I'm reading a book right now all about hauntings...it's very interesting. According to the author ghosts are earthbound spirits, that is, they can't move to a higher plane above earth's atmosphere. This may be because they're afraid of going to hell, they feel like they have unfinished business, their death was too sudden and traumatic, or because a loved one's grief about them is binding them here. People with some degree of psychic sensitivity are more likely to see or sense a presence than people with none whatsoever. Strong negative emotions like anger and fear can also allow ghosts to manifest themselves. Evidently ghosts can be convinced to leave for a higher plane by psychics (usually), when they know that there's no hell to worry about or that everything's okay on earth or whatever.
