¿Se acumula materia fuera del horizonte de eventos de un agujero negro?


34

Según tengo entendido, el tiempo se ralentiza y los enfoques se detienen al acercarse al horizonte de eventos de un agujero negro. He visto que esto explica varios lugares, incluida una breve explicación en el último párrafo debajo: http://en.wikipedia.org/wiki/Black_hole#General_relativity , citado a continuación:

Oppenheimer y sus coautores interpretaron la singularidad en el límite del radio de Schwarzschild como indicando que este era el límite de una burbuja en la que el tiempo se detuvo. Este es un punto de vista válido para los observadores externos, pero no para los observadores que caen. Debido a esta propiedad, las estrellas colapsadas se llamaron "estrellas congeladas", [17] porque un observador externo vería la superficie de la estrella congelada en el tiempo en el instante en que su colapso la lleve dentro del radio de Schwarzschild.

¿Significa esto entonces que no importa en realidad cae en un agujero negro (excepto posiblemente lo que había en su formación)? ¿Esto también significa que la materia se está acumulando justo fuera de su horizonte de eventos? Según tengo entendido, esta sería la perspectiva desde fuera del agujero negro. Si este es el caso, me pregunto si observaríamos una tremenda cantidad de materia que rodea el horizonte de sucesos, pero ¿sería extremadamente rojo?

Editar:

Noté que una respuesta a una pregunta diferente, especialmente la parte final, también proporciona algunas ideas aquí: https://astronomy.stackexchange.com/a/1009/1386

Editar:

¡Estos videos de YouTube que alguien reunió explican muy bien el concepto y parecen indicar que esta idea está ganando terreno!

https://www.youtube.com/watch?v=yZvgeAbrjgc&list=PL57CC037B74307650&index=118 https://www.youtube.com/watch?v=b1s7omTe1HI

Editar:

¡Este nuevo video de YouTube describe esta idea muy bien y la describe como la forma en que funcionan los agujeros negros!

https://youtu.be/mquEWFutlbs


2
Debes citar donde lo lees. Sin embargo, supongo que está hablando de los efectos relativistas (retraso) observados desde un observador distante. ¿Es correcto?
Py-ser

1
Mi opinión personal: esa es la razón (junto con la radiación de Hawking que hace que el BH desaparezca en un tiempo finito, como se ve desde afuera), por qué un horizonte de eventos nunca puede formarse. Pero esa no es (¿todavía?) La opinión de la corriente principal.
Gerald

@ Py-ser: Sí, esto es correcto, estoy hablando de los efectos relativistas.
Jonathan

Respuestas:


23

Sí, tiene toda la razón, desde NUESTRO PUNTO DE VISTA lo hace.

Del libro de Kip Thorne "Black Holes and Time Warps: Einstein's Outrageous Legacy".

“Al igual que una roca caída desde un tejado, la superficie de la estrella cae hacia abajo (se contrae hacia adentro) lentamente al principio, luego más y más rápidamente. Si las leyes de gravedad de Newton hubieran sido correctas, esta aceleración de la implosión continuaría inexorablemente hasta que la estrella, sin ninguna presión interna, sea aplastada a un punto a alta velocidad. No es así según las fórmulas relativistas de Oppenheimer y Snyder. En cambio, a medida que la estrella se acerca a su circunferencia crítica, su contracción se reduce lentamente. Cuanto más pequeña se vuelve la estrella, más lentamente implosiona, hasta que se congela precisamente en la circunferencia crítica. No importa cuánto tiempo espere, si uno está en reposo fuera de la estrella (es decir, en reposo en el marco de referencia externo estático), uno nunca podrá ver la estrella implosionar a través de la circunferencia crítica.

“¿Esta congelación de la implosión es causada por una fuerza relativista general inesperada dentro de la estrella? No, para nada, se dieron cuenta Oppenheimer y Snyder. Más bien, es causado por la dilatación del tiempo gravitacional (la desaceleración del flujo del tiempo) cerca de la circunferencia crítica. El tiempo en la superficie de la estrella implosionante, como lo ven los observadores externos estáticos, debe fluir cada vez más lentamente, cuando la estrella se acerca a la circunferencia crítica, y en consecuencia, todo lo que ocurre dentro o dentro de la estrella, incluida su implosión, debe aparecer en cámara lenta y luego congelar gradualmente ".

