As a practitioner of one of the world's 3 main religions, I was taught that there are other planes of existence, or other dimensions. Although it is yet to be proven by quantum physics or the study of subatomic particles, I for one do believe that different subatomic particles exist in these different dimensions, each with its own governing laws of physics.
In my culture, there are so many stories of fold from "other dimensions" such as the "litttle people," whom purportedly can materialize in our own dimension whenever they choose. And there are also stories of people who got caught in these hidden dimensions, sometimes even taken captive by the little people. I heard from a man (who claimed he has been in that other dimension) that 1 day in their dimension equals 40 of our own days, if you believe that. And the creatures that live there are so fantastic... I couldn't even begin to describe what he said.
I believe each of us gives out an "aura" or life force. I think this so-called life force consists of subatomic particles that are yet to be explained. Then maybe - just maybe - these particles actually can co-exist in different planes of existence... occasionall "punching" a hole in the temporal fabric. Or maybe our life force collects enough of these "inter-dimensional subatomic particles" that literally "clings" to our own, forming some sort of mold that follows our body so precisely, even down to the electrical impulses of our brain. Thus it could be said that we have created a "carbon copy" of ourselves without us even knowing it!
Now what happens to people who unusually strong life force? I think their "subatomic carbon copy" became so strong and pronounced that it can take on its own life and existence and do its own thing. I think we may know these occurences as poltergeists, which usually revolve on people.
During times of crises or intense emotional distress, the brain sends out a much stronger or even overloaded levels of signal. Imagine someone at the moment of a horrifying death, or a wrongful death, or a demise that is so unjust. Maybe the brain sends out a such a cry, a literal "supernova" of thought impulse that solidifies or reinforces the "carbon copy." Then what happens? The body dies but the "carbon copy shell" remains, alone, abandoned. Still retaining some identity of the original person, this shell walks alone and drifts in and out of the different dimensions.
I think this is how a ghost came to be. They are but a living essence void of a body. Some are weak and benign and, with time, will fade away to nothingness. But others may be stronger and can actually influence the subatomic particles of our own dimension, literally "moving" objects or influencing the environment (cold chills, etc). Perhaps they can even merge with a person's body and try to control it (possession). Ghosts can feed off our thoughts and life force too, I suppose. I guess there is an inherent danger when people started worshipping demons or spirits, because these things can actually become stronger when fed with our thought impulses. It is interesting to note that ghosts of animals are so rarely reported, maybe because their self-conscious is at such a low level that they can't create a stable aura.
Heck, I've seen many strange things in my lifetime, a few ghosts even. One even tried to possess me and another actually bit me on the arm. But I guess until now nobody can physically prove that ghosts exist.
If any of you guys have any ideas on the subject, I'd sure love to hear them.