Erwin Schrödinger introduced his famous “Schrödinger’s cat” thought experiment to illustrate the apparent absurdity of one of the key implications of quantum theory. Namely, its implication that something could simultaneously exist and also not exist. Basically, down at the quantum level, a particle can remain in a quasi-state of existence, both existing and also not existing. The particle stays this way until it is observed by an outside system. At that moment it instantly “snaps” to one of the two states.
Schrödinger’s complaint was that this can lead to absurd outcomes, since you could easily tie a macroscopic object – say a house cat – to the fate of a single quantum particle (recipe: place the cat in a sealed box with a geiger counter; when the counter detects a single random quantum event, kill the cat). Quantum theory states that the cat is literally both alive and dead at the same time. Until, that is, somebody opens the box, at which point the cat instantly snaps to one of its two quasi-states: It becomes either a fully alive cat or a fully dead cat.
Yes, this sounds absurd, and people not familiar with quantum theory often respond by saying that we’re just describing the probability that the cat is alive or dead at any given moment. In fact, they say, the cat must always be completely alive or completely dead. But that turns out not to be the case. Strange as it seems, it turns out that Schrödinger’s objection was wrong – quantum theory’s prediction has been experimentally verified to be true. If you run various experiments with actual particles, the “cat is either completely alive or dead” assumption gives you the wrong answer. If you assume this crazy sounding “quasi-state” of an object both existing and not existing at the same time, the results you get match the experimental data perfectly.
Joel and Ethan Coen’s recent film “A Serious Man” is actually a treatise on this very subject, in disguised form. It starts with a reference to Schrödinger’s famous thought experiment, and then proceeds to show – in a very elegant fashion – that even in the domain of human actions, an object can be in a quasi-state of simultaneously both existing and not existing, up until the moment an observer forces the question of whether the object exists or not. At which point the object instantly snaps to one of these two states, as though it had been in that single state all the time.
I won’t spoil the movie for you by saying any more (many have not seen it yet – and I suspect it has not yet been released in various parts of Europe), but I wanted to pay tribute to a moment of cinematic genius: A moral fable that transposes one of the most difficult concepts of quantum theory into human terms, with perfect clarity.
When you see the film, see if you can spot what the “quasi-existing” object is.