Post by: Airthumbs on 29/01/2024 17:13:27
We know there are two things that define the type of star we get, mass and density in space time. I think I got that right! So we calculate the type of star from the amount of mass in a given area. Our sun for example, we know will not become a black hole as it does not have sufficient mass to collapse down that far.
As the mass increases and pressure then we get different types of stars that result in objects incredibly dense, such as a neutron star. This is at a point where the density becomes so high that it overcomes the electrostatic repulsion between protons, allowing them to merge with electrons to form neutrons.
The pattern here seems to be that with increasing density, pressure and mass the atomic bonds of atoms themselves are altered under these conditions creating these dense objects.
Up until this point all the objects are known as stars. Then we get to a black hole, now I see a black hole as just another type of star, a star where the density, mass and pressure have reached a point where it causes the particles in the atoms to become so squashed together that it allows for the creation of this super dense object aka a black hole.
As we now understand blackholes are not eternal objects and I think the idea of infinite mass is just silly. Nothing is infinite and cannot be, it is a mathematical concept that should not be applied to real world physics.
Black holes lose energy though Hawking radiation until it is thought they just kind of evaporate away. However I say that is not the case and cannot be the case. What must happen is that after the density of the Black hole reaches a critical point, where the pressure is no longer able to maintain a singularity, then the black hole, or black star as i like to think of it as, becomes a different type of star, one that is visible again and maybe, just maybe these newly discovered Quark stars might be the candidate I am postulating should exist.
I bet there must be a pretty big bang when the black hole does snap into a less dense entity too? I am not sure which way the energy would go, if you have an area where the very nuclear bonds between atoms is overcome what would happen when they are able to reform those bonds under less extreme conditions?
Post by: paul cotter on 29/01/2024 17:39:30
Post by: Halc on 29/01/2024 18:09:50
We know there are two things that define the type of star we get, mass and density in space time.That would result in a crude classification. Temperature would also be a significant factor, so I think the two-properties definition is incomplete.
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As the mass increases and pressure then we get different types of stars that result in objects incredibly dense, such as a neutron star.Black holes and neutron stars are products of supernovas. They don't just happen as mass increases. Exception: A white dwarf can become a type 1A supernova just by adding mass. These explosions are all pretty much identical and are used as standard luminosity candles across the universe, very useful for measuring distances accurately.
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This is at a point where the density becomes so high that it overcomes the electrostatic repulsion between protons, allowing them to merge with electrons to form neutrons.This assumes compression going on, and yes, supernovas are caused by compression, usually from a collapse of some kind, but not always.
The pattern here seems to be that with increasing density, pressure and mass the atomic bonds of atoms themselves are altered under these conditions creating these dense objects.
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I see a black hole as just another type of star, a star where the density, mass and pressure have reached a point where it causes the particles in the atoms to become so squashed together that it allows for the creation of this super dense object aka a black hole.Not really. A black hole lacks the pressure. The geometery of one tends to pull things apart rather than squish them together. It is misleading to think of them as stars that are even more dense. They're not.
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I think the idea of infinite mass is just silly.If the universe is not of finite size, and has nonzero mass density, then it has to have infinite mass. That's not silly, it's unavoidable. It seems you might be in denial of an infinite universe, but there's nothing contradictory about it.
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Black holes lose energy though Hawking radiation until it is thought they just kind of evaporate away. However I say that is not the case and cannot be the case.Is this topic a speculation then? I will move it to where speculations go since you're pushing personal beliefs.
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What must happen is that after the density of the Black hole reaches a critical pointThey don't have a density at all. For that, you'd need a meaningful volume. It does have a meaningful mass (that and charge and angular momentum. No more).
Post by: SeanB on 29/01/2024 18:16:57
Post by: Airthumbs on 29/01/2024 21:05:42
Both Neutron Stars and Black holes are the result of matter being literally condensed, the matter must be there for the huge gravitational well to exist preventing light escaping in the case of a black hole. You cant just have an empty region of space, not only that but the mass of a black hole can be calculated so I don't understand the response of a moderator stating that there is no mass inside a black hole and that they only rip things to pieces. That cannot be correct.
Post by: pzkpfw on 29/01/2024 21:15:32
... so I don't understand the response of a moderator stating that there is no mass inside a black hole ...
Where was that stated?
Post by: Kryptid on 30/01/2024 00:44:32
When the density drops below the point that gravity escape velocity drops below C
According to current knowledge, that's not how that works. The black hole just becomes a smaller black hole, and that one becomes a still smaller black hole. That continues until you reach a black hole of minimum possible mass (which is currently thought to be around the Planck mass, although some models put it much higher than that). Then you get that black hole vanishing in a final burst of Hawking radiation. Alternatively, it might also just sit there and not evaporate any further (if it's of the extremal variety).
Post by: Airthumbs on 30/01/2024 13:46:05
The consensus currently is that a black hole can exist with a mass of one gram?
This seems a little off? I keep thinking that mass and compression are the key here as that is what is required to bend space time and create this huge gravity well where even light cannot escape. And yet it seems the scientific consensus, amongst whom I don't know, is that once a black hole is formed it remains as a black hole regardless of it's mass?
The geometry referred to by a previous reply is simply the shape of the gravity well as a direct result of the presence of condensed matter, I don't see how that remains unaltered when there is a change in mass, specifically relating to the ability of that mass to bend space time into the geometry required to form a black hole. If there is not enough mass to form that geometry then how can it maintain that shape? I also expect that the critical mass to form a black hole is known and anything below that mass and condensation will not be able to form the geometry of a black hole.
Finally if black holes persist for such a long period of time and only end their lives in a wimpy pop of hawking radiation then we should be observing black holes of all sizes everywhere as they would be the most common cosmological entity. These black holes according to the consensus could be anything from the size of a grain of salt to a water melon and do not require mass to exist?
