In Homer's Odyssey (8th c. BC), while in the underworld Odysseus attempts to hug his mother Anticlea but is unable to do so.
Thrice I sprang towards her, and my heart bade me clasp her, and thrice she flitted from my arms like a shadow or a dream..... “‘My mother, why dost thou not stay for me, who am eager to clasp thee, that even in the house of Hades we two may cast our arms each about the other.... Is this but a phantom (ghost) that august Persephone has sent me, that I may lament and groan the more?
https://en.wikipedia.org/wiki/Shade_(mythology)
Ancient Romans used "umbrae" (shadows) to refer to ghostly spirits, which for me invokes the figures on the wall of Plato's cave
See also the rise of https://en.m.wikipedia.org/wiki/Phantasmagoria in the 19th.
> HAMLET Pale or red?
> HORATIO Nay, very pale.
~1600
I've read of this idea, it's traditional in some cultures, I just don't remember the name of it. I think it's cognate with ideas of doppelgangers and so forth.
I also think there's often an implicit assumption that whatever it is that causes the "imprint" can only reach a certain necessary magnitude that is commensurate with death or dying.
I feel obliged to note this is not my own perspective on things at all, although I admit I like reading about and thinking about these things sometimes as a kind of psychosocial phenomenon, and think it's worthwhile to engage in metaphysical discussions sometimes just as a kind of check.
It's not a theory, just detailed, more self-consistent fiction. Like Tolkien's very detailed descriptions of elves.
I don't see the harm in pondering such theories. After all, the fact we're here and living in the universe at all, means there's a whole bunch of things happening behind the scenes we have no idea about. Perhaps one day, "ghost imprints" will be something science can measure. Or other pseudo-science like telepathy or premonitions, may move into actual science with as yet unknown discoveries. I'm not saying will, but they may.
That is, instead of "ghost-seers dress the ghost", it's the ghost that dresses itself. In fact, that whole paragraph even makes sense once flipped that way:
"[...] ghosts dress themselves, automatically, through unconscious processes. And so we see a ghost in its usual dress because that is the mental picture the ghost has of itself, and this choice of garment is most likely to inspire recognition."
If a ghost is meant to be associated with a spirit or soul, there's no particular reason for them to have any form or be visible at all. But as an exercise in worldbuilding, they can be, and their visual appearance can give all kinds of fascinating clues about their previous existence or the viewers'. I'd rather speculate about that.
When a system has a lot of complexity, it needs a lot of computational resources to be simulated accurately.
When suddenly this complexity is not needed anymore, because the system got "simplified" suddenly. The pockets of available computation diffuse slowly into the environment.
The analog for the scientific person here is like your adaptive grid in the simulation was locally in high resolution because it was needed by the physical process, and suddenly the physical process doesn't need it anymore but the simulation grid stays in high resolution.
When some other high complexity process comes nearby (like another rich soul), it benefits from this increased resolution which usually allows him unconsciously to run his computational wetware in higher gear, like in a form of mildly induced schizophrenia, vivid dreams, or hallucinations.
Brains as general information analyzing devices can perceive the shape of this echo from the past, decoding from the faint ripples the stone that impacted the water.
The mythology of absorbing the essence from the passed is varied across time and places, ranging from soul capturing gems, the fighting to survive against the erosion of time like in Highlander accumulating the energy of your rivals by eating their brain.
Looking at it only as a physical process ("real") will make you miss it. It has to be seen through the lens of the ethereal plane. Information is conserved, but details can be compressed more or less. Degrees of freedom accumulated or used are different things.
However, there's another theory about this (not mine, sadly): "The most common ghosts are the ones that appear dressed in a white sheet with flailing arms. These are people who died while changing their duvet covers and they are condemned to wander in bedrooms forever, trying to find the corners." ;-)
But surely an identity would need to projected onto a ghost to transform it from an unknown haunting in a sheet into a known phantasm recognized by its victim.
Like dimensional digital projectors from our soul or collective consciences onto the sheet to create a ghost seems to be the idea.
I just somehow knew they were a spirit.
Its happened a half a dozen times or so for me, since I was a small child.
Also when people see them that means photons have had to bounce of them and into the observers eyes. The same goes for the sounds they make, they need to move the air molecules for sound to travel.
Or could it be that it all just happens in the observers mind?
But that doesn’t account for poltergeists.
That lead us to a more interesting question, why barn owls are not black?
> "For the face was the face of a woman long dead, and the fingers caressing were fingers of naked bone, and of the body below the waist there was not anything: it melted off into thinnest trailing shadow. Where the eyes of the lover deluded saw youth and grace and beauty, there appeared to the eyes of the watcher horror only, and the emptiness of death." - Lafcadio Hearn, In Ghostly Japan