Humans have been telling ghost stories since long before recorded history. Some of the oldest known hauntings include Homer’s Odyssey in the 8th century BCE, in which Odysseus traveled to the underworld and encountered spirits; the Old Testament telling of the Witch of Endor summoning the spirit of Samuel; and the 1st century CE description of a “specter of an old man with a long beard, rattling chains” haunting Pliny the Younger’s house in Athens. Ghosts, spirits, specters, and demons have been blamed for all sorts of supernatural behavior, but thanks to science, we might finally be able to explain some of it. Except for poltergeists; we’ll leave those up to The Warrens.

When it comes to the human experience, our senses can get us into a whole mess of trouble because they can be so easily fooled or misinterpreted, especially when fear is brought into the mix. It was fear that gripped the late Vic Tandy, a British engineer and lecturer in information technology, while working one night in a research laboratory of a medical manufacturing company in the 1980s. The idea that the labs might be haunted had already been placed in his head by other staff members, but Tandy chalked it up to the machines that constantly operated in the facility. Then, Tandy had the unshakable feeling that someone or something else was in the room with him, although he was quite alone. Something emerged from his peripheral vision, but when he turned to face it, it vanished.

When Tandy returned to the lab the next day, he just so happened to have his fencing sword with him. While polishing it, with the sword clamped in a sturdy vice, he noticed that the blade was vibrating. He surmised that something within the lab must be causing the vibration, and the culprit ended up being a recently installed fan that was vibrating and generating a low-frequency sound known as an infrasound.

These sounds, which occur below the threshold of human hearing, were the subject of pain-inducing experiments performed by the Russian-born French scientist Vladimir Gavreau in the 1960s. Nerdist-favorite Neil deGrasse Tyson chatted about the phenomena that arise due to infrasounds on a 2011 episode of his Star Talk Radio Show, one that was not coincidentally released on Halloween, but was coincidentally titled Spooky Science. (Weird.) Listen to the whole episode here or just his brief explanation on infrasound below:

So Tandy’s ghost turned out to be the result of an infrasound with a frequency around 19Hz, which resonates with the human eyeball and makes things in your peripheral vision–like dust motes–appear larger and scarier than they really are. Tandy then published his findings in the (peer-reviewed) Journal of the Society for Psychical Research; he followed up that paper with a similar one after investigating a reported haunting of a 14th century cellar and finding another case of infrasonic vibrations.

So what’s going on here? It turns out that the infrasonic frequency “can affect humans and animals in several ways, causing discomfort, dizziness, blurred vision (by vibrating your eyeballs), hyperventilation and fear, possibly leading to panic attacks.” If you want to try it for yourself, you can listen to an 18.98 Hz recording on YouTube, but your mileage may vary. You might experience ghostly visions, or maybe even a sense of paralyzing fear similar to that of a tiger’s prey that hears the predator’s low-frequency roar just before it pounces. Or you might not experience anything at all, but better safe than sorry.

Now that you know the ghost frequency, that knowledge might just make your next spooky encounter a little less haunting. Have you experienced any paranormal behavior? Let us know in the comments!

Images: MGM, Star Talk Radio Show