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Chapter 1. A survey of popular models.

Chapter 2. Some results of Einsteins General Relativity (GR).

Chapter 3. A note on the "Schwarzschild radius".

Chapter 4. Do we have "Information Loss" at a Black Hole?

Chapter 5. How does Superstring Theories match up with a Black Hole?

Chapter 6. Planck scale and Wormholes (ER=EPR).

Chapter 7. Inflation, and "defects", and Wormholes.

Chapter 8. More on the Kerr- and Firewall models.

This is a very simple note on Black Holes and (the very "speculative") Wormholes.

Although "Black holes" are not disputed by scientists, contrary, it seems that only just few of them

consider Wormholes as a possible phenomenon in Nature.

Indeed, most leading physicists see no ground for Wormholes, except possibly usable as a nice theoretical excercise

in some aspects of physics. This means that any talk about Wormholes is purely speculative.

(Well, I ly a bit here as you will see below...)

This note is a lightweight text on Black Holes and Wormholes.

In chapter 1, let's first start with an overview of Black Hole models, and ideas on Wormholes.

Next, we will see some results of Einstein's "General Relativity" and how that relates to the "classical"

Black Hole model. Following that, let's see what the "critical Schwarzschild radius" means. Then, progressively, we go

to other, more modern, famous subjects, like the "Information Loss" problem, the Firewall model, the "fuzzball" model

from string theories, the Planckscale (EPR wormholes), Inflation, and other subjects that are related

to Black Holes and Wormholes. I just hope that I managed to present a number of interesting subjects.

Although I am very serious here, creating an entertaining note (fun stuff), is actually my main motive.

It's very important to state here, that a "Black Hole" might be viewed as a "last- or worst case scenario"

that does not conflict with General Relativity...

then although "mathematically" you may say that this asymptotic behaviour could work, we still would

have serious physical interpretation problems.

Many physicists think that "somehow", near the sigularity, General Relativity really has to be replaced by

something else, like "Quantum Gravity".

For Wormholes there are generally speaking really serious hesitations by most scientists, to view them as candidate entities

in Nature. However, considerations from e.g. Quantum Gravity, as well as conjectures of the stucture of

where "Planck scale (ER=EPR) Wormholes" have a central role.

So I lied a bit above. Sure, quite a few physicists turn their heads away when you start about Wormholes.

However, a smaller group of theoretical physicists explore the Planck scale, gravity, quantum mechanics, using wormholes.

These folks are really tuned in on a different wavelength. Their studies are pretty neat, really.

It must be said that those studies strongly increased in volume, since the last 7 years or so.

Mabe the first "idea" of a

who's gravity was so strong that even light would "fall back".

I'am not aware of any older ideas about

His idea was based on the work of Schwartzschild (which work in turn was largely based on Einstein's GR).

view the curving as getting asymptotic.

Usually, it is percieved that a Black hole "begins" at the Schwartzschild Radius (Horizon), since at that metric, light cannot escape anymore.

From a larger distance "outside", SpaceTime is flat. However, as you come nearer and nearer to the Horizon, SpaceTime curves more and more too.

From Eistein's theory, this curvation goes "asymptotically", or stated in terms of "distance", a distance "ds

the Horizon is much more strechted compared to a similar "piece" of SpaceTime "ds

At a certain point, very close to the Horizon, even light cannot overcome, or travel, the asymptotically streched SpaceTime no more.

Hence, we have a sort of black object in SpaceTime.

An important question is: What's "inside" the Horizon....?

But there are some considerations too.

When formulating a theory on Black Holes, scientists differentiate between several initial conditions, like:

- "angular momentum" (rotation),

- charge

The considerations of chapters 2 & 3, where a mass within the critical radius becomes a black hole,

leads to the most "simple" Black Hole model, "the Schwartzschild singularity".

However, it's reasonable to assume that a collapsing mass (which is about to become a black hole), has an angular momentum.

