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Thread: The paradox of Hawking radiation - is matter infinitely compressible?

  1. #1 The paradox of Hawking radiation - is matter infinitely compressible? 
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    The hypothetical Hawking radiation means that a set of baryons can be finally transformed, "evaporate" into a massless radiation - that baryons can be destroyed. It requires that this matter was initially compressed into a black hole.
    If baryons can be destroyed in such extreme conditions, the natural question is: what is the minimal density/heat/pressure required for such baryon number violation? (or while hypothetical baryogensis - creating more baryons than anti-baryons).
    While neutron star collapses into a black hole, event horizon grows continuously from a point in the center, like it this picture from: The Formation and Growth of Black Holes

    As radius of event horizon is proportional to mass inside, the initial density of matter had to be infinity. So if baryons can be destroyed, it should happen before starting the formation of event horizon - releasing huge amounts of energy (complete mc^2) - pushing the core of collapsing star outward - preventing the collapse. And finally these enormous amounts of energy would leave the star, what could result in currently not understood gamma-ray bursts.

    So isn't it true, that if Hawking radiation is possible, then baryons can be destroyed and so black holes shouldn't form?

    We usually consider black holes just through abstract stress-energy tensor, not asking what microscopically happens there - behind these enormous densities ... so in neutron star nuclei join into one huge nucleus, in hypothetical quark star nucleons join into one huge nucleon ... so what happens there when it collapses further? quarks join into one huge quark? and what then while going further toward infinite density in the central singularity of black hole, where light cones are directed toward the center?

    The mainly considered baryon number violation is the proton decay, which is required by many particle models.
    They cannot find it experimentally - in huge room temperature pools of water, but hypothetical baryogenesis and Hawking radiation suggest that maybe we should rather search for it in more extreme conditions?
    While charge/spin conservation can be seen that surrounding EM field (in any distance) guards these numbers through e.g. Gauss theorem, what mechanism guards baryon number conservation? If just a potential barrier, they should be destroyed in high enough temperature ...

    Is matter infinitely compressible? What happens with matter while compression into a black hole?
    Is baryon number ultimately conserved? If yes, why the Universe has more baryons than anti-baryons? If not, where to search for it, expect such violation?
    If proton decay is possible, maybe we could induce it by some resonance, like lighting the proper gammas into the proper nuclei? (getting ultimate energy source: complete mass->energy conversion)
    Is/should be proton decay considered in neutron star models? Would it allow them to collapse to a black hole? Could it explain the not understood gamma-ray bursts?


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    Hey,

    I don`t think there is any particular reason for baryon number to be conserved. In some weak processes I think it`s not. Mathematicaly speaking there is no needed symmetry of standard model lagrangian that would implicate baryon number conservation. Not even CPT symmetry requires this.

    As for proton decay Superkamiokande has put a limit that it`s half life must be greater than something like 10^33 years.

    I don`t think anyone knows what is microscopical nature of black hole matter. Even neutron star model is highly speculative (especialy as you are nearing its core).


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    Hi, I completely agree.
    While Gauss law says that electric field on a closed surface (in any distance) determines charge inside - the whole EM field guards charge conservation (and analogously for spin), there are rather no similar reasons for conservation of other numbers(?), like for leptons of baryons.
    If so, what holds them together is just a potential barrier of their structure - they are some local energy minimums. Energy barriers can be thermodynamically "tunneled" through in high enough temperatures, like maybe of the center of neutron star - it is where I would look for this violation, not in pools of room temperature water as they do.

    But the main question is if black holes can even form, as before getting to infinite density required to start forming the event horizon, they should start burning baryons in the center? (releasing bursts of high energy radiation)
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    Quote Originally Posted by Jarek Duda View Post
    But the main question is if black holes can even form, as before getting to infinite density required to start forming the event horizon, they should start burning baryons in the center? (releasing bursts of high energy radiation)
    Infinite density is not required to start forming the event horizon. The event horizon emerges at the Schwarzschild radius when the matter of the star gravitationally collapses within that radius. Once that happens, you have a black hole - infinite density is not required, it is just the predicted end result when using GR, which is generally accepted to have been pushed beyond its limitations at the singularity, but not at the Schwarzschild radius.

    If black holes cannot form, then what is that optically invisible thing in Sgr A* at the centre of our galaxy that we have watched stars orbiting for over 16 years, where those stars orbit in such a way as to imply they are orbiting an invisible something that is relatively small but with the mass of over 4 million Suns??

    http://www.universetoday.com/22104/b...of-our-galaxy/
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    I don`t know anything about GR or forming of black holes so I can`t help with that. I can help a bit with some other things though.

    Some quantum number must be conserved some are usually conserved. Those that must be conserved are electric and color charge and weak isospin (coming from gauge invariance) and energy, momentum and angular momentum (coming from Poincare invariance). Other numbers like flavor, baryon, lepton number, parity, CP must not be explicitly conserved and their conservation "laws" usualy break in weak interactions.

    I think maybe you misinterpret baryon number. Baryon number is bound to number of quarks not number of baryons. In some extreme conditions like you say center of neutron star two protons collide they for sure can be "destroyed" but this is not decay nor it violates baryon number. Same things happen in LHC basicaly. Two protons collide and create a lot of mess that doesn`t mean that it violates baryon number. Every quark has baryon number 1/3 and every antiquark -1/3. In proton-proton scattering you can among other things create a lot of mesons (quark antiquark pair) but these have baryon number 0 so this doesn`t violate baryon number conservation. It these conditons many high energy processes would cover those few that may violate baryon number conservation.

    So you must distinguish between decay (of basicaly free particle) and scattering that "destroys" the particle but uphold conservation law. There are four main channels through which proton decay may happen: positron 2 gamma decay, antimuon 2 gamma decay (both through virtual pion), and 2 channels of decay into some types of kaon and neutrino (that needs some new speculative bosons). In SKK they look for signs of antimuons or positrons that based on shielding shouldn`t be there and may come from decay of proton inside.
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    SpeedFreak, in materials I could find, like where the picture above was taken from, or this paper there is used looking natural assumption for physical entities: that they should evolve in continuous way, and so horizon had to start with R=0 in the center of neutron star and then evolve to get out of the surface.
    Could you explain, support your claim for discontinuous "emergence" of horizon in nonzero radius?

    About Sagittarius A* ( Sagittarius A* - Wikipedia, the free encyclopedia ), the current observations allows to bound its density from below only by 0.0066 kg/m^3, what is not extremely convincing that it just has to be a black hole with singularity in the center ....
    I would rather focus on observed but not explained gamma-ray bursts ... they have no idea what mechanisms could be behind such huge amounts of energy ... while proton decay: complete matter->energy conversion, provides a natural answer - that massive neutron stars begin another stage of evolution: baryon burning ...