I also think I am right in stating that Planks law must be modified for it to be applicable to black holes as they are not themselves black bodies that emit radiation from a thermal source. The Hawking radiation from black holes represents a loss of energy, leading to a decrease in the black hole's mass over time.
From what I understand to be the consensus I see that it attempts to deal with the end of a blackhole through quantum mechanics in that eventually when the black hole reaches a mass of plank, probability and uncertainly become the ultimate fate of our black hole. I feel that someone has jumped the gun a little on the life cycle of black holes and missed out a key factor which is mass and compression. Without it, there is no hole?
Post by: Kryptid on 30/01/2024 16:40:14
The consensus currently is that a black hole can exist with a mass of one gram?
Yes.
If there is not enough mass to form that geometry then how can it maintain that shape?
Take a look at the formula for the Schwarzchild radius: https://en.wikipedia.org/wiki/Schwarzschild_radius
For any finite mass, a radius exists where an event horizon will form if that mass is concentrated inside of it. It's density that forms a black hole, not mass. However, that formula is a classical one, not taking into consideration the possible quantum effects that may put a lower limit on black hole mass.
do not require mass to exist?
No one said that a black hole of zero mass can exist.
Finally if black holes persist for such a long period of time and only end their lives in a wimpy pop of hawking radiation then we should be observing black holes of all sizes everywhere as they would be the most common cosmological entity.
It's quite possible that they are very common. However, they are also black. That means that only way we can observe them is through their gravitational effects (or if we get lucky enough that a stray, super-high energy particle from an evaporating black hole hits our detectors).
Post by: Airthumbs on 30/01/2024 18:19:02
"Black holes can be classified based on their Schwarzschild radius, or equivalently, by their density, where density is defined as mass of a black hole divided by the volume of its Schwarzschild sphere, Schwarzschild radius is linearly related to mass" (WIKI).
So from what I can tell from reading about this is that it actually seems to support the possibility that once the black hole does not contain enough mass to maintain the gravity well it's radius would become larger than its Schwarzschild radius and is no longer a black hole as light can then escape.
Post by: Airthumbs on 30/01/2024 18:47:08
HALC "They don't have a density at all. For that, you'd need a meaningful volume. It does have a meaningful mass (that and charge and angular momentum. No more)".
I found that in fact density is a vital part of calculation for the Schwarzschild radius of a black hole. And in fact that to exist smaller black holes must have an increased density. The increased density ultimately sets the size limit of black holes with smaller sizes based on the particles being squashed more, until we reach the limit of what can be squashed.
"A small mass has an extremely small Schwarzschild radius. A black hole of mass similar to that of Mount Everest would have a Schwarzschild radius much smaller than a nanometer. Its average density at that size would be so high that no known mechanism could form such extremely compact objects." (WIKI)
So as a black hole gets smaller it must increase in density to maintain the Schwarzchild radius. And in fact you cannot get a back hole with a smaller mass than Mt Everest according to Wiki anyway.
How can an object that is loosing mass become more dense as that is the requirement for a black hole to persist as it gets smaller in size and to maintain it's Schwarzschild radius?
Post by: Airthumbs on 30/01/2024 19:01:10
When the density drops below the point that gravity escape velocity drops below C
According to current knowledge, that's not how that works. The black hole just becomes a smaller black hole, and that one becomes a still smaller black hole. That continues until you reach a black hole of minimum possible mass (which is currently thought to be around the Planck mass, although some models put it much higher than that).
I am a little confused by the improbable existence of such small back holes and in fact for a black hole to reach Plank mass it's impossible? The material required to maintain a Schwarzschild radius does not exist at the density required within such a small volume.
Post by: Eternal Student on 30/01/2024 20:41:19
I want to clarify the following:Yes, pretty much true. Hawking radiation from it may now be quite energetic and frequently emitted so that the Black Hole would be fairly short lived.
The consensus currently is that a black hole can exist with a mass of one gram?
the scientific consensus, amongst whom I don't know, is that once a black hole is formed it remains as a black hole regardless of it's mass?Yes. It can also grow if it absorbs more mass (or something with a mass parameter like another black hole).
The geometry referred to by a previous reply is simply the shape of the gravity well as a direct result of the presence of condensed matter,Sounds very much as if you're basing everything on models of Newtonian gravity. Assuming Newtonian gravity then, yes, some dense matter should be at the centre of black hole. If you don't assume Newtonian gravity but use GR instead then you don't need vocabulary like "gravity well", gravity isn't a force and the source of gravity is anything that provides a component to the stress-energy tensor. So that mass is one source but pressure or a flux of momentum across a surface is also a suitable source.
Finally we need to mention that simple Black Hole solutions such as the Schwarzschild solution for the Einstein Field Equations are actually vaccum solutions. This is possibly a little complicated to explain but the important point is that they describe a solution in a region of spacetime where there is no source of stress-energy. The Schwarzschild solution is static - the metric and curvature of spacetime does not change or depend on time. GR doesn't need to care too much what may or may not have been the original cause of that curvature, once such a curvature exists in a vcacum it will be static (unchanging with time).
I don't see how that remains unaltered when there is a change in massIt doesn't. Black Holes have a mass parameter and if something with mass falls into a black hole then its mass parameter will change (see later for one example). Also if some mass enters a region around a black hole then the Schwarzschild solution is no longer an exact solution for the region - as mentioned it's a vaccum solution so there cannot be any mass in the region.
