We've talked about immeasurable and intangible energy resulting in human consciousness, but some researchers think that the soul is measurable. In fact, they think it weighs exactly 21 grams and that it can be detected escaping the body after death.

This figure was calculated back in 1907 by Duncan MacDougall, a doctor working in Haverhill, Massachusetts. He spent much of his career trying to find evidence of the human soul, with the ultimate aim of capturing an image of it within the body using x-ray.

His most notable work is based around his belief that if humans have a soul, then it must exist in the body as some kind of material, and that material must weigh something. In order to test this, MacDougall converted a hospital bed into weighing scales so that he could measure the change in weight of a patient at the moment of their death.

MacDougall had opted to...