Trevor Cox in American Scientist:
While I was on an expedition to record singing sand dunes, I experienced something quite rare: complete silence. The scorching summer heat kept visitors away. Most of the time my recording companion, Diane Hope, and I were on our own. We camped at the foot of Kelso Dunes, in a barren, scrubby valley with dramatic granite hills behind us. Virtually no planes flew overhead, and only very occasionally did a distant car or freight train create noise. Much of the day there was a great deal of wind, but at twilight and early in the morning the winds calmed down and the quiet revealed itself. Overnight I heard the silence being interrupted only once, when a pack of nearby coyotes howled like ghostly babies. Early on the second morning, while I was waiting for Diane to set up some recording equipment, I had a chance to contemplate real silence. The ear is exquisitely sensitive. When perceiving the quietest murmur, the tiny bones of the middle ear, which transmit sound from the eardrum to the inner ear, vibrate by less than the diameter of a hydrogen atom. Even in silence, tiny vibrations of molecules move different parts of the auditory apparatus. These constant movements have nothing to do with sound; they stem from random molecular motion. If the human ear were any more sensitive, it would not hear more sounds from outside. Instead, it would just hear the hiss generated by the thermal agitation of the eardrum, the stapes bone of the middle ear, and the hair cells in the cochlea.
…A former colleague of mine, Stuart Bradley from Auckland University, has visited Antarctica, another place devoid of vegetation where silence can be heard. Stuart is a tall New Zealander, sporting a fine mustache like a soccer player from the 1970s. Ironically, what Stuart does in Antarctica is make noise and briefly ruin the pristine natural soundscape. He uses a sodar (a sound radar system) to measure weather conditions, sending up strange chirps that bounce off of turbulent air in the atmosphere before returning to the ground to be measured. I asked Stuart if he had experienced silence in Antarctica, and he told me about his time in the dry valleys, possibly the most barren places on Earth, which lack snow and ice cover: “Sitting up on the valley wall on a still day, there was no sound I could identify (except heartbeat? breathing?). No life (apart from me). So no leaves either. No running water. No wind noise. I was certainly struck by the primeval ‘feel.’” Stuart commented on how different this was than the sound of a silent laboratory, “I didn’t get the claustrophobic feel one can get in an anechoic chamber …I suspect this is because, although it was incredibly quiet, it was also a very, very open vista. The valley walls were 1,500–2,000 meters high, and the visibility was amazing!”