I do belive there are two main catagorys of ghosts, the tape theory and intellegent hauntings. We are made of nurons, which work through electronical charge, so for me we can leave memorys on locations, like houses. These can be like recordings of a previous time, a event that affected the person, or something they did all the time. This continues and shows no sign of knowledge of your exhistance.
Im still looking into finding conclusive proof, but every investigation i keep getting amazed by what is found and closer to beliving it.
for me personally, this energy shows explination for evps, for emf fields and for orbs. 99% of the orbs captured on digital cameras are just problems caused by the flash being so close the the lens, but there are some that are spirits trying to show themselfs. I might be wrong with that idea, but i dont mind being wrong sometimes...