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I was confused as to how the researchers created a black hole in a lab, which I hadn't heard of being done before. As far as I can tell, an "analog" black hole

I was confused as to how the researchers created a black hole in a lab, which I hadn't heard of being done before. As far as I can tell, an "analog" black hole is different from a normal black hole in that it doesn't use gravity and only works on acoustic waves or electromagnetic waves, depending on the type [1]. That said I don't really get what's going on. I'd be curious if someone who actually knows what they're talking about could try to clarify how the researchers have a black hole here. EDIT: There's a link[2] to another article at the bottom that describes how the researchers are simulating a black hole. My bad for not catching this earlier. [1]: http://www.phy.olemiss.edu/~luca/Topics/bh/analog.html http://www.phy.olemiss.edu/~luca/Topics/bh/analog.html [2]: https://phys.org/news/2014-10-mimic-hawking-lab.html https://phys.org/news/2014-10-mimic-hawking-lab.html

ojnabieoot 6y ago
Yes, I think it might have been more straightforward to say “Researchers observe stationary Hawking radiation in ‘acoustic black hole’” or something to clarify to laypeople that this is a mathematically analogous but physically very different experiment. I don’t think it’s too difficult to conceptualize that sound waves behave similarly to light waves and that properties of black holes can be “simulated” with sound.
unyttigfjelltol 6y ago
Making a microscopic black hole on the surface of the Earth was #3 on the list of `How to Destroy the Earth`[1], also on HN today. For the first half of the article I was musing at the connection (and implausibility of reading about a research team actually completing the feat). [1] https://news.ycombinator.com/item?id=26204892 https://news.ycombinator.com/item?id=26204892
- nine_k 6y ago
  The smaller the black hole, the faster it evaporates. But having a planet around would instantly make it larger.
  - lumost 6y ago
    Sufficiently small non-charged blackholes would have minimal interaction cross sections with any matter. If such a thing was made with an accelerator, it as well as any material it interacted with would likely fly through the planet and out into interstellar space. Even managing to detect that it had been created would be a substantial challenge.
    - nine_k 6y ago
      I suppose for that its Schwartzschield radius should be much smaller than a typical atom?
      - lumost 6y ago
        aye - the Schwarzschild radius of the entire planet is only 8.87 mm. The radius of a 70kg human is 10^12th times smaller than a hydrogen atom. Presuming it is even physically possible for atom massed black holes to exist - hypothetical hydrogen atom black hole would have a radius 10^41 times smaller than a hydrogen atom. Ultimately the physics of such objects are not well defined, the radius of a hydrogen atom or a proton is defined in terms of electric potentials, calculating the interaction cross section between the quarks in a proton and a hypothetical atom massed black hole is completely ill-defined. At these scales the strong force would dominate - and you'd run into a number of uncomfortable problems which either require hawking radiation to exist or for GR to not conserve energy ( which it doesn't in the classical theory ) but all that being said, whatever collisions created this black hole would surely have left it with a velocity that's a very large fraction of the speed of light.
  - chmod775 6y ago
    So here's just my understanding using basic physics: That kind of gravitational pull can't come from nowhere. If you start from the smallest theoretically possible black hole of about 22 micrograms, it should have the gravitational pull of just that - 22 micrograms. Suppose it doesn't just immediately disappear, it won't even have gravitational pull to move a feather next to it. You could probably even start wadding the feather at it and it wouldn't do much to it, because I don't think that's enough force to even break it apart. If you put a grain of sand on a table you don't expect the gravitation of that grain of sand to break the table apart either. Maybe it'll manage to take in some surrounding air? But in that case you'd have all the time in the world to build a vacuum chamber around it - if you're worried. Likely the black hole would need to be extremely lucky for any (air) molecule to come close enough that it can pull it in, since it'll be a tiny thing in a sea of mostly nothing. In any case, I suppose that in reality the black hole would just dissipate quicker than it could take in mass - because black holes need a lot of new mass to keep going considering the amount of energy/mass they spit out. And only black holes made from a lot of matter (i.e. stars) appear to have the gravitational pull to feed themselves and stay alive, since that's all we can observe in nature. Anyways, that's just using a lot of basic physics that maybe don't even apply to black holes in that way.
karlicoss 6y ago
60 symbols have a good video on analog black holes https://m.youtube.com/watch?v=kOnoYQchHFw https://m.youtube.com/watch?v=kOnoYQchHFw

