Massive amounts of matter are moved together to form a sphere in which the centre is hollow. The depth of the sphere contains enough mass to collapse into a black hole and so the entire sphere collapses into the centre of the sphere…
eg. (----o-----( would be a cross section of the sphere. The ‘o’ would be where the matter collapses to form a sphere of black hole. eg. ((
So what happens to the space inside the hollow sphere black hole?
Would it be disconnected from the rest of the universe? Would it be possible to reconnect (if you were inside the sphere to get out) back to the universe?
If the space inside the sphere was separated from the rest of the universe would time progress at the same speed as the rest of the original universe?
Would the centre of the sphere effectively be zero gravitational intensity? Or would the gravity from outside the universe be able to travel through the black holes ‘skin’ of the outer sphere to influence inside the sphere? I would think this was impossible because space had already been distorted to create an infinite gravity well at the point of the black hole, how could it be distorted any more inorder to effect the space inside?
Take the Earth, and remove everything underneath the crust of the Earth so the vast centre of the sphere is empty. Now say more matter was added to the outside such that the crust had enough mass to collapse into a black hole. It would collapse into the centre of the mass, which would be a sphere at the centre of the crust, i.e. if you were in the centre of the Earth (the void) and watched the crust collapse it would move away from you (to the centre of the crust) and if you watched from the outside it would also move away from you (towards the centre of the crust).
But take the Earth, and think millions of times bigger.
There is space ‘inside’ the black hole. A black hole begins at its event horizon, which is a gravitational point of no return. Past the event horizon, nothing can escape because the escape velocity is greater than the speed of light in a vacuum. The space past the event horizon is essentially cut off from the rest of the universe: It can see the outside, but it can have no communication with it.
(Note how I’m eliding over Hawking Radiation and the fact that black holes evaporate into radiation. It isn’t really germaine to this discussion.)
But space isn’t like matter. It has no inertia, no mass, and no volume. It is simply the absence of mass-energy, that’s all. If something collapses, it takes up less space. That’s all. Saying space collapses really makes no sense, because nothing collapsing results in nothing.
All of the matter would collapse in, not out. A point inside of a hollow sphere of matter would feel no gravitational force from the sphere at all. A piece of the shell would feel a gravitational force only from those portions of the shell closer to the center, as well as probably some sort of force from all the matter outside it pushing down on it. So ultimately, you would get a single, ordinary black hole, with a single, outer event horizon. As with any black hole, someone inside the event horizon would not be able to get out (and would, in fact, be making the close accquaintance of the singulatity in short order), but a person outside would be able to get in, were they idiotic enough to want to.
Your second attempt helped me understand what you were trying to say. You were indicating that the mass would collapse outward from the center of the sphere to somehow form a black hole sphere with a central pocket. It would not occur in this manner. Rather, everything would collapse inward to the center of the sphere, no retained empty spaces in the middle.
At one point I was listening to a discussion on the radio about minimum density vs size. Someone said that a black hole the size of the known universe would have a similar density as the known universe now does. I think that if the universe is closed, then we exist in a black hole?
Irishman, if the sphere was big enough and the skin of the sphere thin enough then there would not be enough central pull to cause the sphere to collapse into the centre. (All force would be directed from the outside of the skin to the centre of the skin and from the inside skin to the centre of the skin also) But if the mass of the sphere was just big enough to collapse but small enough not to collapse to the centre (the skin is thick enough to collapse in on itself, but the sphere is so HUGE that the diameter is too big for the mass of the entire sphere to collapse to the centre of the sphere so just the skin collapses in on itself) of the sphere then you would form a spherical black hole with normal space in the centre.
Chronos, yes there would be no gravitational force at the centre of the sphere IF there was nothing else in the universe. But I’m also asking that if there WAS matter outside of the sphere that it’s gravity would not be felt anywhere INSIDE the sphere because the sphere is a singularity, a point where space is already distorted infinitely and thus any other mass (outside) distorting space to cause a gravitational force on an object INSIDE the sphere would not make it through the singularity *(the sphere). Does that make sense?
Illuvatar, I know it sounds silly, but no matter how big this sphere is, the gravitational pull of the other side will be enough to collapse it. As for the matter outside, in the rest of the Universe, pulling on it, that doesn’t work either. For the same reason. There’s stuff pulling in the opposite direction as well.
Okay okay, now while the setup is ridiculously artificial, that’s okay. It’s a thought experiment. I still think the essence of the original question is very good. To wit, if a part of space were completely cut off from the rest of the Universe by a ring (or whatever) of black holes, would it have any special properties? I don’t know, but my instincts say no. You know how useful it is, though, relying on your instincts when dealing with GR…
Achernar, so your saying that if the sphere was as thick as say 5 stars of 5 solar mass’ side by side that stopped fusing at the same instant (more than enough to create a black hole) , but the space inside the sphere was 17 billion lightyears from one side to the other that as it collapses the sphere would shrink down to a singularity point in the centre of the sphere? The Schwarzschild radius for the 25 solar mass thick sphere would be about 30km isn’t it? But the 17 billion light years would be way too far for the total mass of the surface of sphere to create a black hole.
Two bodies that have mass effect each other via their gravity by distorting space-time along a path between them. But if you put a wall (i.e. the singularity of infinite distortion) between them then no matter how large the gravity (space-time distortion) created by the two bodies the distortion would not be more than the infinite distortion at the singularity. So any matter inside the sphere would be uneffected by any gravity of mass outside the sphere. Because there is no communication of forces, or even the continuity of space-time from the outside of the sphere to the inside of the sphere then by definition isn’t this separated from the universe? Is this correct?