If there is not enough mass to form that geometry then how can it maintain that shape?I'm not sure exactly what is being stated here. If you change the mass parameter of a black hole then there is some change in the curvature of spacetime. For example, a one solar masss BH has the space around it return to nearly flat Euclidean space over a short distance along the radial co-ordinate r. A 100 solar mass BH would still show significant curvature of space at this distance. The "shape" is much the same but there is certainly some scaling. Consider a graph of y = 1/x versus y = 100/x.
graphs.jpg (225.62 kB . 1403x896 - viewed 134 times)These have the same "shape" y=1/x but the blue one is scaled (stretched) up the y-axis. So the red graph looks flat enough at about x-axis position 12 units, while the blue one is still coming in with a significant gradient there.
If there is not enough mass to form that geometry then how can it maintain that shape?See above:
(i) Changing the mass parameter of a BH maintains only the shape or geometry of spacetime but there is certainly some scaling.
(ii) The Schwarzschild solution is a static solution of the EFE, it does not change or evolve with time. That is interesting if you assume that "time" is some god-given thing that exists, it always is just one thing we could define and identify without reference to anything else like a metric or some frames of reference. If you don't assume that then the result is less of a surprise.
When we go about solving the EFE (Einstein Field Equations) we do so without knowing exactly what our co-ordinates are going to mean or represent. For the Schwarzschild solution we may naively assume they are something like spherical (r, θ, φ) co-ordinates for space (so r = a radial co-ordinate from the centre of the Black Hole and θ and φ are polar and azimuthal angles) with t as a time co-ordinate. However, we don't know exactly what the co-ordinates were representing until the full solution of the EFE is actually in our hands. It turns out that the r co-ordinate is not a space-like co-ordinate everywhere. When r < Rs this co-ordinate is actually a time-like co-ordinate and t becomes a space-like co-ordinate. It is apparent that r and t are not the space and time co-ordinates we naively thought we might have when we began to obtain a solution to the EFE.
I know that's complicated so let's phrase it a different way: You may be willing to accept that near a massive object time flows at a different rate to a place far away from the massive object. You may also accept that time flows at different rates according to movement through space. Time is not universal. Once we have a black hole in close proximity, time has been morphed in various ways. It just so happens that with respect to that time which we have around a black hole, the curvature of space shows no change with time. It is impossible to say that the Schwarzschild solution was unchanging with respect to some universal time or if it is just that time has been morphed so much around the black hole that any object in the vicinity of the black hole cannot observe any change in the curvature of space around the black hole.
Anyway, you seem to be worried about whether the gravity around a black hole object should change with time. It doesn't have to, the Schwarzschild solution is a static (time unchanging) solution for the EFE in a vaccum. It's not necessarily coincidence, the black hole has "cheated" and morphed time to ensure this will happen.
Finally if black holes persist for such a long period of time and only end their lives in a wimpy pop of hawking radiation then we should be observing black holes of all sizes everywhere as they would be the most common cosmological entity.I don't know why you think they would have to be the most common - but they do seem to be fairly common.
(i) Finding the big Black Holes: When the LIGO gravitational wave detector was switched on, we thought we'd have to wait years to find anything but we didn't. Within a few minutes (not sure of exactly how long but basically short), we found something. Since then we've been finding plenty of clear examples of BH mergers every year.
(ii) Finding the small ones: This is actually much harder. At a distance r > the tiny Schwarzschild radius, a small black hole of mass parameter δm exerts no more force on something than some ordinary particle of the same mass δm. However, small black holes are one candidate for dark matter. We currently think dark matter makes up about 80% of the mass in the universe. So maybe primordial Black holes are extremely prevalent.
[Various other replies have also come in while I've been writing this and doing stuff - sorry, there may be some overlap and existing answers or discussion already given etc. ]
Best Wishes.
Post by: Eternal Student on 30/01/2024 21:18:52
Hi.
Firstly, you should note that I'm not staff for the forum or anything special but I can spare an hour from my laundry duties and read your article.
Let's go through litle bits from the start.
We know there are two things that define the type of star we get, mass and density in space time. I think I got that right!For main sequence stars, their mass and/or luminosity pretty much tells you everything.
All you really have to tell us is just one thing - the mass of the star. We can then find a model to predict the pressures and density at various depths into it and how this will change with time.
such as a neutron star. This is at a point where the density becomes so high that it overcomes the electrostatic repulsion between protons, allowing them to merge with electrons to form neutrons.Protons can combine with electrons (especially if anti-neutrinos are also available) to form neutrons. There is no need for protons to get close to other protons for this process. The main explanation given (for Neutron stars) is simply that there are too many electrons for such a small region of space and the Fermi exclusion principle will not allow two electrons to have the same quantum state. There are protons available and it seems that the electrons will start combining with them to diminish the number of electrons occupying that space.
now I see a black hole as just another type of star, a star where the density, mass and pressure have reached a point where it causes the particles in the atoms to become so squashed together that it allows for the creation of this super dense object aka a black hole.OK, that's speculation but not unreasonable and it could be like this. If you assume that at least some of general relativity is right or a reasonable approximation for the spacetime around this dense object then some weird things are also going on. You don't have to assume the GR model of a black hole is exactly right but at least be aware that time and space could be behaving quite strangely here. As a result speculation about how these dense objects evolve with time, or move around in space can be quite wrong.
We may all like to imagine a black hole as some simple object that behaves like a ball of stuff I can find in my back yard but nature just may not play by these rules. It can have space and time behaving very oddly in this region.
and I think the idea of infinite mass is just silly.Not sure infinite mass was ever implied by anything. Infinite density maybe.
However I say that is not the case and cannot be the case.That is an honest declaration of what is your opinion and you cannot be faulted for that. Thank you. Let's hear then what you think and why.....
