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The quantum mysteries of black holes

zmgsabst 4y ago
I’ve heard black holes described as “more diameter than the circumference suggests” — to paraphrase Kip Thorne. Is there a point where you’re at “quantum scale” around the singularity but not across the singularity? — like a quantum Einstein ring?
- fartsucker69 4y ago
  What do you mean by "across the singularity"? The singularity is a single point in the center. There's no being across it really.
  - actionfromafar 4y ago
    I'm sure that's right, but on the other hand space itself is getting "denser" nearer to the singularity. I don't know what to make of that.
    - pdonis 4y ago
      > space itself is getting "denser" nearer to the singularity Where are you getting this from? It makes no sense.
  - zmgsabst 4y ago
    When the shortest path lies on some sphere around the singularity where the circumference of that sphere is “quantum scale” but chords passing near the center are not. In the 2D example, is there some area where quantum effects happen in an annulus rather than in a disc because that central stretched region is “too big”.
    - pdonis 4y ago
      > some sphere around the singularity There is no such thing. The singularity is a moment of time, not a place in space.
      - zmgsabst 4y ago
        The event horizon is an example of a sphere around the singularity. So is the photon sphere.
        pdonis 4y ago
        No, this is not correct. The singularity is not a place in space, so it is not possible to have a sphere around it. It makes no sense, just as having a sphere around, say, tomorrow noon makes no sense.
        zmgsabst 4y ago
        Perhaps instead of just saying what standard explanations are “make no sense”, you could try elaborating in any of your posts. Saying that an event horizon or photon sphere isn’t around the singularity of a black hole doesn’t make sense, either. What facts specifically are you trying to articulate about spacetime geometry around a black hole?
        pdonis 4y ago
        > you could try elaborating in any of your posts I already have: the singularity is a moment of time, not a place in space. > Saying that an event horizon or photon sphere isn’t around the singularity of a black hole doesn’t make sense, either. Yes, it does, for the reason I've already given: because there is no such thing as a sphere around a moment of time. > What facts specifically are you trying to articulate about spacetime geometry around a black hole? The fact that the singularity is not a place in space, it's a moment of time.
        4y ago
  - pdonis 4y ago
    > The singularity is a single point in the center. No, it isn't. It's a spacelike line that is to the future of every event inside the hole. It's a moment of time, not a place in space.
- BoGoToTo 4y ago
  Are you sure that quote isn't referring to the length dilation that occurs in a gravity well? Space is non-Euclidean so you can have a sphere with a radius larger than the circumference would allow.
  - zmgsabst 4y ago
    His quote is exactly referring to that: but my question is, are black holes curved enough that you can have a circumference at quantum scale with a diameter above that scale? — ie, at which quantum effects would happen around but not across the singularity.
- pdonis 4y ago
  > I’ve heard black holes described as “more diameter than the circumference suggests” — to paraphrase Kip Thorne. I'm not sure where Thorne said whatever you are paraphrasing, but this description does not apply to black holes. It applies to ordinary gravitating bodies like stars and planets, but unlike them, black holes do not have a well-defined "diameter". The singularity inside the hole at r = 0 is not a place in space, it's a moment of time. So there is no well-defined "spatial distance from the singularity"; that would be like having a well-defined "spatial distance from tomorrow", which makes no sense.
  - karmakaze 4y ago
    Seems a point in space-time, like a point in (longitude, latitude) where at latitude 90, longitude loses meaning.
    - pdonis 4y ago
      Not really, no. What you are describing is a coordinate singularity; but whether a coordinate singularity has a physical meaning or is just an artifact of the coordinates depends on the situation. In the case of the Earth, the coordinate singularity in longitude at the poles is an artifact of the coordinates: the Earth's poles are perfectly good parts of the Earth's surface and nothing physically goes wrong there. You just need to pick different coordinates if you want to cover the poles. The case of the horizon of a black hole in Schwarzschild coordinates is similar: there is a coordinate singularity, but it's an artifact of the coordinates. You can find other coordinate charts that have no coordinate singularity at the horizon. The black hole singularity at r = 0, however, is not an artifact of coordinates. It is a genuine physical singularity, where the spacetime curvature goes to infinity.
