5 ms·

What sonic black holes say about real ones

47 points by Phithagoras 5y ago

JackFr 5y ago
Absolute pure amateur here with no expertise or special knowledge, but could this work lead to new insights about the emergence of turbulent flows, or is thaat currently very well understood?
- phreeza 5y ago
  I think it's one of the situations where the fundamentals are well understood (Navier Stokes equation) but the emergent behavior is so complex that many aspects remain poorly understood.
- Phithagoras 5y ago
  Fluid mech on the whole has a lot left to solve. https://news.ycombinator.com/item?id=30011260 https://news.ycombinator.com/item?id=30011260 looks at this a bit. Author confirmed that superradiance, backreaction, and quasi-normal radiance are all observable in the fluid analog. These observations will likely prove useful for fluid mech as well as astrophys
hammock 5y ago
I read the wikipedia article for sonic black holes before reading this article, and got a decent understanding. Then I came back to this article and just wanted to comment that the graphics are really good and nailed my understanding in an even better way.
neom 5y ago
Is there a good word that describes the somewhat uncomfortable feeling one gets in their stomach when thinking about the magnitude and complexity of reality? Is humbled a feeling? I can't thinking of anything good in English, wondering if any other languages have this word (like how Saudade is in Portuguese)
- krastanov 5y ago
  Existential dread? It can be a pretty exciting feeling. I like how the Kurtzgesagt educational channel on YouTube has it permeate their cosmology/astronomy videos. They even addressed it explicitly in their "nihilistic optimism" video.
  - kadoban 5y ago
    If you like that feeling, read Stephen Baxter's work. Existential dread is the main character in a lot of it, it's quite something. The Xeelee Sequence especially comes to mind.
    - krastanov 5y ago
      My go to is works by Greg Egan (e.g. Diaspora and Schild's Ladder and Permutation City). Thanks for the suggestion, I will check out Baxter.
      - kadoban 5y ago
        Always glad to share. I'll check out Greg Egan, I've heard the name a bunch of times but never actually got to his work yet.
        arrow7000 5y ago
        He is my all time favourite science fiction author. If it's existential dread you're after he delivers it in spades.
- _Microft 5y ago
  Maybe you mean "awe"? https://en.wikipedia.org/wiki/Awe https://en.wikipedia.org/wiki/Awe
  - stronglikedan 5y ago
    No, it's deeper than mere awe. I've felt it once, when contemplating what eternal life would be like. I can see how people would feel it while contemplating the scale of the universe.
PicassoCTs 5y ago
I have a (probably stupid) question - are the tunnels (https://www.indiatimes.com/technology/science-and-future/earth-in-giant-cosmic-tunnel-552046.html https://www.indiatimes.com/technology/science-and-future/ear...) the solar system is currently in - connected to black hole at the heart of our galaxy? Like do black holes extend enormous magnetic tendrils into the surrounding space similar to neutron stars?
- dmitrybrant 5y ago
  Neither black holes nor neutron stars extend any kind of magnetic tendrils. There can be jets of matter that are ejected from the vicinity of a black hole (due to the Penrose process or something similar), and those jets can have electric charge, but that's not what your linked study is about.
deleted 5y ago
[deleted]
andrewflnr 5y ago
It's extremely aggravating that this article assumes the existence of Hawking radiation directly implies the real loss of information in black holes. There's been some work, probably covered in this magazine, on how information may escape black holes via Hawking Radiation. Ed: for instance, https://www.quantamagazine.org/netta-engelhardt-has-escaped-hawkings-black-hole-paradox-20210823/ https://www.quantamagazine.org/netta-engelhardt-has-escaped-... or https://www.quantamagazine.org/the-most-famous-paradox-in-physics-nears-its-end-20201029/ https://www.quantamagazine.org/the-most-famous-paradox-in-ph...
- motohagiography 5y ago
  This triggered my complete layman understanding as well, as this idea of information being destroyed, yet not annhialited via its anti-particles, or just being added to the mass of the singularity sounded like a logical misattrubution. there are so many places for it to "go." Everything else has turbulunce, especially during energy transtions, intuitively there seems like no obvious reason to expect gravity is exempt.
ncmncm 5y ago
