Black Holes: Volume & Forces Explored

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Discussion Overview

The discussion centers on the nature of black hole singularities, specifically addressing whether they have volume and what forces, if any, prevent particles from occupying the same space. The conversation touches on theoretical implications within the realms of general relativity and quantum physics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that black hole singularities may have 0 volume, suggesting that if a singularity exists, it cannot occupy space in the conventional sense.
  • Others argue that the concept of a singularity is ambiguous, as it may not be part of the spacetime manifold, making it difficult to define its dimensionality or volume.
  • A participant mentions that the breakdown of the metric at a singularity complicates the definition of volume, indicating that it is not straightforward to assert whether a singularity has volume.
  • There is a suggestion that the volume of a singularity is not well-defined, with a comparison made to the center of a clock where physical characteristics cannot be attributed to the singularity itself.
  • Some participants challenge the idea of attributing properties like mass, charge, and spin to the singularity, stating that these are properties of the entire spacetime rather than the singularity alone.

Areas of Agreement / Disagreement

Participants express differing views on the nature of singularities and whether they can be said to have volume. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

The discussion highlights limitations in the current understanding of singularities, particularly the dependence on the unification of quantum physics and general relativity, and the implications of the breakdown of the metric in defining physical characteristics.

Invutil
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Do black hole singularities have 0 volume? What forces are keeping the particles from being in the same place?
 
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Invutil said:
What forces are keeping the particles from being in the same place?
If there is a singularity, none, and a singularity has a volume of 0 (otherwise it wouldn't be a singularity, at least not in our universe).
It is unclear if there is a singularity, as we don't have a proper unification of quantum physics and general relativity, and there both are relevant at the same time.
 
We just had a discussion of this: https://www.physicsforums.com/threa...s-equal-to-schwarzschild-radius.841320/unread

The brief answer is that in classical relativity, a singularity is not part of the spacetime manifold. It's not a point or a set of points. There is not even any straightforward way to define whether it's one-dimensional, two-dimensional, or three-dimensional. We certainly can't say whether or not it has volume, because that would require the use of the metric, and a singularity represents a breakdown of the metric.

This may be helpful: https://www.physicsforums.com/threads/boundary-construction-for-of-b-h-and-b-b-singularities.833399/

mfb said:
If there is a singularity, none, and a singularity has a volume of 0 (otherwise it wouldn't be a singularity, at least not in our universe).

This is wrong, for the reasons given above.
 
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Hmm, right. It's probably better to say its volume is not well-defined.
 
mfb said:
Hmm, right. It's probably better to say its volume is not well-defined.

I would just say that there's no "it" whose volume we could even try to define. Classical GR doesn't describe a singularity as a physical or geometrical thing. Asking for physical characteristics of a singularity is like asking what time it is when the tip of the minute hand is at the center of the clock. The dial only exists around the circumference of the circle, not at its center. You might think that a black hole's mass, charge, and spin were properties attributable to the singularity, but GR doesn't actually describe them this way; they're properties of the whole spacetime that are only defined by an observer at asymptotic infinity.
 
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