      - karmakaze 4y ago
        Thanks for the explanation of the difference. To be fair we don't know the physical curvature goes to infinity--the math says it does.
        4y ago
denton-scratch 4y ago
The article is annoyingly superficial. It says: "This [superposition] is most commonly illustrated by Schrödinger’s cat, which can be both dead and alive simultaneously." Schroedinger used the cat example to illustrate his view that a particle being in two mutually-exclusive states at the same time was absurd. He thought it was obvious that the cat cannot be both dead and alive simultaneously.
- blueprint 4y ago
  it's absurd because pretty much every particle of the cat is measured and thus decohered by other particles in the cat
  - SuoDuanDao 4y ago
    I really like the interpretation that if the cat is dead, it can't measure anything and is therefore reliably alive (quantum immortality). Of course, that doesn't change that someone else can observe the cat being dead after opening the box.
    - nathan_compton 4y ago
      At this stage I don't think very many philosophers consider measurement as it takes meaning in quantum mechanics to have anything in particular to do with living creatures or brains or consciousness or anything.
  - nathan_compton 4y ago
    gee wilikers, you solved it!
    - blueprint 4y ago
      you act like I wasn't just talking with someone here on HN who was convinced we "live in a classical world" when in reality everything is governed by the same quantum physics on every scale.
snarfy 4y ago
What is the gravitational force at the singularity? How does that reconcile with the maximum force? c^4/4G It seems like there is a contradiction there. https://www.motionmountain.net/maximumforce.html https://www.motionmountain.net/maximumforce.html
- t8sr 4y ago
  Huh? What are you saying: you don’t think there are black holes? Edit: the page you linked is a random dude who keeps publishing on a single topic that mainstream physics has been mostly ignoring. I wouldn’t go as far as call him a crackpot, but he’s definitely in the fringes. After scanning the site I still have no idea what he’s on about, and a cursory check of published literature seems to support this is at least not an idea most people in mainstream physics would recognize.
  - snarfy 4y ago
    Oh there are black holes. We even have videos [1]. But are they infinitely dense at the singularity or is there a limit? [1] - https://www.eso.org/public/videos/eso1825e/ https://www.eso.org/public/videos/eso1825e/
    - t8sr 4y ago
      I mean, look - arguing about what happens inside the even horizon is kind of fun but ultimately pointless. Just FYI, the site you linked in the parent comment does not represent anything I’d call mainstream physics.
      - snarfy 4y ago
        this is better [1] [1] - https://arxiv.org/abs/physics/0309118 https://arxiv.org/abs/physics/0309118
        t8sr 4y ago
        Not really, that’s just the same guy writing a PDF. It’s not cited, peer reviewed or published in a journal. It’s literally just a dude writing stuff on the internet - that’s not necessarily a problem, but there are literally tens of thousands of people with “great ideas” that marry GR and QM, and none of their theories go anywhere, or make any testable predictions. He makes some bold claims, no predictions and doesn’t seem to get published, which strongly indicates he can’t get past peer review.
t8sr 4y ago
The actual paper is here: https://link.aps.org/doi/10.1103/PhysRevLett.129.181301 https://link.aps.org/doi/10.1103/PhysRevLett.129.181301 The summary says almost nothing, so here’s what I got from the abstract. First some context: we currently don’t have any physics theory that predicts the gravitational field of a particle in a superposition. This isn’t due to a lack of ideas for theories, but in large part because the predicted effects are much too small to run experiments, for at least a few more decades. The paper is about a simulation based one candidate theory for such a gravitational field. The interesting result is that the simulation yields a range of black hole masses predicted by the theory, even though the authors didn’t specifically plug that assumption in. This could be an argument in support of the theory. (But could also be a coincidence, or stem from some underlying math that the researchers didn’t think about, that also underlies the mass prediction, which would mean the result is a tautology.)

