A thought experiment on "ghosts"

I don't believe in ghosts. No one is reaching out from the grave to send you a message or scare you away from an old hotel. But the sheer age and number of ghost stories and legends makes them interesting to think about.  Certainly sane, sober people - most of us surely know at least one - genuinely believe they've encountered something ghostly.

Can one conjure up (hah hah) a situation where something could be "really there" to an observer? I think George Tyrell, in in his book Apparitions, tried the hardest to think this through.

Assume for a moment there is something an objective observer (someone not in a heightened emotional state just due to the location or recent events) perceives as a ghost. The closest thing to a "rational" possibility seems to be that a ghost is some unknown form of energy that lingers near a death and causes the mind of an observer (not the eyes) to perceive a pattern (this is the only idea that offers a semblance of sense about why you'd see a ghost in human form and clothed). There is no consciousness, and it can affect one observer and not another (somehow).

If we further assume this phenomenon exists, then there's the question of what it could and could not do. I can't come up with a thought experiment that lets me see any sort of manipulation of physical objects, like the bouncing flashlight that's making the rounds of the Internet as "proof." However, one could imagine even very small energies doing all kinds of things to the fragile brain, making it manufacture sounds or smells.  

In my mother's childhood home, built in 1790 in Bangor, Maine, was a main bedroom where people occasionally heard a sound like a man's boot being slid off and dropping to the floor (always one, never two). As that bedroom - indeed, that bed - was where an ancestor had died after being invalided out following wounds at the second battle of Bull Run, it wasn't hard to connect the two. There can be all kinds of noises in old houses, though the coincidence in type of sound is certainly interesting. Could energy that is weaker form just a sense impression that isn't visual? 

My wife worked at a Philadelphia hospital with a "haunted room," where apparitions, shadows of people going by the window (on the third floor, at night - Deb saw this one herself) and other things were reported, most interestingly the habit of a printer at the nurses' station (high tech for the 1970s) to produce a strip of vital signs for a patient in that room when there wasn't any patient. Back in the 1980s I write to British "ghost hunter" Peter Underwood on this, and he said he had another report from the same hospital but, due to privacy, could not share it. Deb, a woman of great intelligence (she later added a law degree to her resume) still doesn't know just what to think of her shadow-figure.

Any "ghost energy" wouldn't work at much of a distance (assuming it works like known energies), given the inverse square law and the way energy drops off sharply with distance. My mother was once awakened by a strong smell of raisin toast - my grandfather's unwavering choice of breakfast - on the morning my grandfather died a continent away. A little far for a blip of unknown energy. However, she placed this event in another category: being Catholic, she presumed it was an "I'm ok" sign God had permitted or caused to be manifested for her. Catholic theology warns people to stay away from all aspects of the paranormal as possibly being Satanic (going to a seance out of curiosity is "a very serious sin" according to one official book) but it doesn't rule out God allowing some kind of vision or even contact on a sort of case-by-case basis.
"Ghost energy" also wouldn't work for "phantasms of the living" as the venerable SPR called them. If you think such events are real, there has to be a quite separate explanation. I think we can pretty confidently ascribe this to "mind playing ticks on you," and the same applies for people who meet our hypothetical ghost energy and think it's interacting directly with them, such as by conversing.

That's about as far as I can take this. I don't believe in ghosts - but are we sure we know everything that can cause a person to believe they've met one?