. The first atomic decay would have poisoned it. The
Psi function for the entire system would express this by having in it the living and the
dead cat (pardon the expression) mixed or smeared out in equal parts."
