While others will say that they are the work of the Devil and are demonic in origin. In theory, ghosts are the remnants of what was once a human being. Someone, who at one time, had substance on this earth. They exhibit all the mental attributes that you and I have such as thought, conscience, emotions and emotional needs, morals, calculation, ego, personality and everything that makes up the human psyche. My experiences with ghosts and ghost hunting has served to reinforce this ghost theory and I am grateful.
Life is energy.
Energy can neither be created nor destroyed. Science fact is that energy can only change forms. My suggestion is that ghosts are the what, our life energy. When we die, we are still ourselves. Our life energy still exists, only it cannot reside in a body that no longer functions.