Okay, then, Gustyboy. Become a scientist! Here's a hypothesis for you:

"The human soul has a small yet measurable mass, around 21 grams."

All you have to do now is gather evidence. A bunch of statistics will do for starters. We'll need a large sample of human bodies, each weighed twice, the instant just before and the instant just after death. Don't forget to tell us precisely how you define the instant of death. Any corpse that farts at the point of death, or which has its brow mopped by a tearful relative, will, of course, have to be discounted. In your write-up you will, of course, be telling us exactly how you hoisted a near-corpse, in its final agony, into a super-accurate weighing device, having removed, naturally, any tubing or electronic attachments from it first. Hope you managed to keep the quivering near-cadaver perfectly still whilst in there, let alone prevented the grieving relatives from trying to kill you! OK, once you've established a consistent loss of mass for your large sample of dead 'uns, all you have to do then is demonstrate that what has been lost is a soul and not something else of a slightly more worldly nature. Hmm. Over to you for that bit, but be warned that most scientists interested in your study will come to you with a positive plethora of alternative (and far more plausible) explanations. Finally, your scientific peers will want the account of your study to be detailed enough for them to repeat it with the prospect of the same outcome. Nothing to this science lark, old bean. Much easier than guessing and speculation innit! :-)

And note that nowhere have I said that you are wrong about the soul. But, in order for your assertion to be of interest in any way other than comedic, I shall be needing...guess what...evidence!