"Por curioso que parezca, aún más peculiar fue otra predicción hecha por las fórmulas de Oppenheimer y Snyder: aunque, como lo observan los observadores externos estáticos, la implosión se congela en la circunferencia crítica, no se congela en absoluto como lo ven los observadores que viajan hacia adentro en la superficie de la estrella. Si la estrella pesa unas pocas masas solares y comienza aproximadamente del tamaño del sol, entonces, como se observa desde su propia superficie, implosiona a la circunferencia crítica en aproximadamente una hora, y luego continúa implosionando la crítica del pasado y avanzando a una menor circunferencias ".

“Al observar las fórmulas de Oppenheimer y Snyder desde el punto de vista de un observador en la superficie de la estrella, se pueden deducir los detalles de la implosión, incluso después de que la estrella se hunda dentro de su circunferencia crítica; es decir, uno puede descubrir que la estrella se contrae hasta una densidad infinita y un volumen cero, y se pueden deducir los detalles de la curvatura del espacio-tiempo en la contracción ”. P217-218

Bien, desde nuestra perspectiva, todo el asunto estará agrupado alrededor de la circunferencia crítica y no más. Está bien, este caparazón en teoría puede ejercer todas las fuerzas requeridas en el universo externo, como la atracción gravitacional, el campo magnético, etc. El punto como singularidad que está en el futuro indefinido del agujero negro, (desde nuestro punto de vista) en El futuro indefinido del universo mismo no podría ejercer tales fuerzas en este universo. Esta singularidad solo se "alcanza" cuando un observador recorre la circunferencia crítica y, a través del proceso de dilatación del tiempo, llega al final del universo.

Obviamente, esta es un área de investigación y pensamiento activos. Algunas de las mentes más grandes del planeta están abordando este tema de diferentes maneras, pero hasta ahora no han llegado a un consenso, pero intrigantemente parece estar comenzando a surgir un consenso.

http://www.sciencealert.com/stephen-hawking-explains-how-our-existence-can-escape-a-black-hole

Stephen Hawking dijo en una conferencia en agosto de 2015 que cree que "la información se almacena no en el interior del agujero negro como cabría esperar, sino en su límite, el horizonte de eventos". Su comentario se refiere a la resolución de la "paradoja de la información", un debate de física de larga duración en el que Hawking finalmente reconoce que el material que cae en un agujero negro no se destruye, sino que se convierte en parte del agujero negro.

Lea más en: http://phys.org/news/2015-06-surface-black-hole-firewalland-nature.html#jCp

A mediados de los 90, los físicos estadounidenses y holandeses Leonard Susskind y Gerard 't Hooft también abordaron la paradoja de la información al proponer que cuando algo es absorbido por un agujero negro, su información deja una especie de huella holográfica bidimensional en el horizonte de eventos. , que es una especie de 'burbuja' que contiene un agujero negro a través del cual todo debe pasar.

Lo que ocurre en el horizonte de eventos de un agujero negro es muy difícil de entender. Lo que está claro, y lo que procede de la Relatividad General, es que desde el punto de vista de un observador externo en este universo, cualquier materia que cae no puede pasar más allá de la circunferencia crítica. La mayoría de los científicos luego cambian el punto de vista para explicar cómo, desde el punto de vista de un observador que cae, procederán en un período de tiempo muy corto para encontrar la singularidad en el centro del agujero negro. Esto ha dado lugar a la noción de que hay una singularidad en el centro de cada agujero negro.

Sin embargo, esto es una ilusión, ya que el tiempo que llevará alcanzar la singularidad es esencialmente infinito para nosotros en el universo externo.

El hecho de que el asunto no pueda pasar más allá de la circunferencia crítica quizás no sea una "ilusión" sino muy real. El asunto debe, desde NUESTRO PUNTO DE VISTA, convertirse en un "caparazón" que rodea la circunferencia crítica. Nunca caerá a través de la circunferencia mientras permanezcamos en este universo. Entonces hablar de una singularidad dentro de un agujero negro es incorrecto. Aún no ha sucedido.

