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 reduce a problem to the simplest form imaginable in order to make 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.
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".
References in science
Alan Turing, in his 1952 paper "The Chemical Basis of Morphogenesis", asserted: "a system which has spherical symmetry, and whose state is changing because of chemical reactions and diffusion ... cannot result in an organism such as a horse, which is not spherically symmetrical."
In popular culture
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. [failed verification]
Even without the concept of scientific modeling the joke is sufficiently well known to be indirectly referenced. "Spherical Cow" was chosen as the codename 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.
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