I truly believe what we perceive as ghosts is just there energy left behind by them. Because if a man lives alone and sets in the same spot every day, I am positive his energy could almost indefinitely be embedded in that spot.
It is like how when someone is upset, even if your not looking at them you can feel the feeling in the room. People who can sense the feelings of the air are more prone to perceive ghosts. I believe just like us sensing someones anger, depression, or sadness by being in the room with them, we can also feel it after there death. If a person lives in a house for 30 years alone, and dies alone. I am almost positive its possible for his sadness, grief and depression that filled his rooms could actually stay. Its like how water can soak into things, who says feelings over time could not do the same? When you walk into a church that is always filled with happiness, does it not feel happy, even if your in there alone?
Just felt like ranting.