El camino a través del horizonte de eventos conduce a una singularidad en cada caso, pero está indefinidamente lejos en el futuro en todos los casos. Si estamos en este universo, aún no se ha formado la singularidad. Si aún no se ha formado, ¿dónde está la masa? La masa está ejerciendo atracción sobre este universo, ¿correcto? Entonces debe estar EN este universo. Desde nuestro punto de vista, debe ser solo este lado del horizonte de eventos.

ASOMBROSAMENTE PUEDE SER POSIBLE PROBAR ESTO. El reciente anuncio de ondas gravitacionales detectadas en la fusión de 2 agujeros negros fue acompañado por un estallido de rayos gamma no verificado pero potencialmente coincidente desde la misma área del cielo. Esto es inexplicable desde el punto de vista convencional que sostiene que toda la materia se comprimiría en una singularidad y sería incapaz de volver a salir.

Si 2 agujeros negros se fusionan y emiten rayos gamma ... lo anterior es sin duda una explicación que también es consistente con la Relatividad General. La masa nunca logró atravesar el horizonte de sucesos (desde nuestro punto de vista) y se vio perturbada por la gran violencia de la fusión, algunos escapando. Puede ser un pozo gravitacional profundo, pero un rayo gamma muy poderoso debería poder escapar dada la patada correcta (atracción por un agujero negro aún más grande que se acerca).

Otras observaciones más refinadas de eventos similares, que probablemente sean razonablemente frecuentes, pueden proporcionar más evidencia. No es probable que haya otra explicación creíble.


Gracias por su respuesta, me gustaría ver si esto genera más discusión.
Jonathan

2
One more comment on your original question. The black hole would start like a tiny vapour bubble in the middle of the imploding star which had reached a sufficiently strong gravitational "pressure". It would then expand as surrounding matter and energy fell in and reached its critical circumference, therefore I do not think any matter from the viewpoint of an external observer would be "inside" the critical circumference.
ctrebor

FYI, I am looking for proof / references to award the bounty.
Jonathan

Proof/references for what? There was a considerable reference to Oppenheimer & Snyder. Do you want more?
ctrebor

2
Sus comentarios sobre ondas gravitacionales parecen tener problemas para comprender la diferencia entre la masa y el campo gravitacional. Nada sobre la detección de GW dijo que la masa fue expulsada o convertida de otra manera (dentro) de los agujeros negros en varias formas de radiación. La energía ya estaba presente en los campos gravitacionales, que existen dentro del universo y fuera del horizonte de eventos. Fue esa energía la que se convirtió en radiación. Lo que "realmente" en el agujero es irrelevante: lo que importa son los campos (gravitacional y EM, a saber).
zibadawa timmy

24

What you're describing is basically the "collapsed star" (Eng) or "frozen star" (Rus) interpretation of black holes that was common prior to the late mid-1960s. It was a mistake.

Suppose you are distant and stationary relative to the black hole. You will observe infalling matter asymptotically approaching the horizon, growing ever fainter as it redshifts. Does it mean that matter "clumps" around the horizon? To find out, suppose you throw yourself towards the black hole to try to catch the matter that you see. What you will find is that it fell into the black hole long ago.

In other words, the most sensible way to answer whether or not infalling matter clumps on the horizon is to look at the situation from the frame of that infalling matter. And there, it is clear: no, it does not clump, as it crosses the horizon in finite proper time. (As an aside, for a Schwarzschild black hole, falling from rest is exactly Newtonian in Schwarzschild radial coordinate and proper time.)

The "comoving viewpoint" was recognized by Oppenheimer and Snyder in 1939, but it was not until the 1960s, with the work of Zel'dovich, Novikov, et al., that it was generally recognized as truly significant in the community. In 1965, Penrose introduced conformal diagrams based on the Eddington-Finkelstein coordinates (1924/1958) that showed quite clearly that the stellar collapse is not slowed, but instead continues to a singularity. For an overview of the history of this change of viewpoint, cf. Kip Thorne, et al., The Memberane Paradigm (1986). These topics are commonly covered in many relativity textbooks.