ojnabieoot 6y ago

Yes, I think it might have been more straightforward to say “Researchers observe stationary Hawking radiation in ‘acoustic black hole’” or something to clarify to laypeople that this is a mathematically analogous but physically very different experiment. I don’t think it’s too difficult to conceptualize that sound waves behave similarly to light waves and that properties of black holes can be “simulated” with sound.

unyttigfjelltol 6y ago

Making a microscopic black hole on the surface of the Earth was #3 on the list of `How to Destroy the Earth`[1], also on HN today. For the first half of the article I was musing at the connection (and implausibility of reading about a research team actually completing the feat). [1] https://news.ycombinator.com/item?id=26204892 https://news.ycombinator.com/item?id=26204892

nine_k 6y ago
The smaller the black hole, the faster it evaporates. But having a planet around would instantly make it larger.
- lumost 6y ago
  Sufficiently small non-charged blackholes would have minimal interaction cross sections with any matter. If such a thing was made with an accelerator, it as well as any material it interacted with would likely fly through the planet and out into interstellar space. Even managing to detect that it had been created would be a substantial challenge.
  - nine_k 6y ago
    I suppose for that its Schwartzschield radius should be much smaller than a typical atom?
    - lumost 6y ago
      aye - the Schwarzschild radius of the entire planet is only 8.87 mm. The radius of a 70kg human is 10^12th times smaller than a hydrogen atom. Presuming it is even physically possible for atom massed black holes to exist - hypothetical hydrogen atom black hole would have a radius 10^41 times smaller than a hydrogen atom. Ultimately the physics of such objects are not well defined, the radius of a hydrogen atom or a proton is defined in terms of electric potentials, calculating the interaction cross section between the quarks in a proton and a hypothetical atom massed black hole is completely ill-defined. At these scales the strong force would dominate - and you'd run into a number of uncomfortable problems which either require hawking radiation to exist or for GR to not conserve energy ( which it doesn't in the classical theory ) but all that being said, whatever collisions created this black hole would surely have left it with a velocity that's a very large fraction of the speed of light.
- chmod775 6y ago
  So here's just my understanding using basic physics: That kind of gravitational pull can't come from nowhere. If you start from the smallest theoretically possible black hole of about 22 micrograms, it should have the gravitational pull of just that - 22 micrograms. Suppose it doesn't just immediately disappear, it won't even have gravitational pull to move a feather next to it. You could probably even start wadding the feather at it and it wouldn't do much to it, because I don't think that's enough force to even break it apart. If you put a grain of sand on a table you don't expect the gravitation of that grain of sand to break the table apart either. Maybe it'll manage to take in some surrounding air? But in that case you'd have all the time in the world to build a vacuum chamber around it - if you're worried. Likely the black hole would need to be extremely lucky for any (air) molecule to come close enough that it can pull it in, since it'll be a tiny thing in a sea of mostly nothing. In any case, I suppose that in reality the black hole would just dissipate quicker than it could take in mass - because black holes need a lot of new mass to keep going considering the amount of energy/mass they spit out. And only black holes made from a lot of matter (i.e. stars) appear to have the gravitational pull to feed themselves and stay alive, since that's all we can observe in nature. Anyways, that's just using a lot of basic physics that maybe don't even apply to black holes in that way.

karlicoss 6y ago

60 symbols have a good video on analog black holes https://m.youtube.com/watch?v=kOnoYQchHFw https://m.youtube.com/watch?v=kOnoYQchHFw