Achernar, so your saying that if the sphere was as thick as say 5 stars of 5 solar mass’ side by side that stopped fusing at the same instant (more than enough to create a black hole) , but the space inside the sphere was 17 billion lightyears from one side to the other that as it collapses the sphere would shrink down to a singularity point in the centre of the sphere? The Schwarzschild radius for the 25 solar mass thick sphere would be about 30km isn’t it? But the 17 billion light years would be way too far for the total mass of the surface of sphere to create a black hole.
Two bodies that have mass effect each other via their gravity by distorting space-time along a path between them. But if you put a wall (i.e. the singularity of infinite distortion) between them then no matter how large the gravity (space-time distortion) created by the two bodies the distortion would not be more than the infinite distortion at the singularity. So any matter inside the sphere would be uneffected by any gravity of mass outside the sphere. Because there is no communication of forces, or even the continuity of space-time from the outside of the sphere to the inside of the sphere then by definition isn’t this separated from the universe? Is this correct?
It took me a while to understand what Illuvatar is trying to describe, but I think I figured it out. He’s attempting to create a bounded domain-wall.
Let me explain my terms. A gravitational singularity is a point-discontinuity in the space-time. These are commonly created by black holes. Cosmic strings (not the same as the strings in string theory) are linear discontinuities in the space-time. These, I believe, could have been created during the immediate aftermath of the Big Bang. They are basically “cracks” in space-time. Their large mass would create gravitional-lensing effects (that have not been detected, as of yet).
Domain walls are the two-dimensional space-time discontinuities. I’m not sure how they’re created. Their topology is usually planar, but I see no instrinsic reason you couldn’t have one with a spherical topology. So, yes, you could have a spherical discontinuity, of which the inside would be causally disconnected from the rest of the universe.
The problem is that a bounded domain wall is inherently unstable without exotic matter with negative energy-density (even anti-matter has positive energy-density). Otherwise, the domain wall will be gravitionally attracted to itself and deflate extremely quickly. Only negative matter could exert the necessary pressure to keep the domain wall bubble inflated.
So what will an observer on the inside of the deflating domain wall bubble see? I’m not sure. Maybe the extreme space-time dilation effects will prevent the observer from even seeing the collapse. Everything in the observer’s “universe” will be accelerating away, toward the incoming domain wall. Fascinating idea.
BTW, I don’t believe it would be possible to even create a domain wall bubble without negative matter. You would have to arrange for precisely coordinated gravitional collapses across large volumes of space. Any non-uniformities in the setup will create gaps in the bubble. Gaps are irreparable, even with negative matter. But a careful combination of normal and negative matter could probably allow the creation of the domain wall bubble.
It took me a while to understand what Illuvatar is trying to describe, but I think I figured it out. He’s attempting to create a bounded domain-wall.
Let me explain my terms. A gravitational singularity is a point-discontinuity in the space-time. These are commonly created by black holes. Cosmic strings (not the same as the strings in string theory) are linear discontinuities in the space-time. These, I believe, could have been created during the immediate aftermath of the Big Bang. They are basically “cracks” in space-time. Their large mass would create gravitional-lensing effects (that have not been detected, as of yet).
Domain walls are the two-dimensional space-time discontinuities. I’m not sure how they’re created. Their topology is usually planar, but I see no instrinsic reason you couldn’t have one with a spherical topology. So, yes, you could have a spherical discontinuity, of which the inside would be causally disconnected from the rest of the universe.
The problem is that a bounded domain wall is inherently unstable without exotic matter with negative energy-density (even anti-matter has positive energy-density). Otherwise, the domain wall will be gravitionally attracted to itself and deflate extremely quickly. Only negative matter could exert the necessary pressure to keep the domain wall bubble inflated.
So what will an observer on the inside of the deflating domain wall bubble see? I’m not sure. Maybe the extreme space-time dilation effects will prevent the observer from even seeing the collapse. Everything in the observer’s “universe” will be accelerating away, toward the incoming domain wall. Fascinating idea.
BTW, I don’t believe it would be possible to even create a domain wall bubble without negative matter. You would have to arrange for precisely coordinated gravitional collapses across large volumes of space. Any non-uniformities in the setup will create gaps in the bubble. Gaps are irreparable, even with negative matter. But a careful combination of normal and negative matter could probably allow the creation of the domain wall bubble.
It sounds to me Illuvator that you are describing a possible model (w/blackhole as an example) to explain an oscillating universe with the main point being: what’s in the center and can we cross it?
As far as existing inside the blackhole, not happening, it is basically a big sausage grinder tearing everything that enters it into subatomic particles. That is the energy radiated at the event horizon which is measurable.
So, some energy is capable of escape as it approaches the E.H. but not after.
OK, so let me get this straight: We start with a bunch of black holes, arranged spherically around a central point. These black holes all move inwards, until at some distance from the center, they’re all overlapping (with no gaps between them). The eventual result of this will be a single black hole in the center, and a lot of gravitational waves thrown out of the system. However, if the initial sphere is sufficiently large, it might take a while for this to occur. What would you see in the mean time? My guess is that until they all came in and squished you, it’d look perfectly normal. But I’m not sure.
I think chronos got it. The “wall” of blackholes will attract each other and eventually get so close that everything will be just one big gravity well.
I reckon that if you are inside the shrinking walls you won’t know it cos the walls facing you would be moving out at the same speed the walls outside comes in. But after the inside and outside walls fuse you’ll start to see the walls coming closer but still feel zero gravity…until you get squashed
*Which gives me an interesting thought…this would mean that everything inside the skin of a blackhole would actually be experiencing zero gravity…contrast to what everything outside the skin experiences…which would mean that much of the blackholes gravity would be neutralised…which means that a blackhole dosen’t exist…which means…white hole? =p