3 ms·

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

by kypro 2y 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 2y 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.
- bookofjoe 2y ago
  Like a neutrino
  - isoprophlex 2y ago
    Only not weighing millions and millions of kilograms
  - adastra22 2y ago
    No a neutrino would literally leave no trace. The black hole would harm the cells in its path.
    - Tuna-Fish 2y ago
      A small enough black hole would be very unlikely to hit even one atom in one cell while going through you.
      - adastra22 2y ago
        TFA is about the effects it would have moving through cells.
        Tuna-Fish 2y ago
        Because its gravity would cause a shock wave as it rapidly moved through you, not because it would absorb any material doing so.
        adastra22 2y ago
        I think you are drawing a distinction that is not what I said and not relevant.
- perihelions 2y ago
  The gravitational field would be enormous: 1,000–500,000 times Earth gravity, at one meter's distance, for the range of PBH masses this paper mentions. That's balanced out by the relative speed being a brisk 200 km/s, so the interaction time would be short (microseconds). Still a pretty significant momentum impulse if one flew by.
  - H8crilA 2y ago
    This is analyzed in the paper. There are two sources of problems: gunshot-wound-like, and the effect of transiently highly increased gravity on nearby tissues. The first one seems worse, and is the limiting factor. PS. The paper is very easy to read :)
  - bloopernova 2y ago
    So gravity builds up over time? (Forgive the layman's attempt at understanding) If Bob is floating in space in a capsule, and a very heavy asteroid floats past, the amount that Bob's capsule is moved is dependent on the speed of the asteroid? Does that sort of thing have to be considered when planning the orbits of probes etc? Is Earth traveling fast enough, from the viewpoint of Alice floating near the sun, to have a gravity "tail" or "wake" trailing after it? (Alice near the sun thing is my attempt at a mostly static observer) And of course due to relativity, if Alice was orbiting retrograde to the big heavy object, she'd observe even more effect? I think I need about 6 more cups of tea before I can think about this!
    - sapiogram 2y ago
      > If Bob is floating in space in a capsule, and a very heavy asteroid floats past, the amount that Bob's capsule is moved is dependent on the speed of the asteroid? Yes > Does that sort of thing have to be considered when planning the orbits of probes etc? Yes, it's a primary concern when sending probes to other planets > Is Earth traveling fast enough, from the viewpoint of Alice floating near the sun, to have a gravity "tail" or "wake" trailing after it? If I understand you correctly, then classically (i.e. ignoring relativity), no. Your gravitational acceleration towards the earth depends only your distance to it. If you consider general relativity? It's... complicated.
- Tuna-Fish 2y ago
  > Locally, the black hole would swallow any atoms it comes into contact with and would probably scatter nearby molecules More likely, it would go straight through most atoms without interacting with them. They are tiny and move very fast, if you do the math the likelihood of direct, non-gravitational interactions with matter are somewhere near neutrinos, of which trillions passed through you while reading this sentence. When one does end up eating something, the most significant effect is probably that it wouldn't eat the whole atom, but either just the nucleus, freeing all the electrons, or just an electron, leaving the atom positively charged.
  - cogman10 2y ago
    I wonder what happens to the electrons when/if they interact with the black hole. There's already weird stuff going on there with electrons being particles and waves. So, I wonder what happens when you introduce something like a black hole to the equation. Does it have a charge? I'm assuming it'd break through the electron shell; would it absorb the electron/s upon interacting with the shell?
- mr_toad 2y ago
  > Locally, the black hole would swallow any atoms it comes into contact with Would it be capable of doing that? If the radius of the event horizon is significantly smaller than the radius of a proton, would it be capable of swallowing a proton (and how)?
Ajedi32 2y 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+calculator&assumption=%7B%22F%22%2C+%22EventHorizonRadius%22%2C+%22M%22%7D+-%3E%222%C3%9710%5E17g%22 https://www.wolframalpha.com/input?i=schwarzschild+radius+ca... [2]: https://www.wolframalpha.com/input?i=%28red+blood+cell+size%29%2F%281.485%C3%9710%5E-13+meters%29 https://www.wolframalpha.com/input?i=%28red+blood+cell+size%...
cwillu 2y ago
That's more or less my understanding, yes.
hnuser123456 2y 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.