    Gere, sure producing lots of baryon-antibaryon pairs does not violate the baryon number conservation law. But proton decay, black hole "evaporation" and baryogenesis do.
    Any scenario of proton decay we would assume, in the center of neutron star it would result in just huge energy release: about 1GeW per baryon, mostly in gammas.
    Last edited by Jarek Duda; September 21st, 2013 at 06:27 PM.
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    I would suggest you read

    [astro-ph/9801252] Black Holes : A General Introduction

    In particular read section 2.2 - Spherical Collapse, the contents of which are illustrated in figure 4, which

    shows the complete history of the collapse of a spherical star, from its initial contraction until the formation of a black hole and a singularity. Two space dimensions are measured horizontally, and time is on the vertical axis, measured upwards.
    As you can see, as the surface of the star collapses the event horizon emerges at r = 2M (the Schwarzschild radius) before the surface reaches the singularity.

    The curvature of spacetime is visualized by means of the light cones generated by the trajectories of light rays. Far away from the central gravitational field, the curvature is so weak that the light cones remain straight. Near the gravitational field, the cones are distorted and tilted inwards by the curvature. On the critical surface of radius r = 2M, the cones are tipped over at 45◦ and one of their generators becomes vertical, so that the allowed directions of propagation of particles and electromagnetic waves are oriented towards the interior of this surface. This is the event horizon, the boundary of the black hole (grey region). Beyond this, the stellar matter continues to collapse into a singularity of zero volume and infinite density at r = 0.
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    It makes perfect sense, by the way. The event horizon is simply the radius where the escape velocity is c, and this only requires a finite density of matter within a given radius - it certainly doesn't require the infinite density of a singularity for the escape velocity to be c.

    Think of it like this - once you have enough mass in a small enough area, there will be a radius where the escape velocity is c. THAT is the event horizon, that radius. It makes no sense to say the event horizon comes out from the singularity itself (which might not even exist), all you need is a dense enough mass to produce enough gravity for light not to be able to escape at a given distance from that mass.
    Last edited by SpeedFreek; September 21st, 2013 at 07:03 PM.
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    So instead of emerging horizon from middle you would see less and less light from increasingly smaller spatial angle until you see nothing at all? Btw would that light be strongly red shifted?
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    Quote Originally Posted by Jarek Duda View Post
    Gere, sure producing lots of baryon-antibaryon pairs does not violate the baryon number conservation law. But proton decay, black hole "evaporation" and baryogenesis do.
    Any scenario of proton decay we would assume, in the center of neutron star it would result in just huge energy release: about 1GeW per baryon, mostly in gammas.
    Proton in centre of neutron star wouldn`t decay as it would be participating in endless chain of scatterings (same as for example neutron in nucleus won`t decay). Sure baryogenesis violate conservation law but we agreed that baryon conservation law is no law at all. I`m not sure about that black hole though. I think that basic idea is that particle antiparticle pair is produced near event horizon with one particle entering and other escaping but that wouldn`t violate it either as one particle/antiparticle will be present in black hole. Correct me if I`m wrong with this. I never much looked into black hole evaporation. Currently baryon number violation is known only in some weak interactions.
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    SpeedFreek, the only I see is that this paper does not focus on the problem of formation of event horizon - it is just an introductory paper focusing only on standard situation when horizon is already outside, so there is shown picture not to disturb the reader.
    Is there explicitely written that indeed event horizon does not travel inside, but just discontinously emeges in nonzero radius?
    Sources I have provided focused also on the relevant here situation - before emerging from the horizon...

    So how exactly would you define the moment of event horizon formation? When all mass is inside and then pooof - horizon appears?
    Could you define this mass-nomass boundary more precisely, as there is still a lot of mass outside?
    What if someone would make a deep hole in the star - would he see light from its bottom until the horizon gets out of the whole surface, or maybe the horizon in the hole would move toward him?
    This "hole" in practice is vauum between particles ...

    Gere,
    I am not sure what you mean by "endless chain of scatterings"? Energy usually finds its way to get out of the center of a star - sure there would be a lot of scettering, but statistically this energy should finally leave.
    I imagine that star would start collapsing, finally creating conditions for baryon decay in the center - the initial explosion locally increases temperature, starting larger explosion - but thermodynamically there is some limit of its size, so finally this explosion burns out - preventing the collapse, releasing lots of this energy and decreasing mass of the star.

    The hypothetical Hawking radiation is indeed pair creation just above the horizon - one particle gets inside, while the other has high enough energy to escape. All sources I have seen emphasize that they have to be massless, as escape distance for massive particles would be further.
    Last edited by Jarek Duda; September 21st, 2013 at 07:53 PM.
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    Quote Originally Posted by Gere View Post
    So instead of emerging horizon from middle you would see less and less light from increasingly smaller spatial angle until you see nothing at all? Btw would that light be strongly red shifted?
    Well as I understand it the posited physical process is that the star runs out of fuel to burn in its core and the sudden lack of pressure there causes it to gravitationally collapse. As the outer layers of the star collapse into a smaller area the gravity at the collapsing surface increases until the escape velocity reaches c and light can't escape. At that radius the event horizon (where light cannot escape) emerges as the star collapses within it.

    I think what a distant observer would see is the star start to collapse and get smaller and smaller. As the surface collapses towards the Schwarzschild radius the light from that surface becomes increasingly redshifted until, as the surface passes within that radius, the light cannot escape (redshift goes to infinity). Or something like that, anyway.
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    So how exactly would you define the moment of event horizon formation?
    It's the moment that the escape velocity of any area of space equals c.
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    SpeedFreek, but appears where?
    The density of neutron star decreases near the surface, and there is still a lot of matter outside ... in which radius/density does it emerge?

    Let us assume for a moment that there is hole to the center of the star - when you would stop seeing light from the bottom of this hole?
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    Quote Originally Posted by Jarek Duda View Post
    Gere,
    I am not sure what you mean by "endless chain of scatterings"? Energy usually finds its way to get out of the center of a star - sure there would be a lot of scettering, but statistically this energy should finally leave.
    I imagine that star would start collapsing, finally creating conditions for baryon decay in the center - the initial explosion locally increases temperature, starting larger explosion - but thermodynamically there is some limit of its size, so finally this explosion burns out - preventing the collapse, releasing lots of this energy and decreasing mass of the star.
    I meant that proton will not decay in such conditions. Proton in vacuum at rest may very well decay after some time but if you put it into such dense system it will be in constant interaction with other particles in vicinity effectively preventing any decay. Neutrons in neutron star will not decay either as they don`t decay in nucleus. With increasing temperature you will only make matters worse as you will increase rate of interactions. Proton in neutron star simply won`t decay into positron and 2 gamma. It will probably do a lot of other things bouncing around switching into neutron and back creating small jets but no decay (especialy not one with half life over the age of universe).
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    Quote Originally Posted by Jarek Duda View Post
    Let us assume for a moment that there is hole to the center of the star - when you would stop seeing light from the bottom of this hole?
    If I understand it correctly its like this. Imagine you have giant spyglass from surface to center of collapsing star. During formation of BH and increasing density in the core you would see red shifted light coming from smaller and smaller spatial angle until you would see just red dot in the middle and then nothing. Thats the moment when density is sufficient and BH created. It`s not like horizont comming from middle. It`s like its given by mass but you don`t see it as horizon until density is sufficient you just see consequences of increasing escape velocity as smaller and smaller spatial angle through which light can propagate to you until it`s zero. Thats how I understand it though.
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    Quote Originally Posted by Jarek Duda View Post
    SpeedFreek, but appears where?
    At the radius where the escape velocity equals c, as we keep saying.