A wellknown theory that takes that into account too, is called the "Kerr metric" which leads to the "Kerr Black Hole" model.

Let's take a look at some of the proposed Black Hole models, as they exist today.

The Black Hole has a Horizon ("outside", if one may speak in such a manner), or also called "Schartzschild radius",

at which the escape velocity matches the speed of light, so even light cannot escape anymore.

First, Einstein's

For example, Quantum Mechanics (QM) works in the atomic domain and elementary particles, where General Relativity does not work at all.

For physicists, it is an enormous challenge to, somehow, unite GR and QM. Up to now, that's still not fully solved.

Some say that "Quantum Gravity", once fully matured, or "Superstring Theory", will do the job, one day.

For now, a "singularity" is not nice in any sort of physics, and mathematically, it's a sort of a horror too, since equations

all break down at true singularities.

This type of Black Hole model, is actually the subject of Chapters 2 and 3.

and a White hole is sort of the reverse: it's an entity where

It's tempting to view the Black hole and White hole to be connected in "some" way, where the Black hole sucks in stuff,

and the White hole spits out stuff...

But, the most viable theory that covers a White hole, then demands that the White hole is a small Big Bang in another Universe.

Yes, that's something...

But don't forget: here, we are still only reviewing some popular ideas on our two "objects".

into a Supernova, the corresponding "collapse" of matter will not ultimately end into a singularity,

but at a very small scale, the "loops" will hold a certain metric. Certainly, gravity, and matter-density

will be abnormally strong, just like in section 1.1.1. However, the loop structure would halt the further collapse

of a black hole into a "true" singularity, and that's appealing to physicists.

Due to the high gravity, time "moves" hyper slow. Ultimately, as some physicists say, a "Quantum Bounce"

would change the Black Hole into a White hole, as some of the variants of the Theory predicts.

However, we have not observed that yet (probably), since time is almost frozen, extremely close the Black hole.

Well, that might be a bit of a bad manner of speaking. What we mean is, that matter will not enter a singularity,

and the Horizon (Schwartzschild radius) functions as the unbreakable barrier (the "firewall").

As with all Black Hole models, we have unresolved problems. One might be pretty obvious, when we think about it:

according to GTR, time slows down more and more, when matter comes nearer and nearer to the Black Hole.

Many physicists relate this problem to who actually the observer is, like an observer from a larger distance,

compared to an observer that rides along the falling matter.

Anyway, characteristic of this mode, is that the Horizon (at the Schwartzschild radius), will "accumulate" all

matter (and associated information).

As a collary, it is generally assumed that the 'surface' "A" increases over time.

One interesting idea is that a true physical Firewall exists, that stores information of any object

that was victimized. SpaceTime "inside" however, is so abnormally deformed, that actually nothing can exist,

so victimized matter has not other degree of freedom than to radiate towards the Firewall again.

Formulated in such way, one might say that the Black Hole does not actually exist, but it is the Firewall,

which is the physical placeholder for victimized matter and information.

three spatial dimensions, and one time dimension, also often referred to as a "(3+1)".

As you probably know, theories exists using additional dimensions, which often are assumed to be compactified.

In some "Brane" theories, physicists have assumed a (4+1) space, where the one additional dimension is not compactified,

but it goes undetected anyway, since only "gravity" is "aware" of it.

Applied to Black Holes, the topology might differ from the usual "spherical model" (chracterized by the Schwartzschild Radius).

In particular, donut shaped "Black Rings" seem to be possible.

using Entropy considerations as an important tool to explore further.

This then results in the "Fuzzball" Theory, where the interior has a certain size, and thus avoids the singularity.

Furthermore, string and Branes preserve the "states" of the matter that was victimized, and thus it avoids the "Information loss" problem.

It seems from the literature, that many view this model as a very good cadidate.

See chapter 5 for more information.

a singularity might be expected.

However, that conflicts with other pilers of physics like Quantum Mechanics.

