National Geographic Channel - Original Air Date: 1/24/10
A group of researchers composed of scientists investigates Eastern State Penitentiary, one of the "most haunted" prisons in America. Along the way, the show explains that most ghost hunting expeditions don't have the equipment to actually detect ghosts -- as no one knows what ghosts are made of; they are far more likely (with EMF detectors) to detect their own equipment. The team also posits that ghosts, which are said to pass through walls, cannot be made of normal atoms, though they could be made of neutrinos, which can pass through normal matter. Unfortunately, ghost hunters cannot detect neutrinos. They then show, through experimentation, that people who believe in ghosts are more likely to report strange happenings in the prison; one group is told that the prison is haunted, the other that sightings seldom happen there. The believers report far more strange feelings and experiences than the skeptics.
Another group of scientists posits that sound -- infrasound -- may contribute to people feeling that a place is haunted. A 3D scan of the prison reveals that it seems ideal for magnifying low-frequency sounds. Such sounds can contribute to eerie feelings people get. Once again, they experiment on two groups, one in an area with infrasound, one without. The people subjected to infrasound report far more uneasiness -- and even the scientist running the experiment reports feeling strange. Infrasound works by vibrating body parts, including the eye and inner ear (which controls balance) though it cannot be heard -- it can even cause flashes of light and distorted vision. The scientists are impressed with how strong the reactions are from both believers and skeptics in the infrasound area. They conclude that sound can lead to sightings, especially in a place, like the prison, that will amplify them. They note that though they now have some scientific theories about why ghosts are encountered, they have not disproved the existence of ghosts.
In the final part of the show, the team monitors the prison with a battery of scientific equipment, "a virtual ambush of cutting edge technology," including audio and video and heat sensors. The next day, they return to see what the equipment found. They find a strange sound at 3:15 am, and the thermal camera reveals a spectral blue glow on the ceiling: cold/moisture on a skylight -- rain on the roof, causing infrasound. The researchers suggest that the physical environment of the prison is conducive to people seeing and hearing things, and even picking things up on camera and recorders. Is this a "final" explanation for ghosts? Maybe not, but it does confirm that people, and equipment, can be fooled by natural phenomena.