4 ms·

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

by kamaal 2y ago

gostsamo 2y 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 2y ago
It's extremely small, just very massive.
thrance 2y 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.
- scarmig 2y ago
  > It would pass through you like through butter I know this is just an idiom, but it got me to thinking about just how much easier it would be for the PBH pass through you than a knife through butter. Some back of the envelope calculation gets me 40 orders of magnitude. If you compare the ease of a knife through diamond to a knife through butter, even that difference is many orders of magnitude less than a PBH through the human body.
mytailorisrich 2y 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.
rachofsunshine 2y 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.
tempodox 2y 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.

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

by kamaal 2y ago

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

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 2y ago

It's extremely small, just very massive.

thrance 2y 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.

scarmig 2y ago
> It would pass through you like through butter I know this is just an idiom, but it got me to thinking about just how much easier it would be for the PBH pass through you than a knife through butter. Some back of the envelope calculation gets me 40 orders of magnitude. If you compare the ease of a knife through diamond to a knife through butter, even that difference is many orders of magnitude less than a PBH through the human body.

mytailorisrich 2y 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.

rachofsunshine 2y 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.

tempodox 2y 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.