Why Don't Singularities Instantly Suck Everything In?

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Discussion Overview

The discussion revolves around the nature of singularities in black holes, particularly addressing the implications of infinite density and gravity. Participants explore concepts related to mass, gravity, and the characteristics of singularities, with a focus on theoretical understanding rather than mathematical rigor.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions why a singularity, with infinite density, does not lead to everything in the universe being sucked in instantaneously, suggesting a misunderstanding of gravity's relationship to mass.
  • Another participant clarifies that gravity is based on total mass rather than density, arguing that the mass of a singularity is not infinite, and thus it does not exert infinite gravity.
  • A participant raises a question about how something with no size can have a finite mass, indicating confusion about the relationship between mass and size.
  • Another response elaborates on the concept that mass can remain constant even as density approaches infinity and volume approaches zero, discussing the breakdown of traditional formulas in this context.

Areas of Agreement / Disagreement

Participants express differing views on the implications of singularities and the relationship between mass, density, and gravity. The discussion remains unresolved with multiple competing perspectives on these concepts.

Contextual Notes

Limitations include the lack of clarity on the definitions of mass and density in extreme conditions, as well as the unresolved nature of how traditional physics applies to singularities.

uknova
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I have an interest in physics, I have not studied it at any high levels (as u will soon find out :smile: ), i just like to read and think about it, but I have a question, please don't blind me with maths!

If a singularity at a black hole has infinity density, I'm guessing this means it has infinite gravity. If someone has infinite gravity, won't everything in the universe get sucked into it instantaneously? Why does this not happen?

Sorry if my question sounded a bit dumb, which i guess it probably did!
 
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uknova said:
If a singularity at a black hole has infinity density, I'm guessing this means it has infinite gravity. If someone has infinite gravity, won't everything in the universe get sucked into it instantaneously? Why does this not happen?
The answer is that it doesn't have infinite gravity, gravity is based on total mass rather than density, and the mass of the singularity is not infinite. For example, if the sun were replaced by a black hole of equal mass, the gravitational pull felt by the Earth wouldn't change, so it would remain in the same orbit.
 
how does something that has no size have a finite mass ?
 
uknova said:
how does something that has no size have a finite mass ?
mass doesn't really have anything to do with size, except in the sense that normally mass = density*volume...but obviously this formula breaks down when the density is infinite and the volume is zero, infinity times zero doesn't have a well-defined answer. But obviously if you keep cutting the volume in half while doubling the density, the mass will stay constant, and that's basically what's going on when the matter in a star is being compressed into a singularity.
 
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