by kypro 2y ago

mystified5016 2y 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.

bookofjoe 2y ago
Like a neutrino
- isoprophlex 2y ago
  Only not weighing millions and millions of kilograms
- adastra22 2y ago
  No a neutrino would literally leave no trace. The black hole would harm the cells in its path.
  - Tuna-Fish 2y ago
    A small enough black hole would be very unlikely to hit even one atom in one cell while going through you.
    - adastra22 2y ago
      TFA is about the effects it would have moving through cells.
      - Tuna-Fish 2y ago
        Because its gravity would cause a shock wave as it rapidly moved through you, not because it would absorb any material doing so.
        adastra22 2y ago
        I think you are drawing a distinction that is not what I said and not relevant.
perihelions 2y ago
The gravitational field would be enormous: 1,000–500,000 times Earth gravity, at one meter's distance, for the range of PBH masses this paper mentions. That's balanced out by the relative speed being a brisk 200 km/s, so the interaction time would be short (microseconds). Still a pretty significant momentum impulse if one flew by.
- H8crilA 2y ago
  This is analyzed in the paper. There are two sources of problems: gunshot-wound-like, and the effect of transiently highly increased gravity on nearby tissues. The first one seems worse, and is the limiting factor. PS. The paper is very easy to read :)
- bloopernova 2y ago
  So gravity builds up over time? (Forgive the layman's attempt at understanding) If Bob is floating in space in a capsule, and a very heavy asteroid floats past, the amount that Bob's capsule is moved is dependent on the speed of the asteroid? Does that sort of thing have to be considered when planning the orbits of probes etc? Is Earth traveling fast enough, from the viewpoint of Alice floating near the sun, to have a gravity "tail" or "wake" trailing after it? (Alice near the sun thing is my attempt at a mostly static observer) And of course due to relativity, if Alice was orbiting retrograde to the big heavy object, she'd observe even more effect? I think I need about 6 more cups of tea before I can think about this!
  - sapiogram 2y ago
    > If Bob is floating in space in a capsule, and a very heavy asteroid floats past, the amount that Bob's capsule is moved is dependent on the speed of the asteroid? Yes > Does that sort of thing have to be considered when planning the orbits of probes etc? Yes, it's a primary concern when sending probes to other planets > Is Earth traveling fast enough, from the viewpoint of Alice floating near the sun, to have a gravity "tail" or "wake" trailing after it? If I understand you correctly, then classically (i.e. ignoring relativity), no. Your gravitational acceleration towards the earth depends only your distance to it. If you consider general relativity? It's... complicated.
Tuna-Fish 2y ago
> Locally, the black hole would swallow any atoms it comes into contact with and would probably scatter nearby molecules More likely, it would go straight through most atoms without interacting with them. They are tiny and move very fast, if you do the math the likelihood of direct, non-gravitational interactions with matter are somewhere near neutrinos, of which trillions passed through you while reading this sentence. When one does end up eating something, the most significant effect is probably that it wouldn't eat the whole atom, but either just the nucleus, freeing all the electrons, or just an electron, leaving the atom positively charged.
- cogman10 2y ago
  I wonder what happens to the electrons when/if they interact with the black hole. There's already weird stuff going on there with electrons being particles and waves. So, I wonder what happens when you introduce something like a black hole to the equation. Does it have a charge? I'm assuming it'd break through the electron shell; would it absorb the electron/s upon interacting with the shell?
mr_toad 2y ago
> Locally, the black hole would swallow any atoms it comes into contact with Would it be capable of doing that? If the radius of the event horizon is significantly smaller than the radius of a proton, would it be capable of swallowing a proton (and how)?

Ajedi32 2y 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+calculator&assumption=%7B%22F%22%2C+%22EventHorizonRadius%22%2C+%22M%22%7D+-%3E%222%C3%9710%5E17g%22 https://www.wolframalpha.com/input?i=schwarzschild+radius+ca... [2]: https://www.wolframalpha.com/input?i=%28red+blood+cell+size%29%2F%281.485%C3%9710%5E-13+meters%29 https://www.wolframalpha.com/input?i=%28red+blood+cell+size%...

cwillu 2y ago

That's more or less my understanding, yes.

hnuser123456 2y 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.