Schrodinger's Cat

[Redistribute the Rep]

I just don't get the idea of the "superposition" in the Schrödinger's cat thing. Is there a superposition from the cat's perspective, or just the human's perspective? And what is the materialist perspective on this?

[blake 3:17]

I was going to hazard a guess but on a bit of research found Einstein disagreed with me. Good luck!

[Anglo-Saxon Philistine]

It is useful to keep the context in which the Schroedinger's cat thought experiment was published in mind. In the thirties, it was widely and incorrectly (see e.g. Bohr's "Physics and Philosophy" and his comments on Jordan) assumed that "the prevailing Copenhagen interpretation" (again, it was incorrect to assume that the positions of Bohr, Heisenberg, Jordan etc. constituted one "Copenhagen interpretation" at that stage) implied that physical attributes of objects were dependent on the act of measurement.

Now, the thought experiment was designed to point out how ridiculous this is - in which it succeeded, however as per my previous comment, it was arguing against a minority view (only Jordan and Wigner really claimed anything similar).

Today the thought experiment is used to point out how unintuitive quantum states that can be interpreted as superpositions of several classical states are.

However, however... for the cat to actually be in a noticeable superposition (and what we view as a "classical" cat-object already contains superpositions, for example the wave functions of its electrons are highly delocalised, which is a good thing as otherwise they wouldn't be able to form covalent bonds and the poor cat would quickly decay into a shower of nuclei and electrons - what is usually meant by the cat being in superposition is being in a state that can be described as a superposition of two or more macroscopic positions or states of the cat-object) it would have to be isolated somehow from decoherence effects that would "wash away" the superposition - which means it would either have to be kept in a vacuum at temperatures near absolute zero (which would result in a cat corpse), or it would have to be subatomic.

Now, let's ignore the physiological challenges posed by this subatomic kitten (I think making this pun officially makes me old), and consider it as it is, in superposition between being alive and dead, for example. What does this mean? Well, first of all, "perspectives" don't really play a part, contrary to what some pop-"sci" works claim. The confusion stems from the early days of quantum theory, when people talked about an "observer" in the same sense as Einstein - to denote hypothetical measurements - and from Von Neumann's "solution" to the problem of what "collapses the wave function" (a term that has wide currency in popular culture but limited in physics) of the measurement instrument (the "abstract ego"). What people forget, though, is that Von Neumann wasn't advancing a philosophical theory but trying to dodge the question - the "abstract ego" was his way of saying "now let me do mathematics". And in any case we don't think like that anymore. Well, except the "objective wavefunction collapse people". Those are odd.

Now, what being in superposition actually means for the subatomic cat is a matter of some debate, and I am going to outline two of the most common answers. First, the "mature" Copenhagen position (based on Bohr's position in the early days and developed by Fok and others) is that the various parts of the superposition represent probabilities for the cat to be in one definite state when it is placed in a situation where it interacts with a large classical physical system. The relative-state position (sometimes known as "many worlds") would be that each part of the superposition is realised at all times - the cat is in all parts of the superposition. Physical measuring instruments are themselves in superpositions correlated with how the cat is superimposed - when I detect the cat, using presumably some sort of cat-scintillator, that scintillator will be in a superposition that records the superimposed state of the cat. When I read the output of the scinitllator, I myself will be in a superposition, each part of the superposition corresponding to the belief that the scintillator detected one of the states that were in the original cat-superposition.

Both interpretations - all interpretations of quantum mechanics that are held by actual scientists in fact - are materialist, and none give any special status to the human observer.