It's fair to say that current theories does not fully solve the Black Hole problem.

However, when angular momentum (rotation) is taken into account too, different solutions may pop up.

That the rotation of matter is important, you might see from an ice-skater, which pulls his/her arms towards the body,

and then starts to spin faster and faster.

Roy Kerr (1963) found a "solution" to this problem, which uses multiple "horizons". An apparrant signularity may form, which might

be ring-shaped too. This is often called the Kerr Black hole, or the Kerr Ring.

The recent movie "Interstellar" gave a new impulse to this idea, and I like to present some more information in chapter 8.

Let's next see about Wormholes.

is rather hypothetical (or speculative).

Very rudely, you might say that most people view Wormholes to classify into:

**intra-universe:**connects regions in the same Universe. These are the "classical" ones,

like Wormhole types with names as "the Schwartzschild-", and "Einstein-Rosen" bridges.**inter-universe:**some cosmological models deal with the "Multiverse". In the "baby Multiverse" model,

Wormhole-like structures links multiple Universa.**Quantum Foam - Planck scale:**At the lowest possible scale of SpaceTime, the "vacuum" might consists

of a sort of foam of wormholes. It's a serious idea, under study by a few physicists.

Interestingly, the latest "models" link those sort of wormholes to the Quantum Mechanical feature "Entanglement".

However, most scientists in general, seem to have ideas's on one of these directions.

A "subclassification" exists, in the sense of a "traversable" or "non-traversable" Wormhole.

The term traversable does not neccessary mean that a "spaceship" might use a "traversable" wormhole, but rather

if it would be possible to

The "intra-universe" wormhole, which is most often called the "Einstein-Rosen" bridge, is the one that we

know so well from SF literature- and movies.

Often we think of a Wormhole to be sort of "distortion" (or "defect") in the space-time fabric,

which might connect two different regions in the same universe, so that it might act as a "shorcut" (or tunnel)

between those regions. So, suppose that we have regions "A" and "B", say 2000 lightyears apart,

then light (or Electromagnetic radiation in general), if it takes a conventional path, will take 2000 years to travel from "A" to "B".

However, if A is close to one "mouth" of Wormhole, and B is close to the other "mouth", then the time of the passage from A to B through

the Wormhole

So, this wormhole acts much like a tunnel, with two ends, each in separate regions in spacetime.

The facinating thing is, that it then would allow for an apparent "faster than light" travel, since an alternative "path" is taken,

namely through the "tunnel".

If such a Wormhole would exist, it's often said that

that for now it it is difficult to see how a Wormhole could be used for something like interstellar travel.

But it's fun to speculate and read SF ofcourse.

In general, it is believed that "negative" energy, will lead to "negative" pressure (expansion) on SpaceTime.

mixed them up, and I don't see the precise "naming" as very critical for our simplified discussion.

In this sense, it seems that it cannot be ruled out that a sufficient amount of negative energy would create

the throat and tunnel. Speculation? Yes and No. First, how to end up with "negative energy" is not known yet, although

quantum fluctuations on the Planck scale is believed to produce a "foam" of "+" and "-" spikes.

But, a relation to the macroscopic world is not easy to make, yet.

As an example of a theoretical basis for this, we might take a look at a derivative of one of Friedmann's equations:

So, in case of negative pressure, the term on the rightside of the "=" is positive too, and the expansion (ä / a)

is thus positive. This is ofcourse far from conclusive. However, even this argument shows that there exists

at least some theoretical basis.

Other arguments lead to the perspective that a Wormhole might connect different

Yes..., that's something else indeed.

Above, in section 1.1.2, we already have seen a certain interpretation of this: The Black hole/White hole pair.

It is seen by some cosmologists and physicists that multiple Universes may exist, all having had their own

private Big Bang and possibly evolved to universa with their own vacuum states and different laws of physics.

