[John369 (OP)]

Please help me answer these questions:

1. Inside the event horizon, what does it mean to say space and time change their roles? How does that happen? What are its implications? Would every direction inside event horizon look like it is pointing towards the singularity? How would time pass? What is space inside event horizon? Would singularity be everywhere inside event horizon? Or is it just an illusion and there is only one singularity at the center? Is there infinite density and infinite curving of space and dilating of time inside event horizon? Would there be infinite spaghettification? How would atoms of an object react to such an environment? Even if a futuristic ideally durable vehicle could somehow bend space and travel faster than speed of light, could it still not escape from inside the event horizon? Why wouldn't they be able to escape? If such an ideally durable vehicle could survive inside event horizon, could they survive just about everywhere even absolute zero temperature and negative temperatures? What are other methods of escaping from inside event horizon? Like one half of a virtual particle pair appearing inside event horizon and other half outside, if a hypothetical vehicle could generate enough virtual pairs(like exciting the vacuum somehow) from inside the event horizon, then would some of those particles the vehicle generated appear outside event horizon due to HUP? Would this work and would the vehicle be able to come out of event horizon? Would the boltzmann brain scenario work and the atoms and molecules outside blackhole arranged themselves into an exact replica of hypothetical vehicle? How to calculate probability of something like that happening? Eg. swampman scenario?
2. Is there any way to speed up the black hole evaporation process(eg. from 1e+60 years to a few years or even seconds) by increasing the number of negative side of materializing particle pairs exponentially? How would that work? Goal is to find a way to evaporate black hole as quickly as possible, even if we had to assume highly unrealistic scenarios.

[Kryptid]

Here are some resources that might help make this tricky issue more clear:

https://www.einstein-online.info/en/spotlight/changing_places/

An object traveling faster than light (such as a tachyon) could indeed escape from an event horizon because tachyons travel along space-like geodesics.

There is a way to make black holes evaporate more slowly or even stop them from evaporating altogether: increase the spin or charge on them. When you reach a certain point, what you have is an "extremal" black hole that cannot radiate Hawking radiation and thus does not evaporate. Reversing this and making a black hole evaporate more quickly does not seem to be so straightforward.

As for calculating the probability of a warp drive forming spontaneously from random particles, I'm not sure that can be calculated because we don't know how to construct a warp drive and therefore don't know its required size, density or other such parameters.

[Halc]

Inside the event horizon, what does it mean to say space and time change their roles? How does that happen? What are its implications?

It means one spatial dimension (the radial one, ‘up/down’) becomes time-like, and the time dimension becomes space-like. It is all very much like it is on Earth here, and thus somebody falling into a very large black hole would not notice the crossing of the event horizon. Local physics works the same. He cannot send a signal ‘outward’ because that is no longer a spatial dimension. It is the past, and one cannot send a message into the past, but one can receive a message from the past.

Would every direction inside event horizon look like it is pointing towards the singularity?

All directions are always spatial directions, and thus do not point towards the singularity, just like you cannot point towards or away from the location of the big bang, which is not a location in space, but rather a point in the past, and the opposite direction pointing to the future. It isn’t a direction you can point to with your finger.  The black hole singularity is in the (finite) future of our observer within.

How would time pass?

Quite normally. As I said, our observer falling in has no direct reason to notice an immediate change. The model of time as a thing that ‘passes’ isn’t really compatible with a model of spacetime being discussed. Spacetime says space and time is one 4-dimensional thing, not time that passes and space that doesn’t (different things).

What is space inside event horizon?

Normal 3D space. As I said, you’d not immediately know the difference. Space becomes more curved as the singularity approaches, and you’d notice that, even before the event horizon is crossed if it is a smaller black hole. Doing a hyperbolic pass near a neutron star will kill you even though you don’t touch anything.

Would singularity be everywhere inside event horizon? Or is it just an illusion and there is only one singularity at the center?

It’s not an illusion and its not ‘everywhere’.  It is a time more than a place, but it has a shape that is typically a ring. Only a Schwarzschild black hole has a point singularity, an idealization unlikely to exist in reality.

Is there infinite density and infinite curving of space and dilating of time inside event horizon?

No.  As I said, you’d not notice crossing the event horizon, so time and space would appear no different than just on the outside to you.

Would there be infinite spaghettification?

