Ghostbusters!

You’re home alone in the middle of the night, and a floorboard creaks behind you. The hair on the back of your neck rises. Your heart starts to race. You get a sinking feeling that someone—or something—is standing just out of sight. But when you muster up the courage to look... nothing’s there.

Is your house haunted? Was it just your imagination? Or could it be something else entirely? About 40 percent of Americans believe in ghosts, but so far scientists have found no evidence of paranormal activity.

So what causes these spooky phenomena? There are three leading theories. Find out how sound waves, electromagnetism, and your own imagination may be responsible for the things that go bump in the night.

You’re home alone in the middle of the night. A floorboard creaks behind you. The hair on the back of your neck rises. Your heart starts to race. You get a sinking feeling that someone—or something—is standing just out of sight. But when you get the courage to look . . . nothing’s there.

Is your house haunted? Was it just your imagination? Or could it be something else completely? About 40 percent of Americans believe in ghosts. But so far, scientists have found no proof of paranormal activity.

So what causes these spooky events? There are three leading theories. Find out how sound waves, electromagnetism, and your own imagination may be behind the things that go bump in the night. 

One night at a laboratory in England, something spooky happened. More than 30 years ago, an electrical engineer named Vic Tandy was working late when he was overcome with a strong feeling of discomfort. He was alone, but he couldn’t shake the impression that he was being watched. Out of the corner of his eye, he thought he saw a strange, gray apparition. After a few tense moments, Tandy turned to face the ghost. But as he did, the figure vanished.

After some investigation, Tandy found that an air-conditioning unit in the room was producing infrasound. These low-frequency sound waves vibrated at a rate that was too low for him to hear (see How Sound Waves Work). Even though our ears don’t register infrasound, it can still affect our bodies.

Tandy did more research and discovered that the infrasound was at just the right frequency to vibrate the human eye. He believed that vibrations caused a distortion in his vision—the gray figure from his spooky night at the lab—and his feelings of discomfort. Tandy went on to uncover sources of infrasound at other well-known “haunted” locations in England. He came to believe that most experiences of the paranormal are actually encounters with sources of infrasound.

One night, something spooky happened at a laboratory in England. More than 30 years ago, an electrical engineer named Vic Tandy was working late. He suddenly felt very uneasy. He was alone, but he couldn’t shake the feeling that he was being watched. He thought he saw a strange, gray shape out of the corner of his eye. A few tense minutes passed. Then Tandy turned to face the ghost. But as he did, the figure disappeared.

Tandy did some checking. He found that an air-conditioning unit in the room was producing infrasound. Vibrations from the AC were creating low-frequency sound waves. The number of vibrations per second was too low for him to hear (see How Sound Waves Work). Our ears don’t pick up infrasound, but it can still affect our bodies.

Tandy did more research. He found that the infrasound was at just the right frequency to vibrate the human eye. He believed that vibrations caused his uneasy feelings and a change in his vision. That would explain the gray figure from his spooky night at the lab. Tandy later looked at other well-known “haunted” locations in England. He found sources of infrasound there. He came to believe that most paranormal experiences have a simple explanation. They’re really run-ins with infrasound.

A different theory suggests that encounters with ghost-like phenomena may be caused by small changes in electromagnetic fields (EMFs). An EMF is a field produced by charged objects. The field spreads out from an object as various forms of energy waves (see Energy Waves). Sources of EMFs include just about everything from wall sockets to thunderstorms. Humans can’t directly perceive most of these EMFs. But some scientists think EMFs may affect the brain in subtle ways.

Michael Persinger, a neuroscientist at Laurentian University in Canada, first became interested in the paranormal while he was studying the human brain. He found that applying weak magnetic fields to the temporal lobe—a region of the brain associated with perception and memory—could cause people to have paranormal-like experiences. He wanted to know if this phenomenon might explain ghost sightings around the world. “Almost all great scientific discoveries started by exploring an unexplained phenomenon,” says Persinger. “I knew that investigating these experiences might tell us a great deal more about how the human brain is organized.”