What must happen is that after the density of the Black hole reaches a critical point, where the pressure is no longer able to maintain a singularityYou don't explain how or why pressure would maintain a singularity and it's not obvious why it would. Pressure does not cause or prevent a collapse of some material to a given region. Pressure acts in all directions equally. A pressure gradient is what you will need to cause a net flow of material from one place to another. In the typical star, the pressure is greatest at the centre and falls off towards the outer surface, this causes an outward force that opposes further collapse of any material in toward the centre. So a high pressure at or around the singularity may actually tend to push matter away from the centre rather than pulling matter there and maintaining a region of high density.
then the black hole, or black star as i like to think of it as, becomes a different type of star, one that is visible againNo evidence presented or explanation for the how and why but OK... let's go on and see what you're thinking....
just maybe these newly discovered Quark stars might be the candidate I am postulating should exist....and this at least starts to imply the existance of something we might be able to find. Can we find a star that is noticeably different to others and could have been an object that was a black hole and then evolved and switched on again as a star? If we find one that will be great and some evidence in support of the ideas.
There is already a theorised object called a "quark star" that you may have already seen or heard about (I don't suppose you would have used that term otherwise).
(i) It's theorised and not really supported with a lot of evidence yet.
(ii) The evolution of a quark star is currently suggested to be from Neutron star to a Quark star and not something that happens via an intermediate stage that was a black hole.
if you have an area where the very nuclear bonds between atoms is overcome what would happen when they are able to reform those bonds under less extreme conditions?A theorised quark star shouldn't have recognisable atoms, just some soup of quarks. As such there may not be any inter-atomic bonds.
Overall Summary:
The idea that some kind of matter remains inside "a region" we describe as the event horizon of black hole is not at all a silly idea and a lot of Astrophysicists may also harbour this view. We can't get information out from anyone who has been in that region. It may not be an ordinary region of just space which is why I put quotations around "a region" (it's a region of spacetime and we won't worry too much about if it's just space). Many physicists will assume that GR is just an approximation and it is going to break down somewhere. Using it to predict what happens in a region of spacetime around co-ordinate r=0 in a Black Hole is subject to some error.
The remainder of your article is speculative but not offensive and not necessarily wrong. It's very nice that you have an interest in the world around you and in Physics.
Where you go from here is, of course, entirely up to you. It may be worth keeping in mind that there is no shortage of "new ideas" or things that may revolutionise physics. What is lacking are some extensions of existing theory, some demonstration of flaws in existing theory that may also lead to new discovery and some new theory that is also well supported with experimental data or testing.
Best Wishes.
Post by: Kryptid on 30/01/2024 22:27:28
So from what I can tell from reading about this is that it actually seems to support the possibility that once the black hole does not contain enough mass to maintain the gravity well it's radius would become larger than its Schwarzschild radius and is no longer a black hole as light can then escape.
No, the event horizon radius would shrink in proportion to the shrinking in mass. Remember, all of the mass is concentrated into a singularity of zero size (this is why Halc says it doesn't have a meaningful density. Objects of zero size would have infinite density).
I found that in fact density is a vital part of calculation for the Schwarzschild radius of a black hole. And in fact that to exist smaller black holes must have an increased density. The increased density ultimately sets the size limit of black holes with smaller sizes based on the particles being squashed more, until we reach the limit of what can be squashed.
Density is important for when an object becomes a black hole. You can calculate the density of an object if all of its mass exists within its own Schwarzschild radius. However, it doesn't stay at that density. Since no force exists which can support a mass against such crushing force, it all collapses down into a singularity: an object of infinite density.
So as a black hole gets smaller it must increase in density to maintain the Schwarzchild radius.
We need to differentiate the density of a black hole as its mass divided by the volume of the event horizon versus the density of the singularity. All black hole singularities have the same density: infinite. What the wiki article is referring to is creating such a black hole from non-black hole matter (such as collapsing stars). It isn't referring to an existing black hole undergoing Hawking decay to become a smaller black hole.
The gravitational strength at the singularity is infinite is because the distances involved are zero. This is true for any finite value of mass. So even very tiny masses experience infinite gravitational force and thus the singularity cannot decrease its density to become something else.
However, all of these things are based on classical physics. It's quite possible that a black hole doesn't collapse to zero size due to quantum effects getting in the way. However, such a quasi-singularity would still be extremely small and extremely dense compared to anything else in the Universe.
Post by: Eternal Student on 31/01/2024 00:50:25
Let's do some of your ( @Airthumbs ) later posts but a bit more quickly.
I read up on the Schwarzschild radius concept. From what I can infer from the information it seems that this is used to define a black hole using the amount of mass it takes to create one.No or not well phrased.
Rs = 2GM/c2.
Given any mass, there is always a corresponding Schwarzschild radius.
If, at some time, you were in a situation where this mass, M, was concentrated in a spherical region of space with radius < Rs then a Black Hole would form. However, the formation of a black hole may also be inevitably if you had lower density of matter. We require only that the self-gravity of the particle is sufficient to compress it to a radius equal to the Schwarzschild radius.
You took this bit from Wiki:
where density is defined as mass of a black hole divided by the volume of its Schwarzschild sphereand just need to be aware that this is a definition of convenience. The Schwarzschild radius is a number with units of length, so we can imagine a sphere in Euclidean geometry of that radius. The Black hole has a mass parameter which is a number with units of mass. We can divide the two things and end up with another number which we can call density and has units of mass per cubic metre.
However, we need to notice these things:
(i) The mass parameter of the black hole doesn't force the existance of some matter with that mass at the centre of the black hole.
(ii) The region described by r<Rs in a spacetime diagram was not a description of a spherical region of space. Assuming GR and the Schwarzschild solution correctly describes spacetime, that r co-ordinate has now become a time-like co-ordinate.
So this density parameter is just a number with units that match a physical density. There need not be any matter with a physical mass M in this region and "this region" certainly isn't a spherical region of space with radius = Rs. The density parameter may not be describing the physical density of anything.
