So let’s say a billionaire with unlimited funds comes to you and asks you to run a scientific study, the purpose of which is straightforward: prove, scientifically, the existence or non-existence of the human soul. How would you go about it?

You can use whatever tools you want, including “mediums” and “ghost hunters” and the like. However, in order for their inclusion to be meaningful, their claims must also be scientifically evaluated and shown to be valid.

What are not acceptable – as in any other scientific study – are things like hearsay and Argument From Authority. A religious text describing souls is not useful as evidence; the claims made about the properties of souls in that text must be proven scientifically and rigorously.

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To me this seems like an unwinnable scientific endeavor, at least at current understanding. If someone were to toss unlimited funds my way to prove the existence or lack thereof of, say, Bigfoot, I can at least see how it might be done: show up with a captured Bigfoot, or a corpse, or body parts, or even a good DNA sample, and you’ve proven it.From the other direction, unlimited funds would allow you to chop down and pave over every square foot of forest in North America. If you were to do such an unwise thing, and by the end you’ve found no physical evidence of Bigfoot… well, that might not be mathematical Proof of the non-existence of Bigfoot, but it would be evidence enough that most scientists would consider “Bigfoot does not exist” to be a valid statement.

But souls are by definition not physical, thus testing for them becomes trickier. Of course, science has a long, successful history of proving the non-physical… electromagnetic radiation and gravity/mass being prime example of things that science has measured without actually being able to measure. This has been done by measuring the effects that these non-material forces have on physical objects. You don’t need to have the slightest idea what “gravity” is or how the mechanism underlying it works in order to measure the acceleration of a dropping apple or trace the orbits of planets.

Similarly, if a soul exists, it would seem possible, at least in principle, to measure its effect on physical objects – in this case, people. Exactly *how* is a little fuzzier.

A basic function of the “soul” is to survive the death of the body (a soul that does not survive brain death would seem to be a rather useless sort of thing). This would seem a starting point. Ethics aside, killing people and bringing them back might provide useful data. I don’t mean stopping their hearts and bringing them to the brink of brain death, with all the oxygen-deprivation-delusions that entails… I mean *truly* dead. No brain activity whatsoever. And then bringing them back. This might be achievable via cryogenic freezing; a brain frozen into a solid chunk with no electrical activity whatsoever would not be able to have experiences. If, after freezing and revival (this is, of course, a currently scientifically unsurmounted problem), definite experiences are reported, that might be evidence. These experiences would, of course, have to be factored against the definite possibility that a brain being frozen solid and then thawing again just might do some funny stuff along the lines of dreaming up imaginary experiences…