As we shall see later on, arguments are possible as to why a wormhole might be a bridge between such manifolds.

The "Inflationary Universe" model does not perse focus on Multiple Universes, but some cosmologists have extended

the inflationary model,

For cosmologists who "favor" Brane Cosmology, the existence of multiple "branes" or Manifolds is almost essential

for the theory. It cannot be ruled out that "interactions" between those Branes, might exist.

Next, a few words about the

A very intruiging type are the hypothetical and "nihil sized" wormholes operating at the "Planck length".

This metric is so extremely small, and it is supposed to be the lower limit in scaling down the spacetime fabric.

When we would zoom in the Vacuum, to the most extreme lowest scale possible, the "Vacuum Foam" might be noticable.

That is, not really noticable ofcourse in the sense that we would "see" it, but many scientists assume that the intrinsic

uncertainty in Energy and Time, at this scale, might be the underlying source for the "vacuum fluctuations" like virtual particles.

Some folks reason along the lines that

a trigger for Wormholes.

Some recent theoretical studies, even associate those Planck scale wormholes to "entanglement".

That will be further explained (or "touched") in chapter 6.

intelligent, and very involved in physics. So, what Einstein wrote down, is absolutely not "easy", so to speak.

In GR, Einstein developed his famous "field equations". One equation is this one:

In GR, gravity has curvature effects on the four dimensions of the SpaceTime.

So, a large mass, will noticeably curve SpaceTime.

What the equation says, is actually how much curvature there is in any given region of space, due to "mass" in the vincinity.

The part on the left side of the "=" sign ( G

The part on the right side of the "=" sign ( Τ

So, the "amount" of curvature of SpaceTime is

Indeed, it's directly related, so:

Let's clarify those

For example, a simple number,

The temperature somewhere in a room, can be expressed by a simple number, a

Sometimes we need

at a certain point in space. Also, velocity has a magnitude and direction too.

However, sometimes an extended mathematical object is needed to describe stuff. For example, if you bend a piece of metal,

at any point inside, countless stress points exists, with different magnitudes and directions.

You can use a sort of "stress" tensor to describe the material in such a situation.

The "crux" is, that multiple "stresses" try to form the material to different directions, with "toroidal" (curving) effects,

and you cannot use a scalar, or vector, to describe that. Here, an mathematical extension, a "tensor", does the job.

A tensor can often be used to describe "Operators" (or mappings) too. Often you can write it as a "matrix".

Einstein was so brilliant to decribe gravity is a similar way. We have the curvature of points in SpaceTime, which

can be described by

Actually, this is just (!) one of the

The equation above, also says something fundamentally (in a classical way) about Black holes (and the hypothetical Wormholes).

Suppose the "mass density" is extremely high, then the SpaceTime curvature close to that "mass density" is extremely high too, possibly up to

the point where the "strech" goes to infinity. Or in other words, "ds" as the distance metric, becomes asymptotic.

In case of a Black hole, nothing can escape anymore, not even light (in the GR framework).

Whenever a theory allow for a true singularity, physicists walk on their toes.

Many physicists think that "somehow", near the sigularity, a theory like General Relativity really has to be replaced by

something else, like "Quantum Gravity" (in fact, physicsts try to unify or reconcile, the different theories).

In the extreme, space would be streched so much, and gravity would be so high, that even light would not escape anymore.

This sort of "barrier" (where even light would not escape anymore), is also called a

For example, I you would compress all of the mass of the Earth in into the size of a small marble (9 mm), then the escape velocity

from "Earth" would be the speed of light (c). In that case, the "horizon" would be 9 mm.

If you would do the same for the Sun, you need to compress all mass into a sphere of less than 3 km.

Karl Schwartzschild calculated a "horizon" for any mass ("M") compressed

So, the "horizon" and "critical radius" is the same, actually.

This critical radius is called the

When you, from the "outside", would move towards that radius, the curvature of spacetime increases, and the gravity strongly increases too.

