6 ms·

As far as I know, that very much isn't the case. The singularity is a result of the math, not a trick to simplify it. My understanding is that many researchers

As far as I know, that very much isn't the case. The singularity is a result of the math, not a trick to simplify it. My understanding is that many researchers do think it's a "placeholder" representing our lack of insight into how physics behave at those scales, and not a real physical phenomenon, and that it will one day be possible to work past it. I believe Kerr and Penrose (both of whom did some of the most foundational work on black holes) believe it's a mathematical artifact.

hparadiz 2y ago
My random thoughts on this: - Is the math referring to the center of gravity as the singularity? Because even a sub black hole mass object would have that. - Why is there an assumption that just after a mass becomes a black hole the matter inside it suddenly compresses further when the actual gravity of the object has only slightly increased? - Is there a maximum density of matter in the universe and if the black hole even reaches that? - Wouldn't you need that number to be infinite if the black hole itself is infinitely small? - If the black hole does have a mass inside it... Do the light particles trapped inside the black hole form a blanket around the existing matter?
- Dylan16807 2y ago
  > - Why is there an assumption that just after a mass becomes a black hole the matter inside it suddenly compresses further when the actual gravity of the object has only slightly increased? Yeah, that seems like an important thing to address. Black holes don't even have to be high density, or have much matter in the center at the time of formation. If you arrange enough big chunks of metal into a spherical-shell constellation, then drop them all toward their mutual center, they can reach the threshold to become a black hole before they even start colliding. What happens around that time, and what specifically does "singularity" mean (because I see people using it in very different ways). > - Is there a maximum density of matter in the universe and if the black hole even reaches that? > - Wouldn't you need that number to be infinite if the black hole itself is infinitely small? Black holes are the benchmark for maximum density. The event horizon is always exactly at the limit. By "black hole itself" do you mean something other than the event horizon? But that maximum density depends on size, smaller things can be denser and bigger things have to be less dense.
  - hparadiz 2y ago
    > If you arrange enough big chunks of metal into a spherical-shell constellation, then drop them all toward their mutual center, they can reach the threshold to become a black hole before they even start colliding. When I say "black hole itself" I imagine any combination of mass at it's center that provides enough density to form a gravitational pull that will trap light.
  - pixl97 2y ago
    > What happens around that time I can imagine it's something stupidly energetic. If you don't want them turning into a hot ball of neutrons first you're either going to have to spend a lot of energy keeping them apart or they are going to be orbiting a virtual center and it will take far longer for them to reach the center singularity than you expect. This will follow the laws of the 3(+) body problem so you won't be able to calculate a perfect impact, so the birth of the singularity will be shrouded in very high energy particles escaping. Nature abhors a naked singularity.
    - Dylan16807 2y ago
      It wouldn't be naked, there would be an event horizon. Even approaching the critical density, barely anything would be escaping. But if it's really really big, there wouldn't need to be any notable spaghettification.
- db48x 2y ago
