Curiosity Killed the Cat

On observation, uncertainty, and the door you were asked not to open.

You were asked not to open the door, and you opened it anyway. I would have done the same. This page is an attempt to explain why.

Schrödinger devised his box in 1935 not to describe the world but to embarrass a particular reading of it. If the Copenhagen account were taken literally, he argued, a cat sealed beside a decaying atom would have to be regarded as neither alive nor dead until someone looked. He meant the image as a reductio ad absurdum. Physics, with a sense of humor he did not anticipate, adopted it as a mascot.

What keeps the thought experiment alive is less the physics than the question beneath it: does the world settle into a definite shape on its own, or does it, in some sense, wait for us?

Philosophers were asking this long before quantum mechanics gave the question a laboratory. Berkeley compressed it into three words, esse est percipi: to be is to be perceived. Kant was more cautious. He distinguished between things as they appear to us and things as they are in themselves, and he insisted that the second category would remain permanently closed. On Kant's account, we never truly open the box at all. We only ever see the cat as a cat appears to minds like ours.

Modern physics has rehearsed the same disagreement in its own idiom. Decoherence suggests that the box settles its own affairs long before anyone looks, because the environment does the observing for us. The many-worlds interpretation holds that nothing is ever settled, and that every possibility is realized somewhere. Others maintain that the wave function is not a picture of reality at all, only a ledger of what we know; on that view, opening the box changes nothing about the cat and everything about us. Ninety years on, the question remains open. I find that more reassuring than troubling.

The proverb is older than the physics. Its earliest recorded form, from the late sixteenth century, was "care killed the cat," where care meant worry rather than inquisitiveness. It was anxiety, not curiosity, that was originally thought to be fatal. The drift in meaning says something about us: at some point we began to suspect that wanting to know was the more dangerous habit. The consoling second line, "satisfaction brought it back," arrived later still, as though someone felt the original verdict had been unfair.

Our oldest stories share that suspicion. Pandora lifts a lid. Eve reaches for the fruit. Orpheus turns around. Each is usually read as a warning that knowledge exacts a price. Read more closely, however, they are less warnings against curiosity than acknowledgments that curiosity is irreversible. One cannot unsee a thing. A box, once opened, stays opened.

That irreversibility is precisely what makes the closed box so comfortable. While it remains shut, every outcome is still available. The unsent message is still well received; the unattempted venture is still a success; the unasked question still has the answer one hopes for. Keats admired what he called negative capability, the capacity to remain "in uncertainties, mysteries, doubts" without reaching irritably after fact. It is a genuine virtue. It can also become a place to hide.

Kierkegaard described anxiety as "the dizziness of freedom," the vertigo we feel when we look down at everything that remains possible. Superposition is not a bad description of that state, and observation is what ends it. Something is lost when the box is opened: all the versions of events that did not happen. Something is gained as well: the one that did.

So the cat on the door is dead, and you are responsible. I do not hold it against you. The alternative was to stand in the corridor indefinitely, preserving a possibility at the cost of an answer.

I would rather know. Most days, I suspect that is the whole point.

Curiosity killed the cat. Satisfaction, as the saying goes, brought it back.