At the Schwarzschild radius, the gravity is so strong that even light cannot escape anymore.

Actually, the sphere of the Schwarzschild radius (surrounding the mass) is called the "horizon" since you cannot "see" or observe

anything beyond that horizon. Essentially, it's a "black hole". Why? Because light cannot escape anymore from within that horizon.

Remember that "curvature" in spacetime geometry, has the effect of producing accelerations. Near the horizon, gravity get's so strong that

nothing can escape, not even light.

So, Schwartzschild went to work, armed with the insights produced by Einstein.

Schwartzschild reasoned: "Just imaging a spherical "horizon", with a very heavy mass ("M") inside, and spherical symmetric,

but strongly curved, spacetime surrouding it. Now, for that mass "M", which radius then is the horizon where it holds that

light cannot escape anymore?".

His theoretical framework used a few assumptions:

- We have some mass concentration at some location, but no there is no other "stuff" elsewhere (outside the horizon), like another large mass.
- The system under observation is Spherically symmetric and "time independent".
- Most derivations uses "spherical coordinates" (r,θ,φ) instead of (x,y,z,t).
- There is no angular momentum (of the mass) involved. That would complicate the derivation.
- The "Λ" is assumed to be zero.
- The solution is valid for outside the "Horizon" only.

We just have some steady mass inside some region, which does not grows bigger or gets smaller in time.

Why spherical coordinates? When you deal with a spherical symmetric system, then just like astronomers describe the postions of stars in

the heavens, or sea going folks use positions of stars to determine their location, it's just "natural" to use (r,θ,φ).

Don't you agree that this coordinate system fully describe any postion around the horizon?

You only need a radial distance "r", and two angles, to fully qualify any position in the space surrounding the mass.

However, if we "stay" in one plane only, we can eliminate one angle.

(1): We must also keep in mind, that at a great distance from the Horizon, the curvature is small or even going to flat space again.

Only when you get nearer and nearer towards the "Schwarzschild radius", the curvature gets larger and larger.

(2): Actually the same as (1), but we intuitively feel that the spacetime curvature should be dependent on "r".

(3): Actually, the spacetime curvature should be dependent on (r,θ,φ). But if we limit the solution

for a plane through the centre of Mass, then we can neglect φ

So, instead of studying all points in space around M (then we indeed need r,θ,φ), we just take an imaginary "plane"

where φ is zero. We can still calculate the curvature, but then limited from this "plane" only. However, that's good enough.

There is no need to reproduce the full "derivation" here. I will only show some formula's that were essential in his reasoning.

I am afraid that a full derivation would be utmost boring. So, we will not do that, and it's not neccessary at all!

We "trust" Schwartzschild, and the relation below is facinating. I will explain why it's "great", in a moment.

An important relation Schwartzschild found can be expressed like so:

Fig 1.

Below in figure 1, you see some concentric circles, representing

You see

Now, imagine we place a large "mass density" in the centre of those concentric circles. How space will be "curved",

is now expressed by the "blue" curved lines. The closer you go to the centre, the more asymptotically the blue lines become.

In this situation, where M is present in the centre of the concentric circles,

Note that now "ds" is longer than "dr", but actually is should be the same piece of space.

the length without the mass M (dr), and the length with the mass M (ds).

Again, note that the "lenght"

to the mass "M".

Schwartzschild used the equation above, to finally arrive to a formula for the "Critical Radius":

For any mass "M" a critical Schwartzschild Radius r

says when then mass becomes a "black hole". For example, if the Sun's mass were to be compressed within (about) 2 miles,

then it's a black hole.

Actually, the results are quite spectecular. Although the Einstein Field equations are the fundaments, here Schwarzschild found

a practical solution for a common situation.

open questions and paradoxes. And this subject is "just" one of those open questions.

For this specific issue, is there really a problem?

It depends a bit on your viewpoints. I have noticed that some physicists don't see much of an issue, while most others do.