There eventually would be spaghettification, yes, possibly outside the EH. Not sure of the difference between regular and ‘infinite’ spaghettification. At some point yes, even subatomic matter will be both compressed and pulled apart beyond the ability of even the nuclear strong force to resist.

Even if a futuristic ideally durable vehicle could somehow bend space and travel faster than speed of light, could it still not escape from inside the event horizon?

You’re talking about a time travel device. If you propose one, then you are already discarding all of the physics used to answer the questions above, so I imagine you can make up your own answers. This is how Hollywood does it.

If such an ideally durable vehicle could survive inside event horizon, could they survive just about everywhere even absolute zero temperature and negative temperatures?

A vehicle doesn’t need to be particularly durable to pass through the horizon. You in a space suit (or you sitting on Earth for that matter) would work just fine.

What are other methods of escaping from inside event horizon? Like one half of a virtual particle pair appearing inside event horizon and other half outside

That is new material, which reduces the mass of the black hole by adding a negative mass virtual particle to it. I’m not really sure if adding negative things to something counts as the thing escaping, but its mass goes down, so there’s that.

if a hypothetical vehicle could generate enough virtual pairs(like exciting the vacuum somehow) from inside the event horizon, then would some of those particles the vehicle generated appear outside event horizon due to HUP?

No.  A device cannot be made that generates a virtual particle pair well into its past. That again would be time travel, or at least sending messages to the past.

Would the boltzmann brain scenario work and the atoms and molecules outside blackhole arranged themselves into an exact replica of hypothetical vehicle?

First of all, Hawking radiation is pretty much confined to light and other massless radiation. I cannot build a vehicle out of photons and gravitons and such. Yes, by sheer improbability, a vehicle can appear at a random point in space, complete with you in it, with memory of having fallen into the black hole. That works without the aid of a more original vehicle actually being inside the black hole or not. Is it the same vehicle?

How to calculate probability of something like that happening? Eg. swampman scenario?

Yes, exactly, except there is no need for the original to be destroyed by lightning or whatever means. You are in jail, but a swampman event creates an identical copy of you on the outside, complete with memory of being in jail. Have you escaped or is it a different person? Does it really matter to the one on the outside if the one still in jail is improbably destroyed beyond ability to identify?

2. Is there any way to speed up the black hole evaporation process(eg. from 1e+60 years to a few years or even seconds) by increasing the number of negative side of materializing particle pairs exponentially?

There is no known way to generate negative mass. It would have to be non-virtual and somehow transported to the black hole and dropped in. Doing so isn’t going to extract any of the contents out of the black hole any more than does Hawking radiation.

[Antony Silva]

If we consider a black hole as a relativistic object, then there should be no evaporation, but alas, the theory of relativity does not provide answers to absolutely all questions in modern physics.

Evaporation of black holes is predicted by quantum theory. In a vacuum, particle-antiparticle pairs are constantly being born. If there is no black hole, then the annihilation of particles occurs, and the energy returns to the vacuum and everything becomes as it was. This process is called vacuum polarization or boiling.

[yor_on]

This " Inside the event horizon space and time change their roles " is about mathematics. It's a specific solution to the standard Schwarzschild coordinates. In reality it is about a zone from where noting escapes, not even light. You falling in wouldn't notice time and space 'changing place', and your wristwatch would give you the same clock rate, well, more or less if introducing tidal forces. But without them there would be nothing special happening to you, and you would reach whatever 'center' there is in a, for you, measurable time.

What happens to 'space' inside is that it conforms to gravity and 'shrinks'. And so do you and your meter stick, as defined from a outside far away. Not to you locally defined though. The same goes for the time component, as from a outside it 'slows down', and as the inside is a singularity the 'center' should be a place where a outside observer would say that your clock has stopped, as far as I see. And the same should then go for your 'size' as a guess. Aka, you 'disappeared'

And yes, the 'evaporation' is a quantum physical effect

https://en.wikipedia.org/wiki/Black_hole_information_paradox

[yor_on]

And if you think of it, I would call this a lot more mind boggling than any ideas of taychons existing. If it is correct, but it should be. Inside a Black hole, depending on how you define that 'center' you should disappear from any outside observer, and that is without 'wormhole technology'.
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Locally defined it should look as if space becomes infinite, possibly? The event horizon won't exist for you any more as any direction you choose invariably will lead you only one way, towards that 'center', where or what -ever it is. Some define as if the 'center' is reached as soon as you passed your (real) event horizon. It's pretty weird, a black hole.
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Have a read https://medium.com/the-infinite-universe/the-big-bang-may-be-a-black-hole-inside-another-universe-79ce12613c60
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One assumption I build it on (not the article, that's unrelated) is that 'c' will be 'c' wherever you are, and that 'c' is a equivalence to a locally defined 'perfect clock'. It's not the 'speed' I'm interested in there, it's like a conservation law, the speed doesn't matter, the equivalence do.