Ok, but since it still takes an infinite amount time in the frame adapted to a stationary distant observer, does that mean that the horizon never forms in that frame? It does form: the underlying assumption in the argument that it does not would be either that the infalling matter needs to reach the center for the horizon to form or cross a pre-existing horizon to make it expand. But that assumption is simply not true.

Un horizonte de eventos se define en términos de futuro infinito similar a la luz, más o menos en términos de si los rayos de luz escapan o no si uno espera una cantidad infinita de tiempo. Eso significa que la ubicación del horizonte en cualquier momento depende no solo de lo que sucedió, sino también de lo que sucederá en el futuro. En el marco del observador estacionario distante, a medida que la materia cae hacia el horizonte de eventos, se ralentiza para acercarse asintóticamente ... pero el horizonte también se expande para encontrarlo. De manera similar, la materia de colapso inicial no necesita colapsarse completamente hacia el centro para que se forme el horizonte de eventos.


¿Cómo se puede hacer que el tiempo de vida finito del agujero negro debido a la radiación de Hawking sea consistente con la cantidad infinita de tiempo (futuro) necesario para la expansión del horizonte de eventos (en el marco de tiempo externo)?

No hay necesidad de: [editar] que una coordenada de tiempo particular no cubra el múltiple completo es una falla del gráfico de coordenadas, no del espacio-tiempo [/ editar]. De cada evento, envíe un lugar omnidireccional de rayos de luz idealizados. El horizonte de eventos es el límite de la región del espacio-tiempo desde la cual ninguno de estos rayos de luz escapa al infinito. Esta pregunta tiene una respuesta objetiva: para cualquier rayo de luz dado, escapará o no.

Un observador externo necesitaría esperar infinitamente para saber con seguridad dónde está exactamente el horizonte de sucesos, pero ese es un problema completamente diferente. Con la radiación de Hawking, el agujero negro se contrae, pero no cambia el hecho de que los rayos de luz de algunos eventos no podrán escapar y, por lo tanto, existirá un horizonte de eventos.

Aquí hay un diagrama de Penrose de una estrella esférica colapso de la formación de un agujero negro que se evapora posteriormente:

Penrose diagram of an evaporating black hole

Los rayos de luz corren diagonalmente a ± 45 ° en el diagrama. Tenga en cuenta que hay una región en la que los rayos de luz salientes (que se ejecuta en diagonal inferior izquierda a superior derecha) no escapan y en lugar de cumplir con elr=0 0singularidad (la, línea horizontal undashed en negrita). El horizonte es la misma delr=2metrolínea marcada en el diagrama y su extensión a la estrella: en realidad debería ir de la (discontinua, vertical)r=0 0línea a la izquierda, en lugar de extenderse desde la superficie de colapso de la estrella. Esto se debe a algunos de los rayos de luz (, noninteracting idealizados) desde el interior de la estrella también se producirá un error de escapar al infinito.

Now suppose that on this diagram you draw timelike curves that stubbornly stay away from the horizon, and you insist on using a parameter along them as a time coordinate. Does the fact that you've chosen coordinates that exclude the horizon needs to be made consistent with whether or not the event horizon actually exist? The resolution is simple: if you want to talk about the horizon, stop using coordinates that exclude it.


So is this correct? From a reference point outside the black hole, matter does indeed accumulate (or clump together) approaching the event horizon, but eventually the event horizon expands to engulf it when more matter is accumulating?
Jonathan

2
If you insist on defining 'clumping' that way, yes, though I wouldn't. As for the latter question, actually, no: as the horizon expands, it carries the frozen, redshifted images of the stuff that has fallen in the past outward with it. That's one reason I wouldn't call the former case 'clumping'; rather, the Schwarzschild time coordinate (or appropriate generalization for distant stationary observers) is badly behaved at the horizon at so simply shouldn't be used there.
Stan Liou

1
I don't agree that the external time reference should not be used, as that is what we would "see" if we look at a black hole. It is an interesting point you made that the "image" of all the matter that has fallen in before moves outward when the event horizon expands. Thank you for taking the time to provide a detailed answer too, very thought provoking!
Jonathan

1
@StanLiou How can the finite life-time of the Black hole due to Hawking radiation be made consistant with the infinite amount of time (future) needed for the expansion of the event horizon (in the outer time-frame)?
Gerald

1
"... but the horizon also expands to meet it." How long does that take from the point of view of distant stationary observer?
Kamil Szot

10

We need to think about just where the time dilation effect occurs. By then thinking about the observations from each point of view, that is the free falling object and the external observer, we can come to terms with just what is happening as opposed to what appears to be happening.

