Problems with Schrödinger's cat

Question

I wanted to check my understanding of why exactly the whole "cat in a superposition of alive-and-dead" would never actually happen in the situation described in the Schrödinger's cat thought experiment. These are a few different reasons I had come up with and I want to ask if they are correct:

1. The cat is not in a vacuum, its state - alive or dead - is constantly being measured by the air around it

2. For that matter, the cat is made up of billions of particles - it is constantly measuring its own state itself.

3. "Alive" and "Dead" are vague and involve too many things to describe - they are not simple, perfectly discernable and definable states the same way "spin up" and "spin down" or "decayed" or "not decayed" are.

4. The crux of the thought experiment is that the poison that kills the cat is only released when a specific isolated atom decays - since the atom is in a superposition of decayed and not decayed, "before measurement" (opening the box) the cat must also be in a superposition of alive and dead. But for the poison to only be released when the atom decays there has to be some detector checking whether or not it has decayed so it can activate the poison: it is measuring the state of the atom. So wouldn't the "decayed or not decayed" wavefunction collapse into either just decayed or just not decayed right there and so never involve the cat?

Answer 1

I'll respond to your points individually.

1. The thought experiment assumes the box is a closed system, not interacting with the air molecules, photons, etc. Obviously this is a highly unrealistic assumption (and it's why we can't actually carry out the experiment in real life right now), but it is a thought experiment after all.

2. Doesn't matter. We're concerned with the external observer's measurements, not the cat's measurements.

3. Yes there are many ways to be alive and many ways to be dead. But this doesn't matter. For the purposes of the thought experiment, the conventional and messy ways we measure life or death (ceasing of biological activity and metabolism, starting of tissue decay, etc.) suffice.

4. For the cat, yes, but not for the external observer.

We have actually kind of built systems similar to the Schrodinger's cat thought experiment. They're called quantum computers, or more generally any kind of quantum system that involves isolation from the environment, some internal process, and then measurement. It's just that for the time being, we can only do this with very small systems, or ultracold systems, so they don't involve cats. But the general idea is the same, and the results are the same.

As for Schrödinger's motivation. It's true that the experiment was designed as a way to highlight what he viewed to be an absurdity. However, he wasn't trying to show the weirdness of entanglement, but rather the Copenhagen interpretation which assumes the wavefunction collapses upon opening the box. An alternative to the Copenhagen interpretation, for example, is that the observer themselves enters a superposition of seeing a live cat and seeing a dead cat. However, discussions of interpretations of quantum mechanics is a broad topic.

Answer 2

The thought experiment was designed to illustrate the absurdity of certain interpretations of quantum mechanics, especially those that allocated a special importance to the roles of measurements and observers. Particles interact with each other whether or not their interactions are measured or observed. When the property of some particle or collection of them is 'measured', the particles under observation interact with the particles that comprise the measuring device- there is nothing special about the fact that it is a measurement, and it does not require an observer to be present. Consider the path left by an electron in a bubble chamber- does anyone imagine that the path only exists if it is observed?

Three of your attempts to resolve the paradox include the word 'measurement', so in that sense you are cultivating exactly the absurd assumption that Schrödinger was seeking to highlight when he invented the thought experiment.

There is still no widely agreed explanation of how classical behaviour of macroscopic objects arises from the quantum behaviour of their constituent particles. All we can say with certainty is that it does- cats are never both alive and dead.

Answer 3

Schrodinger's Folly

You have correctly identified the fact that the awful Schrodinger's Cat "thought experiment" is in fact a useless and confusing mess. I personally think of it as Schrodinger's Folly.

The entire "experiment" can be dealt with completely using classical physics and the notion of applying quantum theory in such a way to macroscopic objects is deeply flawed.

About all you can really come away with in such an experiment if, God forbid, you were crazy enough to do it, would be the stunning revelation that you won't know if the cat is alive or dead until you open the box and check. No need for quantum theory there.

Schrodinger was a very clever bloke, but very clever blokes do make mistakes and this is one of them. Whether he actually thought this would help explain superposition is unknown to me, but it has confused multiple generations of students and really we ought to stop teaching this garbage. I cannot recall it ever making the concept of superposition clearer to any student.

Your thinking is basically correct.