[John369 (OP)]

Thanks for the great answers. But I am unable to get the clear picture just yet even after watching the video that dealt with future light cones etc. Please explain in simple terms what would be happening to observer A falling into event horizon(here, uncharged non-rotating black hole only) and we watching from afar.
 
1. Would observer A only appear to be stuck on event horizon due to his light getting red shifted to undetectable frequencies? While observer A himself would have crossed event horizon and towards singularity in proper time?
2. Would observer A's all of particles and information be encoded into 3D black hole's 2D surface? Would the black hole grow very slightly due to observer A's falling into black hole? Would there be dual existence of observer A? From our perspective, he was stuck forever at the surface while he himself became a part of black hole in proper time?
3. At the event horizon, would the observer A see all of time in the universe pass behind him? Eg. at the event horizon, he looked behind and sees time of the universe infinitely accelerated. Would that happen? If not, where would that happen in black hole? Would the blue shifted universe appear very small point like at event horizon and all time passed for universe as seen by observer A?
4. Is there infinite curving of space and dilating of time at the singularity, and hence infinite gravity? Suppose there is 6 km black hole, is there infinite density at its singularity? Or is it false since black hole has finite mass?
5. I really want to know of ways to speed up the black hole evaporation. Please drop some theories, doesn't matter how bizarre they are. Is it possible to determine just how much amount of negative mass would be required to evaporate an earth mass black hole? Would negative earth mass matter be sufficient? Since people have calculated how much negative mass would be required for stabilizing Morris Thorne, and Visser wormholes, is it possible to calculate how much negative mass would be required for completely evaporating an earth mass black hole?
6. Would quantum teleportation on a large scale work from inside a black hole? Hence observer A's all of particles disassembling inside event horizon and reassembling far outside on a fixed machine? Shouldn't the Boltzmann scenario work here even if very rarely? I am unable to understand how tachyons could escape from black holes. What is meant by them traveling along space-like geodesics? How do they travel faster than light? What is so special about them?
7. Would gravitational force/tidal acceleration from an earth mass black hole really be on the scales of quadrillions~quintillions m/s^2? Why is the entropy so high? Would magnetic field be high around a black hole, greater than magnetar? What is meant by surface tides measured in m/s^2/m? If surface tide value is 1e+21 m/s^2/m, does that mean an object standing at 1 meter distance from surface of black hole would experience gravitational force of 1e+21 m/s^2? Time to singularity comes out to be 4e-11 seconds, is this really true? Observer A would be gone and encoded into black hole 2D surface in such a short amount of time? Is effective density being 2e+30 kg/m^3 really true? Does it break at singularity?
8. Is it possible to calculate how much the black hole surface area would increase if an object with suppose 1 earth mass falls inside a black hole? Would that mass simply be added into black hole's total mass? And hence an increase from 9.8 cm^2 to 39.5 cm^2 if a 1 earth mass object falls into 1 earth mass black hole resulting in 2 earth mass black hole?
9. Could black holes come in different shapes? Why are all black holes alike(uncharged non-rotating variety only)? Please explain what prevents a cuboid shaped black hole.
10. What are future and past light cones? What are the effects near event horizon and near singularity? In the case of near singularity, does all future of observer A point towards singularity? Is this what is resulting in the observer A paradoxically sending signal into the past? Can observer A only interact with the past near singularity which can never happen? Just what are the implications of one spatial dimension becoming time-like and time becoming space-like? How would that change something? Does that mean observer A can only interact with 2D space now and all future light cone time pointing towards a single future, singularity? Did observer A became 2D and got encoded onto the surface? So basically, observer A can still move his hands in 2 dimensions but is inevitably going to fall into singularity? What happens to blackbody radiation emitted by observer A? Do they also not make it away from the singularity since all future is towards singularity and getting away from singularity means getting into the past which is impossible? Is this what would prevent even teleportation and entanglement with particles outside event horizon?