My current question about black holes is: It is usually reported that the electron is a dimensionless point, with no extent. But it has mass. Why is it not, then, a black hole? A black hole with the mass of an electron would have an event horizon, which is not a dimensionless point. If it is a black hole, how does the charge "get out" to affect the outside world? If a black hole were given a charge, e.g. by injecting a stock of electrons, would it respond to magnetic fields, as an electron does, without being able to exchange photons with anything? Or, if the electron is not a black hole, why isn't it? An electron and positron annihilate on contact producing a pair of photons, which seems incompatible with their being black holes, unless maybe anti-particles have negative gravitational mass, so that contact gives the pair zero gravitation. Does it make sense to have positive inertial mass, but negative gravitational mass? I don't think that other particles (e.g. neutral, or positively-charged) smashed into electrons are known ever to get absorbed, as we might expect if it were a black hole. If the electron and positron are both dimensionless points, yet somehow not black holes, how do their paths ever succeed in intersecting? If there is some minimum distance where they annihilate, why isn't that the size of the particle?
- alsonote 5y ago
  Electrons' mass is a little strange, in my (limited) understanding. The Standard Model predicts that electrons should be massless, but they gain mass (or maybe easier to say, "massiness") through interactions with the Higgs field. This effectively creates a constant "drag" on electrons, giving them a kind of inertia or "mass". I think this video does a good job explaining it, much better than I could: https://youtu.be/kixAljyfdqU https://youtu.be/kixAljyfdqU
- karlicoss 5y ago
  Cool question, never thought about it! I'm not a physicist, but hopefully will be able to point at the right direction. Guess the short and boring answer is that we don't really know if GR applies at the scales of electrons (or to be more specific, how to apply it), so perhaps the notion of black hole doesn't even make sense, at least conventional sense. If you try speculating about it, there are some interesting points to ponder: 1. We know that black holes should evaporate via Hawking radiation. If you substitute electron's mass in the formula here [1], you get that electron mass black hole should evaporate in 6 * 10^-107 seconds. Clearly we don't see electrons doing that :) (however note that this formula assumes Schwarzschild solution, more about it further) 2. When you reason that if you narrow down electron's radius sufficiently, at some point is has to become a black hole, you kind of implicitly assume that it behaves according to the Schwarzschild metric [2]. This minimum radius at which you'd reason it's a black hole, would be the Schwarzschild radius. However, electron also has charge and angular momentum. Spin is quite different from a bunch of stellar stuff rotating around its axis, and I don't remember the derivation of GR solutions for spinning matter, but if we do speculate here anyway, still feels like we'd need to use the Kerr-Newman metric, which takes charge and angular momentum into the account [3]. If you use that metric, it's not the case anymore that any object with sufficiently small radius could form an event horizon -- if it has enough charge or angular momentum, it won't, so the electron won't be a black hole! However in a sense it only makes things works -- it exposes a naked singularity which we also don't seem to observe. P.S. the article also references "black hole electron" [4], didn't know it was a thing! 3. P.S. I also found this [5], which argues that even if you assume Schwarzschild radius for an electron, at this scale it's possible that the electroweak symmetry is restored, and the electron starts appearing massless. Can't say I'm fully able to follow this argument, so will just leave it here [1] https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_evaporation https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e... [2] https://en.wikipedia.org/wiki/Schwarzschild_metric https://en.wikipedia.org/wiki/Schwarzschild_metric [3] https://en.wikipedia.org/wiki/Kerr%E2%80%93Newman_metric#Overview_of_the_solution https://en.wikipedia.org/wiki/Kerr%E2%80%93Newman_metric#Ove... [4] https://en.wikipedia.org/wiki/Black_hole_electron https://en.wikipedia.org/wiki/Black_hole_electron [5] https://www.reddit.com/r/Physics/comments/7fd7pg/if_an_electron_is_a_point_particle_and_a_black/dqb45lo/ https://www.reddit.com/r/Physics/comments/7fd7pg/if_an_elect...

