In the film 21 Grams (2003), there is a reference to the weight of a soul that runs through the three non-linear stories of characters in a past, present and future. The film’s title is an allusion to actual research done by physician Dr. Duncan MacDougall in 1901.
His plan was to attempt to measure the mass lost by a human when the soul departs the body at death. He built a bed that had balanced platform beam scales sensitive to two-tenths of an ounce. He weighed the initial six patients 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. He started with six patients who were near death. The first subject lost three-quarters of an ounce at death – 21 grams.
He 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 he followed the scientific method and his s results were published in at least one peer-reviewed journal, his conclusion was not widely accepted as scientific fact.
He later measured the weight of dogs under the same conditions and the results were that he found no perceived change in mass. He took this to mean that the soul had weight and that dogs did not have souls.
You might think that MacDougall was a religious man, but his interpretation of the “soul” was not religious. He would define it as more of a “life force.”
Albert Einstein used the word soul at times but he also did not mean it in religious terms. He was not an atheist, but he did not believe in any part of us being immortal.
In most religious, philosophical, psychological, and mythological traditions a “soul” is defined as an incorporeal (not composed of matter; having no material existence), immortal essence of a living being. In Abrahamic religions, immortal souls belong only to human beings.
St. Thomas Aquinas called the soul anima defined as a current of air, or breath, or 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.
In Hinduism, all biological organisms have souls. Religions that profess animism teach that even non-biological entities, like rivers and mountains, have souls. Anima mundi is the concept of a “world soul.”
Those who believed in MacDougall’s research and conclusion (and others since then have tried similar experiments) are really more concerned with the existence of a soul rather than its weight. The weight was the way to show that existence. This kind of research gives comfort to the idea that some part of us survives the death of the body.