[Halc]

Thanks for the great answers. But I am unable to get the clear picture just yet even after watching the video that dealt with future light cones etc. Please explain in simple terms what would be happening to observer A falling into event horizon(here, uncharged non-rotating black hole only) and we watching from afar.

That would be a second observer B (us). The two of us would obviously observe different things.
 

1. Would observer A only appear to be stuck on event horizon due to his light getting red shifted to undetectable frequencies? While observer A himself would have crossed event horizon and towards singularity in proper time?

Yes, to all. A crosses the event horizon in his own proper time. Proper time is observer dependent, and it pretty much means the time on the guy's watch, so if he crosses at his noon, observer B will see A's clock approach but never reach noon.

2. Would observer A's all of particles and information be encoded into 3D black hole's 2D surface?

Black holes don't have a surface, so no. The information preservation thing is not entirely solved for black holes, but in the coordinate space of observer B, A never crosses in, so his information up to noon does exist at any given moment in time, and I think that's what you mean by a 'surface'.

Would the black hole grow very slightly due to observer A's falling into black hole?

Of course.

Would there be dual existence of observer A? From our perspective, he was stuck forever at the surface while he himself became a part of black hole in proper time?

All observers are a worldline, not a point of existence. A's worldline continues on into the black hole. This is all assuming that A stays together, which eventually isn't the case. We're assuming he's falling into a big one and survives the approach.  A stellar mass black hole will kill any human well before he gets to the event horizon, and will be reduced to a series of diverging worldlines.

3. At the event horizon, would the observer A see all of time in the universe pass behind him?

No twice. As I said above, he can't tell when he crosses the event horizon. Assuming he can observe all the way to the singularity, he can observe anything in his past light cone, which includes some events and not others. If B is sending news down to him from Earth, there will be a point at which that news will not reach A before time ends at the singularity. That means that A cannot see the history of the universe, but only a brief bit of time.

Eg. at the event horizon, he looked behind and sees time of the universe infinitely accelerated.

An observer hovering at the event horizon will see this, but not a falling observer. This is nothing special. If I get in a ship with infinite acceleration, I too will see the universe 'infinitely accelerated', at least in front of me.

4. Is there infinite curving of space and dilating of time at the singularity, and hence infinite gravity?

Time dilation is relative, so the proper time of A would be unchanged, by definition. Gravity is spacetime curvature, so it seems correct to equate infinite curvature with infinite gravity.

Suppose there is 6 km black hole, is there infinite density at its singularity?

Size matters not. The solution to the field equations yield infinite density of the singularity of a black hole of any mass. A unified field theory might have a better description than that, but we've no such theory at this time. Current mathematics yields a divide by zero at the singularity, which is why it is a singularity.

Or is it false since black hole has finite mass?

Density is mass/volume, and any small mass can have arbitrarily high density if the volume is reduced enough.

[Halc]

Is it possible to determine just how much amount of negative mass would be required to evaporate an earth mass black hole?

-6e24 kg should do it.

7. Would gravitational force/tidal acceleration from an earth mass black hole really be on the scales of quadrillions~quintillions m/s^2? Why is the entropy so high?

An arbitrarily high acceleration (as measured by something 'hovering') can be had near the event horizon of a black hole of any mass.  As for entropy, I have no idea what you mean.

Would magnetic field be high around a black hole, greater than magnetar?

A black hole has charge and angular momentum, the former of which has no reason to be large. So I'd think no. The magnetic field around black holes is almost entirely due to motion of its accretion disk(s).

What is meant by surface tides measured in m/s^2/m? If surface tide value is 1e+21 m/s^2/m, does that mean an object standing at 1 meter distance from surface of black hole would experience gravitational force of 1e+21 m/s^2?

It means a difference of 1e21 m/s² between the one altitude and the other as measured by a hovering thing, with both points somewhat away from the event horizon. The acceleration is arbitrarily high at the event horizon, and not so elsewhere, so the tidal force must also be infinite there.
As measured by something falling in, there is no gravitational force at all (per equivalence principle), but there still is a finite tidal force, which is dependent on the mass of the BH.

Time to singularity comes out to be 4e-11 seconds, is this really true? Observer A would be gone and encoded into black hole 2D surface in such a short amount of time? Is effective density being 2e+30 kg/m^3 really true? Does it break at singularity?

