Early 20th-century scientists tried to literally weigh the soul leaving the body

Roach recounts experiments, most famously associated with physician Duncan MacDougall in the early 1900s, that attempted to detect a measurable loss of mass at the exact moment of death, on the theory that if a soul is a real substance departing the body, a sufficiently sensitive scale should register the difference.

The experiments involved placing dying patients on specially rigged beds connected to industrial scales, watching for a sudden weight drop at the moment breathing stopped. Some trials reported small, unexplained weight losses; others reported none, or losses easily attributable to moisture evaporation, released gases, or simple measurement error given the crude instruments of the era.

Roach treats this less as a story of fraud and more as a case study in genuinely earnest but methodologically weak science, conducted by people trying to apply the tools of physical measurement to a question that may not be answerable through mass and scales at all.

Takeaway: applying rigorous-seeming instruments to an ill-defined question doesn't make the resulting answer meaningful.