Falling ''into'' a black hole

[Lord Antares]

I always hear people talking about object falling into the black hole, possibly going through a wormhole and exiting in another universe etc.

But isn't this fundamentally impossible? Black holes are completely solid, comprised of matter. Falling ''into'' a black hole is worse than saying falling into the earth from an airplane because the black hole is considerably more dense.

(And this is another thing. I'm supposed to say the black hole is infinitely more dense than the earth because it has infinite density. In principle, this is very easy to understand because the space inside it is completely filled up with 0 cracks inside, therefore infinite density; But isn't this mathematically unacceptable since there should be such a thing as ''the largest possible value before infinity'' in this case if I'm not mistaken)

Therefore, wouldn't something fall ONTO a black hole? I am aware that it would get shredded to bits before it could even reach it, but we're speaking hypothetically, of course. This is why wormholes never made sense to me. It would be pretty funny if in xxxx years we could come up with such an advanced technology, that we would be able to send a spacecraft which resists all of the black hole's forces to try to enter it, and the spacecraft just slammed into the black hole, killing everyone inside.

I would be grateful if someone more knowledgeable corrected me

[Strange]

Things can certainly fall into black holes (but the bit about wormholes and other universes is pretty speculative and may not have any basis in reality).

 

A block hole does not have a solid surface. What is described as the "surface" of a black hole is the event horizon. This is the point (in the simplest case, a spherical surface) where it is not possible for anything inside the horizon to communicate with anything outside. So not light or matter can escape from the event horizon.

 

We don't actually know what really happens inside the event horizon. They only theory we currently have that describes black holes is general relativity. This does indeed say that all matter falls in and reaches the center of the black hole and is compressed to infinite density (a singularity). I don't think anyone believes this is what happens, unfortunately we don't have a theory that says what could stop this. We probably need a theory of quantum gravity to understand what really happens.

 

 

But isn't this mathematically unacceptable since there should be such a thing as ''the largest possible value before infinity'' in this case if I'm not mistaken

 

You are right, there is no largest number (you can always add 1 to get to a larger one). So infinity can be defined as how many numbers there are (the cardinality of the set of integers, for example). This then leads to the idea that there are multiple values of infinity (the cardinality of the set of reals is [infinitely] greater than the cardinality of the set of integers).

 

And that is why no one thinks the singularity is a real thing. It just indicates that they theory no longer applies there.

[imatfaal]

we just do not know anything about what is inside the event horizon of a black hole. We can find out the BH's mass, spin and charge - but nothing else. So you are free to hypothesise about what is interior to the event horizon as long as you don't say anything pops back out into local space. This is all not regarding the huge tidal gravity you will incur - this could be exterior or interior to the Event horizon

[koti]

The dense matter inside a black hole is called a "Singularity" It's a very small object, quantum levell small. By falling into a black hole people mean that you fall into the ridiculously strong gravitational field which the singularity produces. You don't fall onto a black hole, you fall into...it's gravitational field.

[imatfaal]

The dense matter inside a black hole is called a "Singularity" It's a very small object, quantum levell small. By falling into a black hole people mean that you fall into the ridiculously strong gravitational field which the singularity produces. You don't fall onto a black hole, you fall into...it's gravitational field.

 

That is not quite true. The singularity is a prediction of General Relativity - but its very nature (infinite curvature of spacetime) make most people believe it does not exist. Thus you need a melding of GR (high gravity) and QM (the very small) to make sense of the interior of a black hole - this is quantum gravity and the search is still on!

[koti]

 

That is not quite true. The singularity is a prediction of General Relativity - but its very nature (infinite curvature of spacetime) make most people believe it does not exist. Thus you need a melding of GR (high gravity) and QM (the very small) to make sense of the interior of a black hole - this is quantum gravity and the search is still on!

Ha, youre right imatfaal. But that just confirms that you "fall into a gravity field of a black hole" instead of "onto a black hole"

[Strange]

The only theory I am aware of that makes predictions for the inside of the event horizon, so far, is string theory: https://en.wikipedia.org/wiki/Fuzzball_(string_theory)

[koti]

The only theory I am aware of that makes predictions for the inside of the event horizon, so far, is string theory: https://en.wikipedia.org/wiki/Fuzzball_(string_theory)

 

It's an attempt at quantum gravity but imatfaal is right, we are not sure about the true nature of the singularity.

