“Schrödinger’s Cat” memes have got to be one of the most pervasive genres of science memes out there. There are so many examples of this format but they all involve the same thing: there’s a cat in a box and it’s dead and it’s alive (or we aren’t sure which).
A lot of them also involve the cats really disliking Schrödinger or escaping the box, like this one.
But where did this all come from? How did Erwin Schrödinger become associated with feline hatred and unknowable probabilities of cat murder? To figure that out, we are going to have to talk about some early 1900’s physics and delve into an argument between physics giants Niels Bohr and Albert Einstein, which Schrödinger threw his hat into as well.
In the early 20th century, physics was becoming very complicated. Classical physics, like Newton’s laws of motion and the contemporary understanding of light and electricity, were proving insufficient to explain the behavior of atomic and subatomic particles and phenomenons that were starting to be explored in great detail. Instead, thinkers like Einstein and Bohr were beginning to talk about alternative models, like quantum mechanics, to explain what was going on at a subatomic level. Quantum mechanics, despite being a good model for these sorts of things, was a confusing mess for a lot of people, including physicists at the time. Between 1925 and 1927, Bohr and his student Werner Heisenburg developed guidelines and principles for understanding and applying quantum mechanics so that it could be clearly understood by the wider physics community. These came to be known as the “Copenhagen interpretation” of quantum mechanics since they were developed at the Bohr Institute at Copenhagen University (1).
One of the things that came out of this interpretation was the idea of “superposition” where a system exists in all possible states at the same time until it is observed. Upon observation the system collapses into just one possible state (2). This was all well and good for subatomic particles and helped to explain a lot of weirdness that happens at that level, but it had surprising implications on the nature of reality. If atoms (the basis of matter) exist in all possible states until observed, does visible matter do this as well? Is there indeed only one physical reality or do we all create our own personal one when observing and measuring whatever we are looking at?
Einstein hated this implication and published an article (now called the EPR article for its authors Einstein, Boris Podolsky and Nathan Rosen) attempting to show through thought experiment and arguments that the Copenhagen interpretation was incomplete and this whole business of superposition didn’t make any sense (3). After the article was published, Einstein and Schrödinger exchanged letters about it, both agreeing that the Copenhagen interpretation was ridiculous.
To illustrate that point, Schrödinger proposed his now infamous “cat in a box” thought experiment (4). He imagined a cat in a sealed metal box containing a vial of poison, a radioactive element, and a Geiger counter. If the Geiger counter detected radioactive decay, it would trigger a mechanism (5) and smash the vial of poison, killing the cat. Otherwise, nothing would happen. According to the Copenhagen interpretation and superposition, the radioactive element would be in a state of both decaying and not decaying (since nothing was observing it), meaning the Geiger counter should both detect and not detect decay and therefore break and not break the vial. This leads to an absurd situation where the cat dies and also doesn’t. This state of being dead but also not dead persists until someone opens the box to look and the superposition collapses one way or the other.
He argued that such a situation was incredibly foolish and didn’t make any sense, therefore the Copenhagen interpretation must be flawed. It was his way of illustrating the paradox between understanding atoms as a superposition of all possible states and understanding cats (or other collections of atoms) as having one consistent, observable state. It also posed the questions of how long superposition lasts and what can collapse it.
Somehow, that thought experiment and its associated argument morphed into an inability to understand cats in boxes, cats having some sort of ancestral hatred of Schrödinger, and all sorts of other unrelated themes. It is especially bizarre considering that the thought experiment was barely mentioned by the physics community during his lifetime (6). It only became know when physicist Eugene Wigner wrote about it (and his own continuation of the thought experiment) in 1963, which gave it enough attention to be referenced in a book by philosopher Hilary Putnam. The review of that book in Scientific American launched it into the public eye in 1965, thirty years after Schrödinger had proposed it. From there, it apparently sparked a lot of ideas in the science fiction community. Perhaps this roundabout trip into the public imagination explains why everyone knows about the cat and the box, but not the reason it exists in the first place.
2: This is generally what people mean when they say “collapse the wave function” as quantum mechanics views systems in terms of mathematical waves.
3: Einstein, A.; Podolsky, B.; Rosen, N. (15 May 1935). “Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?”. Physical Review. 47 (10): 777–780.
5: He specifies that the mechanism should be “must be secured against direct interference by the cat” because he didn’t trust an imaginary cat not to screw up his thought experiment.
6: PBS NOVA. “Schrödinger’s Cat Lives On (Or Not) at the Age of 80” https://www.pbs.org/wgbh/nova/article/schrodingers-cat-lives-on-or-not-at-the-age-of-80/