I’ve been playing around with Quora recently, which is a new social website revolving around questions and answers. Since some of the questions posed are contentious, it’s possible to get into some quite fun debates on there, although the system of voting and thanking generally means that sane, well-reasoned and well-evidenced answers rise to the top.

In a recent exchange, I ended up posting a very long comment which the Quora software mangled somewhat when I pasted it from Word. I’ve therefore reproduced it here, with a few snippets of the earlier conversation for context. You can see the whole saga, complete with any future additions, here.

Zoletta Cherrystone
I have had more than one ‘ghost’ experience, and completely believe in the spiritual world. I believe this without doubt, because of what I’ve witnessed with my own eyes.

Tom Salinsky
I’ve seen plenty of things with my own eyes which were later proved not to be the case. You’ve never seen an optical illusion before? First-hand testimony is a very poor way to establish objective truths about the world.

Well, Tom, I don’t think there’s a test to prove that pretty much all of us can ‘feel’ when a person is standing behind us, but we all know we can.

I said, earlier, that I’ve had more than one ‘ghost’ experience. It was a huge understatement. I’ve had dozens, from early childhood until the present. Things that simply have no other explanation, and some of which are too connected with a dead relative to dismiss.

An optical illusion is not going to explain away a light switch snapping (I say snapping because this was a very old one, and hard to maneuver) into the off position. Or a book physically being placed in a peculiar way in a room other then where you left it just as you fell asleep with no one else in the house with you. Or hearing your name being spoken aloud in a new house when you’re in it entirely alone, accompanied by other instances of objects being slammed down at key moments (no vibrations, no way for these items to casually fall on their own) and then to make phone calls and find out that the previous owner experienced all the same.

“Am I a man dreaming I’m a butterfly, or am I a butterfly dreaming I’m a man?”

With all the paranormal investigators out there recording voices, snapping photos, and catching things on tape, that’s about as much ‘proof’ that anybody is ever going to get, yet still it is dismissed.

So my question to you now becomes this: What is required to ‘prove’ this phenomena?

This is going to be far too long, but here goes…

ZC: Well, Tom, I don’t think there’s a test to prove that pretty much all of us can ‘feel’ when a person is standing behind us, but we all know we can.

TS: This shows a distinct lack of imagination. Can you really not conceive of a way to test this hypothesis? Here’s one. Blindfold a series of subjects and deafen them by playing white noise in their ears (since this is not a test of one’s ability to see or hear people). According to a predetermined, but random sequence, have people either stand behind them or not, and have the subject indicate when they feel a presence. If they are right much more often than chance would suggest then there is a real ability here. BUT UNTIL A TEST LIKE THIS IS DONE, we can’t say for sure that such a phenomenon exists. Personal testimony is not enough. Confirmation bias will ensure that we remember only those occasions when we ‘feel’ someone behind us and are correct. (I do not give an opinion as to whether this ability is real or not.)

ZC: An optical illusion is not going to explain away a light switch snapping (I say snapping because this was a very old one, and hard to maneuver) into the off position… etc

TS: All of these are artifacts – events in the past for which the only evidence is your testimony, which may or may not be distorted by time, the limitations of your senses and your desire to believe in the existence of spirits. But you don’t get to jump from “I have no explanation for the movement of this light switch / book / strange noise / falling objects, and BECAUSE I HAVE NO EXPLANATION IT THEREFORE MUST BE A GHOST.” You are just substituting one unknown for another. I submit that all of these phenomena, even if they could be definitely established as real (which at the present time, they cannot) could be equally well “explained” by aliens, Jesus, elves, fairies or any other fantasies you choose to invent. Finding out objective truths about the world is not done by identifying apparently anomalous events and then announcing that your predetermined idea is “the only explanation”.

ZC: With all the paranormal investigators out there recording voices, snapping photos, and catching things on tape, that’s about as much ‘proof’ that anybody is ever going to get, yet still it is dismissed.

TS: But not dismissed without reason. Dismissed because the supposed evidence is so weak. “Ghost” photos are routinely analysed and shown to have mundane explanations, but even when no mundane explanation presents itself, my argument above still applies. What you call “ghost”, I call “alien”, and someone else calls “Jesus” and so on, depending on taste, upbringing, bias and so on – depending in no way on the phenomenon itself.

Recording voices is a particularly clear example. So-called EVP (electronic voice phenomena) are generally agreed to be artifacts of recording devices with automatic gain control, coupled with the human brain’s automatic pattern-detecting habits. The former is a matter of electronics. If you have a device which records more when the environment is quiet, it will record more NOISE. Then, a person hoping to hear particular words or phrases will manage to pick them out of that noise. You rubbish my showing how your subjective experiences may be unreliable with reference to optical illusions, but this is an auditory illusion. The phenomenon is known as pareidolia – people finding patterns in randomness – and it explains why people believe they see Jesus in a piece of burnt toast, faces on the surface of the moon and hear voices in static.

Here’s a great example of how easy it is to hear words that aren’t really there – once you know what it is you are supposed to be hearing.

Skeptic and magician Derren Brown was confronted with a devotee of EVP who swore that when he asked questions of spirits, they obediently provided meaningful answers which were recorded during silences on his Dictaphone. When Derren went recording with him and was given the opportunity to ask a question himself, he said “If there really is a spirit there, confirm your presence by remaining silent once I’ve finished speaking.” On playing back the tape, the usual roar of static was heard – exactly as one would expect if the phenomenon was entirely due to automatic gain (and subsequent pareidolia). Exactly the opposite behaviour of the previously always-obliging phantoms.

ZC: So my question to you now becomes this: What is required to ‘prove’ this phenomena?

TS: Just the same as to prove any phenomena. At a minimum: the result must be repeatable (which your accounts of magic light switches and falling objects are not, unless you propose to take me to a haunted house – a proposition I would relish); and it must have a low probability of happening by chance (which is not true of EVP). I have yet to see a piece of evidence for ghosts which would even meet these two criteria, but notice that these are necessary but not sufficient to establish that a particular phenomenon or effect is real. And even if the reality of an effect is established, this doe not in turn immediately allow us to conclude that the cause is a departed spirit. Once again, you only get to jump straight from “unexplained” to “ghosts” by CHOOSING ghosts, not by making a genuine discovery about the world.

The magician and escapologist Harry Houdini devoted many of his later years to exposing the mechanisms used by fraudulent psychics, but nevertheless he hoped against hope that the stories they told were true and that he could be reunited with his beloved mother. Before he died, he arranged with his wife that she should hold a séance every Halloween after his death. He also gave her a secret phrase known only to the two of them. Houdini’s codeword reproduced by a psychic after his passing would have been marvellously strong evidence for the existence of life after death. Sadly, after ten attempts and no appearances by Houdini’s spirit, his wife abandoned the task.

Of course, the real reason that most people don’t believe in ghosts is not because the evidence is so flimsy (although it is). It’s because there is no plausible mechanism which could possibly exist to preserve the personality after death. Every single experiment ever done on the subject shows us that the personality and memories are generated by the brain. After death, that pattern of neurons is destroyed and no possible way exists for that pattern to be preserved, with no power being fed in to the system and with no physical substrate on which the pattern could be recorded.

But I don’t even ask for scientific plausibility. Let’s start with one repeatable, low-probability event, the experiment designed in such a way as to rule out conscious or unconscious fraud. If we discover a genuine phenomenon, then we can start theorising about possible causes.

See, I said this would be too long.