O artigo da Wikipedia sobre Dr. Duncan MacDougall diz,
Dr. Duncan “Om” MacDougall (c. 1866 – October 15, 1920) was an early 20th-century physician in Haverhill, Massachusetts who sought to measure the mass lost by a human when the soul departed the body at death. MacDougall attempted to measure the mass change of six patients at the moment of death. His first subject, the results from which MacDougall felt were most accurate, lost “three-fourths of an ounce”, which has since been popularized as “21 grams”.
21 Gramas é um filme de drama americano de 2003 que faz referência à noção de que a alma humana tem massa, mais especificamente que pesa vinte e um gramas.