Answer: Nuclear Physics

When you think of a barn, you likely think of a large storage building located on a farm. In the teeny tiny world of nuclear physics, however, a barn is an absolutely minuscule measurement of area equal to 1.0×10⁻²⁸ m².

The term originated in the Manhattan Project in the 1940s. Physicists working at Purdue University needed a secret term to refer to the approximate cross-section of the nucleus of an atom. The decision to use “barn” as the term was a clever joke since their research focused on hitting the nucleus with an accelerated particle—an extremely difficult task—but the American English idiom “couldn’t hit the broad side of a barn” suggests someone has aim so poor that they couldn’t hit a large object with a baseball.

There are two derivative units of area measurement used less frequently: the outhouse (1.0×10⁻⁶ barns) and the shed (1.0×10⁻²⁴ barns).