Gravitational Effects of Small Primordial Black Hole Passing Through Human Body

https://arxiv.org/abs/2502.09734

by bookofjoe • 1 year ago

101 101 1 year ago

arxiv.org

odyssey7• 1 year ago

No empirical data observations? Jk, this is an interesting scenario to think about.

Hayvok• 1 year ago

Sadly —

"The number density of primordial black holes with a mass above this cutoff [MP BH > 1.4×1017g] is far too small to produce any observable effects on the human population."

leereeves2• 1 year ago

Sadly? I'm thankful.

1970-01-01• 1 year ago

Black holes killing cancer cells when?

stronglikedan• 1 year ago

Maybe causing?

oldMobileOnWifi• 1 year ago

As long as they aren't controlled by a Therac-25, I'm all for it.

changoplatanero• 1 year ago

10^17g is about 20,000 times heavier than the great pyramid of giza. Funny to imagine something as massive as a pyramid pass through your body and not noticing it.

kypro• 1 year ago

I'm trying to get some intuition for this.

Is the difference that a massive objective hitting you would typically do damage via the electromagnetic force?

But if you consider the gravitation force of the pyramids obviously that's extremely weak compared to the other forces on our body, so we shouldn't expect it to do damage in the same way?

mystified5016• 1 year ago

Remember that gravity falls off in strength with the square of distance. The gravitational field around such a black hole would be immensely strong and absolutely miniscule. The event horizon would be the size of a few atoms.

Locally, the black hole would swallow any atoms it comes into contact with and would probably scatter nearby molecules, but that's it. It'd pass straight through you.

Ajedi322• 1 year ago

Yes. And a 10^17g black hole would have a radius of 1.485×10^-13 meters[1], 50 million times smaller than a red blood cell[2].

[1] https://www.wolframalpha.com/input?i=schwarzschild+radius+ca...

[2] https://www.wolframalpha.com/input?i=%28red+blood+cell+size%...

cwillu• 1 year ago

That's more or less my understanding, yes.

hnuser123456• 1 year ago

Is the difference that a massive objective hitting you would typically do damage via the electromagnetic force?

Yes. PBHs, if they exist, have been constrained to asteroid mass ranges, and at the 10^17g the author concludes would be harmful, their radius would be 0.15 femtometers, or about 1/5 the radius of a proton. Combine that with galactic orbital speeds, and it's just too small and too fast to leave a mark, unless the mass is multiple mountains worth.

kamaal• 1 year ago

How can some thing this big pass through one's body without causing considerable damage, let alone one not notice it?

gostsamo• 1 year ago

high speed means that their is no momentum spread through your tissues. the damage will be the diameter of the thing and this is rather small diameter.

neallindsay• 1 year ago

It's extremely small, just very massive.

thrance• 1 year ago

Because a black hole of that mass would be tiny (smaller than a micrometer according to the article), and gravity is a very weak force. It would pass through you like through butter and bore a tiny tunnel, but it's so small it would probably leave you unharmed.

mytailorisrich• 1 year ago

We're mostly empty space so anything small enough and not charged can pretty much just fly through us.

If it does not hit anything then mass does not really matter as long as small enough not to have big gravitional effect.

rachofsunshine4• 1 year ago

Because it isn't big. It's massive. Those are not the same thing. Our everyday intuitions deal with solids with densities within a couple of orders of magnitude (from very light foamy solids at perhaps 0.1 g/cm^3 to very dense metals around 20 g/cm^3), so the two can never be that far apart in everyday experience. But small black holes are many, many, many, many orders of magnitude denser than that.

When a big solid object (where "big" is "macroscopic") strikes your body at a low speed (where "low" is "a few km/s"), it interacts with the atoms in your body. It applies pressure to your body, primarily the degeneracy pressure[1] that pushes back when electron clouds push up against one another. The interaction tine is long (on the order of milliseconds to seconds), so not only is the applied force high, the force has time to do its work. The push overcomes the mechanical strength of the structures in your body, like the walls of your blood vessels or the membranes of your cells, shattering them and causing the secondary damage of bleeding, organ dysfunction, inflammation, vulnerability to infection, etc.

When our black hole here passes through you, though, it is both extremely small (smaller than an atom, if by "size" we mean its event horizon) and moving extremely fast (about ten times Earth's orbital velocity, or about a hundred times faster than a bullet).