    The density of neutron star decreases near the surface, and there is still a lot of matter outside ... in which radius/density does it emerge?
    A neutron star, by definition, has no event horizon. And as it is already degenerate matter, I don't see how it could suddenly become denser and turn into a black hole, for a star to do that you need the "cascading" effect of gravitational collapse due to a reduction of pressure inside.

    I repeat - you need the matter of a star to be within its own Schwarzschild radius for an event horizon to form. The Schwarzschild radius is the distance from the origin where the escape velocity would be c if all the matter of that star were inside that radius. In the case of the Sun, for instance, the Schwarzschild radius is ~3km. If ALL the matter of the Sun were suddenly compressed to within a radius of 3 km, the escape velocity would be c at that radius. An event horizon would form at that radius, because the surface gravity at that radius would mean an escape velocity of c and that would only happen when the surface of the Sun collapsed within that radius. I don't know how many more ways to put it.

    Quote Originally Posted by Jarek Duda View Post
    Let us assume for a moment that there is hole to the center of the star - when you would stop seeing light from the bottom of this hole?
    This question makes no sense to me. A star cannot suddenly become denser in the centre unless the outer layers collapse inwards for some reason.
    Last edited by SpeedFreek; September 21st, 2013 at 08:49 PM.
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    Gere, neutrons don't decay in nucleus ... don't beta decay. In neutron star there is some thermodynamical equilibrium of neutrons, protons and electrons.
    To get thermodynamical equilibrium for very different: proton decay, you would need that such gammas would often create a new baryon. Sure, there might be also such events, but energy disperse and finally gammas would escape through the surface. As the world outside the star is colder, eventual metastable equilibrium of baryon decay-production would lose energy through the surface.

    About the "hole to the center of neutron star", I have to admit that I don't understand why you think that I would see only a point in the center - the deepest one?
    I would say that the horizon - limit where I can see, would grow while the star collapses: the central part grow in density.
    So the first I would stop seeing would be the center, and the "black level" in the hole would move toward me.
    Of course there would be also red-shift: the closer to the horizon, the stronger.

    SpeedFreek,
    I know the definition of event horizon - I am asking where in neutron star do you think it emmerges?
    If there would be a hole to the center of neutron star, in which level of this hole it would emmerge?
    Maybe you could finally just provide some sources showing that event horizon does not have to behave in continuous way?
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    Quote Originally Posted by Jarek Duda View Post
    SpeedFreak, in materials I could find, like where the picture above was taken from, or this paper there is used looking natural assumption for physical entities: that they should evolve in continuous way, and so horizon had to start with R=0 in the center of neutron star and then evolve to get out of the surface.
    Can you show me exactly where, in the article the picture was taken from or in that paper, it says the horizon had to start with r=0 in the centre and then evolve to get out of the surface? I ask since they seem to be saying the same thing I am saying. That picture, by the way, seems to be referring to infalling particles accreting onto the black hole and causing the event horizon to expand outwards.
    Last edited by SpeedFreek; September 21st, 2013 at 09:14 PM.
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    Quote Originally Posted by Jarek Duda View Post
    SpeedFreek,
    I know the definition of event horizon - I am asking where in neutron star do you think it emmerges?
    If there would be a hole to the center of neutron star, in which level of this hole it would emmerge?
    And I am saying a neutron star has no event horizon. It has a Schwarzschild radius - a radius where, if all the matter of the neutron star would somehow collapse within that radius, an event horizon would emerge as the surface passed within that radius. So the answer is the surface, once the neutron star has collapsed. Unless, that is, you can propose a method where the interior of a neutron star becomes denser whilst the outer layers stay where they are.
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    SpeedFreek, imagine there is a hole to the center of neutron star - like in the picture below, but can be a small hole.
    So you can see all its layers and the deeper one, the more gravity light had to fight with to get to you - the deeper layer, the stronger red-shift you see.
    As physics is continuous, the strength of this red-shift have to behave in a continuous way.
    In one moment its strenth is larger then light can handle - it means that this part gets below the event horizon ... because of monotonicity, mathematically it just had to be the center first!

    If this explanation is not enough for you, I just give up and wait for some sources that it doesn't have to behave in a continuous way. Anyway, goodnight.

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    Quote Originally Posted by Jarek Duda View Post
    But proton decay, black hole "evaporation" and baryogenesis do.
    Hawking radiation does not violate baryon number conservation at all. Where did you get that idea ?

    the problem of formation of event horizon
    There is no "problem" associated with this - where exactly do you see an issue ?

    So how exactly would you define the moment of event horizon formation? When all mass is inside and then pooof - horizon appears?
    The "moment of formation" depends on the observer; there is no universal notion of time here. One might naively say that the horizon has formed at such time when all observers located behind it have a singularity in their future. This is always a local notion though.

    The hypothetical Hawking radiation is indeed pair creation just above the horizon
    We are usually talking fermion pairs, such as a photons decaying into an electron and a positron.

    All sources I have seen emphasize that they have to be massless, as escape distance for massive particles would be further.
    Can you provide a specific example of a process where a particle decays into a massless particle + anti-particle pair, because I sure can't think of any. I'd dearly like to see those "sources" you mention.

    I know the definition of event horizon - I am asking where in neutron star do you think it emmerges?
    It emerges at the point where, during the collapse, all world-lines first end at the singularity. This may or may not be in the interior, depending on the dynamics of the gravitational collapse.

    because of monotonicity, mathematically it just had to be the center first!
    "Monotonicity" is not even a word, and mathematically no such thing follows at all. If you think otherwise, please show us your maths.

    If this explanation is not enough for you, I just give up and wait for some sources that it doesn't have to behave in a continuous way
    It obviously doesn't, this is trivial. At the instance when all observers within a region of space-time have a singularity in their future, their is already a non-zero mass enclosed within that region; this means the event horizon forms spontaneously, and with a non-zero radius, or else it wouldn't be an event horizon. The notion of an event horizon with r=0 makes no sense, it's like wondering what is north of the north pole.
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    Quote Originally Posted by Markus Hanke View Post
    So how exactly would you define the moment of event horizon formation? When all mass is inside and then pooof - horizon appears?
    The "moment of formation" depends on the observer; there is no universal notion of time here. One might naively say that the horizon has formed at such time when all observers located behind it have a singularity in their future. This is always a local notion though.
    Actually, from the perspective of an external observer, the event horizon never forms.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Jarek.

    An event horizon is an apparent (and observer dependent) horizon that arises due to light not being able to escape. It arises when you get a certain finite density within a finite (non-zero) area. As soon as you have enough mass within a small enough region, you get an escape velocity of c at the edge of that region.

