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How Much Does the Soul Weigh?

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Many people like to believe in the idea of a soul, and we often look to the empirical world to bolster our religious or spiritual beliefs, searching for corroborating physical evidence. Just such scientific proof seemed to come in 1907,when a Massachusetts doctor named Duncan MacDougall devised experiments that he expected would actually measure the soul. Using six terminally ill patients on a specially-constructed scale bed, he measured their weight before, during, and after death. His results were mixed, but he concluded that there was indeed a very slight loss of weight, 21 grams on average.

This caused quite a stir at the time, and seemed to be proof of the human soul. Closer examination of MacDougall's methods, however, revealed profound flaws.

MacDougall used a very small sample size (only four of the original six bodies) and his results were inconsistent. Furthermore, the precise moment of death is not always clear even today, and in 1907 medical measurement methods were even cruder. The weight of the soul turned out to be simply the result of sloppy science, but many still believe it a century later.

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Benjamin Radford
Benjamin Radford
Benjamin Radford is the Bad Science columnist for Live Science. He covers pseudoscience, psychology, urban legends and the science behind "unexplained" or mysterious phenomenon. Ben has a master's degree in education and a bachelor's degree in psychology. He is deputy editor of Skeptical Inquirer science magazine and has written, edited or contributed to more than 20 books, including "Scientific Paranormal Investigation: How to Solve Unexplained Mysteries," "Tracking the Chupacabra: The Vampire Beast in Fact, Fiction, and Folklore" and “Investigating Ghosts: The Scientific Search for Spirits,” out in fall 2017. His website is