You're mixing reference frames here. I'll take your word for the 4e-11 figure, but that's proper time for the falling thing. There is no surface on which anything gets encoded in that frame. In external coordinate time, the event horizon is the singularity and a falling thing never reaches it in any amount of time.

8. Is it possible to calculate how much the black hole surface area would increase if an object with suppose 1 earth mass falls inside a black hole?

Sure. You can compute the Schwarzschild radius from mass1, and mass1+Earth, so you just take the difference of those two. Area from a radius is easy enough.

Would that mass simply be added into black hole's total mass? And hence an increase from 9.8 cm^2 to 39.5 cm^2 if a 1 earth mass object falls into 1 earth mass black hole resulting in 2 earth mass black hole?

There you go. Easy, no?

9. Could black holes come in different shapes? Why are all black holes alike(uncharged non-rotating variety only)? Please explain what prevents a cuboid shaped black hole.

A cubeoid doesn't have constant radius, or more to the point, constant potential. Yes, a rotating one isn't perfectly spherical, and its singularity isn't a point.

10. What are future and past light cones? What are the effects near event horizon and near singularity?

Look up what they are on wiki or something. It is really basic, and I've no idea of your level of understanding if you have to ask that. Future light cone of an event at the event horizon is entirely within the black hole, so the radial direction becomes the temporal dimension, whereas it was a spatial dimension (up/down) on the outside. Hence the singularity is in the future of A regardless of what he does. The past light cone reaches outside the black hole, so he can see a finite set of events in the universe in his past, just like we can here on Earth.

In the case of near singularity, does all future of observer A point towards singularity?

Anywhere inside the event horizon, yes.

Is this what is resulting in the observer A paradoxically sending signal into the past?

What past? Yes, he can send a signal in the direction that was 'the past' on the outside, since that dimension is no longer a temporal one to him. There is no paradox in this. He is not sending a signal to any events in the past light cone of any event on the outside of the event horizon, so there is no way to spin this as a paradox.

Can observer A only interact with the past near singularity which can never happen?

No observer can effect anything outside his future light cone, by definition. The singularity is in that cone, so it will happen, but events in his past cannot be effected by him. Maybe you mean ‘the past’ of something else. The question is unclear.

Just what are the implications of one spatial dimension becoming time-like and time becoming space-like? How would that change something?

It would not be noticed. There is still 3 space and one time. Like goes on like normal until the tides start getting stupid.

Does that mean observer A can only interact with 2D space now and all future light cone time pointing towards a single future, singularity? Did observer A became 2D and got encoded onto the surface?

Mixing frames again. Only in B's frame does A stay on this surface. He's contracted, but still very much 3D there.

So basically, observer A can still move his hands in 2 dimensions but is inevitably going to fall into singularity?

He doesn't notice the difference, remember?  The world is still 3D to him, and he moves just fine for a while.
In B's frame, time stops for infalling things, so there is no moving of A's hands at all.

[Halc]

Concerning faster than light escape from a black hole:

6. Would quantum teleportation on a large scale work from inside a black hole? Hence observer A's all of particles disassembling inside event horizon and reassembling far outside on a fixed machine? Shouldn't the Boltzmann scenario work here even if very rarely?

You'd have to define identity first. If I build a swampman of you, is it you? Identity seems to have a pretty clear legal definition only because humans cannot yet do that sort of thing (other things can). If I put McCoy into a transporter, is it him that is beamed to the planet below, or just a fax of him?

I am unable to understand how tachyons could escape from black holes. What is meant by them traveling along space-like geodesics?

It means that multiple points along its worldline are separated in a space-like manner. The interval between them is negative.
So I have a meter stick (a classic space-like object). The tachyon worldline can be at both ends at once (in some inertial reference frame). No object moving at or below light speed can do that.
A tachyon cannot interact with normal matter (similar to dark matter), else locality would be violated. OK, there are quantum interpretations that deny the principle of locality, so I suppose those interpretations would allow interaction with tachyons.

What happens to blackbody radiation emitted by observer A? Do they also not make it away from the singularity since all future is towards singularity and getting away from singularity means getting into the past which is impossible?

A's entire future light cone ends at the singularity, and any light from him is no exception to that. While he is outside the EH, he can still send light back to B.

Is this what would prevent even teleportation and entanglement with particles outside event horizon?

Teleportation is communication, and not possible at > c.  Entanglement is not communication, and so pretty much irrelevant.

[John369 (OP)]

Okay, thanks. I have a few final questions.

