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Using the formula for black hole density, a black hole of this mass would have an average density about the same as the near-vacuum atmosphere of Mars(!) https

Using the formula for black hole density, a black hole of this mass would have an average density about the same as the near-vacuum atmosphere of Mars(!) https://physics.stackexchange.com/questions/26515/what-is-exactly-the-density-of-a-black-hole-and-how-can-it-be-calculated#218816 https://physics.stackexchange.com/questions/26515/what-is-ex...

tlogan 1y ago
And it would take 10 days from event horizon to the singularity.
- dotancohen 1y ago
  How so?
  - proteal 1y ago
    The black hole has two conceptual parts - the event horizon and the singularity. The event horizon is a one-way imaginary shell where once you pass it, you will end up at the singularity which is a point at the center of the event horizon. It’s the hole in black hole. Because the radius of the spherical horizon grows linearly with mass, but the size of the hole is fixed at effectively 0, it allows for a bit of sightseeing on your way to impending doom if the mass of the hole is large enough.
    - reactordev 1y ago
      This is also the light barrier where light can no longer escape the gravitational forces (causing the blackness of the black hole). Your “sightseeing tour” would be a kaleidoscope of light as it brushes past you on its way to the singularity.
      - lazide 1y ago
        Uh, that is the event horizon?
        reactordev 1y ago
        Yup, you’re trapped, so is light, and as gravity bends you and everything around you into pretzels, you’ll see everything yet nothing, as even the light will escape your retinas, before they pop like little grapes. Eventually your atoms will make their way to the center singularity.
        lazide 1y ago
        Yes, I’m not sure why you keep repeating what everyone else is already saying?
        reactordev 1y ago
        This agent lacks context to the rest of the conversation, sorry.
    - kulahan 1y ago
      One of the more mind bending aspects of this is how the horizon becomes inescapable. The singularity is the only “forward” that exists anymore. You cannot conceivably go anywhere else. Every direction becomes “in”.
      - pasquinelli 1y ago
        space becomes time and the singularity becomes the future.
      - kortinador 1y ago
        another way of saying it is that the singularity is a place in time, not in space. it's a place in your future, and you cannot escape your future. in a black hole time and space get switched in a sense.
      - chatmasta 1y ago
        One could say the same thing about death (or life). Once you’re born, death is the only “forward” that exists. You can’t calculate its exact distance but it’s inevitable.
        kulahan 1y ago
        And seeing as how time is only something observed at the macro level and is still completely unexplainable scientifically, you're really hitting the nail on the head here.
        chatmasta 1y ago
        My point is not that they’re scientifically similar but that philosophically there is little difference.
        dur-randir 1y ago
        Hydras tend to disagree.
      - dustingetz 1y ago
- somat 1y ago
  from which perspective? I have yet to wrap my head around it(this usually means I am wrong about something), but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects. https://modern-physics.org/time-dilation-near-massive-bodies/ https://modern-physics.org/time-dilation-near-massive-bodies... This is the origin of my favorite science fiction theory. (little to no actual science but you could write a fun space romp around it) If you get a large enough black hole where the tidal forces will not rip you to shreds instantly, you could just scoot across the event horizon right, now what happens? you can still move around, everything feels normal, but really you have lost half a dimension, everything "out" from the center is completely gone from the universe. Now the theory, back to our universe, What happened to time? why does time only go one way? we can accelerate and decelerate along the time axis, but can't reverse it. Where has our missing half of a time dimension gone?
  - tbrownaw 1y ago
    > but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects. Wouldn't that just mean that the singularity is located infinitely far into the future?
    - nine_k 1y ago
      Isn't it another way of saying that the singularity is never going to exist?
  - idiotsecant 1y ago
    It's not quite true that everything feels normal. If I am standing with my feet toward the singularity, my hand cannot move above my head, the best it can do is fall toward the singularity slower than my head does. Especially at very slow speeds this has some very weird physical effects, not the least of which is the immediate impossibility of all systems that make you 'you' continuing to function.
    - dustingetz 1y ago
pizzathyme 1y ago
Definitely a dumb question but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that. The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding?
- aw1621107 1y ago
  > but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that. That sounds more like a description of the stuff neutron stars are made of. I don't think that description really works for black holes - how exactly do you take a teaspoon out of a black hole? > The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding? The linked Physics.SE answer does a decent job at explaining it, but the short of it is that for Schwarzchild black holes mass ~ event horizon radius, so if you define density as mass / (Schwarzchild volume) you get density ~ 1/(mass^2) - in other words, the more massive a black hole the less dense it is by that measure.
  - jfengel 1y ago
    You can't make a teaspoon of neutroniun, either. The neutrons would immediately drift off and quickly decay (half life about ten minutes). It's just a way of illustrating the density. You actually can have a black hole with the volume of a teaspoon, and it's stable. It will eventually decay by Hawking radiation, but not for umpteen gazillion years until the CMB gets cold enough.
    - aw1621107 1y ago
      > You can't make a teaspoon of neutroniun, either. The neutrons would immediately drift off and quickly decay (half life about ten minutes). Technically speaking that sure sounds like scooping out a teaspoon of neutronium to me. Nothing said it had to be stable :P But in any case, I suppose what doesn't work for me is that when the teaspoon illustration is being used it's in the context of picking out some sample/subset of a larger whole - take a whole neutron star and examine the properties of this supposed representative part of it, same way one might scoop out some ice cream out of a container. While that's technically not totally correct for neutron stars since they don't exactly have a uniform density, I feel that it's usefully-close-enough compared to black holes, since as far as we know all the mass of a black hole is concentrated in a point at its center so your "scoop" is either going to get nothing or everything. > You actually can have a black hole with the volume of a teaspoon, and it's stable. Sure, but at that point I wouldn't use the wording "a teaspoon of black hole"; something more like "teaspoon-sized black hole" would be more appropriate (though to be fair that's still technically somewhat ambiguous).
jiehong 1y ago
That calculation of density is nice, but since we don’t know what’s inside a black hole, it doesn’t mean anything. Passing the event horizon doesn’t mean you’ve reached the potentially ultra dense singularity, but it does mean you won’t escape.
- agos 1y ago
  we don't know how the mass inside a black hole is doing, but we have a pretty solid understanding of the volume and the total mass of black holes
ramraj07 1y ago
Which isn't surprising if you think about it. Imagine the whole nothingness of the solar system being filled with even that density of gas. That's a metric ton of gas.

