B Is there a white hole inside every black hole?

[marees]

This is what I am thinking. How much feasible is it?

1. There is a white hole inside every black hole
2. The white hole spits mass/energy out continuously
3. The mass/energy that is spit out of a white hole drops back into it eventually. This is because of extreme space time curvature around the white hole
4. Ironically this extreme space time curvature of the space around a white hole is caused by the huge mass/energy packed in the white hole
5. Because of continuously spitting mass/energy which keeps falling back in, the white hole (in the 'centre' of the black hole) is constantly 'burning', flickering in shape & direction — like a raging wild fire
6. The outside world is cut off from everything inside the interior of the white hole by the event horizon
7. Classical gravity applies outside the event horizon where it appears as if entire mass/energy inside black hole is concentrated in a centre point inside the black hole — a mathematical singularly
8. Basically there is no Hair outside the event horizon
9. All the space inside the event horizon is curved/pulled in towards the raging/flickering white hole inside
10. Since the white hole is continuously flickering like a raging flame, the space time curvature inside the event horizon is also continuously dancing around pointing towards the flickering white hole
11. Basically there is (a constantly dancing) hair inside the event horizon
12. Here it is best to imagine the space-time outside the event horizon as a 3-dimensional & consistent dough that is gravitational curved/aligned towards the centre (in case of non-rotating) black hole
13. But inside the event horizon the dimensionality of the space time is reduced as if you pressed the dough thru a sieve (see image below)

Right at the event horizon the spacetime is entangled to the white hole.
And Inside the event horizon it is all tiny dynamic continuosuly dancing strands of spacetime constantly realigning to the raging white hole

 

[martinbn]

All of your points are either incorrect or they make no sense.

 

[Dale]

In a Schwarzschild spacetime the white hole is not a location that could be inside the black hole, it is a time that occurs before the black hole. And it does not exist for a black hole formed by collapse.

The dough looks tasty.

 

[PeroK]

Since the white hole is continuously flickering like a raging flame,

Where physics meets creative writing.

 

[marees]

The dough looks tasty.

It is made of rice. Basically rice noodles (string hopper in sri lanka). Goes well with all kinds of spicy curries or with coconut milk

 

[marees]

In a Schwarzschild spacetime the white hole is not a location that could be inside the black hole, it is a time that occurs before the black hole.

Do you have more reading material on this point

 

[Ibix]

Do you have more reading material on this point

Carroll's GR lecture notes, chapter 7 cover it and are free online. Be aware that this is a postgraduate topic.

 

[PeroK]

Carroll's GR lecture notes, chapter 7 cover it and are free online. Be aware that this is a postgraduate topic.

It seems to me that a white hole is a mathematical concept that is largely irrelevant to the physical sciences.

 

[Ibix]

It seems to me that a white hole is a mathematical concept that is largely irrelevant to the physical sciences.

Maybe. Classical ones certainly can't form.

 

[Dale]

I agree. Since it is the beginning of the manifold it cannot have any cause. It would have to just exist, and I don’t even know if such geometry is compatible with something like the Big Bang

 

[javisot]

A white hole is part of the maximally extended Schwarzschild solution in Kruskal coordinates.

The consensus is that they are not physical objects, but I cannot agree that they are not theoretically interesting. A Kleinian spacetime (two temporal dimensions) also doesn't seem to be physical, but it is theoretically interesting, for example.

By theoretically interesting I mean capable of generating scientific literature capable of passing peer review.

 

[Ibix]

I don’t even know if such geometry is compatible with something like the Big Bang

I'm not sure you can even have true black holes in an FLRW universe, because a black hole is a region of spacetime that can't signal to future null infinity and I don't think you can define future null infinity in spacetimes that aren't asymptotically flat. (I can check my memory with Wald tomorrow if necessary.)

That said, you can have ultra-compact objects that only pedants can distinguish from true black holes, and you can have them in closed FLRW spacetime, and you can time-reverse a closed FLRW spacetime to get a closed FLRW spacetime. So unless we have reason to believe that "black holes" merely existing would stop the Big Crunch we probably have to accept that "white holes" (note scare quotes) are not ruled out in an FLRW universe per se. I think you'd have to insert them as an arbitrary initial condition, though, so even with this relaxed definition of white hole I stand by "they don't form".

