21 grams only - and that's the fuss this is all about?
A 20th-century doctor, Dr. Duncan MacDougall of Haverhill, Massachusetts, postulated that the soul is material, too, and therefore has mass. In the early 1900s, he sought to measure the weight purportedly lost by a human body when the soul departed upon death.
MacDougall weighed dying patients in an attempt to prove that the soul was material, tangible and thus measurable. These experiments are widely considered to have had little if any scientific merit, and although MacDougall's results varied considerably from 21 grams, for some people this figure has become synonymous with the measure of a soul's mass.
More details over here
Such a small amount and so much ego it carries! Interesting.
A Hollywood movie on the same concept was made in 2003, called 21 grams starring Naomi Watts and Sean Penn.