This is what I believe, to be a general outline of ghost, apparitions and how they came to be. Now remember this is just MY theory. Time can be seen as an ever running river. That constantly flows, and is always "occurring". So as I'm typing the battle of Hastings is also taking place. Now ghost are infamously known to appear in old buildings and such. The reason why, is because as someone is in there, time is also going on in the time of the ghost. So if a person is laying on a bed, in an old hotel. The action triggers a loop into time that allows the two presents to see into each other. Hence causing the belief that someone is walking up the stairs. When technnically someone IS walking up the stairs. That's why it doesn't happen in modern buildings, although it will eventually. Chances are you won't trigger a response like this on purpose. Anyways this was my first ever thread. It was typed on the spot so it is poorly written. I hope you can connect the dots on the theory I just explained. Has it been brought up before? I'm not sure, I call it the Gerson Ghost Theory!
I hope I got your mind going. Feel free to comment, but don't bash me too bad.