What sonic black holes say about real ones
quantamagazine.org
quantamagazine.org
Ed: for instance, https://www.quantamagazine.org/netta-engelhardt-has-escaped-... or https://www.quantamagazine.org/the-most-famous-paradox-in-ph...
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?
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_e...
[2] https://en.wikipedia.org/wiki/Schwarzschild_metric
[3] https://en.wikipedia.org/wiki/Kerr%E2%80%93Newman_metric#Ove...
[4] https://en.wikipedia.org/wiki/Black_hole_electron
[5] https://www.reddit.com/r/Physics/comments/7fd7pg/if_an_elect...
According to QM. Electrons/positrons aren't a particle but much closer to a probability cloud.
Black holes are fundamentally modified space time. So much, much different than particles.
> 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?
Charge is one of few properties that black holes preserve.
> If the electron and positron are both dimensionless points, yet somehow not black holes, how do their paths ever succeed in intersecting?
Same way two clouds interact. No black holes necessary. Analogy isn't perfect. Two interacting clouds don't obliterate instantly to produce different clouds.
Wikipedia has articles in different languages on it.
"fascinated but also a bit unsettled" "existentially insignificant but strangely exalted" “delightful horror” and a “sort of tranquility tinged with terror.”
from https://erraticus.co/2018/12/04/sublime-experience-kant-scho...
"When I consider the short duration of my life, swallowed up in the eternity before and after, the small space which I fill, or even can see, engulfed in the infinite immensity of spaces whereof I know nothing, and which know nothing of me, I am terrified, and wonder that I am here rather than there, for there is no reason why here rather than there, or now rather than then. Who has set me here? By whose order and design have this place and time been destined for me? The eternal silence of these infinite spaces frightens me."
Kids have a lot of fun playing with water when they are around 3-5. Fluid dynamics is complex, and it takes our brains a long time to observe and get an intuition of it. All that observation, experimentation, (subconscious) hypothesis formulation, testing, adjustment, retesting is a rewarding experience.
After we are about 7, we pretty much finish understanding the world around us. Leaves fall from trees, but not straight, sometimes they go this way and that because of the wind -> all this would have produce a sense of wonder in someone who's only 3 years old, but when you are 7 it's just old news. We switch to learning about the human world, via school. Sometimes it's fun, sometimes not, but whatever.
But when you encounter quantum mechanics, or special relativity, or generalized relativity, or any number of topics in Physics, your intuition fails you big time. You need to go through a new learning process, just like when you were 3 years old. And that's a tremendous lot of fun.
Now, here's the sad part: a person like Frank Wilczek probably knows everything about physics. All the ins and outs of all the physical theories out there, quantum field theory, quantum chromodynamics (he's basically one of its inventors), general relativity, you name it. For him the number of times he can experience the euphoria of such an intellectual rebirth dwindles by the day. But who knows, maybe that's what it looks like from our vantage point, maybe the world at the frontiers of knowledge is still full of wonders for Frank.
Like do black holes extend enormous magnetic tendrils into the surrounding space similar to neutron stars?
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