1. Since black holes have been sucking things, if the observer A goes inside of the black hole, would he see that inside the event horizon, there are photons of light everywhere? Would they be blue shifted or red shifted under the influence of such high gravity? Would the black hole's inside not be black at all but brimming with past light photons? Would it be bright white light or outside visible spectrum?
2. I am still unable to get the implications of all future light cone pointing towards singularity, please give a few more examples. Inside event horizon, can the observer A theoretically do millions of different actions like do reading, play chess, yoga etc. but would be bound to fall into singularity? Meaning, he can do other things except for falling into singularity? For me, if the observer A's all atoms can be rearranged into the exact configuration from surrounding environment, then that would be his identity. So assuming a futuristic quantum teleportation device attached to observer A, if that observer A disassembled inside event horizon and reassembled outside into exact configuration as before(from surrounding molecules), he would have escaped from inside black hole with his identity intact. Would this work?
3. If singularities have infinite density, then why would overall density of black hole be finite, like 2e+30 kg/m^3? Are we ignoring singularity? Since there are a lot of black holes and micro black holes in the universe, does that imply there are brief periods of infinite density and infinite gravity regions everywhere?
4. Can cuboidal and other shaped black holes be simulated(like fixing 8 vertices and all directions inside cuboid point towards a center that would be the singularity)? What shapes can a rotating charged black holes be? Why are most of planets, stars, black holes spherical? How is it related to gravity?
5. If 1 earth mass negative mass could be made in the future, would that completely evaporate 1 earth mass black hole(lifetime 5.6e+50 years) in mere seconds? Are there any leading research currently that hints at how to produce negative mass? If somebody in the future could collect the negative side of materializing particle pair in vacuum and throw 1 earth mass of it into a 1 earth mass black hole, would that evaporate the black hole?

[Halc]

if the observer A goes inside of the black hole, would he see that inside the event horizon, there are photons of light everywhere?

Depends if there is anything emitting them, but there probably are since infalling material glows plenty on the outside, and I see no reason for that not to continue on the inside.

Would they be blue shifted or red shifted under the influence of such high gravity?

Depends on the source of light.  If you look back at Earth, it will be red shifted. If you are in a clould of small lights falling in with you, the lights to the front and back will be red shifted and the ones to the sides blue shifted.

Would the black hole's inside not be black at all but brimming with past light photons?

As I said previously, you can’t tell when you cross the EH.  Things look pretty much the same inside as just outside.  It slowly changes sure.  The have a nice video of what it is like to fall in, but the video only uses light from outside the black hole, not any of it generated by material falling in with you, so there is an area depicted as black, and it grows as you continue to fall.

The grid lines are hard to ignore, but you don’t see those of course as you fall.
No, there are no stars in black holes, so the usual view of points of light here and there goes away. So while light can come from any direction, there probably isn’t a whole lot emitting light except for the general glow that you get from hot material spread all over the place, which in turn is a function of how much material our black hole is ingesting besides you at the moment.  The black hole at the center of our galaxy is a notorious light eater.

Would it be bright white light or outside visible spectrum?

Light from outside red shifts as you fall (the video doesn’t show that), but as what was visible light fades to red, stuff that was in the blue range becomes visible.  So it would appear different, distorted, and not the usual colors. I would not call it bright because light gets dimmer as you red shift it.

2. I am still unable to get the implications of all future light cone pointing towards singularity, please give a few more examples. Inside event horizon, can the observer A theoretically do millions of different actions like do reading, play chess, yoga etc. but would be bound to fall into singularity? Meaning, he can do other things except for falling into singularity?

Yes to all.  The singularity is not a spatial location inside, but a temporal one. It cannot be avoided any more than you can avoid getting to tomorrow. The singularity is an end to time, and thus it is not meaningful to ask what happens one second after hitting the singularity.

3. If singularities have infinite density, then why would overall density of black hole be finite, like 2e+30 kg/m^3?

The singularity has finite mass over zero volume.  The overall density of the black hole is finite mass over nonzero volume. Volume is typically computed as the volume of a sphere with radius the same as the Schwarzschild radius. Hence the difference in density calculations.

Since there are a lot of black holes and micro black holes in the universe, does that imply there are brief periods of infinite density and infinite gravity regions everywhere?

Each back hole has such a singularity, yes. No micro black holes has ever been confirmed. They are a theoretical possibility.

