Schrodinger's Cat Was a Thought Experiment Against Quantum Theory

In 1935, a debate was raging at the heart of physics. The "Copenhagen interpretation," championed by Niels Bohr and Werner Heisenberg, suggested that a particle exists in all its possible states at once—a condition known as superposition—until the moment it is measured. Erwin Schrödinger, along with contemporaries like Albert Einstein, found this idea deeply troubling. Their discomfort stemmed from the notion that reality at the quantum level was fundamentally uncertain and only became definite upon observation. Schrödinger sought to demonstrate the philosophical problems of this interpretation by scaling it up from the subatomic to the macroscopic world.

To do this, he conceived of his now-famous thought experiment. Imagine a cat sealed in a steel box with a "diabolical device": a tiny amount of radioactive material that has a 50% chance of decaying within an hour. If an atom decays, it triggers a Geiger counter that releases a hammer, which shatters a flask of poison, killing the cat. According to the Copenhagen interpretation, until the box is opened and observed, the radioactive atom is in a superposition of both "decayed" and "not decayed." Therefore, Schrödinger argued, the cat, whose fate is linked to the atom, must also be in a superposition of being simultaneously alive and dead.

Schrödinger never intended for this scenario to be taken as a literal possibility. He called it a "quite ridiculous case" to show that the Copenhagen interpretation, when applied to a large-scale object, led to an absurd conclusion that did not match our experience of reality. For Schrödinger, the fact that a cat could not be both alive and dead at the same time proved that the underlying interpretation of quantum mechanics must be flawed. Ironically, the very illustration he designed to critique the theory has become the most famous example used to explain its strange and counterintuitive nature.