" All of our evidence about spirits leads us to believe that they are not solid beings. They should be ethereal and resemble smoke more than they do anything tangible. So how can they cast a shadow? How can they block out light if they are gas like entities? Maybe they are really solid apparitions that are mostly invisible to us, like infrared light is undetectable by the human eye. Maybe ghosts are like paper and our infrared light source is the invisible marker that illuminates them. "

― Zak Bagans , Dark World: Into the Shadows with the Lead Investigator of The Ghost Adventures Crew