# Black Hole Question

## Main Question or Discussion Point

This may be pretty basic but how can black holes have different masses, rotate, obtain material or have mass if black holes are finite points. I'm sure it has something to do with mathematics or theory but it is difficult for me to make any sense of this. Black holes make sense to me until I factor in that they are supposed to be a finite point. Even the fact that they attain mass and matter is confusing. They are a finite spot that can be accessed at all points, 3 dimensions, so where does the matter go?

## Answers and Replies

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bcrowell
Staff Emeritus
Gold Member
We don't really know whether black hole singularities are pointlike. Would it bother you to have ten solar masses compressed to, say, $10^{-105}$ cubic meters (one cubic Planck length)?

This may be pretty basic but how can black holes have different masses, rotate, obtain material or have mass if black holes are finite points.
It IS basic, a fundamental unknown. but not simple. And that is one major reason black holes are so fascinating to theorists. Immense gravity, best described by general relativity, and the physics of the small, best described by quantum theory, come together at the singularities. But so far neither theory can handle the exact description of whatever that "singularity" may be. Quantum gravity is an attempt at such descriptions, not yet fulfilled.

More here, but I think many here would disagree with some of the description:
http://en.wikipedia.org/wiki/Black_hole#Singularity

Note that the words don't say "finite points"....it's a subtle distinction.

And within in the description are contradictions ....
It can also be shown that the singular region contains all the mass of the black hole solution....
versus

It is generally expected that a theory of quantum gravity will feature black holes without singularities,,,
So we have more to learn.

Another perspective in answering the OP question.

I was just reading a section of Black Holes and Time Warps, by Kip Thorne and on page 463 he discusses an interesting feature of black holes discovered by Roger Penrose:

The (singulairty) theorem says, roughly, that any star which implodes to form an apparent horizon must have a singularity inside. ..and was derived from topology...
The theorem simply told us that somewhere inside a black hole, spacetime must come to an end, and anything that reaches that end must be destroyed. HOW it gets destroyed was the province of curvature, THAT it gets destroyed...that there is an end to spacetime...was the province of topology.
That "end" is the singularity. How spacetime gets destroyed there is unknown.