It's not exactly a question for an IT expert. It is a problem in physics, and probably an interesting one for Philosophy too.

There are two scenario's people speak of. Let's see about them.

For the first time, we have a true and brutal "sink" in SpaceTime, which "slurps up" everything.

Anything falling in, has a certain "state" (a Quantum State if you will), which gets

If you like, you can take an example of an Quantum entangled system. Suppose one particle of the system flies into the Black Hole.

What happens with the state of the other free particle? Or what happens to both?

From ElectroMagnetic-, ThermoDynamic-, Nuclear-, Quantum Mechanical standpoints, there is some worries about "Information Loss".

However, it seems that the more

For example, does the present state of a system determines the former and/or future states?

So, folks who believe that

as a possible demolisher of encoded information.

Matter (and thus some sort of information) falls in the "singularity", and nothing changes over there?

Indeed, from a perspective of Quantum Mechanics, particles can be characterized by "states", and all interactions can be viewed

as state changes. Now, if a "sink" really destroys them into a singularity, in fact, something like Volume=0,

then that's tough to digest for physicists.

Mathematically, it can be deduced, as some claim, that

while matter falls in, information "might" not be lost. In a way, states are collected in "some" manner.

Stephen Hawking proposed that a Black Hole "radiates", due to a special effect.

The vacuum is a strange place, really. Virtual particles (a particle and it's anti-particle) can "pop up",

and live for a very short time, before they annihilate each other, producing a photon.

You might interpret that as a consequence of one of Heisenberg's uncertainty relations, although some physicists

are critical to such statement. Since Δ E . Δ t > ℏ / 2, the vacuum can shortly "borrow" Energy

as long as the timespan is short enough.

Anyway, there is hardly any doubt on the existence of "virtual particles", since the clues theretoo are really plenty,

such as the "Casimir effect", or the "Zeemann effect" etc..

Now, when virtual particles are produced near the "critical Schwartzschild Radius", one particle may get "lost"

into the Black hole, while the other one "gets real" and escapes.

This just

This one partner that goes into the Black hole must be "negative" Energy, since the one that escapes becomes real, and is positive.

Yes, the particle that survives is "normal", so has mass and thus Energy.

In other words, suppose a Black hole is on a diet, and does not "eat" matter any further,

There is not much doubt on "Hawking radiation", but it's theoretical only (for now), although some simulations stronly

support it.

Now, there remains the question if "Hawking radiation" possibly solves the Information loss.

There seems consensus among physicists that it does not. At or near the Horizon of the Black Hole, a virtual pair is formed,

and one partner goes in, and the other partner escapes. It is supposed that it contributes to "evaporation" of the Black Hole.

Most physicist does not see "a relation of any kind" of the possible Information inside the Black Hole, and the particle

that escapes.

Here then lies the crux of the Information Loss problem (of scenario 2).

Structured matter falls into the Black Hole. However, if it should evaporate, the structured matter would be gone forever.

So, what happens to the information stored in the black hole if the black hole completely evaporates?

Even this question is very tricky. When space gets very curved, and gravity gets immensly high,

changes quickly too. It's runs slower and slower (according to "pure" General Relativity).

Although GR is not a theory of everything, the "slow" time problem needs to addressed too, before you can say

something substantial about Information Loss. And if space gets curved asymptotically, what happens with a "state"?

In a natural way, you might say that matter "enters" a Black hole at the "horizon" or the "critical Schwartzschild Radius",

as was discussed in chapter 2. However, slow time begins to have effect before that point.

Note 1:

Virtual particles is the reason why (hypothetical)

Their "critical Schwartzschild Radius" is extremely small, so they do not eat. But virtual particles are everywhere,

because the Vacuum is everywhere.

There are other ways how a Black Hole "might" radiate:

- Quantum Tunneling effect.

- Black Body radiation.

