The mind is a very powerful thing, its been said a million times and no one really knows the true power of ones mind.
One of my theories on ghosts is that they are the memories of someone, preserved. Like an astral projection, the power of the mind creates that image because of how much that person is missed. Others that have seen the image could never forget it, so therefore it lives on.
Thats just one of my many theorys.
One thought that I've had, is that ghosts are exiled spirits. If you remember, when Satan rebelled against God, he and 1/3 of the hosts of heaven were cast out. They were sent to this earth to live. Now a lot of those spirits have got to be pretty bored. So I think that the ghosts we see are those spirits appearing in the form of deceased presons, just for their own amusement.
I believe that those we love, who have passed on, keep a close watch on us. My husband's mother died more than 2 years before we met. I worried that she might not approve of me. I am 21 years older than my husband. After we were married I still used to wonder what she thought. Paul, my husband, told me that his mother always said that finding a penny in strange places means someone you've lost is thinking of you. Suddenly we were finding pennies everywhere, even in the dresser of our hotel room on our honeymoon. Ever since whenever we are going through a hard time we will find a penny in an unusual place and Paul will say "Thanks Mum, I love you too" I know now that she is happy for us and will always watch over us.
I carry a neutral perception about ghosts. I have experienced some ghost-like activities in past, but still I consider that they do not exist. I neither accept nor deny their existence. I tend to say they do not exist, firmly !
Ghosts are imprints left on an energetic level in certain locations and with some people. They are usually left there by a strong vibration of emotion or spiritual event, positive or negative.
They are definitely not the actual souls of the dead.
This is proven by the fact that the emotional image of the same person can be found at different locations. The famous ghost of Queen Elizabeth the 1st gives an apparition at Hampton Court and Winsor Castle, at different times and appearing from different ages in her life.
I have walked through a Tudor ghost, and I know our house here also has a presence that we notice from time to time.
I always thought of ghosts the same way the movie "The Others" portrayed it. They are right here with us but sort of on a different plane of existence. The movie "Ghost" also showed that as well. Seems like strong emotion makes the planes crisscross.