  The math is very difficult. More difficult even than that. When ever you are trying to explore the consequences of General Relativity, it is necessary to make some simplifying assumptions. Schwarzschild started with several such assumptions. First, he assumed a completely static system, one that doesn’t change with time. Second, that the mass in the system was spherically symmetrical. He also put the center of the black hole at the origin, and so on. All of these assumptions are there to make the math easier; they’re like using spherical cows in high school. What Schwarzschild found was that this solution had two singularities. There was a singularity at the origin, and a singularity some distance away from the origin, at a radius which is proportional to the mass of the object. In both cases, some term of Einstein’s equations become infinite, and therefore seem to stop describing reality. A couple of years later other physicists proved that by changing the coordinate system in a certain way, that second singularity would go away. That is, this singularity was merely an artifact of one of the simplifying assumptions that Schwarzschild started with, and didn’t represent any real feature of a real black hole. But the radius at which that singularity occurred is still relevant: it tells you how big the event horizon is. Penrose and Hawking proved that the singularity at the center of the black hole cannot merely be a mathematical artifact. Penrose got his Nobel prize for that. > Is the math referring to the center of gravity as the singularity? Because even a sub black hole mass object would have that. Yes, the singularity at the center of a black hole is coincident with its center of mass. But not every center of mass is a singularity. Remember, we only have a singularity if some term of Einstein’s equations for General Relativity goes infinite. In a normal object nothing is infinite at the center of mass. That only starts to happen once the object is compressed into a black hole. > Why is there an assumption that just after a mass becomes a black hole the matter inside it suddenly compresses further when the actual gravity of the object has only slightly increased? There isn’t. This is the most common _conclusion_, based on the math. It’s not a starting assumption. > Is there a maximum density of matter in the universe and if the black hole even reaches that? Unknown. A neutron star is the densest object that can exist which doesn’t have an event horizon. Get any denser, and an event horizon forms which completely hides whatever happens next. > Wouldn't you need that number to be infinite if the black hole itself is infinitely small? Sure, if the mass all falls into the singularity, then the density of the singularity is infinite. There’s really no problem with that. > If the black hole does have a mass inside it... Do the light particles trapped inside the black hole form a blanket around the existing matter? This is a non–sequitur. It’s meaningless. What is really going on here is that mass bends spacetime. This causes our path through spacetime to bend as well. All the gee–whiz effects of relativity, like time dilation, are a result of this bending. Time passes slower for an object moving quickly because its path has been bent so much that it is passing through less of the time dimension than it would otherwise. Light is moving so fast that it doesn’t pass through time at all; from the perspective of the photon no time at all passes between when it was emitted and when it was absorbed, no matter how far it traveled through the intervening space between those events. Inside the event horizon of a black hole, the path of every object is bent towards the singularity. They’re bent so much that time and space swap roles. The singularity is inescapable not because something is dragging you towards it, but because it is literally in your future. From the outside it looks like the singularity is a place, but if you get close enough it becomes a time in your future, beyond which there is no more time. Everything outside the black hole is twisted around into the past, where you can never go. And, unfortunately for you, a stellar mass black hole is not very big. It’s only a few dozen miles to the center, and since we move through time at the speed of light, that is a very short timeline indeed. Your future ends very abruptly, probably faster than thought. That’s why most people conclude that the matter is crushed into the singularity. How could it resist? You’re not going to brace yourself against the walls of the universe and prevent yourself from being dragged forward into the future, no matter how strong you are. But, quantum gravity might change that picture slightly. It may be that the distance to the singularity grows the longer the black hole exists. It may in fact grow at the speed of light, meaning that while the volume of the black hole is not infinite, you never actually reach the singularity and go splat. Your time never actually runs out. You can find some lectures by Susskind about this on Youtube if you like.