One interesting theory, that might resolve the "Information loss", is "Superstring" theory applied to Black Holes,

using Entropy considerations as an important tool to explore further.

It's called the

The theory avoids a singularity alltogether, and thus it sounds quite promising.

See chapter 5 for more information.

Certain mathematics, in conjunction with clever idea's, led to the possibility that the

of the Black Hole's horizon, might be coupled to the absorbed

In that case, the states are probably "not lost", since the Surface Area sort of "describes" all the states.

It's an interesting idea ofcourse. However, probably just not firm enough yet, to be a leading theory in the field.

So, what's the score at this point? Nobody is certain (as espected), or can really proof something.

However, the "Fuzzball Theory" seems promising.

Black Hole Remnants and the Information Loss Paradox (30 Jan 2015, arxiv.org)

Information Loss in Black Holes (S.W. Hawking)(2005, arxiv.org)

Ofcourse, many have a good idea, however, the math is so steep, that it prevents most of us (like me) to get the "nitty gritty" stuff.

Origininally, the (9+1)

Not too long ago, a new derivative theory saw the light, namely

a certain number of supporters, but I am not sure how "popular" this theory really is among string physicists.

It seems to be a (10+2) Theory, but it should not "exactly" be interpreted as having 2 time dimensions.

No doubt that all the Superstring theories are extremely "spicy" for simple mortals like me.

For about the original Stringtheories, a very short synopsys goes like so:

In Superstring Theory / M-Theory, elementary particles are "strings" on a extremely small scale.

Here, the vibrating mode of the string, determines the type of particle. This is quite a uniform statement,

and is very appealing to physicists.

There are "open" strings, and "closed" strings. The open strings are the elementary particles we know so well (quarks, leptons),

while an "entity" as the graviton (force carrier of gravity) is believed to be a closed string.

Remarkably, from mathematical requirements, M-Theory requires 11 dimensions, that is, 10 spatial dimension

and one time dimension. Since our Universe really looks like a (3+1) SpaceTime Universe (that is: 3 spatial + 1 time dimension),

the theory further states that all other extra spatial dimensions are "compactified" (or "curled up"), and thats why they

are "unnoticable" to us. The metric of those "extra" dimensions is so extremely small (10

they go completely undetected indeed.

Furthermore, the concept of a "brane" was introduced, having "n" dimensions (n=0,1,2, etc..), and may be viewed as

a generalization of a "string".

However, in many papers a brane is visualized as a "manifold" or space-like object.

On later moments, it was proposed by some physicists, that not neccessarily all those extra dimensions are "curled up", or "compactified",

and that possibly one (or more) large dimension(s) exists, which are not "noticable" by ordinary open strings,

but contrary, the graviton might be "aware" of it.

As we have seen in chapter 4, a signularity Black Hole, is difficult to reconsile with information states.

Matter falls into the "black hole", while the Singularity does not change (it is a Singularity).

So, a lot of folks see a paradox here: "Information loss".

In the view of many, thus two things were not "ok": (1) the singularity itself, and (2) the paradox of "Information Loss".

- First, it avoids a singularity, since the fuzzball is some region in space.

- Secondly, it probably cures the "Information Loss" paradox.

The Fuzzball theory was firstly published by Samir Mathur and his co workers.

Fig 2. Traditional "singularity" compared to the Fuzzball.

Matter might fall into the Black Hole. But here, it's not a signularity anymore. Strings accumulate or "fuse", in large numbers and density,

so that this object has all properties of our "classical" Black Hole, like the critical radius, from where the gravity

is so large, that even light cannot escape anymore.

Here are some further fundamentals of this amazing theory:

In Superstring theories, particles are strings in a (10+1) space, from which a number of spatial dimensions are compactified.

The vibration of the strings goes in all spatial dimensions.

When matter falls into the Black Hole, the new strings fuse with other strings, forming complex strings or branes.

In the formalism, it is shown that this type of Black Hole is not infinite "dense". It's quite dense ofcourse, but not extremely.