The experience of time

We must remember that an object moving at a certain speed will travel through time (or the 4th dimension) at a slower rate. This does not mean that it moves slower, otherwise it would obviously not be travelling "at a certain speed".

Where time slows is in the ticking of the physical processes of the object itself. In other words, my clock would tick twice as slow according to you as I flew past you at 87% the speed of light. I would be waving my arms normally, but according to you, I would appear to be waving my arms twice as slow and would also appear to be squeezed in size (not really relevant to this).

The falling object's point of view

If you were the object falling into the black hole, you would accelerate as you approached the event horizon, but you would take longer and longer to react to the approach, to the point where you would fall into the black hole in no time at all. From your perspective, your approach to the event horizon would become exponentially faster.

In other words, you would fall incredibly fast into the black hole, but you would have barely registered it in your mind because there just wasn't enough time for you due to relativity.

The stationary observer's point of view

Now, the stationary observer outside the black hole's influence would observe something very different. The light (or rather, information) about your descent would become more and more redshifted, but also take longer and longer to actually reach their eyes.

This means that according to the observer, the falling object would slow down to a halt at the event horizon and have disappeared.

So what really "happened"?

  • The falling object fell in very quickly, but hardly realised it happening
  • The stationary observer would think that the object disappeared and never reached the event horizon.
  • Cooper taps on some gravity books and saves the human race.

How then can the observer see a black hole at all, if from his position, never enough mass falls into it for it to take shape and exist to begin with?
LocalFluff

@LocalFluff What does "see a black hole" mean? If by that you mean observe its gravitational effects, I don't see the problem.
Rob Jeffries

Your first section is mistaken. It takes a finite amount proper time to fall in, i.e. time experiences by the object, such as you. As a cute coincidence illustrating this, for radial freefall from rest into a Schwarzschild black hole, the time it takes to reach the horizon (or any particular Schwarzschild radial coordinate) happens to exactly match the prediction of Newtonian gravity.
Stan Liou

@RobJeffries But then it would remain a neutron star for all outside observers. Black holes would never form for outside observers regardless of how they are observed. One can potentially see a black hole transiting background objects. A non-accreting SMBH doesn't shine at all, while a neutron star with millions of Solar masses very near its surface would be pretty wild.
LocalFluff

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@LocalFluff A neutron star and a black hole are completely different. No neutron star can exist with a radius anywhere near the Schwarzschild radius. That's why you can see a neutron star.
Rob Jeffries

5

The logical consequence is, that an event horizon cannot form, since the first particle slows down asymptotically to zero, just before the event horizon forms (Fermat's infinite descent).

The emergence of the event horizon therefore takes infinite time seen from outside. But due to Hawking radiation a black hole exists only a finite time. Hence an event horizon doesn't form.

The frustrating thing about this is, that you need to be at least Stephen Hawking, to not be called a geek.

The current mainstream way to circumvent this paradoxon is to switch to a purely general relativistic geometry of infalling space-time, which doesn't experience the event horizon. That way you avoid the event horizon as a pole, but you get the singularity at the center of the black hole, governed by yet to investigate physical laws of quantum gravity.