hparadiz 2y ago

My random thoughts on this: - Is the math referring to the center of gravity as the singularity? Because even a sub black hole mass object would have that. - Why is there an assumption that just after a mass becomes a black hole the matter inside it suddenly compresses further when the actual gravity of the object has only slightly increased? - Is there a maximum density of matter in the universe and if the black hole even reaches that? - Wouldn't you need that number to be infinite if the black hole itself is infinitely small? - If the black hole does have a mass inside it... Do the light particles trapped inside the black hole form a blanket around the existing matter?

Dylan16807 2y ago
> - Why is there an assumption that just after a mass becomes a black hole the matter inside it suddenly compresses further when the actual gravity of the object has only slightly increased? Yeah, that seems like an important thing to address. Black holes don't even have to be high density, or have much matter in the center at the time of formation. If you arrange enough big chunks of metal into a spherical-shell constellation, then drop them all toward their mutual center, they can reach the threshold to become a black hole before they even start colliding. What happens around that time, and what specifically does "singularity" mean (because I see people using it in very different ways). > - Is there a maximum density of matter in the universe and if the black hole even reaches that? > - Wouldn't you need that number to be infinite if the black hole itself is infinitely small? Black holes are the benchmark for maximum density. The event horizon is always exactly at the limit. By "black hole itself" do you mean something other than the event horizon? But that maximum density depends on size, smaller things can be denser and bigger things have to be less dense.
- hparadiz 2y ago
  > If you arrange enough big chunks of metal into a spherical-shell constellation, then drop them all toward their mutual center, they can reach the threshold to become a black hole before they even start colliding. When I say "black hole itself" I imagine any combination of mass at it's center that provides enough density to form a gravitational pull that will trap light.
- pixl97 2y ago
  > What happens around that time I can imagine it's something stupidly energetic. If you don't want them turning into a hot ball of neutrons first you're either going to have to spend a lot of energy keeping them apart or they are going to be orbiting a virtual center and it will take far longer for them to reach the center singularity than you expect. This will follow the laws of the 3(+) body problem so you won't be able to calculate a perfect impact, so the birth of the singularity will be shrouded in very high energy particles escaping. Nature abhors a naked singularity.
  - Dylan16807 2y ago
    It wouldn't be naked, there would be an event horizon. Even approaching the critical density, barely anything would be escaping. But if it's really really big, there wouldn't need to be any notable spaghettification.
db48x 2y ago
The math is very difficult. More difficult even than that. When ever you are trying to explore the consequences of General Relativity, it is necessary to make some simplifying assumptions. Schwarzschild started with several such assumptions. First, he assumed a completely static system, one that doesn’t change with time. Second, that the mass in the system was spherically symmetrical. He also put the center of the black hole at the origin, and so on. All of these assumptions are there to make the math easier; they’re like using spherical cows in high school. What Schwarzschild found was that this solution had two singularities. There was a singularity at the origin, and a singularity some distance away from the origin, at a radius which is proportional to the mass of the object. In both cases, some term of Einstein’s equations become infinite, and therefore seem to stop describing reality. A couple of years later other physicists proved that by changing the coordinate system in a certain way, that second singularity would go away. That is, this singularity was merely an artifact of one of the simplifying assumptions that Schwarzschild started with, and didn’t represent any real feature of a real black hole. But the radius at which that singularity occurred is still relevant: it tells you how big the event horizon is. Penrose and Hawking proved that the singularity at the center of the black hole cannot merely be a mathematical artifact. Penrose got his Nobel prize for that. > Is the math referring to the center of gravity as the singularity? Because even a sub black hole mass object would have that. Yes, the singularity at the center of a black hole is coincident with its center of mass. But not every center of mass is a singularity. Remember, we only have a singularity if some term of Einstein’s equations for General Relativity goes infinite. In a normal object nothing is infinite at the center of mass. That only starts to happen once the object is compressed into a black hole. > Why is there an assumption that just after a mass becomes a black hole the matter inside it suddenly compresses further when the actual gravity of the object has only slightly increased? There isn’t. This is the most common _conclusion_, based on the math. It’s not a starting assumption. > Is there a maximum density of matter in the universe and if the black hole even reaches that? Unknown. A neutron star is the densest object that can exist which doesn’t have an event horizon. Get any denser, and an event horizon forms which completely hides whatever happens next. > Wouldn't you need that number to be infinite if the black hole itself is infinitely small? Sure, if the mass all falls into the singularity, then the density of the singularity is infinite. There’s really no problem with that. > If the black hole does have a mass inside it... Do the light particles trapped inside the black hole form a blanket around the existing matter? This is a non–sequitur. It’s meaningless. What is really going on here is that mass bends spacetime. This causes our path through spacetime to bend as well. All the gee–whiz effects of relativity, like time dilation, are a result of this bending. Time passes slower for an object moving quickly because its path has been bent so much that it is passing through less of the time dimension than it would otherwise. Light is moving so fast that it doesn’t pass through time at all; from the perspective of the photon no time at all passes between when it was emitted and when it was absorbed, no matter how far it traveled through the intervening space between those events. Inside the event horizon of a black hole, the path of every object is bent towards the singularity. They’re bent so much that time and space swap roles. The singularity is inescapable not because something is dragging you towards it, but because it is literally in your future. From the outside it looks like the singularity is a place, but if you get close enough it becomes a time in your future, beyond which there is no more time. Everything outside the black hole is twisted around into the past, where you can never go. And, unfortunately for you, a stellar mass black hole is not very big. It’s only a few dozen miles to the center, and since we move through time at the speed of light, that is a very short timeline indeed. Your future ends very abruptly, probably faster than thought. That’s why most people conclude that the matter is crushed into the singularity. How could it resist? You’re not going to brace yourself against the walls of the universe and prevent yourself from being dragged forward into the future, no matter how strong you are. But, quantum gravity might change that picture slightly. It may be that the distance to the singularity grows the longer the black hole exists. It may in fact grow at the speed of light, meaning that while the volume of the black hole is not infinite, you never actually reach the singularity and go splat. Your time never actually runs out. You can find some lectures by Susskind about this on Youtube if you like.