Do blackholes have an internal space? Consider the diagram. Inside the negative space, a "bubble" of sealed space, matter is free to move.

Does your physics knowledge have a "bubble" of free space, where imagination is free to roam?

The vertical axis is an imaginary one in the made up 1-dimensional universe diagram. It shows gravity and where matter tends to move. Space and matter can't be compressed beyond the limit explained here and rebounds in a new direction. My layman theory.

https://www.quora.com/Are-we-in-a-bubble-inside-a-supermassive-black-hole

Edit: the vertical axis shows space curvature and matter moves towards the direction where the numbers are closer together.

Claims like "we are in a black hole that exists within another universe" are the kind of thing that always make me laugh at physicists, and makes me wonder why universities indeed put a lot of funds into such research (which I'm inclined to call "research"). Not meaning to offend, I just find it stunning how the like theories miss the reality check.

Not only will you have a hard time proving your theory unless we can somehow get out of "our universe". We cannot even see very far outside of our little solar system, not with a great amount of certitude, anyway. What we "see" and believe to know about most things outside (and also inside!) our solar system is widely speculation, extrapolation, and more or less plausible theories. For example, we believe that there's liquid water on Mars and that the universe is expanding, but we don't really know whether either of these is really the case. It seems plausible, but that's just it. Now we're extrapolating outside our universe already.

Heck, we cannot even -- under the most favourable conditions, with a year or two of preparation -- reach the next closest planet in our solar system, and we aren't even 100% sure what's living in the deeper parts of the oceans on our own planet. All we know is that every now and then a whale comes up with big, ugly scars.

So, assuming that we do indeed live inside a bubble in a black hole, what's the practical application? What's the point in even knowing, if I don't even know for sure what's happening in my tiny corner of the universe?

Seeing how our bodies are made of matter and thus necessarily have mass, how are we to ever escape from an assumed supermassive black hole and explore the other universe (assuming we even manage to leave our puny solar system and our galaxy and reach the "end" of the universe one day, which is very doubtful)?

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And yet, we do actually design and build experiments to measure and test the existence of other parallel universes, universe collisions, extra dimensions, etc...
The applications are the same as any physics research such as that at the LHC - to understand the nature of the universe is to understand how to control it.
Most of this kinf of stuff is playing in the un-illuminated regions of knowledge relating to gravity. If new black hole theories can get me a hoverboard, launch vehicles and long-range / near-C spaceflight, then that's something we should as a species be doing.

For example, we believe that there's liquid water on Mars and that the universe is expanding, but we don't really know whether either of these is really the case.

Do you have a better explanation for the cosmological red shift than the universe expanding, that has not already been thought of and debunked by those same physicists at whom you laugh? Or a better explanation for the hydrated salts that are thought to indicate liquid water on Mars?

What is this "reality check" you speak of, and what makes you think physicists aren't using it?

Heck, we cannot even -- under the most favourable conditions, with a year or two of preparation -- reach the next closest planet in our solar system

What are you even talking about? Uncrewed probes have reached every planet in the solar system and even some things that aren't actually planets. It takes years of preparation to get one of those off because the hardware involved is decidedly non-commodity and almost every one is unique. Also, orbital mechanics constrains when you can actually launch. The only reason humans haven't gone to other planets yet is a lack of political will.

If new black hole theories can get me a hoverboard, launch vehicles and long-range / near-C spaceflight, then that's something we should as a species be doing.

I'm all for that, but it needs to be somewhat realistic in a sense of "possible at all".

Let's go somewhat "smaller" than universe scale. Everybody knows that matter is made of atoms that cannot be split (this is the verbatim meaning of the word "atom"). Since about 150 years, we know that atoms can be split, and they are composed of smaller particles which are the units of everything. We know that they are undivisible, physical objects which cannot move faster than light, and that they have a well-defined position and that they can only be in one place at one time and that they cannot pass a barrier without traversing it. Well, until a few years ago.

