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In theory, small black holes should kill themselves almost immediately, but this aside - I find the argument that a small black hole is not dangerous because yo

by SeanDav 11y ago

In theory, small black holes should kill themselves almost immediately, but this aside - I find the argument that a small black hole is not dangerous because you have to get really close to it - not a valid argument (as a layman!). Assuming the black hole did not destroy itself and was big enough to attract nearby molecules and atoms, it would suck in all the molecules nearby in an endless stream, getting bigger and bigger and accelerating its growth, until it consumed the earth.

pcl 11y ago
I had the same thought. If the black hole were formed lived long enough to fall to the floor of whatever lab it was created in, it'd presumably basically bore its way to the center of the Earth, aggregating matter (and thus mass) as it went. When it reached the center, I'd expect that its gravity well would pull the rest of Earth into the black hole, unless it somehow found itself in a vacuum large enough to not create a gravity well. That would presumably be a sphere the radius of the amount of core material that is equivalent to the mass of Mt Everest, plus whatever it accreted on its descent. So really, the question is whether or not a black hole that we could create would be able to make it to the floor of the lab... the article sorta touches on this: The gravitational pull of a few micrograms of matter, regardless of how it is arranged, is never dangerous; you wouldn’t get pulled inside out if you ate it. However, you wouldn’t get the chance, since any black hole that we could reasonably create would already be mid-explosion.
- pdonis 11y ago
  > If the black hole were formed lived long enough to fall to the floor of whatever lab it was created in Since the proposed method of creating the hole is to collide particles in an accelerator, we would expect the hole, when formed, to be moving the way particles created in an accelerator move, i.e., at close to the speed of light. So the hole would fly off into space, since it would be moving much, much faster than escape velocity. (Also, as the article notes, the hole would explode due to Hawking radiation soon after it was created.) > unless it somehow found itself in a vacuum large enough to not create a gravity well Not sure what you mean by this. The "gravity well" of the hole is the same whether it's surrounded by vacuum or matter. The only difference is what can possibly fall in.
  - rnovak 11y ago
    wouldn't it only fly into space if it's velocity was in that direction? And....wouldn't it interact with everything along it's path? I mean..it wouldn't be quantum tunneling correct? (I've only taken rudimentary physics related to standard mechanics and electricity/magnetism). But it seems to me, since the LHC is underground, it would have a decent probability of hitting something along it's path to space, or am I way off?
    - evanpw 11y ago
      It would hit things, but that just means that it would drill a hole a couple of atoms wide as it passed through the earth and exited the other side.
      - rlpb 11y ago
        What would be the mass of matter that it captures as it passes through the Earth? That matter has a momentum of zero relative to the Earth[1] and the total momentum of the black hole would therefore be reduced as it drills through. Would this loss of momentum be enough to reduce its velocity below Earth's escape velocity? I guess it depends on the length of the "drill hole", the mass of the original black hole before it left the vacuum in the lab, the size of the event horizon and the original velocity? [1] Technically I suppose it has some momentum due to the rotation of the Earth but I assume that's not significant. If it were significant, it would just mean that there's are "good" and "bad" directions for the escape so a worse case scenario could only get slightly worse, not better.
        drdeca 11y ago
        Are you sure that the total momentum would be reduced? The mass would increase (unless the hawking radiation is fast enough to counteract the mass it is absorbing, which I don't know), so unless something had other forces on it, it would slow down somewhat... but unless some stuff outside of it has momentum significantly changed, I would think that the momentum would stay the same? (assume a frame of reference where the matter it is passing through has roughly no momentum to start with)
bhauer 11y ago
> it would suck in all the molecules nearby in an endless stream, getting bigger and bigger and accelerating its growth, until it consumed the earth. As a layperson, I don't understand this. Are you suggesting it would somehow pull in nearby mass and increase the density of that mass somehow? How would it keep adding mass while sustaining the necessary high density?
- gus_massa 11y ago
  You need initially a very high density and a lot of mass to trigger the black hole formation. Once you are over this threshold, all the mass falls to the center and creates a "singularity" and the final density is "infinity". Any additional mass that enter the event horizon falls to the center and the density is still infinity. (The event horizon get bigger when you add mass. You can image the black hole as a big sphere that is almost empty, except for a few things that are quickly falling to the center. And you have at the center all the remainder mass gathered at one point.)