It's too small to directly "eat" your tissues, and it isn't "pushing them out of the way" by much, either. It interacts with your body by tugging on it. That tugging would be enough to tear your body's structures apart if it were sustained (the tidal forces here are very extreme), but the hole is moving so quickly that while the force is very large, the impulse (force times time) is not. It does devastating damage along the very narrow corridor where it's munching up an atom or three as it goes and where it's applying ultra-extreme forces that matter even over these millisecond timescales, but the corridor of damage is so narrow that it doesn't disrupt the function of your body. (The paper establishes the mass cutoff where this would no longer be so, and where the gravitational shockwave would indeed be enough to start tearing at your body's structures.)

It's kind of like how you can snuff out a candle with your fingers, even though a typical candle flame is not much cooler than the surface of the Sun. The heat flux from the flame to your skin is extreme, but it's applied for such a short period of time that the total energy delivery is tiny and does not deal meaningful damage to the skin.

[1] Electrostatic repulsion plays a role, but degeneracy pressure is the primary thing that makes matter take up space.

tempodox2• 1 year ago

The Schwarzschild radius is 2 G M / c^2. When we assume the cutoff mass of 1.4e14 kg, then the Schwarzschild radius would be 103.966e-15 m ≈ 104 femtometers. A hydrogen atom has a radius of ~ 53e-12 m.

IsTom3• 1 year ago

Gravitationally maybe, but you'd certainly notice the 9 kW of hawking radiation.

simiones• 1 year ago

I believe black holes are not currently emitting any Hawking radiation, because the CMB is far too hot for now. They will start emitting Hawking radiation in the far future, after the Universe has cooled down significantly.

sapiogram3• 1 year ago

What if it passed through you at hyperbolic velocity (with respect to earth)?

rao-v• 1 year ago

I thought this effect would dominate too, but it turns out the paper’s assumptions is that the PBH moves at 100 km/s so we’re talking about 5 joules while it’s inside you and maybe 1000 joules total while it’s in your vicinity. Hardly blood boiling stuff.

ted_dunning4• 1 year ago

Hmmm... I get 18kW for 1.4e17g

Using Julia:

  > using Unitful
  > uconvert(u"W", Unitful.ħ * Unitful.c^6 / (15360 * π * Unitful.G^2) / (1.4e17u"g")^2)
  18171.541554992324 W

This is the same result as on https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati...

clbrmbr• 1 year ago

Wait, do we know there to be PMBs passing through us like neutrinos? Is this a new kind of cosmic ray?

devmor• 1 year ago

An anecdote from one of my former physics professors was that there are theories that PMBs are being constantly generated and annihilated near-instantaneously all over the universe and that odds are astronomically low but one could form inside your body and be so far away from the nearest subatomic particle that it would starve out immediately.

Of course, the very concept of a black hole is still technically only the "best theory" to explain observed gravitational and radio anomalies, so it's always helpful to remember as a layman how distant from us this stuff truly is.

H8crilA2• 1 year ago

Besides being funny this paper also has some points - for example we know that no human has yet died due to a PBH passing through their body, but they very likely would had one passed through them. So that's sort of evidence against their existence. Although the estimated number (estimated towards the end of the paper) of such events per year would be utterly small anyways.

voakbasda• 1 year ago

Hanlon’s Razor suggests no reasonable pathologist would ever label a death as caused by a PBH. It could have happened, but the effects probably looked similar enough to something more common for such deaths to be mislabeled.

mturmon• 1 year ago

Besides being funny ...

I enjoyed this part too -- the author (Robert Scherrer) also offers the following link to an even drier paper: https://my.vanderbilt.edu/robertscherrer/miscellaneous/

jerf• 1 year ago

No.

There is a range of PMBs masses not currently excluded by observation that may explain dark matter, but if dark matter consists of PMBs in that range we're talking on the order of single digits in the solar system per century, not PMBs streaming through you like crazy.

leereeves2• 1 year ago

with a cutoff mass for serious injury or death of approximately MPBH > 1.4×10^17g

Am I misreading or does that say that a PBH with the mass of a million aircraft carriers[1] could pass through a human without killing them?

