To illustrate the concept, the Gemara turns to another, related area of law: the ritual impurity of corpses. “If there is a corpse in a house that has many entrances,” the law holds, “all the entrances are ritually impure.” This is because the corpse might pass through any of the entrances on its way out of the house, and so they are all considered potentially tamei. Once the corpse is actually taken out, however, the tumah only affects the actual entrance used, and the others go back to being ritually pure. Indeed, it’s enough simply to mentally designate one of the entrances as the one that will be used to transport the corpse, in order to remove impurity from all the others. (I’m reminded, as I have been before in the Talmud, of Schrodinger’s Cat: As in quantum mechanics, potentialities don’t turn into actualities until they are observed.)I noted that column here and another column that takes up the same theme here. The analogy with quantum indeterminacy is very imperfect, but is entertaining. There's lots more going on in this week's column, so read it all.
Earlier Daf Yomi columns are noted here and links.