In a later post you took a quote from @Halc that said much the same things:
HALC "They don't have a density at all. For that, you'd need a meaningful volume. It does have a meaningful mass (that and charge and angular momentum. No more)".The only minor difference I would prefer is that Black Holes have a "mass parameter" rather than something that is definitely a mass. However, the mass parameter grows by m if the the Black hole absorbs a particle of mass m, so there is some one-to-one correspondance between the mass parameter of a black hole and the mass that may have gone in to make it.
Anyway, your Wiki density quantity for a BH is not necessarily describing the physical density of anything. With that understanding some of your later comments almost evaporate:
So as a black hole gets smaller it must increase in density to maintain the Schwarzchild radius.There is no need to assume we were ever talking about the physical density of anything.
And in fact you cannot get a back hole with a smaller mass than Mt Everest according to Wiki anyway.I've not seen that article but I'll assume it was talking about how you might form a Black Hole starting from a situation where you just have some mass and space is reasonably Euclidean to begin with. You can try to squash the matter together. Your target density is
(3 c6) / (32. π. G3 . M2) or proportional to M-2 if I've done my calculations correctly.
So when you have more mass (bigger M), you don't have to squash it together as much to form a black hole.
I'll assume Wikipedia then assumes some physical limit on how much we can squash particles of matter together.
That is interesting but just puts limits on our ability to make a Black Hole when we're out here in flat Euclidean space with only some ordinary matter and bit of equipment to play with.
I don't suppose a Black Hole out in space with a mass parameter that is only half the mass of Mount Everest cares if we could have made it by squashing some stuff together or not. As previously mentioned, the density parameter for this black hole is just a number that may not represent the physical density of any sort of object or material it is required to mainatin at its centre.
Best Wishes.
[and again.... I'm still too slow and more replies have appeared....]
Remember, all of the mass is concentrated into a singularity of zero size (this is why Halc says it doesn't have a meaningful density. Objects of zero size would have infinite density).hmmm... mostly OK.
We know any particle of mass m cannot hold a constant radial co-ordinate r once r<Rs, it must travel to the singularity at r=0 where its worldine terminates. However r=0 is a non-removal singularity in the Schwarzschild solution. The Schwarzschild metric does not apply at r=0 and I really have no way to determine the size of the event or point at r=0, if indeed that is an event that exists in my universe. Only if you say "stuff it, I'll just put the numbers in anyway" will you be able to argue that the mass all ends up in a region of space with 0 volume.
Halc said this:
They don't have a density at all. For that, you'd need a meaningful volume.I would imagine Halc is implying the radial co-ordinate r at the Schwarzschild radius, just isn't a spatial co-ordinate - but you'd have to ask him.
Density is important for when an object becomes a black hole.Looks like general agreement with what has been said by myself above.
We need to differentiate the density of a black hole as its mass divided by the volume of the event horizon versus the density of the singularity.Really worried about trying to find the density of the singularity.
It's sufficient to note that the density parameter Wiki suggested isn't describing a physical density of some material inside the event horizon.
What the wiki article is referring to is creating such a black hole from non-black hole matter (such as collapsing stars)....and we're back on the same tracks and in general agreement.
Best Wishes.
Post by: Airthumbs on 31/01/2024 02:59:49
Hi.
Hi there, thank you so much for your very detailed explanation. I am going to try and digest as much of it as possible over the next few days. I think the reason I may have come across as Newtonian is because that is the physics used according to wiki to calculate the Schwarzschild radius.
Best regards....
Post by: Airthumbs on 31/01/2024 03:15:12
Remember, all of the mass is concentrated into a singularity of zero size (this is why Halc says it doesn't have a meaningful density. Objects of zero size would have infinite density).
I do not agree that a singularity is of zero size. I have no reason for my disagreement other than it just doesnt seem to correlate with everything we can observe in the Universe. I thought it was not possible to describe the singularity and yet it seems there is a consensus towards infinity and zero which when you think about it is very counterintuitive.
I am surprised actually that given what we know about space time and how mass effects it, that anyone could consider a singularity to have zero size and infinite mass.
Why do we need to have an infinite mass appear when we know what mass was required to create the black hole? I think that a lot of these scientists must still be on that LSD test or something?
Oh and btw isn't infinite mass the same as stating infinite energy? You guys really think that a singularity has zero size and infinite mass? Really? Seriously? Your not winding me up or anything?
Post by: pzkpfw on 31/01/2024 03:32:03
...
Oh and btw isn't infinite mass the same as stating infinite energy? You guys really think that a singularity has zero size and infinite mass? Really? Seriously? Your not winding me up or anything?
What infinite mass?
Post by: Airthumbs on 31/01/2024 03:37:53
"Do Black Holes have Singularities?
R. P. Kerr
There is no proof that black holes contain singularities when they are generated by real physical bodies. Roger Penrose claimed sixty years ago that trapped surfaces inevitably lead to light rays of finite affine length (FALL's). Penrose and Stephen Hawking then asserted that these must end in actual singularities. When they could not prove this they decreed it to be self evident. It is shown that there are counterexamples through every point in the Kerr metric. These are asymptotic to at least one event horizon and do not end in singularities". https://arxiv.org/abs/2312.00841
The reason I added this reference to a recent paper by R. P. Kerr is that is seems anyone can pick and choose a side as we don't really know? I am drawn to this paper as it seems to be a better approach to finding a solution than reverting to infinity in what seems a desperate attempt to continue with the current consensus which I and other top scientists disagree with.
Nearly all of the responses to my question have included information about a singularity being infinite and of zero size and yet one of the worlds leading scientists on this subject seems to feel that a singularity is a concept not found in real physics. And I would like to add that neither is infinity. Infinity is a concept used to bodge the math to make it fit into a theory.
Post by: Airthumbs on 31/01/2024 03:39:34
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Oh and btw isn't infinite mass the same as stating infinite energy? You guys really think that a singularity has zero size and infinite mass? Really? Seriously? Your not winding me up or anything?