1: the largest aircraft carriers displace about 100,000 metric tons or 10^11 grams

PaulHoule2• 1 year ago

Gravity is a really weak force. Electromagnetic forces generated in your muscles can overcome the gravity of the whole planet, like 6 × 10²⁷ grams.

gottorf• 1 year ago

It's true you can jump, but you do need to achieve 25,000 mph to truly "overcome" Earth's gravity ;-)

holyhowitzer• 1 year ago

What's the actual point of this? So PBHs are hypothetical micro black holes that even if they do exist it's so unlikely to harm humans.

dotancohen• 1 year ago

Until this study was done, we did not know if these objects could have affected humans. Imagine if they _had_ discovered the ability of PBHs to e.g. puncture a lung, blood vessel, or brain synapse. Maybe we would better understand e.g. crib death, or Alzheimer's disease.

Wouldn't any parent line their baby's crib with the mass equivalent of a million aircraft carriers in lead, to protect them?

icapybara• 1 year ago

Are we that out of ideas for crib death and Alzheimer's that black holes would be considered a root cause?

throwway120385• 1 year ago

I think that lead would be a bad material to use, considering a baby's propensity to put everything within reach into their mouths starting at a couple of months of age when they can start reaching. When they start teething they will inevitably start chewing on the soft metal.

doctor_phil• 1 year ago

We have a hard time understanding what dark matter is. There are theories that some of the dark matter could be tiny black holes left over from the big bang, called primordial black holes (PHBs).

How can we detect PHBs if they exist? If they existed in large numbers, would we notice them? The paper says that you would notice a PHB if it went through you, since you would likely die. We are not noticing people dying by mysterious gunshot-like wounds without guns in any large amounts, so there can not be that many PHBs around.

The paper is (weak) evidence against a large amount of PHBs. The paper is also slightly funny.

mplewis9z• 1 year ago

Primordial Hack Bloles?

pavel_lishin2• 1 year ago

For a science fiction take on this - and sorry for spoilers - check out Isaac Asimov's "The Hole Man", written in 1974.

https://en.wikipedia.org/wiki/The_Hole_Man

bookofjoe3• 1 year ago

In 1974, science fiction author Larry Niven wrote a murder mystery with an interesting premise: could you kill a man with a tiny black hole?

Reference: Niven, Larry. “The Hole Man.” Analog Science Fiction/Science Fact (1974): 93-104.

It won the 1975 Hugo Award for Best Short Story.

Borrow it here: https://archive.org/details/holeinspace00nive

https://imgur.com/a/Lu16TDT

HelloUsername• 1 year ago

Also related: Anatoli Bugorski, a Russian retired particle physicist, known for surviving a radiation accident in 1978, when a high-energy proton beam from a particle accelerator passed through his head (https://news.ycombinator.com/item?id=42213629)

JadeNB3• 1 year ago

Also, using this as a plot point though in no way engaging with the science, there's the recent "Omni Loop" (https://www.imdb.com/title/tt28150132).

bookofjoe3• 1 year ago

Thank you so much for this! Never heard of it till I read your comment. Gonna watch it tonight. Bonus: Mary-Louise Parker, one of my favorite actors, stars.

JadeNB3• 1 year ago

As sibling commenter bookofjoe (https://news.ycombinator.com/item?id=43102892) and your link point out, it's Larry Niven, not Isaac Asimov.

pavel_lishin2• 1 year ago

This is genuinely the second most embarrassing thing that's happened to me this week, taking 2nd place to nearly catastrophically flooding the house.

kevin_thibedeau• 1 year ago

David Brin's Earth also posits an experiment that drops a micro black hole into orbit of the Earth's core that goes undetected for some time until it accumulates enough mass to cause problems. Notably, it also predicted glassholes.

CPLX• 1 year ago

Don't forget The Vl'hurgs.

lakkal• 1 year ago

"Artifact", by Gregory Benford, also includes microscopic black hole on Earth.

at_a_remove• 1 year ago

I will throw one in: James P. Hogan's Thrice Upon a Time, from 1980.

Micro black holes, terrorizing the minds of sci-fi writers for decades!

rich_sasha• 1 year ago

Would such "tiny" black holes be stable? I'm thinking Hawking radiation, or indeed the opposite, growing without bounds.

If they are, are they considered as possible "particles" for dark matter? I guess that's what MACHOs are? And won't interact electromagnetically, only really by gravity.

dsr_• 1 year ago

Both of these questions are considered in the article.

Tuna-Fish4• 1 year ago

Hawking radiation gives you a lower bound for the size of a primordial black hole that still exists, at 10^15 g. Primordial black holes largely cannot grow, because they would be traveling very fast, likelihood of interaction with ordinary matter is very small, and there is no mechanism that would slow them down.

