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It's more tricky than that, because inside a black hole things turn really weird. Of course things might get unpredictable close to the singularity if you reall

It's more tricky than that, because inside a black hole things turn really weird. Of course things might get unpredictable close to the singularity if you really assume it is just a ton of matter squished into a tiny point as seen from the outside, but the overall spacetime geometry inside black holes would be untouched by that. Especially if you consider large, supermassive black holes that even have comfortable tidal forces at the horizon. If you now look at black hole geometries in GR, you'll find that the singularity is not a point in space, it is actually a moment in time. Once you cross the event horizon, that moment becomes part of your future, which means that there is absolutely nothing you could do to escape it. So a more accurate description of a singularity would not say "super dense point in space" - it would literally describe it as "the end of time." As in the opposite of the big bang.

mystified5016 2y ago
I really like Penrose's new theory that the singularity is a torus within a bubble of normal space inside the event horizon. The point-like singularity predicted by GR seems obviously implausible, it makes more sense for it to be smeared throughout some volume of space. If I understand correctly, he proposes that the singularity is a compact object rotating about the center so fast that it's more or less a solid torus. Intuitively, it also makes sense that space within a black hole could be more or less normal. Or at least have a consistent curvature that approximates normal space. Conversely, I find the notion of space-time equivalence as illustrated by Penrose diagrams to be quite unconvincing. All we really have is high order approximations of how GR might behave in extreme conditions. I believe that if it ever becomes testable, we'll see some kind of limit to how far space can translate to time. Or that time is more complex than we think. No one really knows for sure, but it's a lot of fun to speculate about!
- lanstin 2y ago
  Space-time equivalence is pretty key to the functioning of the Global Positioning System, and it comes from special relativity. It shows up well before black hole gravitational conditions.
- zardo 2y ago
  > The point-like singularity predicted by GR seems obviously implausible, it makes more sense for it to be smeared throughout some volume of space. If I understand correctly, he proposes that the singularity is a compact object rotating about the center so fast that it's more or less a solid torus. I think the idea there is that there is no singularity. He's taken the prediction for a rotating blackhole (all mass collapses into a 0-volume ring) and supposed that there is a yet to be discovered force that resists infinite compaction leaving a ring of greater than 0 volume.
jiggawatts 2y ago
Personally, I’m not convinced that there is an “inside”. From the outside there doesn’t appear to be one — you never see anything cross the horizon, including the substance that originally formed the black hole! Conversely, observers see the black hole evaporating from just above the surface, with all infalling matter recovered in this way. World lines approach the horizon, hug it closely, then leave. They don’t fall “in”. In my mind scientists filled in a blank with their imaginations, but the blank they are filling in may not even exist as a location. It’s like complex (imaginary) numbers, you can talk meaningfully about solutions to equations: but ordinary +, -, *, / arithmetic “can’t get you there”. A black hole could be like a pinhole stretched out into a larger hole in a stretchy sheet of fabric. From the point of view of an ant walking on the surface the hole is a boundary that can be approached, but not entered, and around it the fabric is highly distorted. There have been some good papers published recently on related topics. For example, Penrose diagrams as typically drawn use a simplification that black holes extend forever forward and backward in time. This allows infinitesimals to add up over infinity, which is a non-physical sleight of hand. Real black holes form over time, and worldlines don’t enter them — they just approach the horizon and then “boil off” in the distant future due to Hawking radiation. There is this obsession in modern physics of clinging to overly simplified models and then treating the edges of their capabilities as real things to discover instead of modelling failures to get past with better models. You can’t climb the mountain range represented by the fold crease in your map.
- sigmoid10 2y ago
  >Real black holes form over time, and worldlines don’t enter them That's not correct. It only appears that way in some forms of diagrams because of their choice of coordinate system or the way they display lines of constant time/space. But all black holes (eternal Penrose and normal ones) have worldlines entering them normally. The claim that these worldlines would suddenly stop at the horizon for no particular reason is pretty wild (but not completely new). I don't think the majority of physicists would doubt that an observer could fall inside a black hole (particularly large black holes with low tidal forces), because from their point of view there would be absolutely nothing unusual happening at the horizon.

mystified5016 2y ago

I really like Penrose's new theory that the singularity is a torus within a bubble of normal space inside the event horizon. The point-like singularity predicted by GR seems obviously implausible, it makes more sense for it to be smeared throughout some volume of space. If I understand correctly, he proposes that the singularity is a compact object rotating about the center so fast that it's more or less a solid torus. Intuitively, it also makes sense that space within a black hole could be more or less normal. Or at least have a consistent curvature that approximates normal space. Conversely, I find the notion of space-time equivalence as illustrated by Penrose diagrams to be quite unconvincing. All we really have is high order approximations of how GR might behave in extreme conditions. I believe that if it ever becomes testable, we'll see some kind of limit to how far space can translate to time. Or that time is more complex than we think. No one really knows for sure, but it's a lot of fun to speculate about!

lanstin 2y ago
Space-time equivalence is pretty key to the functioning of the Global Positioning System, and it comes from special relativity. It shows up well before black hole gravitational conditions.
zardo 2y ago
> The point-like singularity predicted by GR seems obviously implausible, it makes more sense for it to be smeared throughout some volume of space. If I understand correctly, he proposes that the singularity is a compact object rotating about the center so fast that it's more or less a solid torus. I think the idea there is that there is no singularity. He's taken the prediction for a rotating blackhole (all mass collapses into a 0-volume ring) and supposed that there is a yet to be discovered force that resists infinite compaction leaving a ring of greater than 0 volume.

jiggawatts 2y ago

Personally, I’m not convinced that there is an “inside”. From the outside there doesn’t appear to be one — you never see anything cross the horizon, including the substance that originally formed the black hole! Conversely, observers see the black hole evaporating from just above the surface, with all infalling matter recovered in this way. World lines approach the horizon, hug it closely, then leave. They don’t fall “in”. In my mind scientists filled in a blank with their imaginations, but the blank they are filling in may not even exist as a location. It’s like complex (imaginary) numbers, you can talk meaningfully about solutions to equations: but ordinary +, -, *, / arithmetic “can’t get you there”. A black hole could be like a pinhole stretched out into a larger hole in a stretchy sheet of fabric. From the point of view of an ant walking on the surface the hole is a boundary that can be approached, but not entered, and around it the fabric is highly distorted. There have been some good papers published recently on related topics. For example, Penrose diagrams as typically drawn use a simplification that black holes extend forever forward and backward in time. This allows infinitesimals to add up over infinity, which is a non-physical sleight of hand. Real black holes form over time, and worldlines don’t enter them — they just approach the horizon and then “boil off” in the distant future due to Hawking radiation. There is this obsession in modern physics of clinging to overly simplified models and then treating the edges of their capabilities as real things to discover instead of modelling failures to get past with better models. You can’t climb the mountain range represented by the fold crease in your map.

sigmoid10 2y ago
>Real black holes form over time, and worldlines don’t enter them That's not correct. It only appears that way in some forms of diagrams because of their choice of coordinate system or the way they display lines of constant time/space. But all black holes (eternal Penrose and normal ones) have worldlines entering them normally. The claim that these worldlines would suddenly stop at the horizon for no particular reason is pretty wild (but not completely new). I don't think the majority of physicists would doubt that an observer could fall inside a black hole (particularly large black holes with low tidal forces), because from their point of view there would be absolutely nothing unusual happening at the horizon.