B Why do black holes have infinite density, mass, and gravity?

[science_rules]

If stars have finite mass, gravity, and density, why does a black hole have infinite density, mass, and gravity and why doesn't it attract everything around it with such infinite gravity? Also, with infinite density, why are black holes all different sizes?

 

[russ_watters]

...why does a black hole have infinite density, mass, and gravity...

As far as we can tell, black holes don't have any of those characteristics.

 

[science_rules]

In a science documentary, Michio Kaku mentioned that the singularity of black holes have infinite density and infinite gravity. How can laymen expect to learn anything or trust scientists if what some scientists say is not what other scientists believe and scientists never agree with each other about fundamental ideas about the Universe? If what he said is true, it seems then that scientists cannot agree with each other, either that or scientists just make stuff up even if it doesn't make any sense. Same with string theory.

 

[russ_watters]

In a science documentary, Michio Kaku mentioned that the singularity of black holes have infinite density and infinite gravity.

There is some debate on PF as to what "the singularity" means, however Kaku was almost certainly referring to a finite mass in zero volume. In either case, since we can't ever go and check, that doesn't impact what a black hole looks like to us (a region of space with a finite volume, finite mass and finite gravitational field). There is no debate about that. So does that clear it up...?

How can laymen expect to learn anything or trust scientists if what some scientists say is not what other scientists believe and scientists never agree with each other about fundamental ideas about the Universe? If what he said is true, it seems then that scientists cannot agree with each other, either that or scientists just make stuff up even if it doesn't make any sense.

Sorry, but the misunderstanding there is yours; You extrapolated something beyond what he said.
[also, a link would help...]

 

[berkeman]

infinite gravity

Why does an electron have infinite electric field at zero distance?

 

[science_rules]

There is some debate on PF as to what "the singularity" means, however Kaku was almost certainly referring to a finite mass in zero volume. In either case, since we can't ever go and check, that doesn't impact what a black hole looks like to us (a region of space with a finite volume, finite mass and finite gravitational field). There is no debate about that. So does that clear it up...?

Sorry, but the misunderstanding there is yours; You extrapolated something beyond what he said.
[also, a link would help...]

That makes no sense. If Kaku meant that, he should have said so instead of making it confusing and misleading for the laymen. Saying a black hole has infinite density is not the same as saying finite mass in zero volume.

<< Mentor Note -- Insult removed from post >>[/color]

 

[Bandersnatch]

Pay attention to what was said: singularities have infinite density and infinite gravity. This is not the same as black holes having those characteristics. Nor was anything said about infinite mass.

Black hole singularities have 0 volume, so any finite mass they might have will net infinite density, and infinite gravity (since you can get infinitely close to the central mass).

Black holes themselves are regions surrounding the singularity, within which escape velocity is greater than c. Since those regions have finite volume, their density and gravity are finite too.

The extent of that region is dependent on mass encompassed within, so it will vary with varying mass.

 

[russ_watters]

That makes no sense. If Kaku meant that, he should have said so instead of making it confusing and misleading for the laymen. Saying a black hole has infinite density is not the same as saying finite mass in zero volume.

Yes, actually it is:
What happens to "d" in the following function as "v" approaches zero?
d=m/v

And please slow your roll; I'm trying to help.

 

[berkeman]

Yes, actually it is:

What happens to "d" in the following function as "v" approaches zero?
d=m/v

And please slow your roll.

You beat me to it...

 

[DrClaude]

How can laymen expect to learn anything or trust scientists if what some scientists say is not what other scientists believe

You now understand why most physicists roll their eyes at the mention of Michio Kaku...