What infinite mass?
If an object has infinite density then it must have mass? And for that density to be infinite so must mass/energy?
Post by: pzkpfw on 31/01/2024 03:48:23
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Oh and btw isn't infinite mass the same as stating infinite energy? You guys really think that a singularity has zero size and infinite mass? Really? Seriously? Your not winding me up or anything?
What infinite mass?
If an object has infinite density then it must have mass? And for that density to be infinite so must mass/energy?
Yes it has mass. But not infinite mass. Please re-read the posts by Eternal Student and Kryptid. This is covered.
Post by: Eternal Student on 31/01/2024 13:09:42
and yet it seems there is a consensus towards infinity and zero which when you think about it is very counterintuitive.
Stay calm and take a bit of time to read the replies if you want to. When I first used this forum I had a lot of trouble keeping track of who was who. You aren't always getting the "quote" system to work properly and sometimes it appears that a different contributor had said something from a different person - but that's ok, the forum isn't easy to use and I know I got it wrong several times. It can seem like a "them" vs. "me" situation but it isn't. "They" aren't collaborating, "they" are just people giving up some time and trying to help or join a discussion. Indeed "they" will sometimes make mistakes and that includes me. Sometimes there may be a few people with some other agenda, it's a public forum so anyone can use it. You can usually spot people who are just trying to advertise something, for example. If there's a big problem then there's a "report" button at the bottom of the post somewhere and you can have a moderator look at the post - you don't use that if the only problem was that you don't agree with them (it's meant for when the post has become threatening or breeched the policies etc).
As far as I can see the following people have contributed to this thread so far:
You ( @Airthumbs ).
@paul cotter
@Kryptid
@pzkpfw
@Halc
Me ( @Eternal Student )
Of those only 2 have made any comments relating to size or density of the singularity. One of those was me and I have tried to put the brakes on trying to measure the size or density of the singularity. So that leaves only 1 who may have started to use this language and that isn't much of a consensus or majority.
Nearly all of the responses to my question have included information about a singularity being infinite and of zero sizeOnly if you've also been discussing it on other forums or other places.
One of the phrases that has repeatedly come up in several replies is that GR (General relativity) is only an approximation. The appearance of a singularity at r=0 is certainly a concern and one of the main things that suggests GR is simply failing to describe this extreme situation and some new theory like a quantum theory for gravity may be required.
Best Wishes.
Post by: paul cotter on 31/01/2024 14:32:54
Post by: Airthumbs on 31/01/2024 16:36:33
I value the expertise and insights from the responses and I very much appreciate the time people have taken in an attempt to try and answer my question. I have learned a lot but also I feel I have learned that some scientists are blinded by theory and maybe have become a little blind or bias to reality.
I think the word "if" should be used more when relating to theoretical ideas rather than giving facts on theoretical ideas which are not proven or measured in anyway.
A black hole does have mass, we know that, we know how much mass it has due to the gravitational influence it has on other objects nearby. We calculate the mass of a black hole using solar masses as a rubrik. So we know the mass. Density, all we know is that the mass calculated must exist within that region of space time beyond the event horizon, thats all we know. We don't know if there is a singularity, we don't know the density of said theoretical singularity.
And so that brings me back to my original question after side stepping the theoretical responses which to me seem far fetched to say the least.
Maybe a better approach would be for me to ask this...... a black hole has a given mass, we know the size of space it occupies. I am sure it is possible to calculate the following.... given the mass we know for any given black hole and the physical size of the blackhole at what density would that mass need to be to fit inside the physical area?
I mean literally think of it as a sphere of matter condensed no further than it needs to be to fit inside that physical region of space we can observe where a black hole is present. If said matter cannot fit inside that region of space given our current understanding of physics then I will be more open to theory.
Best wishes and thanks again for taking time to respond, I find it fascinating.
Post by: Kryptid on 31/01/2024 16:55:27
hmmm... mostly OK.
We know any particle of mass m cannot hold a constant radial co-ordinate r once r<Rs, it must travel to the singularity at r=0 where its worldine terminates. However r=0 is a non-removal singularity in the Schwarzschild solution. The Schwarzschild metric does not apply at r=0 and I really have no way to determine the size of the event or point at r=0, if indeed that is an event that exists in my universe. Only if you say "stuff it, I'll just put the numbers in anyway" will you be able to argue that the mass all ends up in a region of space with 0 volume.
And so it appears that my understanding of an infinitely-dense singularity is an artifact of the "pop sci" explanation of black holes. I learn something new all the time. Now that I think about it, this is essentially a "divide by zero" problem. That would make the answer undefined as opposed to infinity.
Maybe a better approach would be for me to ask this...... a black hole has a given mass, we know the size of space it occupies. I am sure it is possible to calculate the following.... given the mass we know for any given black hole and the physical size of the blackhole at what density would that mass need to be to fit inside the physical area?
That's more or less the Schwarzschild radius equation (or an alteration of it).
I mean literally think of it as a sphere of matter condensed no further than it needs to be to fit inside that physical region of space we can observe where a black hole is present.
But it isn't. The way that event horizons work is that all matter that crosses it must move inward. This is an effect of how distorted space-time is inside of the event horizon. The matter must move inward as inevitably as you or I must move towards the future. Space and time essentially swap roles like that.
I agree with you that no true singularity exists in a black hole. Relativity doesn't take quantum effects into consideration. We need a picture of quantum gravity to really know what happens in there.
Post by: Origin on 31/01/2024 17:07:14
I have learned a lot but also I feel I have learned that some scientists are blinded by theory and maybe have become a little blind or bias to reality.That is probably because you don't really understand what they are saying.
