well there is a specie like us, the pleiadians... they are a higher vibrational energy beings. They apear totaly invisible to us. since we are low energy compared.

its like clicking on the remote control and you cant see the infrared, but when you aim at a camera digitaly, it will show. So they also have to lower their energy, to make contact with us.

That energy will anyway show as light, bright entities. So i think there is something here that points perhaps that the ghosts are nothing more then they ( the aliens, vibrating in lower energy so they can ve more visible... same with their flying ships.