The world is noisy, so noisy in fact that even things you thought were silent make all kinds of boisterous noises. Some are strange, others terrifying. Here are 10 of the most unexpected.
10. You, when you think you’re being silent
Even master meditators and expert ninjas can’t quite silence the body — at least according to science. It’s always making a racket. You just can’t hear it because, similar to noise-canceling headphones, the brain tunes it out to keep self and other distinct.
Neuroscientists studied this mechanism in electric fish, most species of which have an electrosensory lobe that receives electrical signals both from inside the fish and from its surroundings. It’s able to tell them apart by subtracting electrical signals matching inputs relating to the fish’s behavior, such as motor signals. A swish of its own tail as it swims, for instance, will not register in the same way as something else swishing its tail right by it. There’s a similar mechanism in mammalian brains too, called the dorsal cochlear nucleus (DCN), which subtracts sounds matching our movements from the total auditory input.
Ants typically communicate by chemical signal, but that’s not the only way. They also chirp. And it’s a little like maniacal laughter.
The sounds are produced by what’s known as ‘stridulation’, scraping an abdominal appendage against ridges on the backside — a lot like a spoon against a washboard. Workers sound different to queens; their chirps are of a slightly lower pitch. So when the workers hear the queen, they become more attentive. Researchers have actually found they’ll stand guard around a speaker playing sounds from a queen — maintaining “a hunched-over posture with antennae out and jaws slightly open” for hours.
Maculinea rebeli caterpillars exploit this vulnerability, mimicking queen sounds, as well as smells, to infiltrate colonies and steal the royal treatment — including both feeding and grooming. Beetles also mimic ant sounds for admission to the nests.
OK, so maybe you didn’t think giraffes were silent but think about it: what sound did you think giraffes made? Until recently, biologists assumed giraffes made sounds impossible for humans to hear — similar to the infrasonic “secret language” of elephants. More recently, however, research has revealed that giraffes make perfectly audible (92Hz) humming sounds. But they only make them at night.
This humming is believed to be how giraffes keep in contact in the dark. But there is an alternative explanation: it’s the sound of giraffes snoring or talking in their sleep.
Although fish lack vocal cords, they do make sound — and we don’t just mean by swimming and splashing around. In fact, far from being mute, thousands of the estimated 34,000 fish species worldwide are thought to make noise. Just under 1,000 of these have been documented. You can listen to them here.
Sounds come from rubbing or clicking together bony structures, or from beating the swim bladder like a drum, among other mechanisms. Two species of stingray, for instance, previously thought to be silent, both produce clicks. Just like other animals, these “vocalizations” are used to communicate reproductive and territorial information. And, because sound travels much faster in water, fish are relatively much louder than animals of the land and air; their signals travel much further.
Perhaps the strangest, most terrifying fish noise of all belongs to the three-spined toadfish, which “cries like a baby”.
6. Marine worms
It’s probably fair to say you don’t think much about marine worms at all; but if you do, you probably don’t think they make noise. But they do. And, actually, it’s one of the loudest sounds of any sea-dwelling creature.
Polychaetes, or bristle worms, which are less than 3 centimeters in length, are usually silent — hiding themselves away in sea sponge holes. When threatened, however, they open their pharyngeal muscles to create a bubble, then release the pressure with a shockingly loud, 157-decibel “battle pop.”
By way of comparison, the blue whale’s call — the loudest of any on Earth — is 180 decibels. The sound of a jet plane taking off is 140 decibels. And the human ear drum breaks when exposed to sounds of 160 decibels. But the marine worm’s pop is nothing compared to that of the snapping shrimp’s snap, which at 189 decibels, is capable of breaking glass.
Science has taken a while to catch up to what the intuitive have said for millennia: plants can talk. A 2019 study actually recorded their vocalizations, the “ultrasonic squeals” of plants being cut. The 20-150 kHz sounds, which lay outside the range of human hearing, came from tobacco and tomato plants and were recorded over the course of an hour of cutting. The tobacco produced 15 sounds, while the tomato produced 25. But they don’t just make sound when they’re injured. The researchers noted that “even happy, healthy plants made the occasional noise.”
So the next question is: can they hear? According to a paper in 2013, there needs to be more research in this area — because evidence suggests the answer is yes. Beyond anecdotal reports of singing to plants to encourage strong growth, there exist numerous (albeit now dated) scientific reports that plants germinate and grow at different rates in response to different frequency sounds.
Though 10 billion times softer than a fist connecting with a punch bag, the nanoscale beats of bacteria’s flagella (tails) can be amplified and listened to as sound. And these sounds may help scientists determine whether certain bacteria are resistant to antibiotics — a major concern in a global population increasingly resistant to the treatment.
Bacterial beats are recorded on a graphene-skinned drum, a membrane just one layer of carbon atoms thick. In this way, even the infinitesimally soft sound of a single bacterium’s flagellum can be recorded. When exposed to antibiotics, the beating either stops in a couple of hours or it doesn’t, telling us whether such treatments will work.
Viruses can also be converted to sound, but in a different way and for nothing more than fun. The DNA sequence of COVID-19, for example, has been translated into music that sounds like synth-pop or classical.
Not only do cells make noises, or “songs,” there’s a whole branch of science devoted to their study. Sonocytology is the study and application of cells’ nanoscale oscillations, which, because each different type of cell sings a different song that changes when they’re stressed, can be used to spot diseases early on.
Researchers at the University of Manchester, for example, have differentiated between healthy and cancerous prostate cells by blasting them with infrared light and recording the “squeals.” Like comparing two large orchestras, one of which has an out-of-tune tuba, the difference is there but it’s not easy listening. In fact, the sound of cells is more like a “high-pitched scream.” According to Andrew Pelling of University College London, “if you listened to it for too long, you would go mad.”
Fortunately, they can’t be heard by the naked ear. Sonocytologists record the sounds using an atomic force microscope, which touches cells with a small tip to record oscillations — similar to the way a record player’s needle responds to the bumps in a record.
2. The vacuum of space
It’s a common misconception that outer space is silent. While it’s true that in space no one can hear you scream, scientists have captured some frightening extraterrestrial sounds. And we don’t just mean those eerie planetary radio waves converted by into sound. We mean actual sounds (or proof of them anyway).
Space is mostly a vacuum, of course, which is why sound waves can’t cross it. But there’s enough hot gas and plasma surrounding the supermassive black hole in the Perseus galaxy cluster that sound waves have something to traverse. Needless to say, we don’t have microphones powerful or close enough to pick them up, but the sound waves are unmistakeable.
Extracted from the data, the harrowing baritone of the Perseus black hole was 57 octaves below middle C — so deep that to make it audible, its frequency had to be increased quadrillions (millions of billions) of times.
Even silence isn’t silent — at least to the human brain. Anechoic chambers, with walls designed not only to keep noise out but also to capture and mute any noise within the room, are the quietest places on Earth. The quietest of them all belongs to Microsoft, holding the world record at -20.6 decibels (whereas a silent house is around +40).
However, people who sit in these places for any length of time report not a tranquil silence, or even a disturbing silence, but a lot of strange and terrifying noises. The normally inaudible sounds of the body, for example, are suddenly amplified: “spontaneous firings of the auditory nerve can cause a high-pitched hiss”; people hear their blood pumping; “their digestive system’s symphony of gurgles and blurbs,”; their breath, and so on.
But that’s just the beginning. Sit in true silence for an hour or more and you start hearing all sorts of disembodied noises as well: swarms of bees; old pop songs; wind in the trees; sirens…