The most dangerous thing in your living room is probably still a rogue plug or a Lego brick. But according to some physicists, there could also be thousands of black holes drifting through that same space every year, through your walls, your sofa, even your body, and you’d never know. Not the galaxy-guzzling monsters from Interstellarbut something far stranger: tiny, ancient “primordial” black holes that may have formed in the first heartbeat of the universe. They’re invisible, almost impossible to detect, and some researchers think they might even be what we currently call dark matter.It sounds like the kind of claim you’d hear on a paranoid pseudo-science YouTube channel. It isn’t. This is the stuff serious cosmologists are writing papers about.
What primordial black holes actually are
Black holes, as we usually know them, are formed when massive stars collapse under their own gravity. The core compresses to a point where it becomes a singularity, creating an object from which nothing can escape, no light, no matter.Primordial black holes, however, are a different concept. They don’t require stars to form. “Primordial black holes are black holes created soon after the Big Bang,” said Dr De-Chang Dai, a black-hole researcher at Yangzhou University in China, in an interview with MailOnline“At this period, the temperature and energy density of the universe were very high,” In those first fractions of a second, space wasn’t smooth. Some regions were denser and hotter than others. The idea is that tiny pockets of overdense matter could have been “squished” by their own gravity into black holes before the first atoms, let alone the first stars, had time to form. The range of possible masses is huge. Based on calculations going back to Stephen Hawking, primordial black holes could be anything from 100,000 times lighter than a paperclip to 100,000 times heavier than the Sun. The ones people worry about for cosmology, though, are the microscopic versions: black holes no bigger than a hydrogen atom, but still packing a lot of mass into that point. Over 13.8 billion years, many of them would have slowly lost mass via Hawking radiation —the quantum process that allows black holes to evaporate. Professor Dejan Stojkovic, a black-hole physicist at the University at Buffalo, has argued that some could have shrunk down into “Planck mass remnants” weighing about ten micrograms: “10 micrograms is about the mass of a bacteria.” At that scale, they’d be practically invisible: tiny, dense, dark objects drifting through space, radiating almost nothing.And that makes primordial black holes a very tempting candidate for dark matter—the unseen mass inferred from the way galaxies move but not detectable by direct observation.“Given the lack of conclusive results from both direct and indirect dark matter searches, primordial black holes seem to be the least exotic possibility,” Stojkovic told MailOnline.Although we can’t see or interact with dark matter directly, scientists estimate it could account for around 27 percent of the universe’s total mass.MIT physicist David Kaiser has made a similar point in recent worknoting that even if the earliest primordial black holes have long since evaporated, their fingerprints may linger. “Even though these short-lived, exotic creatures are not around today,” he said, “they could have affected cosmic history in ways that could show up in subtle signals today.” If primordial black holes are dark matter, they wouldn’t just be “out there” between galaxies. They’d be everywhere, including here, right now.
So… are there really black holes in your house?
If you take the dark-matter idea seriously, you can do a simple bit of maths. The result some researchers land on is startling: up to 1,000 primordial black holes could be passing through every square meter of Earth each year. That includes the square meter you’re sitting in. They’d be moving at around 180 miles per second (roughly 300 kilometers per second), zipping straight through rock, metal, flesh and bone. No sparks. No glow. No Hollywood vortex in the ceiling. Just a series of tiny, invisible gravity bullets passing through the planet. So what happens if one goes through you, For the very smallest candidates, the ten-microgram “bacteria-mass” remnants Stojkovic talks about, the answer is: basically nothing. “1000 crossings per year per square meter is not drastic at all since 10 micrograms is about the mass of a bacteria,” he said. “We have trillions of bacteria around us at any moment, though they are not moving very fast.” At that mass and size, the black hole’s gravitational pull acts over such a tiny distance that it wouldn’t meaningfully disturb your cells as it passes through. You would be, at most, microscopically rearranged in a way you’d never notice. Things get stranger when you imagine heavier primordial black holes. Some models allow for masses comparable to asteroids or small moons, still squeezed into a point about the size of an atom. Traveling at hundreds of kilometers per second, one of those punching through Earth would behave less like a rock and more like a bullet through a cloud. It wouldn’t slam into the surface in a fireball. It would pierce the planet, leaving a narrow track, potentially generating unusual seismic signals as it went. If that track intersects with a person, the physics becomes brutal. “If a black hole hit your head, the gravitational forces would tear your brain apart at the cellular level,” one set of calculations suggests, delivering an impact comparable to a .22-caliber rifle round. Death, in that scenario, arrives in microseconds.Dr Sarah Geller, a theoretical physicist from UC Santa Cruz, put it more simply: “Most likely this wouldn’t be great for that person’s health. The primordial black hole would go right through a person, and though it leaves only a very tiny hole, it might impart some velocity and give the person a real kick!” The good news is that this is the extreme end of the parameter space. You’d need a relatively massive primordial black hole, aimed just so, at a human target, at exactly the right moment. “In practice, the chances of such a collision are vanishingly tiny,” Dr Geller said. “It’s much more likely you could succeed in dropping a peanut from an airplane at random into a field the size of a million football fields and hit a single specific blade of grass.”If primordial black holes exist and contribute to dark matter, there could be thousands of them passing through your house, and even through you, every year. There would be no warning, no noticeable effects, and no sensation. It would simply be another strange aspect of the cosmos, too small and too fast for us to detect.