I am sure it is possible to calculate the following.... given the mass we know for any given black hole and the physical size of the blackhole at what density would that mass need to be to fit inside the physical area?The question as stated doesn't make much sense. If I assume when you say the 'size' of a black hole you mean the event horizon, then it is a trivial division problem. The mass of the sun is ~ 2 x 10^30 kg. If that mass was a black hole the radius of the event horizon would be ~ 3 km or 3000M. The volume would be ~ 1 x 10^11 m^3. So the average density of the mass inside the event horizon is ~ 1.7 x 10^19 kg/m^3. That number is of little use of course, since there is no known force or mechanism that can prevent the collapse of the mass to a singularity.
Is there 'really' a singularity at the center of a black hole? The scientific answer is dunno.
Post by: Halc on 31/01/2024 18:21:46
When the density drops below the point that gravity escape velocity drops below CEscape velocity and gravitational 'strength' are neither a function of density nor of compression, not even under Newtonian mechanics.
A black hole doesn't have an escape velocity. There isn't a direction a thing can go (at any speed) that is to the 'outside'. It would be like trying to throw a stone (or shine a light) into 2023.
I don't understand the response of a moderator stating that there is no mass inside a black hole and that they only rip things to piecesThere is no compression inside a black hole. Compression comes from a surface pushing back, like you get anywhere on a neutron star. Nobody has said there is no mass, but ES uses the term 'mass parameter'. Both mean the kind of mass that results in gravity and inertia. The 'mass parameter' is used to distinguish the term from meaning 'material'.
The consensus currently is that a black hole can exist with a mass of one gram?You've not identified any contradiction in the mathematics, so no, it doesn't seem off.
This seems a little off?
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I keep thinking that mass and compression are the key hereThere is no compression in a black hole. Sure, there is compression in a star in the process of becoming a black hole, but it isn't yet a black hole then. If you drop a large rock into a black hole with some sort of meter measuring the stresses on it, it will indicate tension, not compression, all the way down, including well before it crosses the event horizon. The rock will of course be pulled apart as it crosses the Roche limit, which may or may not be inside the event horizon. Phobos is currently approaching the Roche limit of Mars and is already beginning to break up.
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And yet it seems the scientific consensus [...] is that once a black hole is formed it remains as a black hole regardless of it's mass?If enough negative mass drops in, it eventually masses zero and becomes nothing instead of a black hole.
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The geometry referred to by a previous reply is simply the shape of the gravity well as a direct result of the presence of condensed matter.No. Nobody says that.
I read up on the Schwarzschild radius concept. From what I can infer from the information it seems that this is used to define a black hole using the amount of mass it takes to create one.There's no amount of mass that makes a black hole. There are no known means by which a small mass (like that of our sun) can be compressed sufficiently to collapse into a BH, but there are some hypotheses that small ones might have formed incredibly early in the birth of the universe, the so-called primordial black holes. These can be small.
The Schwarzschild solution is a vacuum solution. So for instance, take all the mass that currently exists in Earth's Hubble sphere (a ball about 15 GLY in radius). The Schwarzschild of that much mass is a bit less than 15 GLY, and yet no black hole forms because that mass doesn't exist in what is otherwise a vacuum. So putting a bunch of matter into a sufficiently small space is not enough.
So from what I can tell from reading about this is that it actually seems to support the possibility that once the black hole does not contain enough mass to maintain the gravity well it's radius would become larger than its Schwarzschild radius and is no longer a black hole as light can then escape.There is no other radius that is different from its Schwarzschild radius. Perhaps you suggest a naked singularity, one whose say charge is sufficiently negative to prevent an electron from entering, despite the gravity of the situation.
HALC "They don't have a density at all. For that, you'd need a meaningful volume. It does have a meaningful mass (that and charge and angular momentum. No more)".By that comment I meant that there is no space occupied by matter inside a black hole. Yes, a 'radius' does definie a meaningful volume in Euclidean space, but as ES correctly points out, the spacetime in a black hole is not Euclidean and any 'density' computed in this manner is just a number, no corresponding to actual physical density of matter.
No, the event horizon radius would shrink in proportion to the shrinking in mass. Remember, all of the mass is concentrated into a singularity of zero size (this is why Halc says it doesn't have a meaningful density. Objects of zero size would have infinite density).This makes it sound like matter is still there, squashed into nearly a 'point' in space somewhere. This isn't so. The matter ends when time ends at the singularity, which isn't a point, but simply a region where standard physics is no longer capable of describing the situtation. The singularity is actually a line (Schwarzschild), cylinder plane (Kerr) or a fuzzy combination (Reissner-Nordstr?m) region where time simply ends, matter and all. So matter dropped in a different times ends up in different places at the end.
I do not agree that a singularity is of zero size.Very good. It isn't size zero. But it also doesn't have a meaningful volume. An area maybe. One might express an average density of that area.
I am under the impression that it is not possible to state what is inside a black hole as we lack the tools currently to investigate.This is false. By talking about black holes, you are already implicitly accepting the one theory (Einstein) that posits them, and given that theory, one very much has the ability to describe them.
Take an alternative theory like the Schmelzer theory which denies at least both postulates of special relativity. All the physical predictions are the same, but there is no big bang and no black holes. Matter falling in what are called 'frozen stars' just get stuck on the surface outsize where Einstein would put the event horizon. Time is paused there. Nothing gets compressed. The experience of falling into one of these is simply the end of time, similar to that of a black hole, but without all the nasty disassembly first by tidal forces. Infalling matter remains intact, under tension (never compressed), but in negligible volume, so arbitrarily high density as you measure it.
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So it is a learning curve for me to discover that some people use theory as fact.No theory is fact. If it was, it would be theorem, not a theory. That's the difference. One is proven, one is not.
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Density, all we know is that the mass calculated must exist within that region of space time beyond the event horizon, thats all we know.What we know from the outside is the no-hair theorem, where a black hole has but three properties and no more. Density is not one of the three things. There is nothing corresponding to the usual meaning of the term physical density.