[Lord Antares]

Aha, so the black hole is defined as the inside of the event horizon, rather than the singularity itself?
Then of course, falling INTO the black hole is the correct term.

 

By the way guys, food for thought:

 

why would it be a singularity (i.e. of infinitesimal size/smallest possible size) if mathematically, to get the same density you could just take the volume of all the atoms that make up the ''singularity'' and arrange them in a sphere. I don't mean in a way that a normal object is made, constructed by atoms side by side; I mean to make one consistent object/sphere whose volume would be exactly equal to the volume of all the atoms it contains. Surely, following the same logic, this would result in infinite density, or maximum density if you will. Wouldn't this result in a black hole as well, rather than having to somehow shrink beyond that into a singularity?
I'm really interested to hear this question answered.

[Delta1212]

The problem you run into is that atoms are not actually solid things with a set volume. All distances and volumes are the result of the interactions of various forces on the atomic level. If the strength of gravity grows to infinity at the singularity, that would easily overwhelm all of the other forces and prevent the matter from maintaining any larger volume, even on the atomic level.

[Strange]

why would it be a singularity (i.e. of infinitesimal size/smallest possible size) if mathematically, to get the same density you could just take the volume of all the atoms that make up the ''singularity'' and arrange them in a sphere.

 

If that sphere has non-zero size, then the density will not be infinite: density = mass / volume. So if the volume is anything greater than zero, however small, you will get a finite (but possibly very large) value for density.

 

Also, strictly speaking, division by zero does not result in infinity; it is actually undefined. And that is basically what the presence of the singularity tells us: the theory is predicting something undefined (unphysical).

[koti]

 

If that sphere has non-zero size, then the density will not be infinite: density = mass / volume. So if the volume is anything greater than zero, however small, you will get a finite (but possibly very large) value for density.

 

Also, strictly speaking, division by zero does not result in infinity; it is actually undefined. And that is basically what the presence of the singularity tells us: the theory is predicting something undefined (unphysical).

Infinities are semi-graspable for me in math but infinitely small volume containing mass stuck in an infinitely curved space-time is weirdness to infinty.

[Lord Antares]

 

If that sphere has non-zero size, then the density will not be infinite: density = mass / volume. So if the volume is anything greater than zero, however small, you will get a finite (but possibly very large) value for density.

 

But doesn't that violate the law of conservation of energy?

For example, by that logic, if you took an object the size of the earth and condesned it into a singularity and then took another object the size of 1/10 earths and condensed it to a singularity, they would have exactly the same size and maximum density. Isn't that a loss of matter?

 

Wouldn't it make more sense that the size of a black hole would be the sum of the sizes of the atoms it contains? This wouldn't violate that principle and it would still be maximum density. And it would still consider atoms uncompressable in terms of density unlike the other theory.

Also, the size of the black hole would practically STILL be zero OUTSIDE of the event horizon because it perfectly bends space by 360°, making it, in a way, non-existant in outside space.

I'm only saying this because you guys told me that the singularity theory isn't proven so this one makes more sense to me logically and mathematically.

[Delta1212]

Atoms don't have a set size. There's nothing to sum. And it wouldn't be a loss of matter because the mass is all still there.

 

There's no maximum density (that we know of) except infinity. Sub-atomic particles aren't billiard balls with set volumes that bump into each other. They're for lack of a better term, "fuzzy."

 

You know how, when you push two magnets together, it feels like you're pushing against something before they touch? That's how everything works. Stuff doesn't really "touch", the repulsive field strength of various forces just gets strong enough to prevent things from getting any closer.

 

On the subatomic level, there's no solid magnet at the core to bump into each other. It's just the localized forces interacting. If you push hard enough, you can keep pushing them "closer" together.

 

Now, this may very well be modulated by some aspect of quantum mechanics that does prevent everything from collapsing into a fully realized singularity, but we don't yet know how that would work.

Edited October 21, 2016 by Delta1212

[Mordred]

Along with the last post. A lot of the infalling material is also converted to energy. There is a lengthy paper though technical that may be of interest.

 

http://arxiv.org/abs/1104.5499 :''Black hole Accretion Disk'' -Handy article on accretion disk measurements provides a technical compilation of measurements involving the disk itself.

[Strange]

Wouldn't it make more sense that the size of a black hole would be the sum of the sizes of the atoms it contains?

 

Well the size of the black hole (the radius of the event horizon) is proportional to its mass. I wouldn't worry about trying to make sense of the singularity as there probably isn't one!

