A brief examination of the science behind ghost hunting

In both the 1984 and 2016 versions of the "Ghostbusters" movie, a group of scientists are shunned by academia for insisting that ghosts not only exist, but can be captured using state-of-the-art technology. While these were not the first fictional stories to depict the paranormal as a legitimate science, they are arguably the most iconic.

This article first appeared in Salon.

The archetype of the gadget-bearing scientist tracking down specters and spooks has since become prevalent, particularly in popular TV shows like "Ghost Hunters."

Today, ghosts are considered the realm of pseudoscience because there is no physical "theory" of how or why they might exist. Because of this, it's difficult to prove — or disprove — their existence. Yet throughout history, that hasn't stopped enterprising scientists and technologists from trying to suss out means of "detecting" them.

Most of these attempts are based on folklore accounts of what ghosts are, with an eye toward guessing what kinds of traces they might leave. When it comes to developing ghost hunting technology, the trendy thinking seems to be: Figure out the kinds of physical clues that a ghost might provide that it was present, then build machines that can identify them. This approach is no doubt necessitated by the paradox of trying to use science to detect the inherently ethereal.

If ghosts or spirits exist in our world, that by definition would mean there was an interaction between the realm of matter, and the realm of the metaphysical. Since the metaphysical is, by definition, impossible to quantify (hypotheses like panpsychism exist to explain the existence of one immaterial substance: consciousness), any scientific approach would need to somehow study the residue or other contact points that were left behind by undead souls in the physical world.

To put it more simply: If you're trying to prove that an invisible man is walking around a room, you won't see his feet, but you might hear his steps and discover his footprints.

The difference between an invisible man and a ghost, of course, is that a human being is still made of flesh and blood, and therefore would leave tangible marks on the world around them even if they were invisible. We do not know what a ghost would actually be made of, which means ghost hunters have to guess how a poltergeist would impact its immediate environment. As such, even when ghost hunters use legitimate scientific equipment, they're doing so based on speculation rather than a clear idea of what they need to look for.

Take electromagnetic field (EMF) detectors. These are some of the most frequently used devices among ghost hunters, who seek out anomalies under the assumption that they signify paranormal activity. Some ghost hunters, like those in the science-focused paranormal investigation group Para Science, seek two types of radiating electromagnetic emissions: ionizing and non-ionizing radiation. They argue that the presence of this radiation in certain contexts can indicate a visitation from an otherworldly presence. Yet there are often mundane explanations for what those detectors pick up, as well. EMF can be found virtually everywhere, and unusual EMF detection is far more likely to reflect incomplete scientific knowledge.

"They're surprised that they're getting results in an old house, when in fact there are all sorts of non-ghost sources such as faulty wiring, nearby microwave towers, sunspot activity and so on," Joe Nickell, a senior fellow at an independent research organization called the Center for Inquiry, told NPR on the subject of EMFs and ghost hunting. "Even the electronic equipment — the walkie-talkies and TV cameras and all the other electronic gadgetry that they're carrying with them — have electromagnetic fields."

This is not how ghost hunters perceive it. As a British businessman who sells supposedly scientific paranormal kits told Live Science, "At a haunted location, strong, erratic fluctuating EMFs are commonly found. It seems these energy fields have some definite connection to the presence of ghosts." Although he acknowledged that no one knows why that alleged connection exists, he added "the anomalous fields are easy to find. Whenever you locate one, a ghost might be present.... any erratic EMF fluctuations you may detect may indicate ghostly activity."

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Yet just because people say a place feels haunted and it happens to have EMFs, that does not mean a haunting is the real-life explanation. There are studies which suggest that exposure to certain types of EMF can lead to physical and psychological side effects like paranoia, nausea and a belief that one is having profound experiences. In the 1980s, a Canadian psychologist named Dr. Michael Persinger created a famous "God Helmet" that placed electromagnetic emitting coils around a subject's head. Once the helmet was activated, the wearer's temporal lobes were pounded with EMFs. More than four out of five of the people who had this happen reported feeling a presence of some kind in the room with them, including on some occasions visions of God.

A similar effect may be happening with infrasound, which paranormal investigators have also claimed is a sign of ghostly doings. Low-frequency infrasound, like EMFs, are all around us, and they can have a seemingly enigmatic effect on our minds and bodies as the audio frequency ranges below the normal human hearing range. Everything from the movements of tectonic plates beneath our feet to the rumbling of thunder clouds in the sky can produce low-frequency infrasound. Depending on the origin and nature of the sound, people who are exposed may experience headaches, dizziness and nausea, as well as psychological effects like anxiety and a feeling of dread. Research suggests that infrasound helps inspire, or at least reinforce, perceptions of paranormal encounters.

There is a great deal of other popular ghost-busting technology. Ghost hunters can use infrared cameras and sensitive microphones, special thermometers to measure ambient temperatures and night vision goggles so they can see in the dark. Unlike Ouija Boards, dowsing rods and Ghost Boxes, these are actual scientific instruments that can be used for valid research. All of them, however, run into the same problem as EMF detectors and infrasound monitoring equipment. Because they are being used based on guesses about what a hypothetical ghost might do, rather than empirically and repeatedly demonstrated facts, their efficacy is, at best, questionable.

RELATED: Why real-life ghost hunters hate "Ghost Hunters"

The implications of using pseudoscience to detect ghosts are much bigger than simply figuring out what happens in the afterlife. As scientist Carl Sagan famously wrote in his 1995 book "The Demon-Haunted World: Science as a Candle in the Dark," humanity suffers overall when people collectively lose their appreciation for authentically scientific approaches toward problem-solving.

"I have a foreboding of an America in my children's or grandchildren's time," Sagan wrote, "when the United States is a service and information economy; when nearly all the manufacturing industries have slipped away to other countries; when awesome technological powers are in the hands of a very few, and no one representing the public interest can even grasp the issues; when the people have lost the ability to set their own agendas or knowledgeably question those in authority; when, clutching our crystals and nervously consulting our horoscopes, our critical faculties in decline, unable to distinguish between what feels good and what's true, we slide, almost without noticing, back into superstition and darkness."

This observation lends a sad irony to how science is now providing tools for people who, knowingly or otherwise, are using them in un-scientific ways.