    At the moment when there is enough mass in a small enough space, the event horizon forms at the edge of that space. As more mass comes into that region, the radius where the escape velocity is c becomes larger, so the event horizon moves outwards as more matter accretes. But as Markus says, it makes no sense to consider an event horizon at r=0 - it will already have formed at a larger radius.

    There is no point within a neutron star where gravitational redshift is infinite - there is no event horizon. If something were to happen in the interior of a neutron star that caused a certain region to become dense enough for an event horizon to form and the neutron star to collapse into a black hole, the event horizon would form at the edge of that certain region, not the centre.
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    Quote Originally Posted by KJW View Post
    Actually, from the perspective of an external observer, the event horizon never forms.
    Yes, that's true, and illustrates my point further - it's all observer dependent.
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    Quote Originally Posted by KJW View Post
    Quote Originally Posted by Markus Hanke View Post
    So how exactly would you define the moment of event horizon formation? When all mass is inside and then pooof - horizon appears?
    The "moment of formation" depends on the observer; there is no universal notion of time here. One might naively say that the horizon has formed at such time when all observers located behind it have a singularity in their future. This is always a local notion though.
    Actually, from the perspective of an external observer, the event horizon never forms.
    Is that an external observer at infinity? What about an observer at rest at a certain finite distance? Or an external but in-falling observer?
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    Jarek Duda, you yourself said in the opening post that for the event horizon to form at the centre, the density has to be infinite there. This itself contradicts the notion that the event horizon grows outward from the centre. You mention continuity of physics, but the event horizon is not a physical notion and cannot be defined by local properties of the spacetime. The event horizon is a global notion defined by the transition between light being able to escape to infinity and light not being able to escape to infinity, a discontinuous notion.
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    Quote Originally Posted by SpeedFreek View Post
    Is that an external observer at infinity? What about an observer at rest at a certain finite distance? Or an external but in-falling observer?
    For any of these, light originating at the event horizon is infinitely red-shifted. For the in-falling observer the event horizon is in the future ( he will fall through it ).
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by KJW View Post
    Actually, from the perspective of an external observer, the event horizon never forms.
    Is that an external observer at infinity? What about an observer at rest at a certain finite distance? Or an external but in-falling observer?
    It doesn't require the observer to be at infinity. The observer can be at rest relative to the blackhole at any finite distance from it. However, it's not true for the in-falling observer (my statement assumed that the observer remained forever outside the event horizon).
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    I have to admit that I'm somewhat of a blackhole skeptic. This is based on a general "feeling" that things are not quite right, and not on anything specific that I can point to and say is wrong. Nevertheless, I do acknowledge that to form a blackhole, it is sufficient to bring a large enough mass into a small enough space, and in particular that this does not require the density to be especially high if the total mass is large enough. This rules out "irresistible force / immovable object" type mechanisms for preventing blackhole formation.
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    Quote Originally Posted by KJW View Post
    Jarek Duda, you yourself said in the opening post that for the event horizon to form at the centre, the density has to be infinite there. This itself contradicts the notion that the event horizon grows outward from the centre. You mention continuity of physics, but the event horizon is not a physical notion and cannot be defined by local properties of the spacetime. The event horizon is a global notion defined by the transition between light being able to escape to infinity and light not being able to escape to infinity, a discontinuous notion.
    Indeed, so look at my answer with big neutron star picture - I am asking about light trying to escape from different depths inside the star (assuming there is no other obstacle on the way - assuming a hole).
    The deeper - closer to the center, the more difficult to escape gravity - not true?
    So if in one moment it will be no longer able to escape, such region just had to start in the center - not true?
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    Quote Originally Posted by Markus Hanke View Post
    Can you provide a specific example of a process where a particle decays into a massless particle + anti-particle pair, because I sure can't think of any. I'd dearly like to see those "sources" you mention.
    Higgs, pions decays through three-vertex fermionic loop into two gammas but thats just off topic.

    What is not off topic is that proton will simply not decay into positron and two gamma in neutron star. For that you will need proton free of all interaction at rest for more that 1^34 years. Even if this decay is possible it has no chance of ever happening in these conditions. Proton may be in neutron star annihilated various other ways in some scatterings creating kaons, pions etc. but these processes don`t violate baryon number conservation. Amplitudes for nonviolating processes are simply too great for violating decay to ever happen.

    I am a bit unclear on some things relatvists said here. You say that external observer never sees horizon? This is strange, what would we see close to black hole?

    Lets have a strong light bulb in transparent material. This all has some Schwardschild radius which is not yet event horizon. If we increase density and decrease volume correspondingly what happens? I understand it as event horizon starts forming at that Schwardshild radius. Instead of seeing lightbulb radiate in all direction the spatial angle trough which light can propagate to me is smaller and smaller until I see just a small light cone coming from bulb. After I see nothing event horizon forms. But I don`t understand how external observer never sees it. Why wouldn`t he?
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    Quote Originally Posted by Jarek Duda View Post
    The deeper - closer to the center, the more difficult to escape gravity - not true?
    I don`t think this is true. Such light may be just a bit more red shifted but has no effect on escape velocity.
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    Quote Originally Posted by Jarek Duda View Post
    Quote Originally Posted by KJW View Post
    Jarek Duda, you yourself said in the opening post that for the event horizon to form at the centre, the density has to be infinite there. This itself contradicts the notion that the event horizon grows outward from the centre. You mention continuity of physics, but the event horizon is not a physical notion and cannot be defined by local properties of the spacetime. The event horizon is a global notion defined by the transition between light being able to escape to infinity and light not being able to escape to infinity, a discontinuous notion.
    Indeed, so look at my answer with big neutron star picture - I am asking about light trying to escape from different depths inside the star (assuming there is no other obstacle on the way - assuming a hole).
    The deeper - closer to the center, the more difficult to escape gravity - not true?
    So if in one moment it will be no longer able to escape, such region just had to start in the center - not true?
    But whether or not an event horizon forms at some distance from the centre depends on the total mass inside the corresponding sphere (Birkhoff's theorem). Thus, you're not going to get an event horizon forming near the centre because there is little mass there, and its easier to form the event horizon at greater distances due to greater total mass and lower required average density.
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    Quote Originally Posted by Gere View Post
    I don`t think this is true. Such light may be just a bit more red shifted but has no effect on escape velocity.
    So where is the limit of red-shift? When red-shifts (wavelengths) grow to infinity and in one moment you just stop seeing the object - isn't it exactly the moment of getting below the event horizon?
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    Quote Originally Posted by KJW View Post
    But whether or not an event horizon forms at some distance from the centre depends on the total mass inside the corresponding sphere (Birkhoff's theorem). Thus, you're not going to get an event horizon forming near the centre because there is little mass there, and its easier to form the event horizon at greater distances due to greater total mass and lower required average density.
    So what would we observe looking inside such hole?
    I would say that we would see red-shift growing toward the center. So if in some moment red-shift would grow to infinity somewhere, it had to be the center first - not true?

    Indeed it requires infinite density in the center first ... but it is only one of maaany infinites related with black holes. E.g. in their central point spacetime is no longer even a manifold ...

