The idea that humans have a soul has existed for a very long time. In fact, every culture throughout the world believes in some concept that separates the body from the spirit.
If the soul is an immaterial nature that transcends our material body, then how much does it weigh?
In 1907, a doctor in Dorchester, Massachusetts, attempted to find out.
In an unusual experiment, Dr. Duncan MacDougall was determined to prove that the human soul had mass and could be measured. He took six dying patients, all of whom were selected based on their looming death, and placed them on specially made Fairbanks weight scales.
The intention was to weigh each body before and after death to reveal any differences–five were men and one was a woman. Of course, he took into account bodily fluids and air from the lungs. The average weight loss of each person was 3/4 of an ounce.
In a quote from a New York Times article, Dr. MacDougall described the historic moment:
The instant life ceased the opposite scale pan fell with a suddenness that was astonishing – as if something had been suddenly lifted from the body. Immediately all the usual deductions were made for physical loss of weight, and it was discovered that there was still a full ounce of weight unaccounted for.
Following the experiment, he discussed his findings with some other physicians who were in attendance. It was concluded that the average human soul weighed 21 grams.
Later on in his career, Dr. MacDougall turned away from trying to weigh the human soul and instead tried to capture photographs of it as it left the body.
The following video explains the theory in detail: