Popular Science



SOMETIMES PEOPLE experience an otherworld­ly encounter simply because something in their environmen­t is making a strange noise that sends their bodies into disarray. In the early 1980s, British engineer Vic Tandy was working in the research lab of a medical supply company when a strange feeling came over him. All at once he felt frigid and overwhelme­d with a sense of impending doom. As he paced around the room to calm down, he suddenly sensed an ethereal presence. Moments later, he was sure he saw a gray apparition in his peripheral view. When he whirled around, the specter was gone. Tandy’s colleagues had warned him the facility might be haunted, but the engineer was a skeptic by nature, so he scoured the place for an explanatio­n. The culprit turned out to be a fan that hummed at a rate of 18.9 Hz. Though we can’t sense their quivering, our eyeballs vibrate at a very similar frequency. The sound threw Tandy’s vision for a loop and caused him to see a vague spook. The rogue fan may also have triggered his momentary panic, as studies suggest that certain noises can cause a person’s organs to shake, which makes them hyperventi­late. Waveforms that dwell around this acoustic sweet spot and below are known as infrasound. Though they’re inaudible to human ears, whose range bottoms out at 20 Hz, the interval creates some fairly insidious side effects. In fact, after Tandy published his findings in 1998 in the Journal of the Society for Psychical Research, 18.9 Hz got a reputation as the “fear frequency.” Most of us don’t regularly carry around audio gauges, so it’s hard to know how many hauntings might be explained by a buzzing fan or a rumbling fridge. For Tandy, the fright left him more curious than ever about ghosts. “When it comes to supernatur­al phenomena,” he told a reporter some years later, “I’m sitting on a fence.”

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