for any non beleivers, go to any library and glance through a book on quantum mechanics or just try to read A brief history of time by steven hawkings. There are several theories about "ghosts" ranging from leftover energy to areas where different dimensions are seemingly on top of one another therefor people who are "sensitive" can see or sometimes feel a presence. Keep in mind we as humans dont use but a small percent of our brains capabilities. Think how blind people on have 4 senses but they are all abnormally heightened over a normal persons 5 senses. Take the same concept and transform it onto the metaphysical plane.