You may have seen the film 21 Grams (2003). Buried within its non-linear stories of three characters in a past, present and future swirl was the titular reference to the weight of a soul.

The title refers to research by physician Dr. Duncan MacDougall that dates back to 1901. His goal was to measure the mass lost by a human when the soul departs the body at death. His experiment started with six patients who were near death.  The first subject lost three-quarters of an ounce which has since been popularized as “21 grams”.

He built a light frame bed with delicately balanced platform beam scales sensitive to two-tenths of an ounce in order to weigh the initial six patients all in the end stages of terminal illnesses. He measured before, during, and after the process of death, measuring any change in weight. Once all the weights were taken, he then eliminated all of the reasons that could explain a weight loss.

soul-weightHe said he performed four successful measurements and obtained an average weight loss at the moment of death of 15 grams. MacDougall wanted scientific proof of the existence of the immortal human soul and believed that by recording a loss of body weight at death, he would have shown the departure of the soul immediately following death.

Though his research attempted to follow the scientific method and MacDougall’s results were published in at least one peer-reviewed journal, it was not widely accepted as scientific fact.

Another MacDougall experiment measured dogs under the same conditions and the results were that he found no perceived change in mass, which he took to mean that the ‘soul’ had weight, and that dogs did not have ‘souls’.

His interpretation of the soul was not religious but more of a “life force.” But the term “soul” in many religious, philosophical, psychological, and mythological traditions is defined as incorporeal (not composed of matter; having no material existence). In religious and philosophical applications it is the immortal essence of a living thing.

Abrahamic religions teach that immortal souls belong only to human beings. I found that confusing as a young person when I read that Catholic theologian Thomas Aquinas called the soul “anima.” Although I took that to mean animals, that term is defined as a current of air, wind, air, or breath, or as life or the soul. Sometimes it is connected to animus, meaning “mind.”  Aquinas wrote that all organisms have a soul, but only human souls are immortal.

Hinduism is a religion that teaches that all biological organisms have souls. Religions of animism teach that even non-biological entities, like rivers and mountains, also have souls.  Anima mundi is the concept of a “world soul.”

In 1907, The New York Times wrote about MacDougall’s research in a story titled “Soul has Weight, Physician Thinks” and his results were published that year in the Journal of the American Society for Psychical Research and in the medical journal American Medicine.

“If personal continuity after the event of bodily death is a fact, if the psychic functions continue to exist as a separate individually or personality after the death of brain and body, then such personality can only exit as a space occupying body, unless the relations between space objective and space notions in our consciousness, established in our consciousness by heredity and experience, are entirely wiped out at death and a new set of relations between space and consciousness suddenly established in the continuing personality. This would be an unimaginable breach in the continuity of nature.”

Those who believed then and believe now in the validity of the research probably are more concerned with the existence of a soul than its weight. The research gives comfort to the idea that some part of us survives the death of the body.