 

 

And it would still consider atoms uncompressable in terms of density unlike the other theory.

 

Atoms are compressible. There are neutron stars, for example, where they are compressed so much that the electrons are forced to combine with protons.

 

So, if the singularity (or even something approaching it) did exist, the matter that fell into it would not be in the form of atoms.

[Lord Antares]

I see.

Unfortunately, my lack of knowledge about subatomic particles and quantum physics prevents me from discussing this issue any further. If atoms don't have a volume, then I'm confused.

I understand they may not be like billiard balls, the electron field is scattered everywhere. Even gasses have volumes, but if atoms don't, then I don't even know what to say.

 

Also, if Planck length is a thing, then a singularity isn't, is it?

Sorry for being stubborn but it's just hard for me to believe singularities work. It's supposed to be infinitesimal. That's like saying ''the first number before infinity'', but instead it's ''the first number after zero''. It's just hard to believe.
And why is then Mr. Strange agreeing with me to a degree?

Yes, I know that a singularity would not consist of atoms as obviously it is supposed to be (infinitely?) smaller than them. I just thought that atoms are incompressible and therefore the size of the black hole couldn't be smaller than the sum of the atoms but it seems I was wrong.

[Delta1212]

Most people don't think the singularity is physically realized, but we don't have a good explanation for what actually happens. The math for relativity spikes to infinity at that point, and that's the best framework we currently have for understanding and describing how gravity behaves.

 

We don't have a good system for describing the behavior of gravity on a quantum level, and so we need to work that out in order to, hopefully, gain some insight on what may be happening inside the event horizon.

 

The problem isn't with you taking issue with the idea of a singularity really existing. That's not a controversial view. Your particular proposals for what should (or could) happen instead don't hold up, though.

Edited October 21, 2016 by Delta1212

[imatfaal]

I see.

Unfortunately, my lack of knowledge about subatomic particles and quantum physics prevents me from discussing this issue any further. If atoms don't have a volume, then I'm confused.

I understand they may not be like billiard balls, the electron field is scattered everywhere. Even gasses have volumes, but if atoms don't, then I don't even know what to say.

 

Material has a volume, but if you look closely you find that it is just atoms - often with lots of gaps. Atoms have a volume but again most of it is gaps with a nucleus in the middle. Even the nucleus is not as compact as it could be.

 

Gold is pretty dense - about 2 x 10^4 kg per cubic metre; if you placed it (or most other materials) under vast gravitational pressure then it would collapse. The protons of gold nuclei would be forced into great proximity with the electrons and eventually they would merge (a bit more complicated than this) to form neutrons - you then have a new form of matter composed of neutrons (the original from the gold nuclei and the new ones) in a lump. The density of this stuff - which is what a neutron star is - is around 10^17 kg per cubic metre. Do you see how much of the gold was gaps?

 

There is even predicted a more dense state of matter when the neutrons start approaching each other too much and you get a similar breakdown to a quark matter. There are further wilder hypotheses about higher gravitational pressures - but we cannot find out as these matters (well they are crushed stars in reality) are so dense that they form black holes. Once they form black holes we cannot follow the story any longer.

 

 

Also, if Planck length is a thing, then a singularity isn't, is it?

 

Planck length is a distance - like a yard or a cubit but a different system of measurements and a great great deal smaller. We hypothesise that at scales of interaction and measurement below the planck length then Quantum Mechanical influences are so large that they dominate gravity. We can work with this in some situations. But in a black hole the scale is so small that we need QM and the gravity is so large that we cannot ignore General Relativity.

 

Singularities might be a thing - but it is highly highly unlikely and will require huge changes in the physics; even the physics which predicted the singularity in the centre of black hole. This is a bit of a contradiction so we hope and believe that quantum gravity will find a solution which does away for the predicted singularity

[Lord Antares]

Most people don't think the singularity is physically realized, but we don't have a good explanation for what actually happens. The math for relativity spikes to infinity at that point, and that's the best framework we currently have for understanding and describing how gravity behaves.

 

Actually, I went into this discussion with an theory in which this is the only possible solution. In my view of it, density would rise and rise and at some point jump straight to infinity. It would have the highest possible value before infinity, and then infinite. So this makes me wonder if it has some merit...

