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From Jon and Christopher Fanning, Wilberfoss, East Riding of Yorkshire, UK

I feel compelled to point out the error in David Longhurst’s simplification of Schrödinger’s cat. The box that the cat is sealed in contains a vial of poison gas that will be broken by the decay of the single radioactive atom in the box, whereupon the cat will be killed instantly. As there is only a single atom, the half life is irrelevant; the atom may decay today, tomorrow or at the end of the universe.

So far, the Christmas presents analogy may appear to hold, but this is where quantum mechanics gets weird. It represents the atom as a wave function that gives probabilities of decay, not an actual time of decay. Until we check and resolve the state of the atom, then it has both decayed and not decayed. It isn’t that we don’t know if the cat is alive or dead, it is that the cat is both alive and dead.

So the Christmas presents analogy collapses unless Grandma included a single radioactive element in the package that, when decaying, would destroy a random gift, but only one of them.