4. Can cuboidal and other shaped black holes be simulated(like fixing 8 vertices and all directions inside cuboid point towards a center that would be the singularity)?

Sure, you can assign 8 points in space to define a cube, but then you’d need to rearrange matter such that all future light cones of events on the surface of this cube point entirely inward and past light cones point entirely outward. There seems to be no possible arrangement of matter that can achieve this geometry.

What shapes can a rotating charged black holes be? Why are most of planets, stars, black holes spherical? How is it related to gravity?

Rotating black holes are somewhat oblate, just like any spinning planet. Sea level at the equator is about 40 km further from the center of Earth than at the poles, so Earth is not a sphere. It is related to gravity because matter is always pulled to the lower energy state (downhill), and a cube shape ball of liquid would not be able to support the weight of the 8 mountains.
Black hole event horizons are roughly sphereical not for the same reason a planet is. A sphere is defined by a fixed radius of constant gravitational potential from the black hole mass.  Any fixed radius from a point object is going to define a sphere, not a cube.

[Halc]

More on the sci-fi parts of the topic:

5. If 1 earth mass negative mass could be made in the future, would that completely evaporate 1 earth mass black hole(lifetime 5.6e+50 years) in mere seconds?

’Evaporate’ is a poor choice of words, which implies a slow process. ‘Negate’ would be better.  Yes, putting the two together results in zero mass, and the black hole is gone.
Getting it there is a trick. F=GMm/r² so since m is negative, so is F.  The black hole will be repelled by the thing approaching it and it would result in a chase of sorts. Best to drop smaller bits in from all directions so the black hole has balanced forces acting on it and doesn’t particularly try to get away.

Not sure how you would handle a blob of material made of negative mass. Can’t exactly grab it with tongs.

Are there any leading research currently that hints at how to produce negative mass?

I think that would be big news, so no.

If somebody in the future could collect the negative side of materializing particle pair

Particle pair creation makes two zero mass virtual particles. Positive/negative energy must be imparted to them to make them non-virtual. I’m no expert at the quantum mechanics involved in this, so I can’t say how this works, or probably why it cannot be done. I mean, something falls into a black hole and reduces its mass, so it seems that it must survive as a real thing long enough to do that.

For me, if the observer A's all atoms can be rearranged into the exact configuration from surrounding environment, then that would be his identity.

If the atoms are from the surrounding environment (such as with swampman), how is that observer A’s atoms?
OK, so you don’t mean moving observer A’s atoms to a new place (which can be done by walking), but using different atoms.  OK, so you’ve built a clone, and you say ‘that would be his identity’ which is kind of a vague statement. Does that mean that if some atoms are arranged into a John369 up on Mars using surrounding Mars material, then you are now on Mars? How does the not-you still on Earth feel about that? Who is that person now? Is he driving a stolen car now?
This is what I mean by needing to define identity. There should be clearer answers to such questions if I am to comment coherently about an escape from a black hole.

So assuming a futuristic quantum teleportation device attached to observer A, if that observer A disassembled inside event horizon and reassembled outside into exact configuration as before(from surrounding molecules), he would have escaped from inside black hole with his identity intact. Would this work?

Quantum mechanics does not allow information transfer to the past. Teleportation of sufficient resolution is possible in priciple, but only forward in time at up to light speed, not to the past.  You’ve been talking about swampman and Boltzmann brains, both of which are chance things, not information transfer.  It would be by total accident that a copy of you is produced outside an event horizon that exactly matches some state in the future of you inside the event horizon. There is no way for the future person to be part of the cause of this accident.

[pensador]

What happens to 'space' inside is that it conforms to gravity and 'shrinks'. And so do you and your meter stick, as defined from a outside far away. Not to you locally defined though. The same goes for the time component, as from a outside it 'slows down', and as the inside is a singularity the 'center' should be a place where a outside observer would say that your clock has stopped, as far as I see. And the same should then go for your 'size' as a guess. Aka, you 'disappeared'

Is that correct?

Space curvature causes gravity, which can be viewed as the elongation of space not the contraction. I understand Infinite space time curvature inside a blackhole, does not mean space shrinks to nothing.

No one knows what goes on inside a black hole, lots of speculations exist. To an outside observer the blackhole might appear to be small, but to someone inside, it might appear very very big. The blackhole itself likely rips apart molecules transforming them into photons creating a photon star inside the event horizon.