So if there are some in our galaxy, they would just be zipping about at intergalactic speeds until the heat death of the universe, or until they hit the event horizon of a larger black hole and get absorbed. The present-day universe is just too sparse for them to form or accrete material.

weitendorf2• 1 year ago

Not necessarily. That is only the case for black holes with no charge and angular momentum. Given high enough charge and angular momentum for a given mass, black holes become "extremal" and their hawking radiation/temperature approaches zero. It's argued these are unstable or maybe can't even exist for various reasons, but it's a pretty active area of physics AFAICT https://www.quantamagazine.org/mathematicians-prove-hawking-...

That said, if these were primordial I'd expect their charges to not all be 0, so they'd interact with normal matter.

weitendorf2• 1 year ago

Small black holes can be stable if they have a charge or high angular momentum. These are called extremal [0] black holes - the charge and/or angular momentum counteract the hawking radiation. Some physicists have argued that electrons (stable, very tiny) could technically be described as super-extremal black holes [1]

[0] https://en.wikipedia.org/wiki/Extremal_black_hole

[1] https://en.wikipedia.org/wiki/Black_hole_electron

behnamoh• 1 year ago

New fear unlocked :) seriously though, is it true that a black hole can be as dense as it wants and still be smaller than an atom? at that point (pun intended), how do we even measure its size, given that it bends the space around it?

Ajedi322• 1 year ago

The "size" of a black hold is directly proportional to its mass. Specifically: Mass * 2 * The Gravitational Constant / The Speed of Light Squared: https://en.wikipedia.org/wiki/Schwarzschild_radius

Note that the speed of light squared is a really big number, so black holes are quite small relative to their mass.

lemonberry3• 1 year ago

For as long as I can remember I've had these random hyper-local sharp pains on my body. By the time I register them they're gone. I've always wondered if they were some particle passing through me. I don't know enough about anatomy to know how big something has to be to hit a nerve and have it register it.

jajko• 1 year ago

Not possible in way you describe. Either book an appointment with neurologist or learn to live with it.

lemonberry3• 1 year ago

What an odd comment.

spuz• 1 year ago

Are they localised in the same area or in totally random areas?

lemonberry3• 1 year ago

Random areas

mlhpdx• 1 year ago

Okay, so detecting damage to people from PMBs would be difficult. People are fairly difficult to work with as a specimen anyway, so wouldn’t a more meaningful study be “what easily detectable evidence would be imparted by one?” Holes in silicon wafers?

nolroz• 1 year ago

Oh man, so many questions! Would a PBH passing close enough to Earth to hit a human end up being drawn to the Earth's core or the Sun? Or would the mass/inertia of a rogue PBH be enough to keep it from falling into a local gravity wall and gobbling up the solar system?

ck2• 1 year ago

Stephen Hawking theorized it is even possible there is one hiding in our sun.

Below a certain size it would not be detectable by any current method.

And of course there is a PBS Space Time for that

(edit wrong video)

https://www.youtube.com/watch?v=Q6kJaMf3Lgo

(more awesome here https://www.youtube.com/@pbsspacetime/videos )

rachofsunshine4• 1 year ago

Any object that approaches the Solar System from interstellar space is necessarily moving at least (solar) escape velocity. It's "falling down" into the Solar System's gravity by a distance equal to how far it has to "climb up" to get away in a system with little appreciable friction.

The paper assumes 100 km/s, which is more than double the solar escape velocity at Earth's orbit. The mass doesn't make a difference in the absence of friction and assuming it is much less than the primary body; escape velocity depends only on the mass of the primary.

There would be some "friction" (since the hole would be eating up small amounts of mass on its journey and that mass would be moving at less than solar escape velocity), but without doing any calculations I'm almost certain it's nowhere close to enough to slow it down.

antognini• 1 year ago

"Unfortunately, it is easy to see that the effect of PBH collisions with the human population will always be negligible."

I'm not so sure that is unfortunate.

tempodox2• 1 year ago

But where is the reproducible experiment?

ted_dunning4• 1 year ago

You and I are doing it right now.

Prediction: no effect due to rarity and no effect anyway

Observation: no effect

Theory not falsified.

Gravitational Effects of Small Primordial Black Hole Passing Through Human Body

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