    This sharp point is out of any physics we know - not even GRT can say anything about it as spacetime is no longer a manifold there. To start forming a black hole, you need to start with forming this sharp point first ...
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    Quote Originally Posted by Gere View Post
    I am a bit unclear on some things relatvists said here. You say that external observer never sees horizon? This is strange, what would we see close to black hole?
    The simplest way to view it is to consider that the light at the event horizon can never travel outwards from the event horizon, and therefore can never reach an external observer, no matter how close. It means that the past lightcone from any external observer has lightrays entirely outside the event horizon.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by Jarek Duda View Post
    Quote Originally Posted by Gere View Post
    I don`t think this is true. Such light may be just a bit more red shifted but has no effect on escape velocity.
    So where is the limit of red-shift? When red-shifts (wavelengths) grow to infinity and in one moment you just stop seeing the object - isn't it exactly the moment of getting below the event horizon?
    Yeah I am guessing here a bit but red shift isn`t dominant effect. Dominant is that null geodesics not longer heads outward from event horizon.
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    Quote Originally Posted by Gere View Post
    Higgs, pions decays through three-vertex fermionic loop into two gammas
    Yes, but that's not a particle-antiparticle pair for the purpose of forming Hawking radiation.
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    Quote Originally Posted by Jarek Duda View Post
    So what would we observe looking inside such hole?
    Just a region of space-time which is entirely black and without any structure. That is why it is called a black hole.

    So if in some moment red-shift would grow to infinity somewhere, it had to be the center first - not true?
    No, not true. Not sure why you would think that.

    Indeed it requires infinite density in the center first
    No it doesn't.

    To start forming a black hole, you need to start with forming this sharp point first
    It's exactly the other way around - a gravitational collapse starts with "normal" matter, and ends with a singularity. The event horizon is there before any singularity forms.
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    Quote Originally Posted by KJW View Post
    This is based on a general "feeling" that things are not quite right, and not on anything specific that I can point to and say is wrong.
    The picture isn't wrong, it is just incomplete. There is no way to tell yet exactly what happens if quantum effects are properly accounted for; in fact I'll eat my hat if we still end up a with a singularity prediction. I view black holes simply as the highest state of matter degeneracy, so what goes in "in there" will depend on the fundamental nature of matter. If I was to take a wild guess I'd say it will ultimately boil down to the topology and/or geometry of space-time itself on micro scales. It is almost certain that this will not involve regions of infinite density and curvature.
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    Quote Originally Posted by Jarek Duda View Post
    Quote Originally Posted by KJW View Post
    But whether or not an event horizon forms at some distance from the centre depends on the total mass inside the corresponding sphere (Birkhoff's theorem). Thus, you're not going to get an event horizon forming near the centre because there is little mass there, and its easier to form the event horizon at greater distances due to greater total mass and lower required average density.
    So what would we observe looking inside such hole?
    I would say that we would see red-shift growing toward the center. So if in some moment red-shift would grow to infinity somewhere, it had to be the center first - not true?

    Indeed it requires infinite density in the center first ... but it is only one of maaany infinites related with black holes. E.g. in their central point spacetime is no longer even a manifold ...

    This sharp point is out of any physics we know - not even GRT can say anything about it as spacetime is no longer a manifold there. To start forming a black hole, you need to start with forming this sharp point first ...
    The redshift is total at the event horizon. Inside the event horizon the -coordinate becomes timelike and the -coordinate becomes spacelike, so one can't think of the inside of a blackhole the same way as the outside of a blackhole.

    Suppose one had a spherical mass distribution of uniform density. Suppose this is compressed such that the density remains uniform throughout but increasing over time. When the outermost surface crosses the Schwarzschild radius for the total mass, the event horizon forms at the outermost surface. It can't form anywhere inside the distribution because the mass inside the corresponding sphere is too small (the mass is proportional to , but the Schwarzschild radius is proportional to the mass). While the assumption the uniform density is unrealistic, it does illustrate how the event horizon can form at the outermost surface without originating from the centre or anywhere inside the mass distribution.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Jarek Duda View Post
    So what would we observe looking inside such hole?
    Just a region of space-time which is entirely black and without any structure. That is why it is called a black hole.
    The question was about a hole toward the center of neutron star, just before forming the black hole.
    So for neutron star you should see its center, for black hole you don't see through the surface of event horizon - but what happens between?

    KJW,
    let us focus on the moment of forming the event horizon - how would red-shifts evolve if you could see all internal layers of neutron star?
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    Quote Originally Posted by Jarek Duda View Post
    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Jarek Duda View Post
    So what would we observe looking inside such hole?
    Just a region of space-time which is entirely black and without any structure. That is why it is called a black hole.
    The question was about a hole toward the center of neutron star, just before forming the black hole.
    So for neutron star you should see its center, for black hole you don't see through the surface of event horizon - but what happens between?
    You will continuously see less and less light. But not through effect of red shift but throuh increasingly smaller "number" of null geodesics connecting you and core of star.
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    Quote Originally Posted by Jarek Duda View Post
    KJW,
    let us focus on the moment of forming the event horizon - how would red-shifts evolve if you could see all internal layers of neutron star?
    You would always see the inside of the neutron star and its centre would become increasingly redshifted, but at no time in your future (provided you remain outside the Schwarzschild radius) will you ever see the redshift become total, meaning that you'll never actually see the event horizon forming.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by Gere View Post
    You will continuously see less and less light. But not through effect of red shift but throuh increasingly smaller "number" of null geodesics connecting you and core of star.
    Ok, now I understand why you have said that the last what we would see is the point in the center - because only photons from there could travel perpendicularly to the surface.
    So let us assume that the hole is a cone: widens to exterior, such that from each radius photons can travel perpendicularly to the surface.
    Still the deeper they come from, the more gravity they have to overcome - so isn't the center the first place from where we will stop seeing any photons?
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    Quote Originally Posted by KJW View Post
    You would always see the inside of the neutron star and its centre would become increasingly redshifted, but at no time in your future (provided you remain outside the Schwarzschild radius) will you ever see the redshift become total, meaning that you'll never actually see the event horizon forming.
    So isn't the center the first place where the redshift would grow to infinity - light would stop coming from there?
    Doesn't it meant that this place is below the event horizon?
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    Quote Originally Posted by Jarek Duda View Post
    Quote Originally Posted by KJW View Post
    You would always see the inside of the neutron star and its centre would become increasingly redshifted, but at no time in your future (provided you remain outside the Schwarzschild radius) will you ever see the redshift become total, meaning that you'll never actually see the event horizon forming.
    So isn't the center the first place where the redshift would grow to infinity - light would stop coming from there?
    Doesn't it meant that this place is below the event horizon?
    Think about the consequences of (omitting proportionality constants):

    and , therefore

    Now, for only one (non-zero) value of , with at larger values of . What this means is that if the event horizon is at some location inside the mass distribution, then the mass outside that event horizon would place the event horizon at a greater radius, ultimately placing the event horizon at the outermost surface.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Yup. It's what I have been saying all along and I don't understand why it is such a problem for Jarek.
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    Indeed, it requires that density is infinite there - that is exactly my point: any finite conditions have to be exceeded before start forming the horizon, so if baryons are destructible - they have to be destroyed before.
    Density in the central point of black hole cannot be finite:

