As we creep closer to Halloween, you’re probably beginning to think about planning your costume, decorating your home, and stocking up on seasonal candy. Maybe you’re adding some horror movies to your Netflix queue, or even planning a visit to a "haunted" site. Indulging in ghost stories can be one of the most entertaining parts of Halloween — but is there any evidence that ghosts might be, you know, real?
If you believe in ghosts, you’re not alone. A 2013 Harris Poll found that 43% of Americans do. Additionally, a 2009 Pew Research poll found that 29% of Americans say they've felt as if they've been in touch with someone who has died, and 18% say they've been in the presence of a ghost. A belief in ghosts is certainly not new: folklore about ghosts dates back thousands of years and is present in relics of ancient Mesopotamian (3500 B.C.E. - 400 C.E.) and ancient Egyptian (3150 B.C.E. - 332 B.C.E.) culture.
Despite decades of testing, there is no scientific proof of the existence of ghosts. Part of that is because no one can agree on what a ghost is, exactly. Are they material? Or invisible? Are they human souls? Or some kind of energy? As LiveScience’s Benjamin Radford writes, “With so many basic contradictory theories — and so little science brought to bear on the topic — it's not surprising that despite the efforts of thousands of ghost hunters on television and elsewhere for decades, not a single piece of hard evidence of ghosts has been found.”
That’s right: there is no scientific evidence that ghosts exist. The methods that ghost hunters use on TV — such as capturing ambient noises or electric voice phenomena (EVP) — have often been described as “pseudoscience.”
Over the past few centuries, scientists have suggested many different explanations for why so many people believe they have seen ghosts. Here are some of them:
Variations in the electromagnetic field
Ghost hunters use a tool called an electromagnetic field (EMF) meter to apparently detect ghosts. Normally, these tools are used to identify problems with power lines, electrical wiring, and electric appliances. Electromagnetic fields are everywhere, in various forms.
Some scientists say that our perceptions of ghosts may have something to do with electromagnetic fields. In the 1980s, neuroscientist Michael Persinger hypothesized that excessive magnetic stimulation of the brain led to "out-of-body experiences." According to Nature, Persinger had people wear helmets that targeted their temporal lobes with weak magnetic fields, and found that 80% of people felt "an unexplained presence in the room."
Variations in infrasound
Infrasound are sounds below the range of hearing. Some animals, including elephants, can hear it, but we can't. However, studies have indicated that humans feel some effects of infrasound, including nausea, disorientation, and "general unpleasantness." In one 1998 scientific paper, engineer Vic Tandy investigated his own experiences in a supposedly "haunted lab." While working there, he and others experienced feelings of distress and depression, cold shivers, heard sounds seeming to come from unexpected places, and Tandy even saw an apparition of a figure.
Investigating, Tandy found that he "and his colleagues were sharing their lab with a low frequency standing wave" caused by a new fan in the extraction system. Tandy concluded, "a 19hz standing air wave may under certain conditions create sensory phenomena suggestive of a ghost."
Other scientists have conducted similar experiments, with similar conclusions. In one study, psychologist Richard Wiseman arranged for people to attend two concerts: one that featured infrasound, and one that didn't. Twenty-two percent of audience members in the infrasound concert reported "feeling uneasy or sorrowful, getting chills down the spine or nervous feelings of revulsion or fear," according to NBC.
Carbon monoxide poisoning
In a popular TED Talk, journalist Carrie Poppy tells the story of being "haunted." She felt like she was being watched, felt a pressure on her chest, heard "whooshing" sounds, and cried every night. Then, she posted about her experience on a forum for ghost skeptics... who told her it sounded like she had carbon monoxide poisoning. She called the gas company. They were right. And Poppy isn't alone. Several other "haunted houses" have been discovered to be the site of a carbon monoxide leak.
Some scientists say ghosts are likely the result of sleep paralysis. This occurs when there's a disconnect between the body and mind when you're going into or out of REM sleep. The result is a feeling of paralysis and "waking dreams," often nightmares.
