Imagine a supervillain attacking you with his unique superpower of creating small black holes. An invisible force zips through your body at unimaginable speed. You feel no push, no heat, yet, deep inside your body, atoms momentarily shift in response to the gravitational pull of something tiny yet immensely dense — a primordial black hole (PBH).
What would this do to you? Would it cause minor, localized damage, or would it simply rip through your entire body? Physicist Robert J. Scherrer from Vanderbilt University investigated this very scenario. His study examines what happens when a tiny black hole, like the ones formed in the early universe, passes through the human body.
Primordial black holes
The question is, of course, theoretical; but it does start from a realistic scenario. Unlike regular black holes that form when massive stars collapse, primordial black holes are thought to have emerged in the first fractions of a second after the Big Bang. While “regular” black holes typically weigh millions or billions of times more than the Sun, these PBHs could be incredibly small, with masses ranging from tiny asteroids to planets.
These black holes are theoretical, but some scientists speculate that PBHs might even make up part of the mysterious dark matter that fills the cosmos. This means they could be silently drifting through space — and occasionally through Earth itself. So there’s a chance there could be lots of these small black holes throughout the universe.
So what if, hypothetically, one of them passed right through you? The key difference compared to something like a bullet is size. Even though it’s incredibly mass dense (even a miniature black hole is still a black hole), it would be extremely small.
If a PBH were to pass through you, it wouldn’t collide like a traditional object. Instead, it would distort the space-time around it and pull on your atoms with its intense gravity. The study estimates that to cause serious injury, a PBH would need to deposit at least 100 joules of energy inside the body — the equivalent of a .22 caliber rifle bullet. In order to reach that energy, a black hole passing at 200 km/s would need to weigh at least 1.4 × 10¹⁷ grams or 140 million tons to do major damage to the human body.
For perspective, that mass is comparable to a large asteroid, but it would be compressed into something far smaller than an atom because of the sheer gravitational force.
What about tidal forces?
There’s another mechanism through which a miniature black hole could damage your tissues: a tidal force. Basically, the gravitational distortion caused by the black hole could leave more disaster in its wake. However, in order for this to happen, Scherrer’s calculations show that at least 7 × 10¹⁸ grams (7 billion tons) — 50 times more massive than the threshold needed to cause a fatal shock wave.
Essentially, the initial shockwave would be far more devastating than the tidal force. In other words, in order for a PBH to have lethal force, it would need to weigh about 140 million tons.
“Intriguingly, the smallest PBH mass that can lead to significant human injury lies near the lower bound on PBH dark matter,” the researcher writes.
Since we don’t know whether PBHs actually exist nowadays, this brings up an important question. If PBHs are linked to dark matter, how likely is it that a PBH has ever passed through a human body? After all, we are on a celestial body moving through space, there’s dark matter all around us apparently. So have we never encountered one?
Scherrer estimates that even if PBHs existed in large numbers, the chance of one passing through a human in a given year is roughly 1 in 10¹⁸ — or once every 100 billion years. That’s around 10 times the age of the universe; the odds of that happening are as big as winning the lottery 1 million times in a row.
Would we even detect a PBH if it doesn’t do any damage?
This is very speculative, but if a small PBH were to pass through your body without causing harm, it could be (in theory) detected, though not with today’s technology.
Scientists speculate that a PBH moving through Earth could leave behind microscopic tunnels of disrupted atoms. In theory, these could be detectable with incredibly advanced scanning techniques — though nothing like that exists yet.
Some researchers have suggested looking for seismic disturbances or strange particle interactions as signs of a passing PBH. But as of now, there’s no direct evidence that PBHs even exist, let alone that they’ve passed through a human.
While the idea of a tiny black hole silently piercing through your body is an intriguing thought experiment, the actual probability of it happening is close to zero. And even if one did, it would have to be exceptionally massive (by microscopic standards) to cause harm.
The study preprint was published in arXiv and has not yet been peer-reviewed.
