Are black holes actually holes?

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that information can not escape a black hole sic why would that be the default position?
 
DaveC426913
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I'm having trouble discerning whether your questions are inter-related.
Are you still asking about why the curvature is well-defined at the EH? Or is this a new question? I'll assume it's a new question.

that information can not escape a black hole sic why would that be the default position?
What do you mean by 'default position'? Do you mean why do scientists assume it to be so?

Well, it's not an assumption. Einstein's GR predicts BHs. With sufficient mass in a compact enough volume, space-time becomes so curved that even light cannot escape - the escape velocity exceeds c. Having GR predict such a possibility, we went looking for it, and found it.

If light cannot escape the gravity well of a massive object, then neither can information.
 
From the National Science Foundation:

Black holes are extremely dense pockets of matter, objects of such incredible mass and miniscule volume that they drastically warp the fabric of space-time. Anything that passes too close, from a wandering star to a photon of light, gets captured. Most black holes are the condensed remnants of a massive star, the collapsed core that remains following an explosive supernova. However, the black hole family tree has several branches, from tiny structures on par with a human cell to enormous giants billions of times more massive than our sun.
[ . . .]

HOW ARE BLACK HOLES STUDIED?
Black holes have long inspired the imagination yet challenged discovery. However, from a combination of theory and observation, scientists now know much about these objects and how they form, and can even see how they impact their surroundings.
[ . . . ]
So, how does one study a region of space that is defined by being invisible?
Theorists can calculate properties of black holes based on their understanding of the universe, and such discoveries have come from a range of great thinkers, from Albert Einstein to Stephen Hawking to Kip Thorne. However, despite being so powerful, it's hard to see something that does not emit photons, let alone traps any light that passes by.

Now, nearly a century after scientists suggested black holes might exist, the world now has tools to see them in action. Using powerful observatories on Earth, astronomers can see the jets of plasma that black holes spew into space, detect the ripples in space-time from black holes colliding, and may soon even peer at the disc of disrupted mass and energy that surrounds the black hole's event horizon, the edge beyond which nothing can escape.
# # #
https://www.nsf.gov/news/special_reports/blackholes/
 
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Black holes are extremely dense pockets of matter, objects of such incredible mass and miniscule volume that they drastically warp the fabric of space-time.
Ironically:
-black holes are vacuum
-there is no meaningfull way to assign a volume to them
-there is no meaningfull way to assign a density to them
-there is no fabric of space-time
-they don't warp space-time, they are speciffically warped space-time


Long live pop-science!
 
davenn
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Ironically:
-black holes are vacuum
-there is no meaningfull way to assign a volume to them
-there is no meaningfull way to assign a density to them
-there is no fabric of space-time
-they don't warp space-time, they are speciffically warped space-time


Long live pop-science!

haha yup, agree with you...
and there's more

astronomers can see the jets of plasma that black holes spew into space,
The jets, that have actually been observed for many years, at radio wavelengths, don't come from
within the black hole as such but from an area OUTSIDE the black hole
 
The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 "to promote the progress of science; to advance the national health, prosperity, and welfare; to secure the national defense..." NSF is vital because we support basic research and people to create knowledge that transforms the future. This type of support:
  • Is a primary driver of the U.S. economy
  • Enhances the nation's security
  • Advances knowledge to sustain global leadership
With an annual budget of $8.1 billion (FY 2019), we are the funding source for approximately 27 percent of the total federal budget for basic research conducted at U.S. colleges and universities. In many fields such as mathematics, computer science and the social sciences, NSF is the major source of federal backing.
We fulfill our mission chiefly by issuing limited-term grants -- currently about 12,000 new awards per year, with an average duration of three years -- to fund specific research proposals that have been judged the most promising by a rigorous and objective merit-review system. Most of these awards go to individuals or small groups of investigators. Others provide funding for research centers, instruments and facilities that allow scientists, engineers and students to work at the outermost frontiers of knowledge.

[. . .]

