1. ELECTROMAGNETIC FIELDS
For decades, a Canadian neuroscientist named Michael Persinger studied the effects of electromagnetic fields on people’s perceptions of ghosts, hypothesizing that pulsed magnetic fields, imperceptible on a conscious level, can make people feel as if there is a “presence” in the room with them by causing unusual activity patterns in the brain’s temporal lobes. Persinger studied people in his lab wearing a so-called “God Helmet,” finding that certain patterns of weak magnetic fields over someone’s head for 15 to 30 minutes can create the perception that there’s an invisible presence in the room.
Infrasound is sound at levels so low humans can’t hear it (though other animals, like elephants, can). Low frequency vibrations can cause distinct physiological discomfort. Scientists studying the effects of wind turbines and traffic noise near residences have found that low-frequency noise can cause disorientation, feelings of panic, changes in heart rate and blood pressure, and other effects that could easily be associated with being visited by a ghost.
For instance, in a 1998 paper on natural causes of hauntings, engineer Vic Tandy described working for a medical equipment manufacturer, whose labs included a reportedly haunted room. Whenever Tandy worked in this particular lab, he felt depressed and uncomfortable, often hearing and seeing odd things—including an apparition that definitely looked like a ghost. Eventually, he discovered that the room was home to a 19 Hz standing wave coming from a fan, which was sending out the inaudible vibrations that caused the disorienting effects. Further studies also show links between infrasound and bizarre sensations like getting chills down the spine or feeling uneasy.
Shane Rogers, an engineering professor at Clarkson University, spent months touring reportedly haunted locations looking for not-so-paranormal activity: mold growth. Preliminary research indicated that some molds can cause symptoms that sound pretty ghostly—like irrational fear and dementia. “I’ve watched a lot of ghost shows,” he told Mental Floss in 2015.
4. CARBON MONOXIDE POISONING
In 1921, a doctor named W.H. Wilmer published an odd story about a haunted house in the American Journal of Ophthalmology. The family who lived in this haunted residence, called the H family in the medical literature, began experiencing weird phenomena when they moved into an old house—hearing furniture moving around and strange voices in the night, feeling the presence of invisible specters. They reported being held down in bed by ghosts, feeling weak, and more. As it turned out, a faulty furnace was filling their house with carbon monoxide, causing aural and visual hallucinations. The furnace was fixed, and the H family went back to their lives, sans ghosts.