47 points by Phithagoras 5y ago

Absolute pure amateur here with no expertise or special knowledge, but could this work lead to new insights about the emergence of turbulent flows, or is thaat currently very well understood?

phreeza 5y ago
I think it's one of the situations where the fundamentals are well understood (Navier Stokes equation) but the emergent behavior is so complex that many aspects remain poorly understood.
Phithagoras 5y ago
Fluid mech on the whole has a lot left to solve. https://news.ycombinator.com/item?id=30011260 https://news.ycombinator.com/item?id=30011260 looks at this a bit. Author confirmed that superradiance, backreaction, and quasi-normal radiance are all observable in the fluid analog. These observations will likely prove useful for fluid mech as well as astrophys

hammock 5y ago

I read the wikipedia article for sonic black holes before reading this article, and got a decent understanding. Then I came back to this article and just wanted to comment that the graphics are really good and nailed my understanding in an even better way.

neom 5y ago

Is there a good word that describes the somewhat uncomfortable feeling one gets in their stomach when thinking about the magnitude and complexity of reality? Is humbled a feeling? I can't thinking of anything good in English, wondering if any other languages have this word (like how Saudade is in Portuguese)

krastanov 5y ago
Existential dread? It can be a pretty exciting feeling. I like how the Kurtzgesagt educational channel on YouTube has it permeate their cosmology/astronomy videos. They even addressed it explicitly in their "nihilistic optimism" video.
- kadoban 5y ago
  If you like that feeling, read Stephen Baxter's work. Existential dread is the main character in a lot of it, it's quite something. The Xeelee Sequence especially comes to mind.
  - krastanov 5y ago
    My go to is works by Greg Egan (e.g. Diaspora and Schild's Ladder and Permutation City). Thanks for the suggestion, I will check out Baxter.
    - kadoban 5y ago
      Always glad to share. I'll check out Greg Egan, I've heard the name a bunch of times but never actually got to his work yet.
      - arrow7000 5y ago
        He is my all time favourite science fiction author. If it's existential dread you're after he delivers it in spades.
_Microft 5y ago
Maybe you mean "awe"? https://en.wikipedia.org/wiki/Awe https://en.wikipedia.org/wiki/Awe
- stronglikedan 5y ago
  No, it's deeper than mere awe. I've felt it once, when contemplating what eternal life would be like. I can see how people would feel it while contemplating the scale of the universe.

PicassoCTs 5y ago

I have a (probably stupid) question - are the tunnels (https://www.indiatimes.com/technology/science-and-future/earth-in-giant-cosmic-tunnel-552046.html https://www.indiatimes.com/technology/science-and-future/ear...) the solar system is currently in - connected to black hole at the heart of our galaxy? Like do black holes extend enormous magnetic tendrils into the surrounding space similar to neutron stars?

dmitrybrant 5y ago
Neither black holes nor neutron stars extend any kind of magnetic tendrils. There can be jets of matter that are ejected from the vicinity of a black hole (due to the Penrose process or something similar), and those jets can have electric charge, but that's not what your linked study is about.

deleted 5y ago

[deleted]

andrewflnr 5y ago

It's extremely aggravating that this article assumes the existence of Hawking radiation directly implies the real loss of information in black holes. There's been some work, probably covered in this magazine, on how information may escape black holes via Hawking Radiation. Ed: for instance, https://www.quantamagazine.org/netta-engelhardt-has-escaped-hawkings-black-hole-paradox-20210823/ https://www.quantamagazine.org/netta-engelhardt-has-escaped-... or https://www.quantamagazine.org/the-most-famous-paradox-in-physics-nears-its-end-20201029/ https://www.quantamagazine.org/the-most-famous-paradox-in-ph...

motohagiography 5y ago
This triggered my complete layman understanding as well, as this idea of information being destroyed, yet not annhialited via its anti-particles, or just being added to the mass of the singularity sounded like a logical misattrubution. there are so many places for it to "go." Everything else has turbulunce, especially during energy transtions, intuitively there seems like no obvious reason to expect gravity is exempt.