###
https://www.nsf.gov/about/glance.jsp
 
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Doesn't matter, they contradict what textbooks on general relativity say.
 
jbriggs444
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PAllen
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Funny that just today I was wondering about how to address the intuition that a BH has a density when it really doesn't (at least per GR) - it is mostly vacuum, and suffered a topology change making volume not meaningful, and you can basically get almost any volume you want depending on how you slice it. I came up with the following:

For a collapsed body, the state you currently see from the outside is of the body epsilon before the surface passed into the horizon. This will always be true, with ever shrinking epsilon (and a very generous definition of 'see'). This past state you currently see does have a meaningful volume and density (it is coordinate dependent, but there are defensible 'reasonable coordinates'). However it is not simply using the Schwarzschild radius in a Euclidean geometry sphere formula - the interior geometry is not at all flat, and is given by some complex Ricci curvature along with Weyl curvature. However, to rough order of magnitude, the simple approach would work ok, giving you a sense of how low the density of a supermassive BH would have been in the past, if it formed all at once. Of course, supermassive BH do not form all at once, so a low density state just before horizon crossing has never existed for them.

In this limited past (or hypothetical past for the supermassive case) sense you can give some meaning to density intuitions. You are answering: if this event horizon I detect evidence of, were the result of a monolithic collapse leading to that horizon state (assuming truth of no hair theorem), then the density just before horizon crossing would be such and such.
 
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Do we need to make it so complicated? Make a very large box around the black hole. Consider how much volume it would have without the black hole, consider how much accessible volume it has with the black hole. Subtract. It gives a volume of the order of the Schwarzschild radius cubed. Not sure how to define the accessible volume for rotating black holes, but it gives at most a numerical prefactor.
 
PAllen
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Do we need to make it so complicated? Make a very large box around the black hole. Consider how much volume it would have without the black hole, consider how much accessible volume it has with the black hole. Subtract. It gives a volume of the order of the Schwarzschild radius cubed. Not sure how to define the accessible volume for rotating black holes, but it gives at most a numerical prefactor.
The problem I have with this is that the volume of box with the BH, treated with spacelike slices, can be infinite for perfectly reasonable slices. So you are really doing infinite - infinite equals some finite value.

Maybe my argument seems complicated, but it sidesteps this problem by going to the past, before the interior topology change.
 
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The problem I have with this is that the volume of box with the BH, treated with spacelike slices, can be infinite for perfectly reasonable slices. So you are really doing infinite - infinite equals some finite value.

Maybe my argument seems complicated, but it sidesteps this problem by going to the past, before the interior topology change.
Honestly I think sidesteping the sigularity is missing the point as the emergence of the singularity within the event horizon is considered one of the reasons we "know" GR can't be the final say as it is generally accepted that the emergence of infinities are evidence of the break down of a theory. Perhaps more importantly because no observations can emerge from within a black hole's event horizon any interpretation of what, if anything, exists inside a black hole is inheretly outside the scope of science as it can not be falsified. With the observations of M87*'s photon sphere, the distance at which light orbits the black hole and thus the closest we could ever hope to see light to a black hole, and gravitational waves produced by two black holes merging we can say that fudamentally unless indicated by some new theory of everything these observations rule out anything not observationally indistinguishable from a black hole. The question of if a Black hole is actually a hole is so far outside the fields of science.
 
Drakkith
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The question of if a Black hole is actually a hole is so far outside the fields of science.
Science may not be able to answer every detail of what a black hole is, but we can certainly put many constraints on it, and I believe that we can confidently say that a black hole is not a 'hole' in the normal sense of the word.
 
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Science may not be able to answer every detail of what a black hole is, but we can certainly put many constraints on it, and I believe that we can confidently say that a black hole is not a 'hole' in the normal sense of the word.
True in the familiar 3D sense at the very minimum so I guess I can agree with that but the main point I had wanted to convey was the limitations of science as much of the conversation seemed focused on the interior of a black hole. We have lots of untested hypothesizes out there and I am leery about supporting any of them acknowledging the lack of observational tests. As there is a long history of wild theorizing disconnected from observations.
 

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