You're referring to the concept of the "soul" or vital energy, often associated with spiritual or paranormal beliefs. The idea of a measurable weight for the soul is indeed intriguing and has been explored in various contexts.

The notion you mentioned, specifically the 21-gram measurement, likely originates from a study conducted by Dr. Duncan MacDougall, an American physician, around 1901. MacDougall's research was based on his observation that animals, particularly dogs, would occasionally stop breathing after death and then resume breathing with a small twitch or jerk, which he speculated might be indicative of a vital energy or "soul" escaping the body.

MacDougall performed a series of experiments to measure this effect. He placed scales under the cages of mice and other small animals as they passed from life to death. The idea was that if there was indeed a measurable soul (or vital energy), it would be weighed on these scales at the moment of death.

The results, however, were not conclusive, and later studies have attempted to replicate MacDougall's findings but with mixed results. Many scientists have challenged the validity of his experiments, suggesting methodological flaws, contamination from environmental factors, or even errors in measurement that could explain any observed effect.

Regarding the specific number 21 grams, this was a finding mentioned by Dr. MacDougall during one of his experiments where he claimed to have measured an average weight loss at death (which would be interpreted as the "soul" leaving) of about 21.3 grams in mice. However, these findings are not widely accepted as conclusive evidence for the existence of a measurable soul.

The scientific community generally approaches claims of a measurable soul or vital energy with skepticism due to the lack of replicable and rigorous studies supporting such notions. From a biological standpoint, death is understood as the cessation of all physical functions in living organisms, including heart activity, brain function, metabolism, and other physiological processes that characterize life.

While the idea of measuring the weight of the soul remains an intriguing concept, it is indeed often dismissed as a coincidence or a result of methodological errors. Scientific inquiry requires rigorous testing to establish any phenomenon's validity, and such tests have not convincingly supported the notion of a measurable soul based on 21 grams. nostr.fmt.wiz.biz