ncmncm 5y ago

My current question about black holes is: It is usually reported that the electron is a dimensionless point, with no extent. But it has mass. Why is it not, then, a black hole? A black hole with the mass of an electron would have an event horizon, which is not a dimensionless point. If it is a black hole, how does the charge "get out" to affect the outside world? If a black hole were given a charge, e.g. by injecting a stock of electrons, would it respond to magnetic fields, as an electron does, without being able to exchange photons with anything? Or, if the electron is not a black hole, why isn't it? An electron and positron annihilate on contact producing a pair of photons, which seems incompatible with their being black holes, unless maybe anti-particles have negative gravitational mass, so that contact gives the pair zero gravitation. Does it make sense to have positive inertial mass, but negative gravitational mass? I don't think that other particles (e.g. neutral, or positively-charged) smashed into electrons are known ever to get absorbed, as we might expect if it were a black hole. If the electron and positron are both dimensionless points, yet somehow not black holes, how do their paths ever succeed in intersecting? If there is some minimum distance where they annihilate, why isn't that the size of the particle?

alsonote 5y ago
Electrons' mass is a little strange, in my (limited) understanding. The Standard Model predicts that electrons should be massless, but they gain mass (or maybe easier to say, "massiness") through interactions with the Higgs field. This effectively creates a constant "drag" on electrons, giving them a kind of inertia or "mass". I think this video does a good job explaining it, much better than I could: https://youtu.be/kixAljyfdqU https://youtu.be/kixAljyfdqU
karlicoss 5y ago
Cool question, never thought about it! I'm not a physicist, but hopefully will be able to point at the right direction. Guess the short and boring answer is that we don't really know if GR applies at the scales of electrons (or to be more specific, how to apply it), so perhaps the notion of black hole doesn't even make sense, at least conventional sense. If you try speculating about it, there are some interesting points to ponder: 1. We know that black holes should evaporate via Hawking radiation. If you substitute electron's mass in the formula here [1], you get that electron mass black hole should evaporate in 6 * 10^-107 seconds. Clearly we don't see electrons doing that :) (however note that this formula assumes Schwarzschild solution, more about it further) 2. When you reason that if you narrow down electron's radius sufficiently, at some point is has to become a black hole, you kind of implicitly assume that it behaves according to the Schwarzschild metric [2]. This minimum radius at which you'd reason it's a black hole, would be the Schwarzschild radius. However, electron also has charge and angular momentum. Spin is quite different from a bunch of stellar stuff rotating around its axis, and I don't remember the derivation of GR solutions for spinning matter, but if we do speculate here anyway, still feels like we'd need to use the Kerr-Newman metric, which takes charge and angular momentum into the account [3]. If you use that metric, it's not the case anymore that any object with sufficiently small radius could form an event horizon -- if it has enough charge or angular momentum, it won't, so the electron won't be a black hole! However in a sense it only makes things works -- it exposes a naked singularity which we also don't seem to observe. P.S. the article also references "black hole electron" [4], didn't know it was a thing! 3. P.S. I also found this [5], which argues that even if you assume Schwarzschild radius for an electron, at this scale it's possible that the electroweak symmetry is restored, and the electron starts appearing massless. Can't say I'm fully able to follow this argument, so will just leave it here [1] https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_evaporation https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e... [2] https://en.wikipedia.org/wiki/Schwarzschild_metric https://en.wikipedia.org/wiki/Schwarzschild_metric [3] https://en.wikipedia.org/wiki/Kerr%E2%80%93Newman_metric#Overview_of_the_solution https://en.wikipedia.org/wiki/Kerr%E2%80%93Newman_metric#Ove... [4] https://en.wikipedia.org/wiki/Black_hole_electron https://en.wikipedia.org/wiki/Black_hole_electron [5] https://www.reddit.com/r/Physics/comments/7fd7pg/if_an_electron_is_a_point_particle_and_a_black/dqb45lo/ https://www.reddit.com/r/Physics/comments/7fd7pg/if_an_elect...