Le 03/03/2026 à 20:44, Thomas 'PointedEars' Lahn a écrit :Richard Hachel wrote:But a black hole, what is it a hole in?>
It is NOT a hole in something. That is a common misconception.
>
It is a region of spacetime (so _a part_ of spacetime, NOT a hole in it)
from which nothing can get out, and any light emitted from just outside of
it is invisible and undetectable. That is why it would look, and indeed
does look, like a hole [...]
>
It is also a hole in the sense that objects can (but do not have to) fall
into it. Because they can never come out again (according to general
relativity), this region is like a hole in the ground, like a hole in
_space_ if you will.
I struggle to grasp the concept of a hole in a vacuum.
AISB, it is not actually a hole, just something that has some of a hole's
properties. Please read more carefully.
And even more so to understand the concept of spacetime metric near a
black hole,
That is not so. A spacetime metric can describe a black hole *and* its
vicinity. For example, the Schwarzschild metric describes the spacetime
around a spherically-symmetric distribution of mass/energy. It is not
restricted to black holes, was not even discovered because of that; indeed,
Schwarzschild found it because he wanted to describe the spacetime around
celestial objects that were known at the time, like stars and planets.
But this metric has a region where the radial coordinate of an event is
r < 2 G M/c^2. When a (nearly) spherical object (like the core of a star)
collapses to this radius or a radius smaller than that, this region becomes
a Schwarzschild black hole, whose outer event horizon is at the
Schwarzschild radius, r = R_S = 2 G M/c^2. Points on this (imagined)
surface are "points of no return" (as I described before).
Due to the conservation of angular momentum, natural black holes are
probably not Schwarzschild black holes, but are better described by the Kerr
or Kerr--Newman metric for a rotating spacetime.
while physicists have never been able to explain to me all
their errors, contradictions, and falsehoods when they discuss a simple
special relativity problem (everything always ends in contempt and
insults).
The error is yours. If you do nothing else, then at least watch the
excellent videos (by physicists, some of who are experts in the field) that
I referred you to.
So you'll forgive me for not taking your word for it when you talk about a
hole in a vacuum, singularities, and other ridiculous and inappropriate
mathematical abstractions.
They are not ridiculous, and they are not just mathematical abstractions.
Black holes have been *observed*, in particular two supermassive ones, one
in the center of the galaxy M87 (M87*), and the one (that had long been
assumed from radio emissions) in the center of the Milky Way (Sagittarius
A*). I already referred you to an article that shows the reconstructed
image of the former (we can only observe it with radio telescopes, so the
measured radiation has to be converted to colors by computer).
All observations of black holes so far are in good agreement with the
predictions that have been made based on general relativity. IOW, the
theory *works*, that is why we keep using it.
--
PointedEars
Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.
| Date | Sujet | # | Auteur | |
| 3 Mar 26 |  Black hole | 48 | Richard Hachel |
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