I’ve heard black holes described as “more diameter than the circumference suggests” — to paraphrase Kip Thorne. Is there a point where you’re at “quantum scale” around the singularity but not across the singularity? — like a quantum Einstein ring?

fartsucker69 4y ago
What do you mean by "across the singularity"? The singularity is a single point in the center. There's no being across it really.
- actionfromafar 4y ago
  I'm sure that's right, but on the other hand space itself is getting "denser" nearer to the singularity. I don't know what to make of that.
  - pdonis 4y ago
    > space itself is getting "denser" nearer to the singularity Where are you getting this from? It makes no sense.
- zmgsabst 4y ago
  When the shortest path lies on some sphere around the singularity where the circumference of that sphere is “quantum scale” but chords passing near the center are not. In the 2D example, is there some area where quantum effects happen in an annulus rather than in a disc because that central stretched region is “too big”.
  - pdonis 4y ago
    > some sphere around the singularity There is no such thing. The singularity is a moment of time, not a place in space.
    - zmgsabst 4y ago
      The event horizon is an example of a sphere around the singularity. So is the photon sphere.
      - pdonis 4y ago
        No, this is not correct. The singularity is not a place in space, so it is not possible to have a sphere around it. It makes no sense, just as having a sphere around, say, tomorrow noon makes no sense.
        zmgsabst 4y ago
        Perhaps instead of just saying what standard explanations are “make no sense”, you could try elaborating in any of your posts. Saying that an event horizon or photon sphere isn’t around the singularity of a black hole doesn’t make sense, either. What facts specifically are you trying to articulate about spacetime geometry around a black hole?
        pdonis 4y ago
        > you could try elaborating in any of your posts I already have: the singularity is a moment of time, not a place in space. > Saying that an event horizon or photon sphere isn’t around the singularity of a black hole doesn’t make sense, either. Yes, it does, for the reason I've already given: because there is no such thing as a sphere around a moment of time. > What facts specifically are you trying to articulate about spacetime geometry around a black hole? The fact that the singularity is not a place in space, it's a moment of time.
        4y ago
- pdonis 4y ago
  > The singularity is a single point in the center. No, it isn't. It's a spacelike line that is to the future of every event inside the hole. It's a moment of time, not a place in space.
BoGoToTo 4y ago
Are you sure that quote isn't referring to the length dilation that occurs in a gravity well? Space is non-Euclidean so you can have a sphere with a radius larger than the circumference would allow.
- zmgsabst 4y ago
  His quote is exactly referring to that: but my question is, are black holes curved enough that you can have a circumference at quantum scale with a diameter above that scale? — ie, at which quantum effects would happen around but not across the singularity.
pdonis 4y ago
> I’ve heard black holes described as “more diameter than the circumference suggests” — to paraphrase Kip Thorne. I'm not sure where Thorne said whatever you are paraphrasing, but this description does not apply to black holes. It applies to ordinary gravitating bodies like stars and planets, but unlike them, black holes do not have a well-defined "diameter". The singularity inside the hole at r = 0 is not a place in space, it's a moment of time. So there is no well-defined "spatial distance from the singularity"; that would be like having a well-defined "spatial distance from tomorrow", which makes no sense.
- karmakaze 4y ago
  Seems a point in space-time, like a point in (longitude, latitude) where at latitude 90, longitude loses meaning.
  - pdonis 4y ago
    Not really, no. What you are describing is a coordinate singularity; but whether a coordinate singularity has a physical meaning or is just an artifact of the coordinates depends on the situation. In the case of the Earth, the coordinate singularity in longitude at the poles is an artifact of the coordinates: the Earth's poles are perfectly good parts of the Earth's surface and nothing physically goes wrong there. You just need to pick different coordinates if you want to cover the poles. The case of the horizon of a black hole in Schwarzschild coordinates is similar: there is a coordinate singularity, but it's an artifact of the coordinates. You can find other coordinate charts that have no coordinate singularity at the horizon. The black hole singularity at r = 0, however, is not an artifact of coordinates. It is a genuine physical singularity, where the spacetime curvature goes to infinity.
    - karmakaze 4y ago
      Thanks for the explanation of the difference. To be fair we don't know the physical curvature goes to infinity--the math says it does.
      - 4y ago