That is an interesting point, and very thought provoking. It will be interesting to see what further discoveries are made about black holes. I wonder still about the matter that was "inside" the black hole when it formed (e.g. I would think this matter is indeed inside the black hole / event horizon). Although, if it is correct that the "image" of the matter expands with the event horizon, even that matter could be on the edge of the event horizon from an external view point.
Jonathan

@Jonathan If you assume e.g. the Schwarzschild solution, the simplest form of a black hole, from an outside observer you need to distinguish three zones: the space-like, the light-like, and the time-like zone. The light-like zone corresponds to the event horizon. If you transform properties of matter between these zones they change their physical properties so much, that the term "the matter is" doesn't make much sense, neither "matter" nor "is". One space dimension changes roles with time.
Gerald

1
@Jonathan One way of thinking may be, that the information of the matter is stored at the event horizon, some fluid-simulations indicate a fractal structure of the event horizon due to infalling matter; this might be a way to overcome the information paradox. That's neither the Schwarzschild nor the Kerr solution.
Gerald

1
I wonder if we could actually "peek under the skirts" of a black hole if there'd be any 'there' at all. We can't of course, and anyone that asserts a singularity exists inside a black hole is simply saying that the mathematical model they're using says there is one. If all of the mass/energy that makes up a black hole was compressed into a two dimensional surface at the event horizon, is there any way to observationally tell the difference? Swiss cheese has holes in it, but no one asserts that the holes are Swiss cheese.
Howard Miller

@Gerald FYI, I am looking for proof / references to award the bounty.
Jonathan

4

Thought provoking cosmologists!

I'm uber late to this discussion as I see it has been ongoing for literally years and don't know if there is still anyone monitoring this thread, but here' goes.

I studied astrophysics at UC Berkeley in the late 80's so perhaps my info is a little dated, upfront apologies if so. I spent a lot of time thinking about this problem for the past 30 years and have postulated a couple ideas.

First, these conjectures are based on the presumptions:

  • time stops at the event horizon
  • an in-falling observer into the EH looking backward would watch the universe rapidly age to heat death
  • non-charged, non-rotating, solar-mass black hole
  • a star of 2-3 solar masses is sufficient to overcome neutron degeneracy pressure and form a black hole (call it 2 for the discussion)

If true, then conjecture:

  • start with star of say 3 solar masses
  • we must consider an even horizon's existence and parameters from its "birth"
  • minimum Schwarzschild radius is only 12 miles (2 solar masses)
  • original main sequence star radius appx 100,000Km (100M+ Km for red giant)
  • observer is orbiting star initially
  • star burns through last percentages of helium and cascade collapses directly to black hole
  • as star collapses, some amount of matter contracts to within 12 miles of star centroid (call it 2 solar masses)
  • Event horizon now mathematically is formed and time STOPS for all matter at that radius
  • Matter outside that radius continues to fall in since time has not yet stopped creating a compression sphere around the EH
  • Matter already INSIDE the EH continues to fall. (it has momentum that must be conserved). OR, does time STOP WITHIN the EH as well throughout the entire Schwarzschild sphere causing all that matter to FREEZE in position (reletive to the outside observer? (unknown) (perhaps time REVERSES?!)
  • The outside observer would watch the matter at the EH STOP falling and radiating
  • The in-falling matter looking back at the universe would now watch the universe rapidly age, perhaps even to its death?
  • If so, this means that all in-falling EH matter, after the EH has formed, is trapped at the EH until the black hole evaporates.
  • Which also leads to a huge COMPRESSION of the in-falling matter in successively faster time frames falling in from behind.
  • In the given example, this is an entire solar mass of matter all rapidly compressing and increasing in pressure. (At the EH time has stopped so no interaction is going on from the perspective of our orbiting solar observer, but successively less time dilated layers further away from the EH compress into the equivalent of a whole new star burning its fuel in fempto-seconds to many seconds. I.E. SUPERNOVA)
  • AND there is the gravitational attraction imbalance that has now been caused between the solar mass of matter at the EH and the 2 solar masses inside the SW
  • In fact, all blackholes formed by stellar collapse should begin life as a 12 mile wide schwarzschild radius of 2 solar masses.
  • Growth of blackhole sizes of this type (excluding primordial black holes) should ONLY be due to EH matter accretion or merging of black hole's EH's.
  • No matter should ever fall into (or through) the EH in our lifetimes, or even the lifetime of the universe as long as we maintain that an observer falling into a blackhole sees the universe rapidly age behind him/her (the future)
  • Therefore, all detection of radiation from black holes is due to interactions of matter very near the EH
  • Which begs the question, does GRAVITY transcend the EH?
  • If not, a black hole should lose "2" solar masses at is creation (can only test if we can measure the mass before an after its creation in perhaps a visible binary pair supernova
  • But if gravity DOES transcend the EH as accepted, then the gravity of the solar masses at the EH should be exerting an opposing force on the matter inside, DECELERATING the collapse inside the EH!
  • Also, there should be a "ringing" effect "heard" by our new gravity wave detectors as the matter inside doesn't just collapse infinitely into a singularity but "bounces" and reverberates from gravity and different layers of time dilation
  • As a though, this COULD even result in a "torus" of sorts with dimensionalities being swapped or reversed (time/distance), rather than a singularity
  • Add to this the planck density with these opposing internal forces and we possibly end up with some bizarre space-time topologies.
  • PURE speculation: The environment INSIDE the black hole starts to look a whole lot like our own universe's history from the big bang (white hole?) if you simply change time's arrow. (universe isn't expanding as we perceive but compressing into a torus with different distances from our viewpoint having different levels of time dilation)
  • As an undergrad I wrote a paper that our universe is the inside of a black hole and I have seen many theories gravitating (sorry) to this solution over the past 30 years
  • Including the most recent ideas that our universe is a compressed (3D) hologram on a 4 dimensional "sphere" that represents an event horizon equal to the entropy of our entire known universe. Elegant.