The size of the associated "critical Schwartzschild Radius", corresponds nicely with that of the classical (singularity) model,

which looks like a real plus for this theory.

The complexity of the strings/branes is supposed to conserve the "states" of the matter that was victimized into

the Black Hole. Furthermore, this horizon is not strictly defined, but is "fuzzy", meaning that interactions with fields "just outside"

the horizon might happen, which counteracts the "Information loss" problem too.

In the model, the Black Hole's "fuzzy" horizon thus radiates (some?) Information back to the Universe.

The fuzzball proposal for black holes: an elementary review (arxiv.org)

Are Black Holes Fuzzballs? (www.spacetoday.org)

Fuzzball (string theory) (wikipedia)

due to large fluctuations (or Quantum Mechanical "uncertainties"), at, or around, the Planck length?

Creation of Wormholes, is often associated with

that quantum uncertainties truly exist at the smallest scales of SpaceTime.

So, from such a viewpoint, further theoretical investigations are certainly justified.

Indeed, quite recently, say the last 10 years or so, a revival took place leading to many publications.

Black Hole as a Wormhole Factory (arxiv.org)

Let's discuss that article,

The article is fully supporting the notion that the Planck-scale “spacetime foam”,

can be used to explain the existence of Planck-scale Wormholes.

Extremely small black holes may exist. Due to the quantum fluctuations

negative energy states are unavoidable, and it is further assumed that such quanta entered the initial Black Hole,

as a part of the Hawking radiation process (quanta goes "in", related quanta "escapes").

Remember, when virtual particles are produced near the "critical Schwartzschild Radius", one particle may get "lost"

into the Black hole, while the other one "gets real" and escapes.

Stated in other words, but it's actually the same, is when you look at from a "quantum fluctuations" viewpoint.

The negative energy might thus result in the creation of a Wormhole throat (remember from section 1.2,

that negative energy is required for producing a wormhole).

As is further assumed with any Black Hole, Hawking radiation takes place, and in the end, a very small (micro) Black hole

might fully evaporate. However, the authors argue that radiation stops when the Black Hole's mass nears

the "Planck mass", at which point precisely, the Black Hole's Horizon

What then might result, is a singularity which is shielded by the Wormhole's throat.

In upper article, mathematics is in place that support this proposition.

Actually, any Black Hole (like the "large" regular ones, indeed do have a Horizon/Schwartzschild radius).

The authors then even go a step further by making it plausibe, that the micro black holes might function as

a "Wormhole Factory", since negative energy-quanta's will frequently meet the micro black hole.

Splitting Spacetime and Cloning Qubits: Linking No-Go Theorems across the ER=EPR Duality (arxiv.org)

ER=EPR, GHZ, and the Consistency of Quantum Measurements (arxiv.org)

ER stands for "Einstein-Rosen" bridge (a type of intra-universe Wormhole: see section 1.2).

EPR is short for "Einstein-Podolski-Rosen" in which those three physicists published a famous article, where they

expressed doubt on the completeness of Quantum Mechanics (sort of).

EPR is also often associated with the phenomenon of "Entanglement", in which the state of 2 (or more) particles,

are intertwined in such a way, that the wavefunction (or state vector) cannot be written as a product state.

It means that you need both particles to write down the state of an observable.

It can lead to amazing measurements, if both particles are seperated (by a large distance), and a measurement

on one particle, seems to have an instanteneous effect on the outcome of a similar measurement of the other particle.

This has puzzled the scientific community for a long time, and it still does.

It was this fact that made Einstein to label it "

Some theoretical physicists, exploring the Planck scale, black holes, and wormholes, in the quantum foam,

proposed that Entanglement actually is due to

Those two black hole pairs are actually the endpoints of a Planck-scale quantum wormhole.

The two articles above, althoug somewhat different in the motivation, shows us a theoretical framework

to support the core claim above.