Duncan MacDougall (doctor)

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Duncan MacDougall
Born c.1866

October 15, 1920(1920-10-15)

(aged 54)
Residence Haverhill, Massachusetts, USA
Citizenship American
Nationality American
Fields Biologist
Known for attempting to determine the mass of a soul

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". Of the four successful measurements he obtained an average weight loss at the moment of death of 15 grams. The total average unaccounted for weight loss in these four subjects was found to be approximately 29 grams.

Ideas about the 'soul'[edit]

NYT article from March 11, 1907

In 1901, MacDougall weighed six patients while they were in the process of dying from tuberculosis in an old age home. It was relatively easy to determine when death was only a few hours away, and at this point the entire bed was placed on an industrial sized scale which was reported to be sensitive to "two-tenths of an ounce". He took his results (a varying amount of unaccounted for mass loss in four of the six cases) to support his hypothesis that the 'soul' had mass, and when the 'soul' departed the body, so did this mass. The determination of the 'soul' weighing 21 grams was based on the loss of mass in the first subject at the moment of death.

MacDougall later measured fifteen dogs in similar circumstances and reported the results as "uniformly negative," with no perceived change in mass. He took these results as confirmation that the 'soul' had weight, and that dogs did not have 'souls'. MacDougall's complaints about not being able to find dogs dying of the natural causes that would have been ideal led one author to conjecture that he was in fact sacrificing the experimental animals, as is standard practice in scientific experiments.[1] On March 10, 1907, before MacDougall was able to publish the results of his experiments, New York Times broke the story in an article titled "Soul has Weight, Physician Thinks". MacDougall's results were published in April of the same year in the Journal of the American Society for Psychical Research and the medical journal American Medicine.


Later researchers showed that MacDougall's experimental results were flawed, due to the limitations of the available equipment at the time, a lack of sufficient control over the experimental conditions, and the small sample size. The physicist Robert L. Park raised objections to MacDougall's findings in his book Superstition: Belief in the Age of Science,[2] while the psychologist Bruce Hood wrote that "Because the weight loss was not reliable or replicable, his findings were unscientific."[3]

In popular culture[edit]

  • MacDougall's experiments are mentioned and reenacted in the 1978 film Beyond and Back.
  • A fictional American scientist named "Mr. MacDougall" appears as a character in Gail Carriger's steampunk adventure novel Soulless, as an expert in the weight and measurement of souls.
  • MacDougall and his experiment were a subject in a 2011 episode of Science Channel's Dark Matters: Twisted But True.
  • The idea from these experiments show up in the Dan Brown novel The Lost Symbol.
  • 21 Grams is a 2003 American drama film which references the notion that the human soul has mass, more specifically that it weighs twenty-one grams.


  1. ^ Mikkelson, Barbara; Mikkelson, David P. (October 27, 2003). "Soul Man". Snopes. Retrieved February 17, 2007. 
  2. ^ Robert L. Park. (2009). Superstition: Belief in the Age of Science. Princeton University Press. p. 90
  3. ^ Bruce Hood. (2009). Supersense: From Superstition to Religion - The Brain Science of Belief. Constable. p. 165

External links[edit]