We’ve all heard at least one ghost story in our lifetime. It seems that everyone and every place has come in contact with the paranormal. Statistically, around 45% of Americans believe in ghosts, and as many as 18% of the American population says they’ve actually come in contact with a spirit. That’s a pretty significant number for what could be considered by some as a total hoax.
Many theories have been proposed as to what ghosts actually are. Are there possible scientific explanations for that shadow following you in an empty house? How about that tingling sensation on the back of your neck in a dark room? Lastly, what about demons? Do they really invade our world to leave claw marks on our backs while we sleep?
Let’s investigate ten possible theories for these paranormal wanderers that are rooted in science rather than the supernatural.
Related: 10 Interesting Pseudosciences and Hoaxes
10 Sleep Paralysis
Probably the most common explanation for why we see ghosts is sleep paralysis. Sleep paralysis “is like dreaming with your eyes open,” says Dr. Baland Jalal. As a neuroscientist, Dr. Jalal studies sleep paralysis at the University of Cambridge in England. He explains that we often experience very lifelike dreams during REM—rapid eye movement—sleep. While in REM sleep, our eyes can move around fairly rapidly under closed eyelids. However, the rest of our body doesn’t—or can’t—move. People may experience this and think they are paralyzed. However, the inability to move is likely “to prevent people from acting out their dreams.”
A lot of the most common examples of supernatural behavior can be explained by this neurological phenomenon: hallucinations, the physical presence of someone or something sitting or lying on a body, and even demon scratches. Yep, you most likely feel something did really happen, but you were in a terrifying awake-dream state instead.
9 Power of Suggestion
The use of suggestion is a powerful tool, and well-known studies have been done, but only recently have we investigated the power of suggestion with regard to paranormal events. In fact, some might say the entire Spiritualist movement is based on this theory of trickery.
In 2003, Richard Wiseman conducted two experiments for the British Journal of Psychology. The purpose was to examine the power of suggestion in a séance setting, asking whether belief in the paranormal made participants more prone to suggestion. The first experiment consisted of a fake medium who held a séance. During the evening, the psychic inferred that the table had moved. About one-third of the participants later reported that the table did move—though the table remained stationary throughout the experiment. They had wrongly reported the movement. Believers in the paranormal were more likely to misreport such activity than disbelievers.
Paranormal believers were more inclined to believe in the suggestions made or inferred by the medium than disbelievers following the next set of fake séances as well—with one caveat. They only reported that something happened when the suggestion aligned with their personal belief in the paranormal. For example, if the fake medium suggested that an object had not moved when in fact, it had—through trickery, of course—believers were no more likely to accept the suggestion than disbelievers. Overall, around one-fifth of the participants believed they had witnessed genuine paranormal phenomena.
It’s unknown whether the verbal suggestion directly affected the participants’ perception of the event, their memory of the event, or both. An existing belief in the paranormal did reveal the group’s likelihood of reporting a paranormal event when it didn’t happen, whether through true belief, suggestion, or demand characteristics—essentially, subtle cues that reveal to the participants what the experimenter expects to find or how the participants are expected to act. Still, the result is the same: a large minority of the participants reported that certain objects had moved and that they had witnessed genuinely paranormal events.
8 One Mysterious Planet
It might be cheating to say this, but sometimes supernatural occurrences can be explained by weird, yet not supernatural, things the Earth does every day.
Consider the Oracle of Delphi. Some considered the Pythia’s trance state supernatural and paranormal. She could speak to the spirits, the gods, and any other mythical, magical being to tell the future. People came to Delphi from hundreds of miles just to listen to her visions and see the ancient medium commune with invisible otherworldly beings. Was it all a hoax? Probably not. Scientists are pretty much in unanimous agreement that hydrocarbon gases from bituminous limestone under the Earth where Delphi sat probably brought on the Pythia’s trance.
In fact, a geological team from Wesleyan University found ethane, methane, and ethylene in spring water near the oracle. All the magical fumes inside the Oracle’s cave? Probably just some extremely toxic gasses. We may not all be suffering from faultline gas poisoning when we see our long-lost grandmother, but some of the oldest tales of the supernatural come from a time where furnaces were poorly regulated, mercury was on the loose in food and drink, and candle flames were notorious for throwing shadows. Eventually, those stories get passed down, revamped, and modernized to create some scary ghosts.