    You have forgotten the density here:
    and , therefore
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    Rubbish. Go back to what I said in post #4 and think it through.
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    Quote Originally Posted by Jarek Duda View Post
    Indeed, it requires that density is infinite there - that is exactly my point: any finite conditions have to be exceeded before start forming the horizon, so if baryons are destructible - they have to be destroyed before.
    No, that's wrong. Their density simply has to exceed a certain limit, at which point the event horizon forms and the gravitational collapse becomes inevitable. However, the collapse itself takes a finite amount of ( proper ) time, during which the event horizon already exists, even if there isn't a singularity yet.
    It remains to be noted that baryons would cease to exist long before that - the state of matter immediately preceding a collapse would be ( according to current understanding ) something called a quark-gluon plasma, i.e. a plasma of asymptotically free quarks and gluons at extremely high temperatures and pressures. No baryons would exist under these conditions at all.
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    Quote Originally Posted by Jarek Duda View Post
    and , therefore
    This is meaningless, because a black hole is not a solid, isotropic sphere of matter. Even if it was, the above formulas are valid only in flat Euclidean 3-space, which is not what we are dealing with in the vicinity of a black hole.
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Jarek Duda View Post
    Indeed, it requires that density is infinite there - that is exactly my point: any finite conditions have to be exceeded before start forming the horizon, so if baryons are destructible - they have to be destroyed before.
    No, that's wrong. Their density simply has to exceed a certain limit, at which point the event horizon forms and the gravitational collapse becomes inevitable. However, the collapse itself takes a finite amount of ( proper ) time, during which the event horizon already exists, even if there isn't a singularity yet.
    Exactly.
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    If you want believe in black holes, you have to cope with that singularities/infinities are their essential parts.
    The curvature is infinity in the center - when exactly it gets there? Not in the moment of starting forming the horizon?
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    Quote Originally Posted by Jarek Duda View Post
    Indeed, it requires that density is infinite there - that is exactly my point: any finite conditions have to be exceeded before start forming the horizon
    No. Reread what I said in post #42.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by Jarek Duda View Post

    This sharp point is out of any physics we know - not even GRT can say anything about it as spacetime is no longer a manifold there. To start forming a black hole, you need to start with forming this sharp point first ...
    This where you keep going wrong and repeating it won't change that.

    The "sharp point" is the predicted end result using GRT, AFTER the event horizon has formed at the Schwarzschild radius. We keep telling you this. The "general introduction" paper I linked earlier tells you this. The article and the paper you linked also tell you this. The singularity at r = 0, if it exists, forms at a finite proper time after the event horizon forms at r = 2M.

    The black hole exists once you have an event horizon, regardless of whether there is a singularity or not.
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    Quote Originally Posted by Jarek Duda View Post
    If you want believe in black holes, you have to cope with that singularities/infinities are their essential parts.
    The curvature is infinity in the center - when exactly it gets there? Not in the moment of starting forming the horizon?
    It is you who obviously doesn't want to believe in black holes. You aren't even reading the contents of your own links about them, let alone anyone elses.
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    The deeper - closer to the center, the more difficult to escape gravity - not true?
    Not true. See the Shell Theorem.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

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    Quote Originally Posted by Jarek Duda View Post
    If you want believe in black holes, you have to cope with that singularities/infinities are their essential parts.
    Not true. The prediction that there is a singularity at its centre relies on two assumptions :

    1. There are no quantum effects which need to be considered
    2. Space-time is torsion-free everywhere

    We already know that (1) is unphysical, because quantum effects do play a role here; it is just that in the absence of a consistent model for quantum gravity we don't know exactly what that role is. As for (2) - this relies on the fact that we are using the Levi-Civita connection in GR, but there is at least a possibility that some other model ( for example Einstein Cartan gravity, or teleparallelism ) describes the universe more accurately. The jury is still out on that, but we know that if there is torsion in space-time, then singularities will not form.

    Everything considered, I think we are reasonably sure that black holes do indeed exist ( the observational evidence and theoretical understanding is quite overwhelming in that regard ), but we would not expect the singularity at its centre to be physical.
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    Quote Originally Posted by Markus Hanke View Post
    Their density simply has to exceed a certain limit, at which point the event horizon forms and the gravitational collapse becomes inevitable.
    This statement is misleading for it suggests that it's the density that determines whether or not an object is a blackhole. While it is true for an object of a given mass, the critical density depends on the mass, decreasing with mass. This is why one can't invoke stronger resistance forces to prevent blackhole formation.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by SpeedFreek View Post

    This where you keep going wrong and repeating it won't change that.

    The "sharp point" is the predicted end result using GRT, AFTER the event horizon has formed at the Schwarzschild radius. We keep telling you this. The "general introduction" paper I linked earlier tells you this. The article and the paper you linked also tell you this. The singularity at r = 0, if it exists, forms at a finite proper time after the event horizon forms at r = 2M.

    The black hole exists once you have an event horizon, regardless of whether there is a singularity or not.
    That's precisely what I said too, but he just keeps ignoring all the points being made.
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    Ok, I give up this discussion for today. Let us take a break and talk in a few days.
    Please just think what would you see from an empty cone toward the center of collapsing nuetron star - which part would you stop seeing first?
    Also think about intristic spacetime curvature of the central point - it is finite for neutron star, infinite for black hole (having event horizon) - what is the last moment when it is finite/the first when it is infinite?
    Also maybe find a source supporting claim that event horzion does not have to behave in a continuous way ...
    Best,
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    Quote Originally Posted by KJW View Post
    This statement is misleading for it suggests that it's the density that determines whether or not an object is a blackhole. While it is true for an object of a given mass, the critical density depends on the mass, decreasing with mass. This is why one can't invoke stronger resistance forces to prevent blackhole formation.
    True of course, sorry for having been sloppy and inaccurate. I rushed this post a little...
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    Quote Originally Posted by Jarek Duda View Post
    Please just think what would you see from an empty cone toward the center of collapsing nuetron star - which part would you stop seeing first?
    The event horizon.

    what is the last moment when it is finite/the first when it is infinite?
    That question makes little to no sense; the moment you determine the central point to have infinite curvature is when you are right in it. If you are outside the event horizon, you cannot tell what happens at or beyond the horizon, because that region of space-time is not causally connected to you. This has been pointed out several times now.

