One of the key concepts in physics, and science overall, is the notion of a 'field' which can describe the spatial distribution of a physical quantity. For instance, a weather map shows the distributions of temperature and pressure (these are known as scalar fields), as well as the wind speed and direction (known as a vector field). Almost everyone wears a vector field on their head—every hair has an origin and an end, just like a vector. Over 100 years ago L.E.J. Brouwer proved the hairy ball theorem which states that you can't comb a hairy ball flat without creating whorls, whirls (vortices) or cowlicks.