Schrödinger’s Cat Explains State of Superposition

no cats harmed in the making of famous quantum mechanics thought experiment

By Jonny Lupsha, Wondrium Staff Writer

The famous “Schrödinger’s cat” is more than a joke about the unknown. It’s a hypothetical way of understanding an idea in quantum mechanics known as superposition. This week on Wondrium, philosophy meets physics.

One of the most famous ideas in science is that imagined in the Schrödinger’s cat thought experiment. If a cat is in a cage covered by a box and we press a button that’s connected to a canister of poison, and that button press has a 50/50 chance of releasing the poison, we don’t know if the cat is alive or dead until we look. In a sense, it’s both alive and dead.

Unfortunately, this poor feline has become an oversimplified example and misused as a symbol for anything possessing two seemingly opposing qualities. So, what does it really mean? In his video series The Great Questions of Philosophy and Physics, Dr. Steven Gimbel, who holds the Edwin T. Johnson and Cynthia Shearer Johnson Distinguished Teaching Chair in the Humanities at Gettysburg College in Pennsylvania, lets the cat out of the bag in an episode about the scientific idea of interpretation.

A Very Thorough Answer

Erwin Schrödinger was an Austrian-Irish physicist whose work in science led him to win the Nobel Prize in 1933. He eventually gave the world Schrödinger’s equation, which Dr. Gimbel referred to as “the central law that governs the quantum world” and is completely unlike those of Einstein or Newton.

“From those normal theories […] what we get in solving the equations for some physical context are measurable values for observable quantities,” he said. “The velocity will be 4,000 miles per hour, or the time will be five milliseconds. But not with quantum mechanics.”

Schrödinger’s equation, Dr. Gimbel said, gives us a mathematical combination of every possible state the system could be in. Not only that, but each of those possibilities is connected to a term that tells the likelihood that when the related experiment is done in the lab, scientists will find the system in that state. This combination is called the state of superposition.

Curiosity Killed and Didn’t Kill the Cat

Knowing this, the thought experiment about Schrödinger’s cat makes a bit more sense. It begins with the cat in a cage covered by a box through which we cannot see, and outside the box is a button.

“When we push the button, two electrons are emitted, which are what we call spin-correlated,” Dr. Gimbel said. “Spin is just a physical quantity that has only two values: up and down. According to quantum mechanics, before we measure the spin, the two particles are both in superposed states. Let’s make it so that it is 50/50 that the particle would be up or down.”

In the box is a spin detector that measures one of the electrons to see if it’s in an up or down state. If the detected spin is up, nothing happens. If the detected spin is down, a circuit connected to the detector releases a canister of poison that kills the cat. The detector, the poison, and the cat are all physical systems, but they become a part of the quantum system because the electrons are emitted in their superposed state, so the entire sadistic cat-killing device becomes part of that superposed state.

“What that means—and this is the weird payoff—is that before I look inside the box, the cat is in a state of superposition of alive and dead,” Dr. Gimbel said. “Not that it is alive or dead and I don’t know which. It is both fully alive and fully dead in some strange metaphysical combination we have never observed in reality and can’t really make sense of.

“But that is exactly what the theory tells us.”

The Great Questions of Philosophy and Physics is now available to stream on Wondrium.

Edited by Angela Shoemaker, Wondrium Daily