Apologies for the terribly long winded comments here. I'm sure the idea has more holes than swiss cheese. Which is what the universe starts to look like with all these little pocket universes forming that we can't interact with!

The question and theanswer that could take use to the next level of understanding of these concepts is this:

Can an event horizon change shape?

If the matter is time-dilation-locked to the event horizon, it cannot move (relative to the EH). If in-falling matter can witness the end of the universe, or even just a very long time, then the matter is time-dilation-locked by definition. If it is NOT TD-locked, an in-falling observer SHOULD NOT BE ABLE TO SEE THE UNIVERSE RAPIDLY AGE BEHIND THEM.

Then for if the EH can change shape, either:

  • matter needs to move with the EH (acceleration? momentum? free energy?)
  • OR the EH, being a mathematical definition, can move irrespective of the location of the matter, thereby changing the amount of time-dilation on the matter, slowing/speeding/stopping matter outside the EH, or UNKNOWN effects if it was already inside the EH. (presumably an EH will always INCREASE in size, but what about shape?)
  • back to shape: Can an EH be ellipsoid? Pancake? If it can change from sphere to pancake, does this not mean that matter that was already inside the EH near the spherical radius has now EMERGED FROM THE BLACK HOLE as it were if that radius suddenly shrinks? (unless, again, it is somehow dragged with the EH)
  • if this is the case, would not black hole mergers allow for matter from within the EH to escape there by constituting a whole new form of black hole emission other than Hawking radiation? How would we detect this? How would we know?

I think the answer lies squarely with LIGO and more powerful versions of this instrument to be brought online in the future. Observing changes, arrival times, spectrum comparisons, and eventually direction, of gravity waves and their associated gamma ray bursts from merging black holes will help us pin down exactly what happens when event horizons collide!

Thanks for taking the time to review these ideas!


2
1) Put your text between two stars, so: *this text*, so it will be italic. 2) 3 Sun masses is far not enough to produce a black hole. 3) Time stops on the EH only for the far observers, objects falling in the EH experience nothing while they pass it. 4) All capital texts don't look very good, I suggest to use the italic formatting (or, double stars make your text bold).
peterh says reinstate Monica

And do something about your wall of text. If you want people to read your contribution make sure it is easy to read.
Jan Doggen

Very interesting feedback, and definitely thought provoking! Would be interesting to see if future observations (especially LIGO observations of merging black holes) "shine more light" on if time is indeed frozen at the event horizon. It is an interesting thought that the event horizon should not be able to change shape if time is frozen there! Definitely thought provoking.
Jonathan

4

Several wonderful yet technical answers have been given, and I cannot add anything to those very nice answers that explain why it is not useful to think black holes get "frozen" at their event horizons. But I can give an answer with a more essentially useful philosophical perspective, which is that the central lesson of relativity is that reality involves a bunch of things happening at various places and times, so reality is something local. As such, if you want to know what happened at some place and time (regardless of how you decide to give numbers to that place and time, that's like choosing how to coordinatize the surface of the Earth), then you should ask someone who was at that place and time!