    Also maybe find a source supporting claim that event horzion does not have to behave in a continuous way ...
    This does not need any source, because it is trivial and has already been explained to you. Your claim on the other hand definitely requires a citation.
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by KJW View Post
    This statement is misleading for it suggests that it's the density that determines whether or not an object is a blackhole. While it is true for an object of a given mass, the critical density depends on the mass, decreasing with mass. This is why one can't invoke stronger resistance forces to prevent blackhole formation.
    True of course, sorry for having been sloppy and inaccurate. I rushed this post a little...
    I figured it was an important correction to make, given the context of this thread.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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    Quote Originally Posted by Jarek Duda View Post
    Ok, I give up this discussion for today. Let us take a break and talk in a few days.
    Please just think what would you see from an empty cone toward the center of collapsing nuetron star - which part would you stop seeing first?
    Also think about intristic spacetime curvature of the central point - it is finite for neutron star, infinite for black hole (having event horizon) - what is the last moment when it is finite/the first when it is infinite?
    Also maybe find a source supporting claim that event horzion does not have to behave in a continuous way ...
    Best,
    Jarek
    I give up too. You definitely aren't reading the paper I posted or the paper you posted. There is the source.

    Also, an observer outside the body in question, looking in, is observing the apparent or coordinate time, rather than the proper time according to a particle at the radius in question. These notions of time are not the same.
    Last edited by SpeedFreek; September 22nd, 2013 at 10:45 AM.
    "Ok, brain let's get things straight. You don't like me, and I don't like you, so let's do this so I can go back to killing you with beer." - Homer
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    Quote Originally Posted by KJW View Post
    I figured it was an important correction to make, given the context of this thread.
    And you were quite right to point it out. Sloppiness on my part...
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    Quote Originally Posted by Jarek Duda
    which part would you stop seeing first?


    Find an old monitor or TV with a brightness knob and slowly turn it down. What part of the screen becomes black first?
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    After Stephen Hawking "There are no black holes": Stephen Hawking: 'There are no black holes' : Nature News & Comment
    now from PhysOrg Researcher shows that black holes do not exist :
    "But now Mersini-Houghton describes an entirely new scenario. She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation. However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole."

    What is nearly exactly what I was saying: instead of growing singularity in the center of neutron star, it should rather immediately go through some matter->energy conversion (like evaporation through Hawking radiation or in other words: some proton decay) - releasing huge amount of energy (finally released as gamma ray bursts), and preventing the collapse.
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    Quote Originally Posted by Jarek Duda View Post
    After Stephen Hawking "There are no black holes": Stephen Hawking: 'There are no black holes' : Nature News & Comment
    now from PhysOrg Researcher shows that black holes do not exist :
    "But now Mersini-Houghton describes an entirely new scenario. She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation. However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole."

    What is nearly exactly what I was saying: instead of growing singularity in the center of neutron star, it should rather immediately go through some matter->energy conversion (like evaporation through Hawking radiation or in other words: some proton decay) - releasing huge amount of energy (finally released as gamma ray bursts), and preventing the collapse.
    Mff, the whole "paper" is centered around the claim that certain (not all) BH cannot form due to the fact that Hawking radiation precludes the formation due to evaporation effects. But Hawking radiation is not a confirmed effect, actually it is quite debatable that it exists. So, a claim based on another unproven claim, more like a castle of cards.
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    Quote Originally Posted by Jarek Duda View Post
    After Stephen Hawking "There are no black holes": Stephen Hawking: 'There are no black holes' : Nature News & Comment
    now from PhysOrg Researcher shows that black holes do not exist :
    "But now Mersini-Houghton describes an entirely new scenario. She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation. However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole."

    What is nearly exactly what I was saying: instead of growing singularity in the center of neutron star, it should rather immediately go through some matter->energy conversion (like evaporation through Hawking radiation or in other words: some proton decay) - releasing huge amount of energy (finally released as gamma ray bursts), and preventing the collapse.
    For a Hawking radiation to occur, there has to be a black hole. But very small black hole evaporate very quickly. So I am under the impression that the idea of this paper is that as soon as a very small black hole forms at the center of a collapsing star, it evaporates faster than it can accumulate mass.

    Is it really what this paper means?
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    Quote Originally Posted by Nic321 View Post
    Quote Originally Posted by Jarek Duda View Post
    After Stephen Hawking "There are no black holes": Stephen Hawking: 'There are no black holes' : Nature News & Comment
    now from PhysOrg Researcher shows that black holes do not exist :
    "But now Mersini-Houghton describes an entirely new scenario. She and Hawking both agree that as a star collapses under its own gravity, it produces Hawking radiation. However, in her new work, Mersini-Houghton shows that by giving off this radiation, the star also sheds mass. So much so that as it shrinks it no longer has the density to become a black hole."

    What is nearly exactly what I was saying: instead of growing singularity in the center of neutron star, it should rather immediately go through some matter->energy conversion (like evaporation through Hawking radiation or in other words: some proton decay) - releasing huge amount of energy (finally released as gamma ray bursts), and preventing the collapse.
    For a Hawking radiation to occur, there has to be a black hole. But very small black hole evaporate very quickly. So I am under the impression that the idea of this paper is that as soon as a very small black hole forms at the center of a collapsing star, it evaporates faster than it can accumulate mass.

    Is it really what this paper means?
    No, she claims that the EH and that the singularity do not even get to form . See here.
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    Quote Originally Posted by Howard Roark View Post

    No, she claims that the EH and that the singularity do not even get to form . See here.
    Thank you for the link.

    WOW! I understood a little bit that's amazing.

    The question I am wondering is, would that same type of rebound happen for a collapsing universe. Would a big crunch automatically give rise to a rebound/new big bang?

    Science is full of surprises, that's what makes it interesting!
    Last edited by Nic321; September 26th, 2014 at 02:43 PM.
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    Quote Originally Posted by Nic321 View Post
    Quote Originally Posted by Howard Roark View Post

    No, she claims that the EH and that the singularity do not even get to form . See here.
    Thank you for the link.

    WOW! I understood a little bit that's amazing.

    The question I am wondering is, would that same type of rebound happen for a collapsing universe. Would a big crunch automatically give rise to a rebound/new big bang?

    Science is full of surprises, that's what makes it interesting!
    You are welcome. I predict that PhysLettB will have to retract the paper in the next 6 months (it takes that long for the editors to admit that they have a lot of egg on their faces).
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    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
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    Quote Originally Posted by Nic321 View Post
    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
    I think not, I would argue that only an apparent horizon ( future or past ) is needed, but not necessarily an event horizon. I might very well be wrong on this though. I did find this paper which appears to support my stance :

    http://cds.cern.ch/record/504365/files/0106111.pdf

    At present I understand Hawking radiation to be the product not of an event horizon, but rather of the process of graviationally collapsing matter itself. But I still stand very much at the beginning of my studies of this and other QFT/CST phenomena, so I may well change my mind later when I understand this underlying physics better.
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Nic321 View Post
    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
    I think not, I would argue that only an apparent horizon ( future or past ) is needed, but not necessarily an event horizon. I might very well be wrong on this though. I did find this paper which appears to support my stance :

    http://cds.cern.ch/record/504365/files/0106111.pdf

    At present I understand Hawking radiation to be the product not of an event horizon, but rather of the process of graviationally collapsing matter itself. But I still stand very much at the beginning of my studies of this and other QFT/CST phenomena, so I may well change my mind later when I understand this underlying physics better.
    Thank you for the link, I will have a look at it this evening - I hope I can understand something..

