Is the Global Hum Rocking Your World?

Can you hear the "Global Hum"? Tens of thousands all over the planet claim they can hear a strange, perpetual background "hum" (sometimes referred to as the "Worldwide Hum"). Many describe it as an ongoing, low-frequency sound like that of a big truck idling a mile away, 24/7. Some areas, like Taos, New Mexico, have been famous for such a hum for decades.

"Whenever I wake up it is there and it is unbelievably loud. When nobody else can hear it you think you are going nuts, and it just wears you down,” one resident of southeastern England recently told the Guardian newspaper. “I have been desperate to get away from it," he continued, "so I have stayed with friends—and even moved house.”

Theories about the hum's origin range from volcanic action to distant highways to alien aggression. Ultra-low-frequency radio messages aimed at Navy submarines (only very, very low-frequency radio waves can successfully travel underwater) have also been blamed; while these frequencies cannot be heard by the human ear, through a process called "microwave auditory effect" the energy used to generate them can jostle the skull's internal seas, which in turn twerk the auditory nerve.

One clue to the Global Hum's nature may lie in the fact that the vast majority of people reporting the phenomenon live in urban areas (see the Worldwide Hum map). Most city residents are so attuned to urban background noise that they're not even conscious of it, but it can bother those who do notice, as this writer found when researching a book on silence a few years ago.

The constant background hum I heard in New York—it was there at 4 a.m. and noon and 9 p.m. and always, in fact—sounded to me like a deep breathy rush, so that I ended up calling it "the monsterbreath." To the extent I could parse the noise, it seemed, and still seems to come from thousands of HVAC systems and the constant hiss of tens of thousands of tires rolling forever throughout the city.

But research also provided other clues. The Earth itself, probably through the instrument of plate tectonics, associated volcanoes, and the vibrations they elicit in the atmosphere, plays a sound in the frequency range of 2 to 7 millihertz. Lightning emits very low-frequency radio waves (audible online through VLF receivers at spaceweather.com). Scientists figure that the atmospheres of Mars and Venus generate notes similar to Earth's. There's even music in space: a black hole in the Perseus cluster emits a tone that researchers say is equivalent to the b-flat note on a piano. Although it is impossible for humans to hear such low frequencies, it's also conceivable that input similar to the microwave auditory effect registers in some fashion on our consciousness.

Closer to home, the aggregate effect of noise overdose inevitably increases the incidence and severity of tinnitus, aka sound generated by the auditory system itself. Western societies are dangerously noisy: by way of example, 113 million Europeans suffer the effects of 65 dB sound, many times over the limit at which noise begins to damage the nervous system. Tinnitus is, therefore, a common phenomenon. But for most people it is also so low in impact, relatively speaking, that many who experience its effects are not aware of them, let alone of their cause.

The fact that so many of us live in the crowded urban areas mentioned above means that the noise of tinnitus is drowned out by the monsterbreath or by even louder sirens, bus engines, and subway trains. When we do find ourselves in the country or some other much quieter place, we suddenly become conscious of the persistent, soft keening our own hearing apparatus makes; if we don't know it's tinnitus, we may blame traffic, or Navy radios.

Or the Global Hum.

Or aliens.