“Some people have visions where they feel something is trying to strangle or choke them or they have a sense of impending doom,” Dr. Priyanka Yadav, a sleep specialist at the Somerset Medical Sleep for Life Center in Hillsborough, N.J., told NBC. “They’ll often see someone coming into their room and they’re not able to move or talk or scream or do anything." Scientists say this is the reason ghosts usually "haunt" at night — they're really just dreams.
Many "haunted houses" are creepy and old... and may be home to dangerous mold. One study found that mycotoxins — toxins produced by certain fungi — can lead to delirium, dementia, pain syndromes, movement disorders, and balance or coordination disorders.
“I’ve had an interest in ghost stories and paranormal exploration and shows and other things for a long time,” researcher Shane Rogers told Mental Floss. “Back in grad school watching these shows I thought, ‘Jeez, some of these places they’re going into are pretty dingy and moldy. I wonder if there’s some kind of a connection.’”
Many patients with dementia have reported seeing ghosts, and hallucinations are one symptom of dementia. "I get hallucinations where I think there are ghosts living in our garden," one man with dementia told BuzzFeed.
It's so common that there's a term for it: Nearing Death Awareness. “Those who are dying and seem to be in and out of this world and the ‘next’ one often find their deceased loved ones present, and they communicate with them. In many cases, the predeceased loved ones seem [to the dying person] to be aiding them in their ‘transition’ to the next world," Rebecca Valla, a psychiatrist in Winston-Salem, N.C., told the Washington Post.
If you're hearing about a ghost from a young kid, scientists say it's likely just their imagination. "Children are hard-wired to learn through imaginative and pretend play, and therefore they can slip between reality and fantasy much more easily than adults," Aleta G. Angelosante, PhD, a child and adolescent psychiatrist at NYU Langone, previously told Refinery29. "While an adult might dismiss something they see quickly out of the corner of their eye as 'nothing' or have a reality-based explanation, children might insist they saw a ghost or a fairy or some other creature."
"Blind spots" in our vision
If you've ever seen something spooky out of the corner of your eye, then turned to see nothing there, you know that sometimes our peripheral vision just isn't that accurate. As Psychology Today explains, each eye has a blind spot about 18 degrees to either side. Our brain compensates for what our peripheral vision can't see,"[making] educated guesses about what we’re looking at, and its editing is highly biased by expectations, history, context, and desires." The problem is, sometimes these guesses are wrong, and we think we see things that aren't really there — and some scientists say that "ghosts" can be explained by these wrong guesses.
The power of suggestion
Scientists say that we've heard so many ghost stories growing up, it's only natural that we think we see ghosts. One study examined how this works: participants watched a video of a "psychic" seemingly bending a key with psychokinesis, and were then exposed to a negative, positive, or no social influence. People who were exposed to the positive social influence — someone telling them they definitely saw the key bend — were more likely to report also seeing the key bend.
However, experts in other fields say that ghosts fall outside the realm of what science can prove or disprove. Writing for the BBC, anthropologist and mythology scholar Tok Thompson points out that many cultures believe in ghosts, and that this belief is even more predominant in Asia than in the U.S. or U.K. — about 90% of Taiwanese people report having encountered ghosts.
Ghosts across cultures, he adds, “are often seeking justice from beyond the grave. They could make such demands from individuals, or from societies as a whole,” as in reports of sightings of the ghosts of murdered slaves and Native Americans in the U.S. “In this way, ghosts reveal the shadow side of ethics. Their sightings are often a reminder that ethics and morality transcend our lives and that ethical lapses can carry a heavy spiritual burden,” he writes.
So, while you won’t find any scientific studies proving that ghosts are real, a quick google — or a question posed to friends — will no doubt uncover dozens of ghost stories. As for whether these experiences were a trick of the mind or a real encounter, that’s something you’ll have to decide for yourself.