7 Low Frequency Sounds
If you’re a frequent watcher of televised ghost hunting shows, you may know about EMF readers. Supposedly, a ghost can manifest itself using the electromagnetic fields in the room. If that frequency is high enough, theoretically, ghosts could just appear and move objects all by themselves. The thing about EMF readers is that they’re incredibly unreliable. Things like cellphones and camera batteries can set off the meters. (LINK 14) However, it turns out there is some science behind EMF and ghostly behavior.
The explanation is something known as the “fear frequency.” Human ears (especially adults) have trouble hearing low-frequencies below ~20 Hertz (or infrasound). However, the body can still sense them, often causing feelings of uneasiness, chills, or “nervous feelings of revulsion and fear.”
This theory helped solve a local ghost story. On Coventry University’s campus, there’s a 14th-century cellar supposedly home to a ghost. That is until lecturer Vic Tandy examined the room and found infrasound levels that explained the paranormal experiences. So, is it a ghost giving you the creeps? Probably not. It’s just your body experiencing a very normal reaction to the environment around it.
6 Mold and Fungus
Let’s face it, if you walk into a decrepit hospital or haunted house, you’re already going to be on edge about ghostly apparitions. Perhaps you’re in an area where wiring isn’t a problem, so we don’t have to worry about EMF. There’s not a living soul for miles, so human interference is also out. What about black mold? Asbestos? Rye ergot? There’s a high probability all the abandoned buildings have some of these toxic molds hanging out in the damp basements, deteriorating ceilings, and closed-up rooms, in addition to wafting through the air.
It’s possible all the ghostly sightings are just a result of bad air quality in “haunted” places. Associate Professor of Civil & Environmental Engineering Shane Rogers said, “The links between exposure to toxic indoor molds and psychological effects in people are not well established; however, notably, many hauntings are associated with structures that are prime environments to harbor molds or other indoor air quality problems.”
The mold theory could also be an example of what paranormal investigators sometimes call “demonic activity.” On television, you might see someone instantly feel sick, feel a choking sensation, or experience headaches or lightheadedness when they come across a malignant spirit. Yet, they feel instantly better when they leave the space to get fresh air. Assuming it was an actor putting on their best performance, these symptoms are also a physical manifestation of being exposed to toxic mold and fungus. Sorry to burst your bubble, but it’s probably not a demon. It’s just your body telling you to get out and get fresh air.
5 Mind/Body Disconnect
Feeling like a ghost or another supernatural presence is nearby? It’s likely caused by a glitch in how our brain processes self-awareness and our sense of place in space. The brain is a complex organ and can create supernatural manifestations, even if your body isn’t quite aware it’s happening. When our brains inaccurately represent our bodies in space, it can potentially create a second representation of the body, which is no longer perceived as “me” but as someone else, a “presence.”
To demonstrate this, a team of Swiss neuroscientists figured out how to conjure those spirits in a lab. The team studied the brains of a dozen patients who all suffered from neurological disorders and claim to have had experiences with ghosts. MRI results showed that they all had abnormal activity in three brain regions involved in self-awareness, movement, and positioning themselves correctly in space.
Next, the researchers looked at a dozen healthy volunteers. They blindfolded their subjects and asked them to move their arm in a predetermined way. The participants were connected to a robot in front of them (the main robot) while a second robot was behind them (the second robot). The participants were unaware of the second robot, which was programmed to mimic the arm movements against the participant’s back. For example, if the participant made a circle then a triangle with their arm, the second robot would lightly “trace” the circle and triangle on the subject’s back.
When the second robot completed the movement at the same time the participants moved, they didn’t report feeling anything unusual. Then, the researchers had the second robot perform the series of movements after a few seconds delay, altering the participant’s temporal and spatial perception. After a few minutes, the researchers asked the participants how they felt. Unaware of the study’s goal, several participants claimed to have felt a presence around them, with others reporting that there were ghosts in the room. A few did not complete the experiment, requesting to leave the room before the experiment was finished.
