. If we assume he provides no false evidence, then the mere statement "You are dead" should be already considered sufficient evidence, no?
Even if not, the next natural inclination would be to demonstrate power over souls/minds. This would most easily be done simply by causing me to believe in the afterlife directly and making me aware of this causation of belief while doing so. (This doesn't, I feel, impede rationality because it does not prevent me from reassessing the situation based on my newfound set of priors.) Alternatively, causing me to experience mindspaces hitherto unavailable to me would also help in demonstrating a separation of traditional physiology and mentality. Witnessing all places on Earth simultaneously, or other such parlor tricks, would also do nicely there.
Would they prove the legitimacy of the supernal claim of an afterlife? No, not at all. But they would demonstrate a separation between cognition and physiology, from which the extraordinary nature of a specific afterlife would be lessened to the point where merely being shown it would qualify as justification for naive belief.
You unexpectedly find yourself sitting in a windowless room across from a gray-haired gentleman. You didn't wake up there; you were walking down the street and cut to camera two, a white windowless room with a table and two chairs. After a moment, the gentleman speaks:
"You are dead, killed instantly by a small meteorite. Incidentally," he smirks, "you have lost Pascal's Wager. You may 'cross-over' once you can accept that you are dead. I am here to help in that endeavor and can present any evidence you desire."
You, being a stone-cold rationalist, will only reach this conclusion on the basis of solid evidence. He, being extremely ethical, will neither present false evidence nor attempt to undermine your rationality. What can he do to convince you that you have died?
I suspect there is nothing he could say or do to convince you of this. Rather, for any sufficiently "final" definition of physical death, there's no way he can demonstrate that you have somehow come out the other side. That's my wager: there is no sound way to convince someone, even while in the afterlife, that there is such a thing; thus, we should never believe in an afterlife knowing that we could never accept it even if actually there.
Am I wrong? Has this been proposed before? Is there any thing which, while actually true, could never be demonstrated in this manner?
I think that, if correct, this may point to a special class of untruths. Sort of... Bayesian contradictions, things which could never be sufficiently demonstrated.
Naturally, lukeprog's earlier post has me thinking on religious lines.