Schrödinger’s Menagerie

Cat in a box. Credit: Flickr user Wolfgang Lonien, adapted under a Creative Commons license.

Cat in a box. Credit: Flickr user Wolfgang Lonien, adapted under a Creative Commons license.

Paul Halpern via PBS Nova:

Erwin Schrödinger loved animals.

That may come as a surprise to those who associate Schrödinger most closely with his cat paradox. Of all of Schrödinger’s accomplishments, including the Nobel-Prize-winning development of the quantum wave equation that bears his name, that hypothetical thought experiment, occupying just a few paragraphs in a single paper, is what sticks in the public memory. It has also earned Schrödinger an undeserved reputation for animal cruelty.

Yet his family knew better. As related by his daughter Ruth Braunizer, Schrödinger’s dog Burschie (“Laddie”) offered great comfort to the family throughout the dark days of World War II. No family scene was complete without their beloved collie.

Why would a lover of animals imagine something so cruel? For the same reason that, 80 years later, Schrödinger is still branded a cat-hater: preposterous analogies are memorable.

Schrödinger was a master of vivid analogy. He loved literature and drama, particularly the writings of the ancient Greeks and eastern mystics, and drew upon such sources for ways of expressing his ideas. His theatrical lectures captivated audiences with references to commonplace situations with which they might identify and have a laugh.

In fact, Schrödinger’s cat is just one member of a whole zoo of (imagined) animals that Schrödinger pressed into service to bring his analogies to life: Schrödinger’s menagerie!

Schrödinger’s Cat

The epitome of ridiculousness, Schrödinger’s cat paradox explores the extreme ramifications of quantum entanglement, a term he coined to describe how a single quantum state can encompass multiple, separate objects. Although Schrödinger pioneered the wave version of quantum mechanics, he was flummoxed by how his ideas were reinterpreted by Max Born and others as a probabilistic theory that allows for sudden, discontinuous transitions from one particle state to another. As Werner Heisenberg and John von Neumann suggested, observation of a mixed quantum state—representing, for example, a range of position values–can trigger it to collapse into an unblended state, pertaining to, for instance, a single position value. If the initial state describes an entangled set of particles, then the entire state collapses at once, immediately affecting all of the particles in question.

As a believer in continuous transformations, rather than sudden changes, Schrödinger found preposterous the idea that a scientific measurement could instantly spur a cavalcade of transformations. Therefore he developed the idea of linking a cat’s fate to that of a decaying radioactive sample by making a Geiger counter the trigger for the release of poison. Just as the sample would be in a mixed quantum state before observation, so would be the cat—in a bizarre superposition of life and death.

While Schrödinger hoped that his thought experiment would stimulate a rethinking of quantum assumptions, the collapse idea has remained the mainstream approach, with only a minority of theorists supporting alternative notions such as the Many Worlds Interpretation (in which the cat would be alive in one parallel universe and dead in the other). As for the cat itself, it has become a symbol of ambiguity.

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