tlogan 1y ago

And it would take 10 days from event horizon to the singularity.

dotancohen 1y ago
How so?
- proteal 1y ago
  The black hole has two conceptual parts - the event horizon and the singularity. The event horizon is a one-way imaginary shell where once you pass it, you will end up at the singularity which is a point at the center of the event horizon. It’s the hole in black hole. Because the radius of the spherical horizon grows linearly with mass, but the size of the hole is fixed at effectively 0, it allows for a bit of sightseeing on your way to impending doom if the mass of the hole is large enough.
  - reactordev 1y ago
    This is also the light barrier where light can no longer escape the gravitational forces (causing the blackness of the black hole). Your “sightseeing tour” would be a kaleidoscope of light as it brushes past you on its way to the singularity.
    - lazide 1y ago
      Uh, that is the event horizon?
      - reactordev 1y ago
        Yup, you’re trapped, so is light, and as gravity bends you and everything around you into pretzels, you’ll see everything yet nothing, as even the light will escape your retinas, before they pop like little grapes. Eventually your atoms will make their way to the center singularity.
        lazide 1y ago
        Yes, I’m not sure why you keep repeating what everyone else is already saying?
        reactordev 1y ago
        This agent lacks context to the rest of the conversation, sorry.
  - kulahan 1y ago
    One of the more mind bending aspects of this is how the horizon becomes inescapable. The singularity is the only “forward” that exists anymore. You cannot conceivably go anywhere else. Every direction becomes “in”.
    - pasquinelli 1y ago
      space becomes time and the singularity becomes the future.
    - kortinador 1y ago
      another way of saying it is that the singularity is a place in time, not in space. it's a place in your future, and you cannot escape your future. in a black hole time and space get switched in a sense.
    - chatmasta 1y ago
      One could say the same thing about death (or life). Once you’re born, death is the only “forward” that exists. You can’t calculate its exact distance but it’s inevitable.
      - kulahan 1y ago
        And seeing as how time is only something observed at the macro level and is still completely unexplainable scientifically, you're really hitting the nail on the head here.
        chatmasta 1y ago
        My point is not that they’re scientifically similar but that philosophically there is little difference.
      - dur-randir 1y ago
        Hydras tend to disagree.
    - dustingetz 1y ago
somat 1y ago
from which perspective? I have yet to wrap my head around it(this usually means I am wrong about something), but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects. https://modern-physics.org/time-dilation-near-massive-bodies/ https://modern-physics.org/time-dilation-near-massive-bodies... This is the origin of my favorite science fiction theory. (little to no actual science but you could write a fun space romp around it) If you get a large enough black hole where the tidal forces will not rip you to shreds instantly, you could just scoot across the event horizon right, now what happens? you can still move around, everything feels normal, but really you have lost half a dimension, everything "out" from the center is completely gone from the universe. Now the theory, back to our universe, What happened to time? why does time only go one way? we can accelerate and decelerate along the time axis, but can't reverse it. Where has our missing half of a time dimension gone?
- tbrownaw 1y ago
  > but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects. Wouldn't that just mean that the singularity is located infinitely far into the future?
  - nine_k 1y ago
    Isn't it another way of saying that the singularity is never going to exist?
- idiotsecant 1y ago
  It's not quite true that everything feels normal. If I am standing with my feet toward the singularity, my hand cannot move above my head, the best it can do is fall toward the singularity slower than my head does. Especially at very slow speeds this has some very weird physical effects, not the least of which is the immediate impossibility of all systems that make you 'you' continuing to function.
  - dustingetz 1y ago