 

[javisot]

I'm not sure you can even have true black holes in an FLRW universe, because a black hole is a region of spacetime that can't signal to future null infinity and I don't think you can define future null infinity in spacetimes that aren't asymptotically flat. (I can check my memory with Wald tomorrow if necessary.)

https://arxiv.org/pdf/2308.07374, "Black holes embedded in FLRW cosmologies"

 

[Ibix]

https://arxiv.org/pdf/2308.07374, "Black holes embedded in FLRW cosmologies"

Yes - you can cut a spherical cavity into an FLRW universe and fill the hole with part of a Schwarzschild universe (i.e. the McVitie metric) and similar things. But whether that is a black hole spacetime in the strict sense, I am not sure.

Like I say, maybe only pedants can tell the difference.

 

[PeterDonis]

I'm not sure you can even have true black holes in an FLRW universe, because a black hole is a region of spacetime that can't signal to future null infinity and I don't think you can define future null infinity in spacetimes that aren't asymptotically flat. (I can check my memory with Wald tomorrow if necessary.)

That's correct. More precisely, in an FLRW universe with zero cosmological constant, it's correct. In fact I'm not even sure if there is a consistent solution that joins a portion of Schwarzschild spacetime that includes the black hole region to a portion of an expanding FLRW spacetime with zero cosmological constant. (There is, of course, such a solution joining to a collapsing FLRW spacetime--the 1939 Oppenheimer-Snyder solution! But in that solution, the FLRW region is interior to the Schwarzschild region, not exterior.)

With a positive cosmological constant, the causal structure is different; you basically have Schwarzschild-de Sitter spacetime, where there is a black hole region and an event horizon, defined as the region that can't send light signals to the cosmological horizon, and its boundary. In other words, the cosmological horizon now plays the same role as future null infinity does in asymptotically flat spacetimes.

That said, you can have ultra-compact objects that only pedants can distinguish from true black holes, and you can have them in closed FLRW spacetime

But none of those solutions have actual event horizons, and none of them have the causal structure of Schwarzschild spacetime. The causal structure of any such solution will be the same as that of FLRW spacetime (with zero cosmological constant) by itself. The ultra-compact object is just a matter region within that spacetime.

So unless we have reason to believe that "black holes" merely existing would stop the Big Crunch we probably have to accept that "white holes" (note scare quotes) are not ruled out in an FLRW universe per se.

No, this is not correct, at least not if "white hole" means "something that changes the causal structure". See my remarks above. Note that the time reverse of my remarks is also valid (see below for further unpacking of what that means).

I think you'd have to insert them as an arbitrary initial condition, though

It's worse than that. You would have to find a causal structure that could accommodate both a white hole (something like the past singularity and white hole region of Schwarzschild spacetime) and an FLRW spacetime with zero cosmological constant. As above, I don't think such a causal structure is even possible.

 

[PeterDonis]

you can cut a spherical cavity into an FLRW universe and fill the hole with part of a Schwarzschild universe (i.e. the McVitie metric) and similar things. But whether that is a black hole spacetime in the strict sense, I am not sure.

Like I say, maybe only pedants can tell the difference.

I'm not sure the McVittie metric actually has a maximal extension that works the way the paper you reference implies. I note that the paper contains no Penrose diagrams; a Penrose diagram is what I would want to see to be able to see whether there is a global causal structure that makes sense for the McVittie case (per my previous post, I don't think there is).

 

[Ibix]

No, this is not correct, at least not if "white hole" means "something that changes the causal structure".

I was here referring to the time-reverse of an ultra-compact stellar remnant that isn't a true black hole, but is functionally indistinguishable from one. I agree that the impossibility of defining a true black hole in an FLRW spacetime also rules out true white holes.

I'm not sure the McVittie metric actually has a maximal extension that works the way the paper you reference implies.

Actually, @javisot referenced it, not me. I admit I haven't read it in detail, but I don't think it's attempting to prove anything about causal structure, is it? It's a counter-argument to the "black holes are dark energy" hypothesis, and I don't see that it cares if the exact solutions are "proper" black holes or not.

 

[javisot]

Actually, @javisot referenced it, not me. I admit I haven't read it in detail, but I don't think it's attempting to prove anything about causal structure, is it? It's a counter-argument to the "black holes are dark energy" hypothesis, and I don't see that it cares if the exact solutions are "proper" black holes or not.

Exactly, the paper concludes that black holes are not dark energy, it does so as indicated in the title by adding black holes in FLRW, but I admit that I don't understand many technical details.

 

[javisot]

What "black to white transition" proposes is that the final conditions of a common evaporating black hole (not at all exotic in principle) are the initial conditions of a white hole (this is the exotic part). The final object, as Ibix indicates, is called a remnant, and it is especially small.