Another theory explains ghost-like phenomena in a different way. It suggests that small changes in electromagnetic fields (EMFs) may be the cause. An EMF is a field produced by charged objects. The field spreads out from an object as different forms of energy waves (see Energy Waves). Sources of EMFs are all around. They include almost everything from wall sockets to thunderstorms. Humans can’t sense most of these EMFs directly. But some scientists think EMFs may still affect the brain.

Michael Persinger is a neuroscientist at Laurentian University in Canada. He became interested in ghosts while studying the human brain. He applied weak magnetic fields to the brain’s temporal lobe. This area of the brain involves perception and memory. He found this could cause people to have paranormal-like experiences. Could this explain ghost sightings around the world? He wanted to find out. “Almost all great scientific discoveries started by exploring an unexplained phenomenon,” says Persinger. “I knew that investigating these experiences might tell us a great deal more about how the human brain is organized.”

Persinger created a device that applied weak EMFs to specific regions of a person’s brain. During Persinger’s experiments with the device, about 80 percent of participants in his studies experienced at least one strange “paranormal” sensation, such as an unexplained presence, vivid images, or strong emotions. Persinger thinks many ghostly experiences are caused by similar EMFs found naturally in the environment.

Not everyone is convinced by Persinger’s work, however. Christopher French, a psychologist at the University of London in England, decided to test both the EMF and infrasound theories. French and his team installed electromagnets and infrasound generators in a London apartment and invited volunteers to visit. The participants were told that they might be subjected to EMFs, infrasound, both, or neither. Some volunteers experienced symptoms of a supernatural encounter. But French says he didn’t find enough evidence to prove that EMFs or infrasound were factors.

“These ideas are interesting and worthy of further study, but the evidence is at best mixed in their support,” says French. “For now, the jury is still out, and we must await the results of future studies.”

Persinger built a device that applied weak EMFs to certain areas of a person’s brain. Then he did experiments with the device. About 80 percent of people in his studies had at least one strange “paranormal” experience.  They reported powerful images, strong emotions, or feelings that someone was there. EMFs like these are found naturally around us. Persinger thinks they cause many ghostly experiences.

But not everyone is sure that Persinger is right. Christopher French is a psychologist at the University of London in England. He wanted to test the EMF and infrasound theories. French and his team put electromagnets and infrasound sources in a London apartment. Then they asked volunteers to visit. They told the visitors that they might meet with EMFs, infrasound, both, or neither. Some volunteers felt symptoms of a paranormal experience. But French says he didn’t find enough proof that EMFs or infrasound were the cause.

“These ideas are interesting and worthy of further study, but the evidence is at best mixed in their support,” says French. “For now, the jury is still out, and we must await the results of future studies.”

Infrasound and EMFs aren’t the only theories that could explain ghostly phenomena. These occurrences could also be psychological—having a mental instead of a physical cause.

French argues that suggestibility—the tendency that people have to misperceive or misremember events in line with their expectations—is a big factor. “If you are told that a particular building is haunted, you are much more likely to notice even slightly anomalous experiences, such as unexplained noises, and to attribute them to ghostly intervention,” he says.

Scientists may not agree on what causes paranormal experiences, but that won’t stop them from continuing to investigate the mysterious—and sometimes scary—parts of our world. It’s that act of inquiry that’s most important, says Persinger. “The subject matter of science is the unknown. The scientific endeavor is seeking to understand the mechanisms behind the phenomena around us.”

Infrasound and EMFs aren’t the only theories. Another says that ghostly events could be psychological. That means they could have a mental cause instead of a physical one.

French believes that suggestibility plays a big role. That’s the tendency of people to view or remember things the way they expect, instead of the way they really are. “If you are told that a particular building is haunted, you are much more likely to notice even slightly anomalous experiences, such as unexplained noises, and to attribute them to ghostly intervention,” he says.

Scientists may not agree on what causes paranormal experiences. But they’ll keep on studying the mysterious—and sometimes scary—parts of our world. That act of asking questions is what’s most important, says Persinger. “The subject matter of science is the unknown. The scientific endeavor is seeking to understand the mechanisms behind the phenomena around us.”