pizzathyme 1y ago

Definitely a dumb question but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that. The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding?

aw1621107 1y ago
> but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that. That sounds more like a description of the stuff neutron stars are made of. I don't think that description really works for black holes - how exactly do you take a teaspoon out of a black hole? > The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding? The linked Physics.SE answer does a decent job at explaining it, but the short of it is that for Schwarzchild black holes mass ~ event horizon radius, so if you define density as mass / (Schwarzchild volume) you get density ~ 1/(mass^2) - in other words, the more massive a black hole the less dense it is by that measure.
- jfengel 1y ago
  You can't make a teaspoon of neutroniun, either. The neutrons would immediately drift off and quickly decay (half life about ten minutes). It's just a way of illustrating the density. You actually can have a black hole with the volume of a teaspoon, and it's stable. It will eventually decay by Hawking radiation, but not for umpteen gazillion years until the CMB gets cold enough.
  - aw1621107 1y ago
    > You can't make a teaspoon of neutroniun, either. The neutrons would immediately drift off and quickly decay (half life about ten minutes). Technically speaking that sure sounds like scooping out a teaspoon of neutronium to me. Nothing said it had to be stable :P But in any case, I suppose what doesn't work for me is that when the teaspoon illustration is being used it's in the context of picking out some sample/subset of a larger whole - take a whole neutron star and examine the properties of this supposed representative part of it, same way one might scoop out some ice cream out of a container. While that's technically not totally correct for neutron stars since they don't exactly have a uniform density, I feel that it's usefully-close-enough compared to black holes, since as far as we know all the mass of a black hole is concentrated in a point at its center so your "scoop" is either going to get nothing or everything. > You actually can have a black hole with the volume of a teaspoon, and it's stable. Sure, but at that point I wouldn't use the wording "a teaspoon of black hole"; something more like "teaspoon-sized black hole" would be more appropriate (though to be fair that's still technically somewhat ambiguous).

jiehong 1y ago

That calculation of density is nice, but since we don’t know what’s inside a black hole, it doesn’t mean anything. Passing the event horizon doesn’t mean you’ve reached the potentially ultra dense singularity, but it does mean you won’t escape.

agos 1y ago
we don't know how the mass inside a black hole is doing, but we have a pretty solid understanding of the volume and the total mass of black holes

ramraj07 1y ago

Which isn't surprising if you think about it. Imagine the whole nothingness of the solar system being filled with even that density of gas. That's a metric ton of gas.