The world is noisy, so noisy in fact that even things you thought were quiet make all sorts of frantic sounds. Some are weird, some are scary. Here are 10 of the most unexpected.
10. You, when you think you are silent
Even meditation masters and seasoned ninjas can’t completely silence the body — at least not according to science. It’s always making noise. You just don’t hear it because, like noise-canceling headphones, your brain tunes it to distinguish itself from others.
Neuroscientists have studied this mechanism in electric fish, most species of which have an electrosensory lobe that receives electrical signals from both inside the fish and from its surroundings. It can tell the difference by subtracting electrical signals that correspond to inputs related to the fish’s behavior, such as motor signals. The flick of your own tail while swimming, for example, will not register as the same as something else flicking its tail next to it. There’s a similar mechanism in the mammalian brain called the dorsal cochlear nucleus (DCN), which subtracts sounds that correspond to our movements from the general auditory input.
9. Ants
Ants usually communicate using chemical signals, but that's not the only way. They chirp, too. And it sounds a little like maniacal laughter.
The sounds are produced by what is known as “stridulation,” scraping the abdominal appendage against ridges on the backside — much like a spoon on a washboard. Workers sound different to queens; their chirps are slightly lower pitched. So when workers hear the queen, they become more attentive. Researchers have actually found that they will stand guard around a speaker playing the queen’s sounds, maintaining a “hunched posture with antennae and slightly open mouth” for several hours.
Caterpillars Maculinea Rereli exploit this vulnerability by mimicking the queen's sounds and odors to enter colonies and steal royal treatment, including feeding and grooming. Beetles also mimic ant sounds to enter nests.
8. Giraffes
Okay, so you may not have thought that giraffes were silent, but think about it: What sound did you think giraffes made? Until recently, biologists assumed that giraffes made sounds that humans couldn't hear, like the infrasonic "secret language" of elephants. But more recently, research has shown that giraffes make a very audible (92 Hz) humming sound. But they only make it at night.
It is believed that this hum is how giraffes maintain contact in the dark. But there is an alternative explanation: it is the sound of giraffes snoring or talking in their sleep.
7. Fish
Even though fish don’t have vocal cords, they do make sounds—and we don’t just mean swimming and splashing. In fact, thousands of the world’s roughly 34,000 species of fish are thought to make noise. Just under 1,000 of them have been documented. You can listen to them here.
Sounds come from bony structures rubbing or clicking against each other, or from beating the swim bladder like a drum, among other mechanisms. For example, two species of rays, previously thought to be silent, produce clicking sounds. As in 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 land and air animals; their signals travel much further.
Perhaps the strangest and most terrifying fish noise of all is that of the three-spined toad, which "cries like a baby."
6. Marine worms
It's probably fair to say that you don't think about sea worms at all; but if you do, you probably don't think they make noise. But they do. And, in fact, it's one of the loudest sounds of any sea creature.
Polychaetes, or bristle worms, are less than 3 centimeters long and are usually silent, hiding in the burrows of sea sponges. However, when threatened, they open their pharyngeal muscles to create a bubble, then release the pressure with a shockingly loud 157-decibel "battle pop."
By comparison, the blue whale's cry — the loudest on Earth — is 180 decibels. A jet plane taking off is 140 decibels. And a human eardrum ruptures when exposed to 160 decibels. But the crack of a sea worm is nothing compared to the snapping sound of a shrimp, which, at 189 decibels, is strong enough to shatter glass.
5. Plants
It took science a while to catch up with what intuition had been telling us 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 are beyond the range of human hearing, came from tobacco and tomato plants and were recorded over the course of an hour of cutting. The tobacco made 15 sounds, and the tomato 25. But they don’t just make noise when they’re being cut. The researchers noted that “even happy, healthy plants made noise from time to time.”
So, the next question is: do they hear? According to a 2013 paper, more research is needed in this area, as the evidence suggests the answer is yes. In addition to anecdotal reports of plants being sung to stimulate vigorous growth, there are numerous (albeit outdated) scientific reports of plants sprouting and growing at different rates in response to sounds of different frequencies.
4. Bacteria
Although 10 billion times softer than a punch on a punching bag, the nanoscale beating of bacteria’s flagella (tails) can be amplified and heard as sound. And these sounds can help scientists determine whether certain bacteria are resistant to antibiotics, a serious problem for a global population that is becoming increasingly resistant to treatment.
The bacteria's beating is recorded on a graphene-coated drum, the membrane of which is only one layer of carbon atoms thick. Even the infinitely quiet sound of a single bacterial flagellum can be recorded this way. When exposed to antibiotics, the beating either stops after a couple of hours or does not, which tells us whether such treatments will work.
Viruses can also be converted into sound, but in a different way and for no more than entertainment. The DNA sequence of COVID-19, for example, has been translated into music that sounds like synth-pop or classical.
3. Cells
Cells don’t just make sounds or “songs,” there’s a whole branch of science devoted to studying them. Sonocytology is the study and application of nanoscale cell vibrations, which, because each individual cell type sings its own song that changes with stress, can be used for early detection of disease.
Researchers at the University of Manchester, for example, distinguished between healthy and cancerous prostate cells by shining infrared light on them and recording their “squeals”. It’s like comparing two large orchestras, one with an out-of-tune tuba – there’s a difference, but it’s not easy to listen to. In fact, the cells sound more like “a high-pitched scream”. According to Andrew Pelling of University College London, “if you listen to it for too long, you’ll go crazy”.
Fortunately, they are not audible to the naked ear. Sonocytologists record the sounds using an atomic force microscope, which touches the cells with a tiny tip to record vibrations, much like the way a record needle responds to the beats of a record.
2. Space vacuum
It's a common misconception that outer space is silent. While it's true that no one can hear you scream in space, scientists have detected some spooky extraterrestrial sounds. And we don't just mean those creepy planetary radio waves converted to sound. We mean real sounds (or evidence of them).
Of course, space is mostly a vacuum, so sound waves can't travel through it. But there's enough hot gas and plasma around the supermassive black hole in the Perseus galaxy cluster that sound waves have something to travel through. Needless to say, we don't have powerful microphones or are close enough to pick them up, but the sound waves are unmistakable.
The heart-wrenching baritone of the Perseus black hole extracted from the data was 57 octaves below middle C—so deep that its frequency had to be increased quadrillions (millions of billions) times to make it audible.
1. Silence
Even silence isn’t quiet—at least not to the human brain. Anechoic chambers, with walls designed not just to block out noise but to trap and muffle any noise in the room, are the quietest places on Earth. The quietest of them all belongs to Microsoft, which holds the world record at -20.6 decibels (while a quiet house is about +40).
However, people who sit in these places for any length of time report not a quiet, or even an uneasy, silence, but a variety of strange and terrifying sounds. Normally inaudible body sounds, for example, suddenly become louder: “spontaneous stimulation of the auditory nerve can produce a piercing hiss”; people hear their blood pounding; “a symphony of gurgling and chattering from their digestive system”; their breathing; and so on.
But that's just the beginning. Sit in complete silence for an hour or more, and you'll also begin to hear all sorts of disembodied sounds: swarms of bees; old pop songs; wind in the trees; sirens...
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