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I am looking for a confirmation (or correction) of my thinking about the nature of the black holes. As I am not a physicist and only a physics enthusiast, my understanding is probably very simplified, so please forgive me - it is not ignorance, just me trying to comprehend some of the mysteries of the universe.

When I try to imagine what a black hole really is, I find that the name "black hole" is actually very confusing. What I understand from what I have read is that, of course, a black hole is not any hole after all, i.e. it is not a portal to another universe (as sometimes shown in sci-fi movies) or any other kind of hole in the spacetime of our universe. I imagine that a black hole is just a very massive object, more massive and more dense than a neutron star. So massive that it does not let any light leave its area of gravitation - therefore we perceive it as a black hole - black point on a sky - with its borders being the event horizon - the point beyond which nothing can ever go back (as the speed necessary to do that would be higher than the speed of light ergo impossible). Therefore, calling it a black hole is a simplification.

To put it in a simple perspective - there might be a black, rubber ball on my carpet that my cat is playing with - it is black, so it does not reflect light. When I look at my room there is this one, oval point where there is nothing - no light coming from - but I know it is not a hole in spacetime, it just does not emit any light, so I do not see it, but it is still there.

Of course, in case of a black hole, there is also a matter of gravity - which can be spotted - but this is simply a result of that whatever is inside a black hole is much more denser and heavier than my cat's toy. One way or another, not emitting any light (due to being black and just absorbing light or being so massive that the light cannot escape) is not an evidence of not existing/being a hole in space etc.

Is my understanding, in this simple perspective, any right?

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Imagine an economic equivalent of a black hole. A distant civilization doesn't want us to watch their Television shows anymore.

Someone decides that by law no broadcasts will be made beyond a specific time on their planet. But maybe they hate turning off their stations so they instead take the recorded shows and take that last hour of shows and play the first half hour over an hour. Then they play the next 15 minutes of show over the second hour. Then play the next 7.5 minutes of show over the third hour. Then play the next 3.75 minutes over the fourth hour. And so on.

It's not black. It's just getting boring. And you could claim there are new TV shows on that planet and we have to go there to watch them. But that's just a theory. Maybe they ran out of ideas, maybe there will be a part of the transmission where they admit that if we are patient.

The same thing happens with a black hole. We get actual signals from every place and time from before the horizon forms. We don't actually know the horizon forms. And we don't see it form. And when we look and listen we get signals from before it formed and we keep getting them, forever. Though they do get boring. The plots are super slow.

So when someone claims there is a beyond, that's a big claim. And it could be tested. But we can't write home about the test results. So it's not really the same kind of science as other claims.

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Black holes come in various flavors, and the whole stable of them remain an active area of study for astrophysicists, theoretical physicists and mathematicians; there are lots of (technically) interesting aspects of these objects which, when understood, can be translated into fascinating stories about could happen in and around them. Kip Thorne's Black Holes and Time Warps gets at some of these (some of which were explored in the movie Interstellar). Roger Penrose has also written many things with the goal of making a human interpretation of technical/mathematical details (e.g., the Penrose process).

The primary/defining characteristic of a black hole is its event horizon, and your description of that from the outside is correct. The one-way passage rule implies that no light (or anything else) will come out. This is why it is called "black": it emits no light from its surface. The implications of the structure for its neighborhood are also interesting: a compact highly-massive object causes violent orbital dynamics and collisions (accretion disks, jets); even objects in "regular" orbits have strange non-Newtonian characteristics (e.g., Zoom-Whirl orbits); the observation of near-BH objects from afar is affected by extreme time dilation and gravitational redshifts (as described by Timeaus).

What happens beyond the event horizon is a completely different story. Some of these facts are well-described in the popular literature, e.g., (i) your time inside is finite --- you will hit the singularity because it is your future: the spatial coordinate which had been "radius" outside the horizon becomes a time coordinate, pointing to a last moment in time at $r=0$, (ii) the tidal effects of gravity could cause a spaghettification which might cause an uncomfortable last days/minutes. I saw a recent talk that explained a similarly distasteful "pancake-ification" process for infall within a spinning black hole.

But in some sense the event horizon really is a boundary to a different universe. The topology of the spacetime inside a black hole is different than the spacetime outside. For example, the Schwarzschild black hole has a time-translation symmetry outside the horizon, which makes it static, eternal, and unchanging as view from outside. But inside the horizon that "time" coordinate becomes spatial: a new infinite spatial dimension opens up upon crossing the horizon. There's a fairly recent paper by Marios Christodoulou and Carlo Rovelli asking "How Big is a Black Hole?", in which they calculate the volume inside that event horizon boundary. What they find is that, in some cases, "there might be room inside it for a spacelike surface [that is] larger than our universe". More complicated black hole solutions (than Schwarzschild) present more opportunities for internal weirdness. So, while the "black" term is a sufficient descriptor for looking at the thing from the outside, the word "hole" really only scratches the surface on what lies inside.

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