Is a Black Hole the Most Dense Object in the Universe?

Click For Summary

Discussion Overview

The discussion centers around the concept of density in relation to black holes, specifically whether a black hole represents the most dense object in the universe. Participants explore theoretical implications, the limits of current physical theories, and the nature of density in different reference frames.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant calculates a mass that could create a black hole, leading to a derived density that suggests extreme values, questioning if this is the maximum density possible.
  • Another participant identifies the calculated density as Planck Density, indicating that at such densities, current theories of General Relativity (GR) and Quantum Mechanics (QM) may not apply effectively.
  • Some participants propose that, similar to the speed of light, there might be a limit to density in a given reference frame.
  • Others argue that classical theory does not impose a density limit, as density is coordinate system dependent, allowing for arbitrarily large values in certain systems.
  • Questions arise regarding the definition of point particles and their densities, such as that of an electron, which complicates the discussion of density limits.

Areas of Agreement / Disagreement

Participants express differing views on whether there is a maximum density for objects like black holes, with some suggesting limits based on theoretical frameworks and others asserting that no such limits exist in classical theory. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants acknowledge the limitations of current theories in extreme conditions and the lack of experimental data to support claims about density at such scales.

aise0603
Messages
6
Reaction score
0
Mass falling into a black hole will approach the center of the black hole at a given velocity. As it approaches the center of the black hole, from our reference frame, there is time dialation. In fact, at some given closeness, a unit of Planck time, in the mass's reference frame, is longer than the age of the universe.

Gravitational time dilation outside a non-rotating sphere
to = tf(1-2GM/(rc2))1/2

if to = Planck time
tf = the age of the universe
r = Planck distance

solve for M to find the smallest amount of mass that could possibly create a black hole

Ms = 1.09 X 10-8 kg




Density = Ms/Vs = 6.15718 X 1095kg/m3

Is that the most dense that anything could be in the universe?
 
Physics news on Phys.org
What you have calculated is so called Planck Density:
http://en.wikipedia.org/wiki/Planck_units

It means that at such density we can't use GR or QM as is
We need to use more advanced theory which does not exist yet.
 
But could it be that in a given reference frame, nothing can be more dense than this? Just like nothing can travel faster than the speed of light, in a given reference frame.
 
In what context do you want us to answer your questions?
As Dmitry mentioned, we have good reason to expect our current theories won't match nature very well in these regimes. And we definitely don't have experimental data from these regimes either. So no "real" answer can be given right now.

But if you are just asking what classical theory like GR says, then the answer is no: there is no density limit. Density is coordinate system dependent, so we can choose a coordinate system which makes it arbitrarily large if we wish. So there is no classical limit on density.

Even ignoring the coordinate system issues, what would you consider a point particle. For example, what is the density of an electron?
 
JustinLevy said:
In what context do you want us to answer your questions?
As Dmitry mentioned, we have good reason to expect our current theories won't match nature very well in these regimes. And we definitely don't have experimental data from these regimes either. So no "real" answer can be given right now.

But if you are just asking what classical theory like GR says, then the answer is no: there is no density limit. Density is coordinate system dependent, so we can choose a coordinate system which makes it arbitrarily large if we wish. So there is no classical limit on density.

Even ignoring the coordinate system issues, what would you consider a point particle. For example, what is the density of an electron?

Typical...
 
aise0603 said:
Typical...

Typical what? It was a good answer to your question.
 

Similar threads

Undergrad Falling through the event horizon of an evaporating black hole
  • · Replies 51 ·
2
Replies
51
Views
6K
High School Theories about light and time near a black hole
  • · Replies 20 ·
Replies
20
Views
3K
High School Question about the Entropy of a Black Hole Singularity
  • · Replies 17 ·
Replies
17
Views
4K
Undergrad Black hole inside of a black hole.... can it be done?
  • · Replies 114 ·
4
Replies
114
Views
10K
High School Is there a lining to our Universe?
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad Observing Black Holes in Finite Time
  • · Replies 10 ·
Replies
10
Views
2K
Graduate Do Black Holes have Singularities?
  • · Replies 20 ·
Replies
20
Views
3K
High School Universe Becoming a Black Hole: What Would It Look Like?
  • · Replies 15 ·
Replies
15
Views
2K
Undergrad Observing a Collapsing Shell: Time Dilation Explained
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Falling into a Black Hole: Blueshift Questions Explored
  • · Replies 11 ·
Replies
11
Views
5K