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Maybe a better approach would be for me to ask this...... a black hole has a given mass, we know the size of space it occupies.No, we don't have a meaningful value for the 'size of space it occupies'. A black hole doesn't occupy space. All of its events are in the future of all events in the rest of the universe, so that makes it in a way something that doesn't yet exist at all, let along have a volume. You can jump into one and still see the universe outside, (can't do that with the Schmelzer theory), but the spatial volume is arguably infinite in there, or perhaps finite but super large, and it changes over time.
What there isn't is material. All the stuff that fell in a year ago? That doesn't exist anywhere, relative to say somebody jumping in. It's not squished into a small location somewhere. There's no squishing going on.
This is me doing the best I can explaining things. I am sure I have made mistakes, and would probably be significantly corrected on a forum with people who know this stuff better than I don.
Post by: pzkpfw on 31/01/2024 18:59:38
(A) Black holes were predicted based on current knowledge of gravity, atoms, etc: a bunch of stuff. Then evidence for their existence was found.
(B) It's not that they were seen first and a bunch theories were generated to explain them.
It'd be a pretty big coincidence to find something expected by predictions that turn out to be entirely wrong.
That isn't to say everything is known (e.g. exact nature of the (not?) singularity), but if you want to dispute what a black hole is, you can't just fling ideas out like it's case (B), you need to understand the knowledge in case (A) and find where that's wrong.
Post by: Airthumbs on 31/01/2024 20:48:57
And you are quite right, I do not have the academic expertise in physics which is why I am using this forum. You almost seem offended that I would wish to participate in a discussion about something I want to learn more about.
However I still don't understand why you state emphatically that there is singularity inside a black hole when we just don't know what is inside in reality. I have found all of your responses to unhelpful and in fact you seem to enjoy pointing out that I do lack knowledge as you have used this rhetoric in one of my previous posts. now I don't bother reading them as it appears you quote me on everything except the fact that what you state is essentially fiction regarding a singularity.
Post by: paul cotter on 31/01/2024 21:26:50
Post by: Airthumbs on 31/01/2024 23:13:18
Halc is simply trying to explain the intricacies of black holes by taking quotes and explaining the relevant errors. Unless one has a good grounding in GR(which I certainly don't) many statements may seem counter intuitive and difficult to grasp. I have never found Halc to take pleasure in correcting errors and I have seen him go to great lengths when some posters fail to understand some critical point with way more patience than I could ever muster.
Evidently that patience is understandably wearing thin....... here are a few notes I would like to add in response to certain statements that I found to be intriguing and subsequently would like to highlight them here......
1,Einstein himself did not specifically define black holes in his equations; rather, the concept emerged as a consequence of his theory.
2, Einstein's theory of general relativity provided the mathematical framework that allowed for the possibility of singularities to exist, particularly in the context of black holes. However, Einstein himself was initially skeptical about the existence of singularities.
3, When Karl Schwarzschild found a solution to Einstein's field equations that described a black hole, it contained a mathematical singularity at the center. This singularity implied a point of infinite density, which was a concept Einstein found troubling and at odds with his intuition about the physical universe.
4, Einstein interpreted the singularity as a mathematical artifact, suggesting that it might be a sign that general relativity breaks down under extreme conditions rather than a true representation of physical reality. He famously referred to singularities as "naked" singularities, indicating a problem with the theory rather than a physical phenomenon.
OK, so it seems I and Einstein share something in common, however, I still reckon a black hole is just a very dense object and the singularity as I said before is a creation of math to justify the solution, and in a much more scientific way I believe that Einstein basically said the same thing.
Post by: Eternal Student on 01/02/2024 01:58:38
HALC are you an expert on the contents of a black hole?He hasn't been inside one and returned - but he is regarded as an expert on GR (General relativity) by most regulars.
Let's be objective for a moment:
What will happen in most forums is that the regulars will start to rally around another established member. We're just human beings so that will also happen here. Fortunately, Halc is big enough to take a little knock back from someone so we don't need to worry about him too much. Meanwhile, it should be apparent that hostility isn't going to win a lot of favour and people will just go and watch "Jerry Springer" if they want to see some friction.
the singularity as I said before is a creation of math to justify the solution, and in a much more scientific way I believe that Einstein basically said the same thing.Hmmm.... How on earth could the mathematicians be made to look like the "bad guys" in that?
Wikipedia has several (20 ?) definitions for "singularity". https://en.wikipedia.org/wiki/Singularity
This is the one mathematicians use:
In mathematics, a singularity is a point at which a given mathematical object is not defined, or a point where the mathematical object ceases to be well-behaved in some particular way, such as by lacking differentiability or analyticity
Example: The equation y = 1/x has a singularity at x=0. Why? The variable y is well defined on all real values of x except when x =0 because division by 0 is not defined.
The Schwarzschild metric has the term (1 - rs/r) in it.
That's undefined at r=0 because there would be a division by 0.
.... and that's really all there is to it.
There is a mathematical singularity in that formula. You can't change that. It's just a statement about the behaviour of a mathemtical term.
What can happen is that another person, often a physicist, comes along and hears something else:
You say: There's a singularity at r=0.
They hear: There's a point in space where density become infinite.
The mathematicians weren't suggesting "the singularity" was viewed as some physical object or even as some point in spacetime. The equations are singular at r=0 and no mathematical trick like a transformation of co-ordinates can remove that singularity. Mathematicians go out of their way to consider the spacetime manifold for the Schwarzschild to be something that specifically excludes the point r=0. Whatever it is, and it may be nothing at all, that thing cannot be included in the same spacetime that I would also be in. It's only a few people, mainly physicists, who decided a spacetime manifold shouldn't just have a hole or puncture in it, they wanted to include r = 0 as some sort of point in spacetime.
Best Wishes.