 

 

Material has a volume, but if you look closely you find that it is just atoms - often with lots of gaps. Atoms have a volume but again most of it is gaps with a nucleus in the middle. Even the nucleus is not as compact as it could be.

 

I know and this is exactly what I am talking about. I wasn't talking about outside volume. I was thinking of the inside volume of the smallest possible particles if such a thing is known. You guys said that this would be the neutron, which I'm happy with, but then there's quarks and quantum physics particles and it all gets confusing there.

[Delta1212]

The problem is that there is no highest possible density before infinity.

[Lord Antares]

What do you mean?

Isn't that mathematically wrong? For a black hole with infinite density to appear:

1) If there is no highest possible density before infinity, then matter would have to gradually get denser and denser until it reaches infinity which is impossible because if would take infinite time.

 

2) If it gets denser and at some point jumps to infinity, then there is a highest density value; the point at which it jumped to infinity, no?

 

Sorry for being stubborn guys, but I don't like accepting something until I've fully understood what the other person means. For example, when someone tells me ''this is wrong because QUANTUM SCIENCE'', that doesn't satisfy my curiosity and didn't make me learn anything.

In other words, reaching infinity is logically impossible unless unless there is an exact point before infinity. Reaching infinity gradually can obviously not be achieved.

Edited October 22, 2016 by Lord Antares

[imatfaal]

What do you mean?

 

Isn't that mathematically wrong? For a black hole with infinite density to appear:

A. I would lose the idea of infinite density / singularity as the thing which is inside a black hole. Something is inside the Event Horizon and at present we don't know. It has a density which means that its radius is lower than its schwartzchild radius and that's about all we can say

 

1) If there is no highest possible density before infinity, then matter would have to gradually get denser and denser until it reaches infinity which is impossible because if would take infinite time.

 

B. Yep - another good reason to avoid singularities and infinities

 

 

 

2) If it gets denser and at some point jumps to infinity, then there is a highest density value; the point at which it jumped to infinity, no?

 

C. Yep - that doesn't work either. There is no figure that is the highest - you can always add one; and infinity is always way off in the distance. It is not a normal number

 

 

 

Sorry for being stubborn guys, but I don't like accepting something until I've fully understood what the other person means. For example, when someone tells me ''this is wrong because QUANTUM SCIENCE'', that doesn't satisfy my curiosity and didn't make me learn anything.

 

In other words, reaching infinity is logically impossible unless unless there is an exact point before infinity. Reaching infinity gradually can obviously not be achieved.

 

OK - the maths of general relativity tells us that at the centre of a black hole is a singularity; a place where space is infinitely curved or where matter is compressed to a point. For lots of reasons - some of which you have touched upon - we do not believe this is correct; it is generally felt that general relativity is beyond its realm of application. You have to use other tools to get your head round this problem; unfortunately we don't know what these other tools are yet! We do know the tool-box is based upon quantum physics.

 

This is something we just don't know! Lots of pop-science rubbish will tell you we know - but we do not.

[Lord Antares]

C. Yep - that doesn't work either. There is no figure that is the highest - you can always add one; and infinity is always way off in the distance. It is not a normal number

 

 

You understood everything I said except this part. I know there isn't a number before infinity, this is not the point.

I mean the highest possible density before the structure of atoms/protons/whatever is the appropriate base particle breaks down. (breaks the nuclear force?)

From then on, I could see how the density could reach infinity but I would use the term ''maximum density'' instead of ''infinite density'' for clarity.

 

In my theory, the radius of a black hole would mathematically turn up as either zero or infinitesimal (I'm not 100% sure on this one) WHEN MEASURED FROM OUTSIDE the event horizon. Inside, it could be any value it pleases (that is not the theory itself; that would be stupid, but it is a result of the theory). In this theory, infinite density wouldn't be any kind of impossibility or spawn any paradoxes.

 

I know none of this probably makes any sense to you, but I don't want to post the full theory until I've learned more about physics.

 

 

[zapatos]

 

OK - the maths of general relativity tells us that at the centre of a black hole is a singularity; a place where space is infinitely curved or where matter is compressed to a point. For lots of reasons - some of which you have touched upon - we do not believe this is correct; it is generally felt that general relativity is beyond its realm of application. You have to use other tools to get your head round this problem; unfortunately we don't know what these other tools are yet! We do know the tool-box is based upon quantum physics.

 

Great explanations imatfaal. ++1

 

Do you happen to know if Einstein also recognized that GR was beyond its realm of application?