by SeanDav 11y ago

pcl 11y ago

I had the same thought. If the black hole were formed lived long enough to fall to the floor of whatever lab it was created in, it'd presumably basically bore its way to the center of the Earth, aggregating matter (and thus mass) as it went. When it reached the center, I'd expect that its gravity well would pull the rest of Earth into the black hole, unless it somehow found itself in a vacuum large enough to not create a gravity well. That would presumably be a sphere the radius of the amount of core material that is equivalent to the mass of Mt Everest, plus whatever it accreted on its descent. So really, the question is whether or not a black hole that we could create would be able to make it to the floor of the lab... the article sorta touches on this: The gravitational pull of a few micrograms of matter, regardless of how it is arranged, is never dangerous; you wouldn’t get pulled inside out if you ate it. However, you wouldn’t get the chance, since any black hole that we could reasonably create would already be mid-explosion.

pdonis 11y ago
> If the black hole were formed lived long enough to fall to the floor of whatever lab it was created in Since the proposed method of creating the hole is to collide particles in an accelerator, we would expect the hole, when formed, to be moving the way particles created in an accelerator move, i.e., at close to the speed of light. So the hole would fly off into space, since it would be moving much, much faster than escape velocity. (Also, as the article notes, the hole would explode due to Hawking radiation soon after it was created.) > unless it somehow found itself in a vacuum large enough to not create a gravity well Not sure what you mean by this. The "gravity well" of the hole is the same whether it's surrounded by vacuum or matter. The only difference is what can possibly fall in.
- rnovak 11y ago
  wouldn't it only fly into space if it's velocity was in that direction? And....wouldn't it interact with everything along it's path? I mean..it wouldn't be quantum tunneling correct? (I've only taken rudimentary physics related to standard mechanics and electricity/magnetism). But it seems to me, since the LHC is underground, it would have a decent probability of hitting something along it's path to space, or am I way off?
  - evanpw 11y ago
    It would hit things, but that just means that it would drill a hole a couple of atoms wide as it passed through the earth and exited the other side.
    - rlpb 11y ago
      What would be the mass of matter that it captures as it passes through the Earth? That matter has a momentum of zero relative to the Earth[1] and the total momentum of the black hole would therefore be reduced as it drills through. Would this loss of momentum be enough to reduce its velocity below Earth's escape velocity? I guess it depends on the length of the "drill hole", the mass of the original black hole before it left the vacuum in the lab, the size of the event horizon and the original velocity? [1] Technically I suppose it has some momentum due to the rotation of the Earth but I assume that's not significant. If it were significant, it would just mean that there's are "good" and "bad" directions for the escape so a worse case scenario could only get slightly worse, not better.
      - drdeca 11y ago
        Are you sure that the total momentum would be reduced? The mass would increase (unless the hawking radiation is fast enough to counteract the mass it is absorbing, which I don't know), so unless something had other forces on it, it would slow down somewhat... but unless some stuff outside of it has momentum significantly changed, I would think that the momentum would stay the same? (assume a frame of reference where the matter it is passing through has roughly no momentum to start with)

bhauer 11y ago

> it would suck in all the molecules nearby in an endless stream, getting bigger and bigger and accelerating its growth, until it consumed the earth. As a layperson, I don't understand this. Are you suggesting it would somehow pull in nearby mass and increase the density of that mass somehow? How would it keep adding mass while sustaining the necessary high density?

gus_massa 11y ago
You need initially a very high density and a lot of mass to trigger the black hole formation. Once you are over this threshold, all the mass falls to the center and creates a "singularity" and the final density is "infinity". Any additional mass that enter the event horizon falls to the center and the density is still infinity. (The event horizon get bigger when you add mass. You can image the black hole as a big sphere that is almost empty, except for a few things that are quickly falling to the center. And you have at the center all the remainder mass gathered at one point.)