denton-scratch 4y ago

The article is annoyingly superficial. It says: "This [superposition] is most commonly illustrated by Schrödinger’s cat, which can be both dead and alive simultaneously." Schroedinger used the cat example to illustrate his view that a particle being in two mutually-exclusive states at the same time was absurd. He thought it was obvious that the cat cannot be both dead and alive simultaneously.

blueprint 4y ago
it's absurd because pretty much every particle of the cat is measured and thus decohered by other particles in the cat
- SuoDuanDao 4y ago
  I really like the interpretation that if the cat is dead, it can't measure anything and is therefore reliably alive (quantum immortality). Of course, that doesn't change that someone else can observe the cat being dead after opening the box.
  - nathan_compton 4y ago
    At this stage I don't think very many philosophers consider measurement as it takes meaning in quantum mechanics to have anything in particular to do with living creatures or brains or consciousness or anything.
- nathan_compton 4y ago
  gee wilikers, you solved it!
  - blueprint 4y ago
    you act like I wasn't just talking with someone here on HN who was convinced we "live in a classical world" when in reality everything is governed by the same quantum physics on every scale.

snarfy 4y ago

What is the gravitational force at the singularity? How does that reconcile with the maximum force? c^4/4G It seems like there is a contradiction there. https://www.motionmountain.net/maximumforce.html https://www.motionmountain.net/maximumforce.html

t8sr 4y ago
Huh? What are you saying: you don’t think there are black holes? Edit: the page you linked is a random dude who keeps publishing on a single topic that mainstream physics has been mostly ignoring. I wouldn’t go as far as call him a crackpot, but he’s definitely in the fringes. After scanning the site I still have no idea what he’s on about, and a cursory check of published literature seems to support this is at least not an idea most people in mainstream physics would recognize.
- snarfy 4y ago
  Oh there are black holes. We even have videos [1]. But are they infinitely dense at the singularity or is there a limit? [1] - https://www.eso.org/public/videos/eso1825e/ https://www.eso.org/public/videos/eso1825e/
  - t8sr 4y ago
    I mean, look - arguing about what happens inside the even horizon is kind of fun but ultimately pointless. Just FYI, the site you linked in the parent comment does not represent anything I’d call mainstream physics.
    - snarfy 4y ago
      this is better [1] [1] - https://arxiv.org/abs/physics/0309118 https://arxiv.org/abs/physics/0309118
      - t8sr 4y ago
        Not really, that’s just the same guy writing a PDF. It’s not cited, peer reviewed or published in a journal. It’s literally just a dude writing stuff on the internet - that’s not necessarily a problem, but there are literally tens of thousands of people with “great ideas” that marry GR and QM, and none of their theories go anywhere, or make any testable predictions. He makes some bold claims, no predictions and doesn’t seem to get published, which strongly indicates he can’t get past peer review.

t8sr 4y ago

The actual paper is here: https://link.aps.org/doi/10.1103/PhysRevLett.129.181301 https://link.aps.org/doi/10.1103/PhysRevLett.129.181301 The summary says almost nothing, so here’s what I got from the abstract. First some context: we currently don’t have any physics theory that predicts the gravitational field of a particle in a superposition. This isn’t due to a lack of ideas for theories, but in large part because the predicted effects are much too small to run experiments, for at least a few more decades. The paper is about a simulation based one candidate theory for such a gravitational field. The interesting result is that the simulation yields a range of black hole masses predicted by the theory, even though the authors didn’t specifically plug that assumption in. This could be an argument in support of the theory. (But could also be a coincidence, or stem from some underlying math that the researchers didn’t think about, that also underlies the mass prediction, which would mean the result is a tautology.)