Call it The Acoustics of "The Twilight Zone." Episodes depicting the creepy feeling people get in "haunted" places may be reality TV after all.
Two British scientists have shown that "infrasound" - sound pitched too low for human hearing - can induce such feelings. It's the latest report from a research frontier that has fascinated scientists for decades.
Human-made and natural infrasound is around us all the time. Some animals, such as elephants and whales, use it for long-distance communication. Nuclear test ban monitors use it as part of their strategy to detect illegal bomb tests. Atmospheric scientists use it for a variety of purposes, including listening instrumentally for the rumble of distant storms. Some infrasound sources, such as ocean waves, can be detected thousands of miles away.
Humans can't hear anything pitched lower than 20 hertz. But we often can feel it just as we can feel (as well as hear) the bass booms from the souped-up audio system in a car a block away. If you tune into this low-frequency sound range, you find what two scientists call "a virtual symphony" of infrasound.
Reviewing the subject in Physics Today, Alfred Bedard (with the National Oceanic and Atmospheric Administration) and Thomas Georges (with the NOAA/Colorado State University Corroborative Institute for Research in the Atmosphere) note that these unheard, but sometimes felt, sounds are as intense as sounds we can hear. They report that the infrasound power radiated by the strongest atmospheric storms is estimated to be equivalent to the electric power consumed by a city with 100,000 population. That kind of power makes it possible to isolate the signature of a distant storm or other infrasound source from the cacophony that instruments detect. There's even an infrasound background called "the voice of the sea" that probably is generated by ocean waves in storms around the world.
Drs. Bedard and Georges also point out that winds blowing over mountain ranges can generate infrasounds that last for days. They speculate that increases in suicides reported from the Alps and the western United States "may be due to some as yet unknown biological response" to such infrasound events. The British experiments, reported during the recent meeting of the British Association for the Advancement of Science in Manchester, England, may shed light on this.
Richard Lord with Britain's National Physical Laboratory and Richard Wiseman at the University of Hertfordshire described experiments in which infrasound was mixed into contemporary music. Some listeners reported uneasy, nervous, or chills-down-the-spine feelings. Professor Wiseman told the meeting that "these results suggest that low-frequency sound can cause people to have unusual experiences even though they cannot consciously detect infrasound," according to a Reuters report.
The unheard infrasound "symphony" has become an important tool for nuclear test-ban monitoring and for atmospheric, avalanche, and earthquake research. And it now appears that, if you have creepy feelings in creepy places, you don't have to look for supernatural sources. Just blame them on the real-life acoustics of "The Twilight Zone."