One of my books is an edited edition of Sir Arthur Conan Doyle's The New Revelation, subtitled, for my version, "The Annotated, Debunked, and Exposed Edition." From time to time I include it in my daily cycle of Twitter posts, the majority of which are intended to sell books. Not too long ago, a reader noted that, while he hadn't read the book, he questioned whether I could really disprove the "private" revelations of a Medium.
I didn't see much point in responding on Twitter, but I'll mention the obvious response now. There's no reason for me to attempt to disprove such revelations, for the entire burden of proof is on the Medium to show that these revelations are correct and, more importantly, that the only possible source for them was the spirit of a dead person.
That's how it works. The person asserting something to be true has the burden of proof. If you say, "There is a God," and I say, "I don't believe you," it's not up to me to show he isn't there, it's up to you to show that he is.
If one were to ask, "What constitutes the strongest disproof of God as conventionally perceived," I think the most obvious answer would be, "There is more than one religion." Doesn't it seem logical that, if an omniscient, omnipotent God actually existed, and had revealed himself, everyone would worship in the same manner? Why would a genuine God reveal himself as a cosmic unity to the Jews, as a tripartite unity to Christians, and as again a unity, but with a conflicting set of laws and history, to the Muslims? Not to mention as half of a dualistic divinity to Zoroastrians, a flying snake to the Aztecs, a polytheistic monotheistic entity to the Hindus, and any number of other forms to various cultures over the centuries. If he were real, and there was only one of him, why wouldn't all cultures have perceived him in the same way?
An interesting quirk in Christianity, by the way, is the question of whether God is to be perceived as a Trinity or a Unity. Jesus is asked to name the most important commandment in the Gospels, and the answer quoted is almost always the version from Matthew, "Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind." (Matt. 22:37) Luke has it the same way.
The thing is, of the three synoptic Gospels, Matthew and Luke are both largely based on Mark, which was written first. Both also differ from Mark in one very important way. While these two give the answer to "What is the most important commandment" in this way, Mark begins what is, in fact, a quoted passage, one verse earlier, saying, "And Jesus answered him, The first of all the commandments is, Hear O Israel; the Lord our God is one." (Mark 12:29) A rather important omission, one might argue, for it suggests that Jesus, while considered a part of the Trinity, was himself a Unitarian who didn't see himself as divine. The reason it was left out of Matthew and Luke is obvious; the reason no one ever excised it from Mark is somewhat more obscure. After all, no one seemed to have a problem with tacking a dozen verses onto the end of Mark, including four purporting to be a command to evangelize the world from a risen Jesus.
The living Jesus generally seemed pretty indifferent to anyone who wasn't Jewish. He might help out a gentile from time to time, but usually only after a good bit of prodding. The Gospels, written after the Pauline epistles, and at a time when the Church was trying to establish a tradition of Jesus as having once lived on earth in human form, would later be modified to conform to what the established church was teaching. Since the appeal of Christianity was almost entirely to gentiles, it was necessary to include a mission to that polity. Imagine the chagrin of modern Christians if they thought Jesus would return and ignore them because they're not Jewish.
Jesus himself seemed to be preaching a kind of early reformed (as distinct from Reform) Judaism. Whether Jesus himself was entirely mythical, or based on an actual person, is a matter for a different essay. Historically, if he was a real person, he made no obvious impact on the contemporary world. The New Testament speaks of earthquakes, darkness, and walking dead people at the time of his execution, yet apparently no one living in Jerusalem, or anywhere else for that matter, at the time noticed any of this. Josephus, who was not a contemporary of Jesus (he was born from seven to eleven years after Jesus' execution), supposedly mentions him twice, but one of the mentions is an obvious interpolation, and the other seems to be about someone else who just happens to have the same (rather common) name.
More significantly, while Josephus has very little good to say about Herod the Great, the one crime he never accuses him of is the "slaughter of the innocents." This suggests that either this biblical massacre actually involved only a handful of infants or, more likely, that it simply never happened. It's the sort of thing Herod would have done, had he believed there was a threat to his reign, but none of his contemporaries nor any first century historians other than the Gospel writers ever accused him of it.
As to claims that no one would believe these things if they were not true, all manner of miraculous events were reported at the birth of each of the Kims in North Korea, and the people there seem to have no trouble believing them. Many American Conservatives believe everything Donald Trump says, even though the man often seem pathologically incapable of telling the truth even when there's no reason not to.
Returning to psychic phenomena, we must always ask the question, "Which is more logical? that a Medium is communicating with someone's dead relative? or that the Medium is relating things he learned from other source, or, for that matter, is simply saying something comforting and the client is subconsciously attaching significance to it?" No Medium has ever produced statistically significant result under properly controlled conditions. Watching psychic mediums at work on television almost always reveals their methods to anyone paying attention.
More often than not, the Medium starts with something vague, and that would likely apply to a fair number of the people in the audience. Receipt of a message from someone whose name begins with "R," for example. In a room holding a couple hundred people, someone is going to have a recently deceased relative named Robert, Roger, Rachel, Richard, Reinhardt, Rose, Ruby, or some other "R" name. The audience member supplies the actual name, and the Medium then tells the audience member that he's correct, it's from that person.
This is basic cold reading. The audience member actually supplies most of the information, while the Medium continues to throw in vague comments that his victim will only remember later if they prove to be correct. If the victim fails to provide sufficient feedback, the Medium is unable to give it back to the victim, and eventually will end up saying that the spirits are being reticent that day, or that conditions aren't conducive to psychic transference, or some such twaddle.
Psychics do have one thing in common with most clergy. Either they are deliberate frauds, or they have succeeded in deluding themselves that what they are delivering is actually true. There is, after all, zero evidence that consciousness continues after physical death. "Near death" experiences cannot be entered into evidence, for their very name categorizes them as living experiences. "Near death," after all, means "not dead yet." Dreams seem entirely real while we're experiencing them, and what is more natural than for someone who believes he or she is dying than to dream about an afterlife?
Still, the experience is created in one's own brain, and nothing truly suggests that we are capable of experiencing anything once the brain stops functioning. No one has ever actually died and then returned to life to tell what the experience was like. Lots of people have almost died and related their dreams and hallucinations, but no one has literally died and come back.
Perhaps the best thing is to recognize that death will be no more unpleasant than were the 13.72-billion years each of us spent not existing before we were born. It's virtually impossible for a human being to imagine not existing, because none of our conscious memories can be formed before our brain starts to function, and we won't retain long-term memories of anything until three or four years after that. Our entire consciousness has been spent existing. Even if we recognize that the end will simply be oblivion, we somehow can't help feeling we'll be conscious of not being conscious.
On the bright side, the one thing that's almost certain about dying is that the majority of us will never realize that it's happened. We'll just lose consciousness and never regain it. We'll be no more aware that we've died than a glacially-deposited boulder in the middle of a creek realizes that it's wet. We won't see our long-gone family members, but we won't be conscious of not seeing them, either.
Looked at philosophically, discarding belief in an afterlife makes actual life far more significant.