According to this simple rule, we should imagine asking someone falling past an event horizon if a black hole has formed yet or not. They will say it has, and they will say they get to that central black hole in a finite time. Whether or not you get to receive that message is a more difficult issue, but they will say it all the same because reality happens somewhere, and we can always imagine someone there to experience it-- and ask them. Or at least, imagine what they would say in cases where communication gets difficult or impossible.

If you follow that one simple rule, then all these apparent coordinate paradoxes disappear immediately. Coordinates are a useful language for making calculations, but they are not a useful language for making assertions about "what is." That is an issue for observation, and all observations are local-- no one ever observes a coordinate, and way too much is made out of arbitrary coordinate choices.


1
"all observations are local" - this simple statement packs a punch! Copenhagen Interpretation ... entanglement ... there is no such thing as an independent reality?
Chappo Says Reinstate Monica

1
Not accessible to science, anyway. Science must be empirical, so it must be observer based, so it can only describe local events. That may limit its scope. It's how we keep invisible faeries out of science, but we don't know what else we lose. Still, if someone somewhere is saying the black hole has formed, and that they are crossing an event horizon, then we must allow the black hole does exist-- even if we know we can never receive the message and therefore cannot generate a global concept from our own observations.
Ken G

Einstein was deeply troubled by the realisation that reality is relative, which is why he wrote to Schrödinger in 1950, "You are the only contemporary physicist, besides Laue, who sees that one cannot get around the assumption of reality, if only one is honest. Most of them [other physicists] simply do not see what sort of risky game they are playing with reality—reality as something independent of what is experimentally established."
Chappo Says Reinstate Monica

1
I am always surprised by that attitude, because it seems clear to me that we will always be limited by our ability to perceive. There was never any guarantees that we would be able to perceive reality in some kind of pure form-- it was always going to be what passes our filters. Even the choice to do science presents additional filters, where was the guarantee nothing would ever be lost?
Ken G

0

An observer falling into a black hole does not see himself fall into the singularity unimpeded. The black hole will always evaporate before infinity, therefore the infalling observer will fall to the center of an evaporated black hole and find nothing special other than universal heat death.


1
And by the way, physicists everywhere seem to be confused about what happens when you add infinity. Ignore black hole evaporation. The claim is that physics holds similarly true in all frames of reference. Except there is no frame of reference for a far away observer, because after an infinite amount of time, the infalling subject still never falls past the horizon. So there is no obvious reason to say the infalling observer will have a normal experience at time=infinity. You don't get to add infinity or divide by infinity. You have lost touch with physical concepts when you try to do it.
Smart guy

1
The whole issue arises from an invalid analytical extension. It's like trying to describe the universe as a photon would see it unfold. The universe would exist only with two states: t=0 and t=1. The two states would share no discoverable relationship and would be truly arbitrary, because the photon experience requires dividing time by infinity, and is therefore meaningless to talk about.
Smart guy

I don't see what is wrong with this answer, assuming black holes actually do evaporate due to hawking radiation, and time dilation is such that the observer falling into the black hole observes the future of the universe. Might be nice if the answer elaborated on this a bit. Definitely an intriguing thought! In this case, I don't believe infinite time is involved, because a finite amount of time would pass before the black hole evaporates. Also see: astronomy.stackexchange.com/questions/2524/…
Jonathan

2
It's wrong because the infaller reaches the center in a short time, on their own clock. They just don't care about the time coordinate being used by some person at infinity, and we should not use a nonlocal time coordinate to say 'what is going on' somewhere else. This is one of the central lessons of relativity-- reality is local, so ask the person on the scene. All else is just coordinates, and way too much is made of coordinates.
Ken G

Indeed, this is similar to the issue that arises in cosmology-- the "observable universe." Beyond the edge of that, there be dragons, that we assume away with a swipe of the cosmological principle-- yet all we know is that we will never know the full, global, universe, and whatever else it might contain that some observer is experiencing but we never will.
Ken G
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