Imagine for a moment that a tiny black hole were to pass through your body. Would it be fatal? While such an event might seem straight out of a science fiction novel, researchers have studied the question from a scientific perspective. Although the odds of this occurring are infinitesimal, this scenario provides a fascinating opportunity to explore the effects of these cosmic objects and the nature of gravity.
Primordial black holes: small singularities
To understand what would happen if a minuscule black hole passed through our body, we first need to define what a primordial black hole is. Unlike the massive black holes formed from the collapse of large stars, a primordial black hole would be much smaller and might have a mass on the order of that of an atom or perhaps several times that of the Earth. These theoretical black holes could have formed shortly after the Big Bang and could be responsible for the mysterious dark matter that makes up a large portion of the universe.
According to the theory, their size and mass could vary widely. In the scope of this article, researchers focus on those with masses comparable to that of an asteroid, i.e., roughly 10¹³ to 10¹⁹ kilograms. A mass in this range would imply a diameter of at least one micrometer.
Tidal forces: gravity at the microscopic scale
One of the principal dangers posed by a black hole is its gravity. The closer you get, the stronger the gravitational pull becomes. This gives rise to tidal forces: differences in gravity that act differently on an object depending on how far its various parts are from the black hole’s center. These forces can cause devastating effects on an object or a person who gets too close.
Imagine a black hole the size of an asteroid. Although small, its tidal forces would operate in a highly localized manner. If it passed through a limb or the abdomen, the effect would be akin to a needle piercing the skin. Indeed, the tidal forces in such a tiny region are relatively weak and should not cause fatal damage unless they act on more sensitive areas of the body.
However, if the black hole were to traverse the head, the situation would be far more serious. Brain cells, being far more sensitive to gravity differences, could be destroyed rapidly. In fact, even a difference in force as small as 10 to 100 nanonewtons could be enough to rupture brain cells. Such tearing would be fatal, because the brain is extraordinarily vulnerable to trauma.
Shock waves: the energy impact
Tidal forces would not be the only danger. Another potentially devastating effect would be shock waves. When a black hole passes through an object, it indeed creates a density wave that travels through the material. This wave exerts enormous pressure on cells and transfers thermal energy, which can cause substantial physical damage. Shock waves are far more destructive than simple tidal forces.
For a black hole to generate a shock wave powerful enough to cause significant bodily harm, it would require a mass of about 1.4 × 10¹⁴ kg, that is, a mass within the primordial black hole range. That mass would be more than sufficient to produce a shock wave with energy comparable to the impact of a .22-caliber bullet. These shock waves would destroy cells, cause internal burns, and could lead to severe tissue degradation. It would be a quick and painful way to die.
An infinitesimal probability
Although this scenario is fascinating, it remains highly theoretical. The probability that a primordial black hole would pass through a human body is incredibly small. The vastness of space works in our favor here. Primordial black holes could exist, but their extremely low density in the universe makes such an impact on an individual almost impossible. The odds that such an event would occur due to the trajectory of a primordial black hole are indeed on the order of one in ten trillion.
