Some of the things we encounter in our lives seem to be simply inexplicable, but our innate curiosity urges us to attempt to explain inexplicable events nonetheless. By experimenting and making educated guesses, scientists have learned that most of the phenomena we once considered unexplainable can actually be explained by using the laws of physics. One superstition that has stood the test of time is society’s beliefs in ghosts.

Nearly every culture believes in some kind of spirit that exists beyond the human dimension. Elves, spirits, djinns, ghosts – whatever you may call them, they have seemingly existed in human culture since the dawn of time. However, scientists at the National Physical Laboratory in England have reason to believe that we people haven’t really been seeing ghosts at all; rather, we have been sensing auditory distortions!

Normally, humans hear sounds that are above 20 Hertz, a frequency of sound. We can only hear sounds that are higher-pitched than 20 Hertz. Frequency is not to be confused with the intensity (more commonly, volume) of a sound, which is measured in decibels. Sounds with low frequencies cannot be heard, but our bodies can still sense them. If the intensity of a sound is high enough, in other words, if it’s “loud” enough, your body will feel it. Think about how a car with a big sound system shakes because of the bass. You don’t hear the music very well, but you can still feel the vibrations (and so can the car).

Back to ghosts. Studies show that infrasound between 7 and 19 Hertz can cause feelings of fear and panic in humans. Our eardrums pick up these sounds and transmit them to our brain without setting off our auditory sense. To study the effects of these sounds on human organs, researchers from the University of Hetfordshire conducted an experiment where they played music with and without tones of 17 Hertz frequency in the background. When the participants heard (or felt, rather) the music with the 17 Hertz tones, they felt nervous, anxious, and fearful. They also felt pressure on their chests and chills down their spine. These are the feelings that most people describe when they experience a paranormal event. It is suggested by the researchers who conducted these experiments that infrasound (sound below 20 Hz of frequency) is present at supposedly haunted sites. Upon examining the frequencies present at advertised haunted houses, researchers detected several wavelengths of infrasound being emitted. They hypothesize that these frequencies caused feelings of panic and dread among visitors (Sydney Morning Herald).

But what does being in the presence of infrasound have to do with feeling fear, anxiety, and nervousness? It may have something to do with natural sources of infrasound: volcanoes, earthquakes, tiger roars, and strong ocean waves. Our bodies may have evolved to detect the sounds that we cannot hear, and we may have evolved to fear these dangerous sounds.

Research conducted by Vic Tandy, a lecturer at Coventry University, suggests that infrasound can even cause ghost sightings. Tandy knew that that our eyes resonated at 19 Hertz. When he started seeing ghostly grey figures in his laboratory, he began monitoring the frequency of all the laboratory equipment. Tandy discovered that a malfunctioning fan was emitting a frequency of 19 Hertz, caused his eyes to resonate which caused. Once he fixed the fan, the ghosts stopped appearing. He conducted similar monitoring experiments at a supposedly haunted Warwick Castle and detected the same frequency, 19 Hertz. He found that the right frequency can cause not only the emotions associated with a paranormal encounter, but also the visual aspects of one (Pilkington).

Just like other seemingly unexplainable phenomena, ghost sightings have long perplexed scientists. But with the help of some simple monitoring equipment, scientists have been able to unravel some of the mystery that surround haunted houses. So next time you think your house is haunted you may want call an engineer, rather than a sprit medium.