Nowadays, we know that they are composed of even smaller "things", and that everything we have encounter in nature is made of either three "things" or one "thing" and an "anti-thing", and that "four thing" and "five thing" particles exist.

Contrary to what must obviously be true, they do not have a clearly defined position and speed. We know that some can travel faster than light, and we most certainly know that particles can be in two locations at the same time or pass a barrier without traversing it.

How do we know?

Well, because although it may be difficult to show, it can be shown, these things can be touched and they can be transformed into "something that works". There is even a very practical application for them.

The quantum tunnel effect demonstrably works because it's how every $4.99 USB drive that you plug into your computer stores its data. The people who developed the first ever flash memory didn't do that by accident. They did it because they realized that if the tunnel effect was "real", they could use it to trap electrons the way we do a quadrillion times (or more often) every day now. And guess what, it works.

Difficult as it may be, it's possible because the stuff that you need is all around you.

Now, stuff at the other end of the universe, or even outside our universe, that's a different matter. It's just impossible to "access" by any realistic means. You cannot possibly tell what is "outside the universe", or how it might look like and work.

Your point of view as a human is the point of view of a microbe living on a mite's butt living on a camel's butt. The camel looks at the sun setting on the horizon and thinks "this is where the world ends". But you look at the mite's butt and think "this is where the world ends". There is no way you could possibly ever see the horizon, or the "end" of the world.

Do blackholes have an internal space?

Having had many discussions on physics and black holes with my brother --- a professor of astrophysics specializing in supernova events and black holes -- I can assure you your question and your image make no sense.

A black hole is a collapsed star that is dense enough to trap light in a gravity well.

There is no magic of holes in the fabric of the universe, no time loops, no holes or loops in reality. They're just really big, super-dense stars, or multiple stars all collapsed together, and they operate with basic gravity.

Fiction writers love to play with black holes. They're used for time travel, jumping across distances, and traveling to parallel universes. While those features may or may not exist in other ways, they have nothing to do with black holes.

The best analogy I've heard over the years is that of snow and snowballs. You can start with individual snowflakes that are mostly empty. Then you can collect those snowflakes as a large pile; roughly this is a regular star. You can take that big pile of snowflakes and compact them into a ball; roughly analogous to a neutron star. You can take that big ball and crush it until it melts from big fluffly flakes into cold liquid, refreezing as solid ice; roughly this is what happens to a black hole.

It is not zero space, it is still matter that takes up space, but it is packed so densely that gravity overwhelms the forces that normally cause atoms and molecules to spread out; they are collapsed so that the empty space normally present between subatomic particles is squished and collapsed together. Instead of a ball of atoms that is millions of miles around, it has been squished like an ice ball until it is only a few hundred miles around. No special loops required, just gravity.

Not only will you have a hard time proving your theory unless we can somehow get out of "our universe". We cannot even see very far outside of our little solar system, not with a great amount of certitude, anyway. What we "see" and believe to know about most things outside (and also inside!) our solar system is widely speculation, extrapolation, and more or less plausible theories. For example, we believe that there's liquid water on Mars and that the universe is expanding, but we don't really know whether either of these is really the case. It seems plausible, but that's just it. Now we're extrapolating outside our universe already.

There's a good deal more to it than belief - it's actually quite disingenuous of you to try to reduce science to the same level as a faith or belief system.

Part of the definition of a scientific theory is that it must make predictions that can be tested; unless a scientific theory can be proven false, it's not a scientific theory. Our understanding of the universe is based on scientific theories that are continuously tested and either verified, modified or discarded.

To take the expansion of the universe: that's not based on belief. That's based on a known and verified physical property of waves and direct observations. Plausability, extrapolation and speculation don't even come into it.

I already wrote this somewhere else. If the curvature of space around a gravity source is proportional to the square root of distance, like the gravitational time dilation formula, then negative distance (internal space) becomes a complex number and gets an extra dimension - the real number and the imaginary. Is there any truth to that?