Spherical cow



The spherical cow is a humorous metaphor for highly simplified scientific models of complex phenomena. Originating in theoretical physics, the metaphor refers to physicists' tendency to develop toy models that reduce a problem to the simplest form imaginable, making calculations more feasible, even if the simplification hinders the model's application to reality.

The metaphor and variants have subsequently been used in other disciplines.

History
The phrase comes from a joke that spoofs the simplifying assumptions sometimes used in theoretical physics.

"Milk production at a dairy farm was low, so the farmer wrote to the local university, asking for help from academia. A multidisciplinary team of professors was assembled, headed by a theoretical physicist, and two weeks of intensive on-site investigation took place. The scholars then returned to the university, notebooks crammed with data, where the task of writing the report was left to the team leader. Shortly thereafter the physicist returned to the farm, saying to the farmer, "I have the solution, but it works only in the case of spherical cows in a vacuum.""

It is told in many variants, including a joke about a physicist who said he could predict the winner of any race provided it involved spherical horses moving through a vacuum. A 1973 letter to the editor in the journal Science describes the "famous story" about a physicist whose solution to a poultry farm's egg-production problems began with "Postulate a spherical chicken".

Cultural references
The concept is familiar enough that the phrase is sometimes used as shorthand for the entire issue of proper modeling. For example, Consider a Spherical Cow is a 1988 book about problem solving using simplified models. A 2015 paper on the systemic errors introduced by simplifying assumptions about spherical symmetries in galactic dark-matter haloes was titled "Milking the spherical cow – on aspherical dynamics in spherical coordinates".

References to the joke appear even outside the field of scientific modeling. "Spherical Cow" was chosen as the code name for the Fedora 18 Linux distribution. In the sitcom The Big Bang Theory, a joke is told by Dr. Leonard Hofstadter with the punchline mentioning "spherical chickens in a vacuum", in "The Cooper-Hofstadter Polarization" episode. In the space gravity simulator educational video game Universe Sandbox, a spherical cow was added as a user-placeable object in March 2023.