The Ghost in the Machine
In the early 1980s, engineer Vic Tandy was working late in his laboratory in Warwick. The lab, known to be "haunted," often produced strange feelings among staff. That night, Tandy felt a growing sense of unease and cold sweats, then saw a grey, indistinct figure appear in his peripheral vision. When he turned to face it, the figure vanished. As a man of science, he dismissed it. The next day provided a physical clue. While fixing his fencing foil, he clamped the blade in a vise and noticed it began to vibrate uncontrollably. This observation led him away from paranormal theories and toward a physical one: a standing sound wave.
Tandy began to investigate, using instruments to measure the ambient sound in the room. He discovered a persistent, low-frequency sound wave that was strongest in the center of the lab—exactly where he had seen the apparition and where the foil vibrated most intensely. The source was a newly installed extractor fan. The frequency of this sound was 18.98 Hz, just below the threshold of normal human hearing, which is around 20 Hz. This infrasound was felt, not heard. The resonant frequency of the human eyeball is approximately 18 Hz, according to NASA research. Tandy theorized that the 18.98 Hz wave was causing his eyeballs to resonate, producing optical illusions like the grey figure in his peripheral vision. The feelings of anxiety and depression were also consistent physiological reactions to infrasound exposure.