When people experience “ghosts,” there can be any number of physical and/or psychological things going on. The causes are so numerous that there is no way I could describe them in any kind of a meaningful way without writing a whole book or three on the subject, but I can tell you about some general principles, and a few specific ones, that account for the ghostings. And I’ll provide info on books that go into this subject in much more detail.

But let’s DIP OUR TOE IN.

Scientific inquiry didn’t really come about for a long, long time—so we were forced to try to come up with explanations for why the world worked the way it did. Some of these explanations are awesome. Some are very weird. Most, we pay no attention to today—they would seem absurd. Some we do.

Ghosts explain a lot of things. In the biggest sense, they provide an explanation of what happens to people when they are no longer with us. And for hundreds (thousands) of years, they explained weird noises, common physical phenomena we now understand, unfortunate things, and fortunate things. A window is open that was definitely locked last night? Ghosts. That noise upstairs? Ghosts.

But sometimes people saw things—and still see things—that cannot possibly be there! GHOSTS!

Well, more likely, your brain doing its job, but in a weird way. You brain has many tasks to perform, but one of the primary tasks is to take all that STUFF out there, STUFF that is not you, to take it in as various kinds of information, and it make it make sense. And loads of times, the picture has pieces missing. The data is simply not there. It’s the brain’s job to fill in the blanks. To do this, your brain creates illusions. It will do this whether you want it to or not. You don’t know it’s happening. And you need this. Without illusion, our mental landscape would be very different and impoverished indeed.

And it starts with expectation—the kind of standard background filler the brain sticks in, often based on previous data. Imagine a foggy road. If you see a form moving down a road, but you can’t quite make out what it is—but you know it’s likely to be a car. It’s not likely to be a giant, sentient hamburger bun that’s grown wheels, for example.* You think: car. You see: car.

You might not be seeing much at all, though.

When you look out into the world, you see one continuous stream of color vision with a wide field of view with no holes or defects.  This is a fundamental illusion.  Each eye has a blind spot, quite a big one. Your brain fills in this gap with a guess of what it thinks is there. Likewise most of your field of view is actually black and white, but once again the brain fills in the gaps. Your vision is not really a continuous stream, but is constantly stopping and starting, but your brain edits out the gaps. It may even change what’s there.

Here’s one example of how the brain changes around what’s really going on. MEET THE MCGURK EFFECT: awesome name for an awesome thing.

So how does this relate to ghosts?  Like this: our brains take the expectation we have of the world and try to match that up with the sensory data coming in. The disparity is created because the model of the world is stronger than the actual sensory data. If the senses do not contradict the expectation from our mental models too strongly, then what we perceive is not the real concrete outside world but our expectation of it. We can’t help but perceive it that way. The McGurk Effect works whether you know about it or not, because the expectation is so built in, it is impossible to reason out.

If you see a shape at a window, your brain may think there might be a person peering out, so if the shape doesn’t contradict the shape of a person (think of the shapes that clouds make – sometimes they look like things) you might perceive a person to be there whether they are or not. 

Your brain really wants to see faces. Like, it wants to see faces so bad, it will put them in when they are not there. Faces and your brain are an OTP.

Likewise if you hear a bump or an unusual sound in the night caused by an old building creaking as it cools at night, if it doesn’t contradict too strongly the expectation of a voice or a footstep, then you may perceive it as such.

Does not prove there are no ghosts? No. But it does suggest that there are alternative explanations to some people’s experiences of ghosts. WE HAVEN’T EVEN SCRATCHED THE SURFACE.

Some recommended reading: Ghost Hunters: William James and the Search for Scientific Proof of Life After Death by Deborah Blum. Over a hundred years ago, spiritualism (ghostings, séances and the like) were all the rage. And Science got interested. Serious study was devoted to the topic, and players such as William James of Harvard University, Sir Arthur Conan Doyle, and Harry Houdini were all involved in the quest. Everything about this book is awesome.

* This has only happened once, that I know of.