Once again, the presence of a ghost could just be your brain having a glitch in its self-awareness. This time, it’s a totally normal and natural phenomenon called pareidolia. Pareidolia is the same function of the brain that causes us to see images in clouds or facial features on intimate objects—you know, the image of the Virgin Mary on a grilled cheese sandwich.
Pareidolia is an ancient ability that may have helped our early ancestors survive by enabling us to identify potential hidden dangers in our environment—was that something in the grass over there? In his 1995 book The Demon-Haunted World: Science as a Candle in the Dark, Carl Sagan helped spread the claim that pareidolia is why we see certain ghostly apparitions.
It’s a phenomenon that explains how our brains interpret light and shadows or figures in the distance on an eerie, foggy battlefield. It’s not that there isn’t something there to see; it’s just your brain filling in missing pieces to create an image that isn’t really there.
3 Energy Displacement
Bear with me on this one. It’s an Einstein theory to prove ghosts exist. Let’s assume ghosts are very real, and it’s not an act of supernatural but rather an act of valid scientific theory for why they appear among us.
Paranormal researcher John Kachuba says in his book Ghosthunters, “Einstein proved that all the energy of the universe is constant and that it can neither be created nor destroyed… So what happens to that energy when we die? If it cannot be destroyed, it must then be transformed into another form of energy. What is that new energy?… Could we call that new creation a ghost?” (LINK 4) It’s theorized that all the electricity that keeps our bodies moving is the same that manifests spirits. That’s why ghost hunters rely so heavily on devices to measure that energy.
In fact, Einstein’s theory is still valid, and we do have science to explain what happens to all that energy when we die. However, the answer is not “turns us into ghosts.” After a person dies, the energy in the body goes into the environment—that’s where all organisms’ energy goes after death. When we die, our energy is released in the form of heat. If we are eaten by animals or insects or taken in by plants via the nutrients left behind in the soil by a decomposing body, this energy is then transferred into these animals, insects, or plants. When cremated, our body’s energy leaves us as heat and light.
Consider plants and animals for a moment. Have you ever seen a ghost cow? A ghost Venus Fly Trap? Probably not. When we eat dead plants and animals, we consume their energy and convert it for our own use. Our bodies metabolize food for energy, completing the cycle. To believe that a person’s energy would remain long after the body is gone is highly suspect. Our energy does not remain as a spirit comprised of electromagnetic energy but rather in the form of heat and chemical energy.
2 Unprocessed Trauma
I’m not a therapist, but one very common explanation of why the living sees the dead has to do with how our brain processes (or doesn’t process) trauma.
Based on a study of 88 people who sought psychiatric care from 1974 to 1984, Dr. Lenore Terr proposed that many ghost reports are really the result of hallucinations and illusions drawn from horrible and often life-threatening experiences. PTSD sufferers have reported seeing, hearing, smelling, or “feeling the presence of” ghosts or other beings. Some of the children who had been attacked by animals described being “haunted” by animal spirits.
After a trauma, some people believe that they have psychic abilities. Severe trauma can lead to hallucinations, where what the brain is trying to process on the inside manifests itself as outside voices or images. The trauma may be from a short-term event like a car accident or more long-term events like prolonged domestic violence or child abuse. The inability or fear of dealing with the trauma can enable the sufferer to see or believe they see apparitions and other paranormal activities. These experiences may be the unconscious mind forcing the sufferer to finally deal with their trauma, leading to the end of the “hauntings.” 
1 Positive and Negative Ions
I know this sounds a bit like Ghostbusters to bring up ions and proton packs, but it’s based on some real science to explore the supernatural. By nature, a negative ion is an atom that carries an extra electron in its shell and vice versa for a positive ion.
Some paranormal researchers claim that spirits can hinder normal ion balance in the atmosphere. In contrast, others say ghosts use the ions’ energy to manifest or interact with the physical world. I wouldn’t trust a ghost hunter with an ion meter. It’s all very unreliable technology to base results on. You see, ions are caused by all kinds of natural phenomena like weather, solar radiation, and radon gas. It all comes down to how one interprets the evidence.
However, positive and negative ions can affect the moods of the living. Negative ions can make us feel calm and relaxed, while positive ions can give us headaches and nausea. This might explain why people who live in “haunted” houses describe fatigue, headaches, and illness. When they feel an ion imbalance, they may think paranormal, not normal.