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“ Kehle and Unger started with a black hole that doesn’t rotate and has no charge, and modeled what might happen if it was placed in a simplified environment ca

“ Kehle and Unger started with a black hole that doesn’t rotate and has no charge, and modeled what might happen if it was placed in a simplified environment called a scalar field, which assumes a background of uniformly charged particles. They then buffeted the black hole with pulses from the field to add charge to it.” Just finished the article. Surely this can’t be the basis right? I mean everything in the universe is in motion and spins… It did say that spinning work would require extra more complicated math but hmm. Did Hawking et al look at spinning or static black holes in 73 when they did their proof? Imma gonna attempt to read the paper to get more context. I’m sure all the math will go way over my head tho.

gustavus 2y ago
> I mean everything in the universe is in motion and spins… My understanding is that is a pretty open question as to whether or not blackholes due spin at all, or if they are all uniform apart from mass. Last I heard they do have temperature and electric charge and mass. Another question is what does the concept of motion even mean for a singularity. How do you define the concept of distance in a non-euclidean space for an object to move through in the first place. What can the idea of movement even mean for an object that has a horizon beyond which it functionally becomes cut off from the rest of the universe.
- roywiggins 2y ago
  Probably all physical black holes have some spin because they gain it from the matter that falls into it: it's conservation of angular momentum, basically. There are precise mathematical versions of rotating black holes: https://en.wikipedia.org/wiki/Kerr_metric?wprov=sfla1 https://en.wikipedia.org/wiki/Kerr_metric?wprov=sfla1
- drdeca 2y ago
  Black holes spin. (I think this is reflected in the data from LIGO about the gravitational waves from mergers?) This spinning isn’t about the singularity spinning, but the frame dragging around the event horizon.
JKCalhoun 2y ago
I took that to mean that, in theory, beginning with a scalar field, it is mathematically possible... Not that this would be a real-life means that such a thing could come about. The "proof" they found the flaw in said a thing was mathematically impossible — they showed otherwise.
eigenket 2y ago
Maybe it'll help here to point out that if you start with a spinning black hole there's an easy way to stop it spinning. You just chuck in matter with the angular momentum going the opposite way to its spin until all the angular momentum has cancelled out. Then you can do the fancy stuff from this paper with your new spinless black hole.

gustavus 2y ago

> I mean everything in the universe is in motion and spins… My understanding is that is a pretty open question as to whether or not blackholes due spin at all, or if they are all uniform apart from mass. Last I heard they do have temperature and electric charge and mass. Another question is what does the concept of motion even mean for a singularity. How do you define the concept of distance in a non-euclidean space for an object to move through in the first place. What can the idea of movement even mean for an object that has a horizon beyond which it functionally becomes cut off from the rest of the universe.

roywiggins 2y ago
Probably all physical black holes have some spin because they gain it from the matter that falls into it: it's conservation of angular momentum, basically. There are precise mathematical versions of rotating black holes: https://en.wikipedia.org/wiki/Kerr_metric?wprov=sfla1 https://en.wikipedia.org/wiki/Kerr_metric?wprov=sfla1
drdeca 2y ago
Black holes spin. (I think this is reflected in the data from LIGO about the gravitational waves from mergers?) This spinning isn’t about the singularity spinning, but the frame dragging around the event horizon.

JKCalhoun 2y ago

I took that to mean that, in theory, beginning with a scalar field, it is mathematically possible... Not that this would be a real-life means that such a thing could come about. The "proof" they found the flaw in said a thing was mathematically impossible — they showed otherwise.

eigenket 2y ago

Maybe it'll help here to point out that if you start with a spinning black hole there's an easy way to stop it spinning. You just chuck in matter with the angular momentum going the opposite way to its spin until all the angular momentum has cancelled out. Then you can do the fancy stuff from this paper with your new spinless black hole.