Before I go into this, I firmly declare that no, I dont believe in ghosts. That being said...
I think some of the problem with the idea of ghosts and other paranormal stuff is the way we approach them. For several months, there was a show I used to watch called "Haunting". The reason I would watch it week after week was to look for similarities. I was curious to see if the similarities I found would lead me to think in a certain direction about what these people were going through. To find something that ALL of them had in common so that I could apply some rationality to them. Now, granted, this is by no means a scientific study of paranormal activity, it was just me watching TV and using an analytical approach to what was occuring. I have never spent any time looking anything up about ghosts, as I dont really care about that subject, but I do love to learn things that I dont know. I think of it much the same as people who watch shows like "24" with plot lines that twist and turn from week to week, all the while trying to figure out what is going on. (Just so you dont all think I am nuts).
Anyway, I found very little to be consistent in all the shows, and most of the people I think were nut jobs, but I would say a majority of them had children involved in some way. I would also say that a lot of the ghosts, while they were alive, had traumatic experiences, which led them to be "haunting" a house. Again, this is not scientific, it was just me watching TV, thinking about it logically to trying and explain some of it without the slightest bit of evidence to back it up, other than the show. (Really, Im not nuts!)
I came up with 2 possibilities, just thinking about it from the "data" (HAHA) I got from the TV shows.
1. What if a human brain, during times of extreme stress can imprint some sort of magnetic field on an area or a physical object. Much like a magnet, when touching something metal can impart some of its magnetism to the metal object (Hysteresis). During some of the shows, people would bring in "Paranormal investigators" with magnetic field detectors that would be going bananas wherever the people in the house said the "ghosts" were. And if this was the case, other people may be able to "pick up" on these signals that are either strong or weak forces. Again, most of these shows had children involved so I rationalized that maybe children could pick up on them easier than adults. How they take shape, I have no idea. Is it true? No I dont think so, but I tend not to toss every supernatural experience that people have into the scrap heap without giving it a thurough logical overview in my own mind.
2. What if houses or objects have something like a "physical memory" (not the same as the computer term). What if a person, again under extremes of stress can impart memory or experience on an area which could be recalled and even amplified by specific types of people. Children or perhaps people already under stress may pick them up better than others. Stress and fear both have the ability to cause our heart rate to go up, our senses to heighten, our bodies to tense up in preparation for action. Why would it be such a stretch to think it could heighten our ability to sense things that we dont know about yet?
Bottom line. Do I believe in ghosts or supernatural spirits that are somehow trapped between this world and the next? No way. Do I believe that some (a few maybe) could really be experiencing something beyond our ability to describe it logically and scientifically? Yep, as scientists, we don't know everything yet, so I think we have to at least concede the possibility that they are experiencing something that we cant, as yet, explain. Someday we might know more, but for now, I think we could safely giggle to ourselves about the whole idea of supernatural hauntings and ghosts.