May 16, 20193 min read

Why did Schrodinger put a cat in the box?

Updated: Jan 24, 2020

Schrodinger's cat: an abstract image of a cat in a state of both dead and alive in accordance with Schrodinger's thought experiment — Schrodinger's cat

If there was ever a famous cat in science, then it’s Erwin Schrodinger’s imaginary cat who was placed in a box as part of a thought experiment. It was the 1930s, and quantum mechanics was being the standpoint of many debates between two of the greatest minds of the 20th century, Albert Einstein and Neils Bohr. Albert Einstein, who stood on the side of the classical interpretation of physics, was unsettled by the strangeness of quantum mechanics and in his conversations with Neils Bohr, to whom quantum mechanics owe much, he often interpreted his doubts about the nature of quantum particles, which Bohr and a few other scientists believed in. Einstein, who was fascinated by thought experiments, gave this relatively new field of science, multiple perspectives. Whilst, Einstein showed his trouble in believing things like quantum superposition and the uncertainty principle, he admired Neils Bohr’s interpretation and views on the subject, and they both had the utmost respect for each other even in their debates.

Arthur Fine's 'The Shaky Game: Einstein, Realism and the Quantum Theory', looks at Albert Einstein's views on quantum mechanics. Just like Bohr, Erwin Schrodinger was a good friend of Einstein, and they were scientists caught in the chaos that ensued Europe under Hitler's regime. While they both had their fair share to contribute toward quantum mechanics, they shared a similar view about the non-realistic nature of the subject in their letters[1].

In May 1935, the famous EPR paper[2] was published by Albert Einstein, Boris Podolsky, and Nathan Rosen in an attempt to prove the incompleteness of quantum mechanics. According to Neils Bohr and Werner Heisenberg, a quantum system remained in a state of superposition, until the act of observation collapsed that superposition into one or another of the possible states. The EPR paper tried to mathematically show that wave function does not contain complete information about reality, and thus the quantum interpretation was inadequate. Einstein demonstrated further thought experiments, the notable of which involved a charge of gunpowder exploding and not-exploding at the same time in relation to the Copenhagen interpretation[3] of quantum mechanics, which he found absurd and nonsensical in the real world.

But it is when Schrodinger read about this thought experiment in 1935, that he went through the trouble to create one on his own. Enter Schrodinger’s cat.

To illustrate and agree with Einstein’s views about quantum mechanics, Schrodinger thought about a cat[4] placed inside a sealed box. In the box is also a Geiger counter, which contains a small quantity of radioactive uranium, the quantity so small that there is a probability of an atom decaying and not decaying in an hour. If the decay happens, then a relay system triggers a hammer that breaks a small flask of hydrogen cyanide, a highly poisonous chemical compound. If at all this happens, it would almost certainly kill the cat, but if the decay didn’t happen, the cat would be alive and well. But if the Copenhagen interpretation held, then it would mean that the cat could be in a state of superposition, a state of both dead and alive at the same time until the act of observation collapsed this superposition into either one of the two possible outcomes. Einstein was pleased with the thought experiment, for the wave function, which consists of the state of the cat being both dead and alive were not realistic in the physical world, thereby making a strong statement against the Copenhagen interpretation of quantum mechanics.

So, there it is. While the cat-in-a-box experiment is strongly associated with the fundamentals of understanding quantum physics, its purpose was, in fact, to prove the ‘non-realistic’ nature of it. But eventually, Neils Bohr and his colleagues would win the argument paving the way for quantum mechanics into our daily lives, and Schrodinger’s cat often takes center stage to deal with the bizarreness of the subject. Though the 'dead and alive cat' is a real scenario, it does not apply to macroscopic items, but rather only to subatomic particles like electrons, thus, leading to an array of misinterpretations of the thought experiment.

Why did Schrodinger put a cat in the box?

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