21 grams experiment

What it is

The 21 grams experiment was an attempt, made just over a century ago in the United States, to find out whether the soul can be weighed. Duncan MacDougall, a doctor in Haverhill, Massachusetts, placed the beds of dying patients on large scales and watched the dials as life ended. Six people were measured; in only one case did the reading drop, by about 21 grams. MacDougall took this single result as a hint that the soul has physical weight. Other researchers did not accept it: the trial used too few subjects, the gear was too coarse, and most results did not fit the idea. Even so, the figure caught on, and the claim that a soul weighs 21 grams spread through films, books and songs long after the work itself was set aside.

Where it comes from

MacDougall, a doctor practising in Haverhill, Massachusetts, began the work in 1901, picking out nursing-home residents whose deaths were expected soon. He wanted a scientific verdict on whether a soul exists and leaves the body when life ends. His report was slow to appear: the New York Times broke the news first, with a headline saying a physician believed the soul had weight, and his findings reached print only in 1907, in the American Society for Psychical Research's journal and in the medical periodical American Medicine. A rival physician, Augustus P. Clarke, attacked the work within weeks, and the pair argued in print for the rest of that year. MacDougall spoke in 1911 of photographing souls but published nothing further, and he died in 1920 with the experiment never repeated.

How it is done

Six nursing-home patients took part, four of them dying of tuberculosis, one of diabetes, one of an unnamed illness. MacDougall chose wasting diseases so that the patients, already exhausted, would lie still enough for careful weighing. When a death drew near, the whole bed was moved onto a large industrial balance able to register 5.6 grams, and readings were compared as breathing stopped. He also weighed fifteen dogs after death, on the view that people have souls and animals have none; finding no sick dogs for the trial, he is presumed to have poisoned healthy ones. One patient's reading dropped 21.3 grams as death came, two others showed small losses, one lost weight and gained it back, and two records were discarded over scale problems.

Tools and materials

The whole trial hung on one instrument: an industrial balance placed under the entire bed of each patient, exact to within about 5.6 grams. That figure fixed what could be detected at all, and sceptics later argued such gear was too coarse to settle the question. In 2005 the physician Gerard Nahum proposed a different tool for the same job, an array of electromagnetic detectors meant to catch energy leaving the body at the final moment, an idea that found no buyers.

What it is for

MacDougall wanted to settle, by measurement, whether the soul exists as a physical thing. His working idea was that a soul has weight, that it departs when life ends, and that a fine enough balance would register the departure. He treated the dogs as a control: if animals have no souls, their weight should not change. He took the single 21-gram drop as support for the idea, though he conceded in his own report that nothing could be concluded from a single case, and that far more trials were needed. The work is remembered less for its results than for the belief it seeded: that the human soul weighs, specifically, 21 grams.

What people believe

The trial rested on two convictions: that human beings have a soul which slips free when life ends, and that animals have none. MacDougall added a further assumption, that this departing soul is not only a matter of faith but has mass, and so can be caught on a balance like any other change in the body. That step moved the question from religion into measurement, which is why the report appeared in psychical research circles, where such tests were then being attempted. The wider public kept the number rather than the caveats, and the claim that a soul weighs 21 grams became a piece of common folklore.

How scholars and sceptics see it

Criticism began almost at once. Clarke argued in American Medicine that a dying body warms as the lungs stop cooling the blood, so extra sweating could account for a loss of about 21 grams, while dogs, which lack sweat glands, would lose nothing that way. Karl Kruszelnicki later called the work selective reporting, since only one patient in six fitted the claim, and asked how the instant of death could be fixed with the instruments then available. Robert L. Park wrote that the trials now carry no scientific merit, and psychologist Bruce Hood judged the findings unscientific because they were neither reliable nor repeatable. Richard Wiseman files the experiment among curiosities almost certainly not true, and a 2013 Snopes review judged the methods suspect, the sample far too small and the measurements too imprecise.

Compare and confuse

The idea drew later imitators. In late 2001 physicist Lewis E. Hollander Jr. reported weighing sheep and a goat at death; seven adult sheep briefly gained, rather than lost, between 18 and 780 grams before settling back to their starting weight. A 2009 review by Masayoshi Ishida in the same journal questioned how Hollander expressed the result, though the underlying force remained unexplained, and he flagged possible scale faults in two cases. In 2005 Gerard Nahum proposed his electromagnetic detectors as a follow-up, offering the plan to Yale, Stanford and Duke and to the Catholic Church without takers.

Today

The experiment failed as science but flourished in entertainment. The film 21 Grams borrowed its title, and the number turns up in Japanese manga (Gantz, One Piece), a podcast, television episodes including one of Ted Lasso and a 2022 story on the series Evil, and songs titled "21 Grams" by acts from Looptroop Rockers to Fedez and August Burns Red. MacDougall and his work appear in the 1978 documentary Beyond and Back, a fictional "Mr. MacDougall" weighs souls in Gail Carriger's 2009 novel Soulless, a soul-weighing test features in The Lost Symbol the same year, and a 2016 puzzle hunt hid the phrase "you're now 21 grams lighter" in a contract selling a soul.

Questions people ask about 21 grams experiment

Good reading and sources

• 21 grams experiment on WikipediaEncyclopedia
• Wikidata recordOpen data