    I believe that's what the article you posted in the other thread said - that it is the fact that the matter collapses which is the cause of the Hawking radiation -, unless I misunderstood.
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    Quote Originally Posted by Nic321 View Post
    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
    Yes, like the one on super-luminal neutrinos traveling at speeds larger than the speed of light.
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    Quote Originally Posted by Howard Roark View Post
    Quote Originally Posted by Nic321 View Post
    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
    Yes, like the one on super-luminal neutrinos traveling at speeds larger than the speed of light.
    Ah you took that one seriously? Interesting Howard Roark.
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    Quote Originally Posted by Nic321 View Post
    Quote Originally Posted by Howard Roark View Post
    Quote Originally Posted by Nic321 View Post
    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
    Yes, like the one on super-luminal neutrinos traveling at speeds larger than the speed of light.
    Ah you took that one seriously? Interesting Howard Roark.
    No, I didn't. I am an experimental physicist, I knew that theirs must be a flawed setup.
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    Quote Originally Posted by Markus Hanke View Post
    Quote Originally Posted by Nic321 View Post
    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
    I think not, I would argue that only an apparent horizon ( future or past ) is needed, but not necessarily an event horizon. I might very well be wrong on this though. I did find this paper which appears to support my stance :

    http://cds.cern.ch/record/504365/files/0106111.pdf

    At present I understand Hawking radiation to be the product not of an event horizon, but rather of the process of graviationally collapsing matter itself. But I still stand very much at the beginning of my studies of this and other QFT/CST phenomena, so I may well change my mind later when I understand this underlying physics better.
    The author says that Hawking's radiation is purely a kinematic effect, and fundamentaly doesn't have anything to do with GR, which is suprising( to me at least... ) .

    So from what I understand, the authors who say that the black holes don't form think that only an apparent horizon forms during the collapse, which is enough to cause the Hawking radiation to occur and 'evaporate' the matter of the star.

    By the way, the author of your paper thinks that the Hawking radiation is similar to the Unruh radiation.
    Secondly, there are simple linguistic issues of definition: How far can we push the Hawking effect before we should give it another name? As argued in this article, based on the physics there is a very good case for keeping the name the same for the effect in arbitrary “effective geometries”, no matter how derived. Some would even argue that the Hawking effect and Unruh effects are fundamentally identical; I prefer to view then as distinct, possibly as two sides of the same coin — the response of the quantum vacuum to externally imposed conditions.
    It is interesting to see the two types of radiation as 'two sides of the same coin'.
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    Quote Originally Posted by Howard Roark View Post
    Quote Originally Posted by Nic321 View Post
    Quote Originally Posted by Howard Roark View Post
    Quote Originally Posted by Nic321 View Post
    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
    Yes, like the one on super-luminal neutrinos traveling at speeds larger than the speed of light.
    Ah you took that one seriously? Interesting Howard Roark.
    No, I didn't. I am an experimental physicist, I knew that theirs must be a flawed setup.
    Ok Howard.

    But the problem about the neutrino speed result was an experimental issue. It was likely that it was an experimental error.


    What this article says has nothing to do with an experiment which was probably false.

    For sure these researcher may well be wrong, but hasn't their paper been peer-reviewed? I don't understand why you don't take it more seriously. These guys are specialists of QFT in curved space time and black holes, so I think you need serious arguments to counter theirs.
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    Quote Originally Posted by Nic321 View Post
    Quote Originally Posted by Howard Roark View Post
    Quote Originally Posted by Nic321 View Post
    Quote Originally Posted by Howard Roark View Post
    Quote Originally Posted by Nic321 View Post
    Well anyways even it if it is wrong, it still raises a interesting question about the Hawking radiation: can there be a hawking radiation without an EH?
    Yes, like the one on super-luminal neutrinos traveling at speeds larger than the speed of light.
    Ah you took that one seriously? Interesting Howard Roark.
    No, I didn't. I am an experimental physicist, I knew that theirs must be a flawed setup.
    Ok Howard.

    But the problem about the neutrino speed result was an experimental issue. It was likely that it was an experimental error.


    What this article says has nothing to do with an experiment which was probably false.

    For sure these researcher may well be wrong, but hasn't their paper been peer-reviewed?
    Yes, this is a theoretical paper, I was responding to your snickering. It is not unusual for theoretical papers to being wrong, in my experience, I have caused three to being retracted as being wrong.


    I don't understand why you don't take it more seriously. These guys are specialists of QFT in curved space time and black holes, so I think you need serious arguments to counter theirs.
    I already pointed out the major flaw in the paper. I intent to write a formal refutation and submit it, I am sure that there will be dozens of such refutations. I do not plan to give out all my arguments in this thread.
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    The main question here is if the baryon number is ultimately conserved?

    Violation of this number is required by
    - hypothetical baryogenesis producing more matter than anti-matter,
    - many particle models, like supersymmetric,
    - massless Hawking radiation - black holes would have to evaporate with baryons to conserve the baryon number.

    From the other side, there is a fundamental reason to conserve e.g. electric charge: Gauss law says that electric field of the whole Universe guards charge conservation.
    In other words, adding a single charge would mean changing electric field of the whole Universe proportionally to 1/r^2.
    We don't have anything like that for baryon number (?) - a fundamental reason for conserving this number.

    Indeed the search for such violation (by proton decay) has failed, but this search was performed in room temperature water tanks.
    One of the question is if required conditions can be reached in such conditions: if energy required to cross the energy barrier holding the baryon together can be spontaneously generated in room-temperature water. In other words: if Boltzmann distribution of size of random fluctuations still behaves well for such huge energies.

    If baryon number is not ultimately conserved, it would rather require extreme conditions, like while Big Bang (baryogenesis) ... or in the center of neutron star, which will exceed all finite limits before getting to infinite density required to start forming the black hole horizon and the central singularity.
    Such "baryon burning phase" would result in enormous energy (nearly complete matter -> energy conversion) - and we observe this kind of sources, like gamma ray bursts, which "The means by which gamma-ray bursts convert energy into radiation remains poorly understood, and as of 2010 there was still no generally accepted model for how this process occurs (...) Particularly challenging is the need to explain the very high efficiencies that are inferred from some explosions: some gamma-ray bursts may convert as much as half (or more) of the explosion energy into gamma-rays." ( Gamma-ray burst - Wikipedia, the free encyclopedia )

    So we have something like supernova explosion, but instead of exploding due to neutrinos (from e+p -> n), this time using gammas - can you think of other than baryon decay mechanisms for releasing such huge energy?

    NASA news from 2 days: NASA?s NuSTAR Telescope Discovers Shockingly Bright Dead Star | NASA

    about 1-2 solar mass star, with more than 10 millions times larger power than sun ... is no longer considered as a black hole!
    Where this enormous energy comes from?
    While fusion or p+e->n converts less than 0.01 matter into energy, baryon decay converts more than 0.99 - are there some intermediate possibilities?
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