Infrared Cameras and Ghost Hunting
More often than not, infrared cameras create false-positive readings that amateur ghost hunters mistake for ghostly activity.
II recently saw an episode of the "reality" TV show Ghost Hunters, and the T.A.P.S. team used an infrared camera to look for ghosts. At one point a camera captured a form in the general shape of a person near a wall--but everyone is accounted for and the ghost hunters see nothing except via the camera. Any idea what that was?
Ghost Hunters is the world's top ghost-themed television show, and it has been misinforming the public about both ghosts and science for six seasons (see "Ghost-Hunting Mistakes: Science and Pseudoscience in Ghost Investigations" on page 44 of this issue). The Ghost Hunters team prides itself on using modern technology to detect ghosts and other paranormal phenomena, and infrared cameras are among their staple devices. Like the other scientific gear that ghost hunters employ, infrared cameras are valid and useful devices when used correctly.
More often than not, infrared cameras create false-positive readings that amateur ghost hunters mistake for ghostly activity. Without seeing the specific video clip that you are referring to, it's impossible to know exactly what was recorded, but in my years of ghost investigations I have encountered many similar readings. To uninformed audiences and unscientific investigators, the fact that an infrared camera reveals a human-shaped form where clearly no one is around can seem very spooky and mysterious. There is, however, often a perfectly rational and scientific explanation.
The first step to explaining the nature of these "ghostly auras" is understanding the nature of the electromagnetic spectrum. Visible light--the light that our eyes can see--makes up only a fraction of the electromagnetic waves in the world. The next-lowest category of frequency below visible light (and above radio waves and microwaves) consists of infrared electromagnetic waves. In a nutshell, infrared cameras simply allow us to see a lower-frequency wavelength, detecting variations in heat instead of light.
Heat is of course far less transient than light; if we turn off a light switch in a closed room, the area goes dark almost instantly. But if we turn off a source of heat--including body heat--in an area or room, the heat may remain long after the source has been removed. This can seem mysterious to amateur ghost hunters.
At an investigation I carried out last year for the TV show MysteryQuest, one of the ghost hunters used a forward looking infrared (FLIR) camera to detect a foot-long vertical warm spot on a pillar. No one in the room could explain what caused it; one person suggested it was a sign that a ghost had been watching us. In fact I had seen one of the ghost hunters leaning against the pillar a few minutes earlier, and the warm spot matched exactly the height and shape of the man's upper arm. All the ghost hunters swore that none of them had leaned against the pole, but when I suggested they review a video tape, they saw I was correct. If they had not been recording that area (or if I hadn't seen the investigator create the warm spot), it likely would have remained mysterious. This is quite common on TV ghost-hunting shows, and it is likely the explanation for what you saw.