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Death by Primordial Black Hole

Rejected submission by Anti-aristarchus at 2021-06-07 22:07:33 from the Death by Snuusnuu? dept.
Science

As if GRBs were not enough to worry about, now the threat of PBHs (not to be confused with PHBs) is being made manifest!
Article at Scientific American [scientificamerican.com].

In the infant universe, a substantial enhancement in the radiation density on the scale of the cosmic horizon could have made some small regions behave as a closed universe and sealed their fate in isolated collapses to black holes.

The typical variations that are actually observed in the cosmic microwave background radiation had an initial amplitude that is a hundred thousand times smaller than needed to make black holes. But these variations can only be observed on large spatial scales. It is possible that rare density enhancements of a much larger amplitude were generated on very small scales as a result of new physics at high energies. Although existing cosmological data just allows for that, there is added motivation to consider this hypothetical possibility because of the existence of dark matter.

So, there might be black holes of a very small scale?

Most of the matter in the universe is dark, and despite searches for signatures of related elementary particles on the sky or in laboratory experiments, none were found so far. Primordial black holes (PBHs) could potentially make the dark matter. Various astrophysical constraints rule out PBHs as the dark matter if they have either low or high masses, but allow for a range of masses between a billionth and a thousandth of the mass of the moon—similar to asteroids with a size ranging between one and a hundred miles.

And because of the threat of asteroid impacts:

This led to the construction of survey telescopes like Pan STARRS and the forthcoming Vera C. Rubin Observatory, which can fulfil two thirds of the congressional goal. These surveys take advantage of the sun as a lamppost that illuminates the dark space near us. An early alert would allow us to deflect dangerous asteroids away from Earth. But PBHs do not reflect sunlight and cannot be identified this way ahead of impact. They do glow faintly in Hawking radiation, but their luminosity is lower than a mini light bulb of 0.1 watt for masses above a millionth of the mass of the moon. Is this invisibility a reason for concern?

In particular, if PBHs in the allowed mass range make up the dark matter, one may wonder whether they pose a threat to our life. An encounter of a PBH with a human body would represent a collision of an invisible relic from the first femtosecond after the big bang with an intelligent body—a pinnacle of complex chemistry made 13.8 billion years later. Although this constitutes a meeting of an extraordinary kind between the early and late universe, we would not wish it upon ourselves.

Oh, great. Not only dangerous, but you never see them coming!

One would naively expect that such a small object passing through our body would only result in a minor injury confined to a limited cylindrical trail of microscopic width. This would be the case for an energetic particle, like a cosmic ray, passing like a miniature projectile through our body. But this expectation ignores the long-range influence of gravity. The attractive gravitational force induced by a PBH of the abovementioned mass would shrink our entire body by several inches during its quick passage. The pull would be impulsive, lasting 10 microseconds for the typical PBH speed of 100 miles per second in the dark matter halo of the Milky Way galaxy. The resulting pain would feel as if a tiny vacuum cleaner with a tremendous suction power went quickly through our body and shrunk its mussels[sic], bones, blood vessels and internal organs. The dramatic bodily distortion would create severe damage and cause immediate death. How likely is it for us to experience a fatal event of this type during our life?

Well, at least it is not spagettification, so there is that. But back to the question of how worried should we be.

Gladly, a back-of-the-envelope estimate relieves all worries. If PBHs of the above mass make the dark matter, the chance of a PBH passing through our body during our entire lifetime is miniscule, only one part in 1026. This translates to a small probability of order 10–16 for a single death in the entire population of eight billion people living on Earth at present. The likelihood of one death increases to 10–9 if the current population size persists for another billion years, after which the expanding sun is expected [scientificamerican.com] to boil off all oceans on Earth. And if we assume similar statistics concerning stars within other galaxies, then only up to a trillion people in the entire observable volume of the universe might be killed by the passage of PBHs through their bodies. It is extremely safe to assume that any of us will not be one of these people. The total number of deaths might be larger in the multiverse if it contains many more volumes with similar conditions, and if even more dangerous [arxiv.org] types of dark matter exist in parts of it.

Blinded by science, reassured by statistical probability? I hear that Vitamin E, or Colloidal silver, or thoughts and prayers, can ward off PBH full body tranversal. But that could be poppycock.


Original Submission