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Geometry of a black hole 
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#1
Sep2513, 02:52 PM

P: 326

I was watching a documentary about the universe and it claimed that black holes were sometimes as small as 2 kilometers across. Now before this, my general understanding of a black whole was that it had no physical extent in space, that it was just a 1 dimensional singularity, and the black planet looking thing was just where the point of no return started. So if I were sucked into a black hole, would I eventually run into a very dense mass 1 kilometers across or would it just be empty space all the way down to the singularity?



#2
Sep2513, 03:24 PM

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P: 6,109

The 2 km refers to the outside dimension. No one really knows what happens inside a black hole. General Relativity and Quantum thoery don't work together  new theory is needed.



#3
Sep2513, 03:36 PM

Mentor
P: 3,954

 That's just a part of the black hole, not the whole thing. The whole thing is the event horizon and everything inside it.  We can't very well look inside the black hole to see what's at its center, but it's unlikely that there's really a pointlike singularity. At very small distance scales we have to pay attention to quantum mechanical effects; general relativity doesn't consider these, so its predictions cannot be completely trusted when very large masses are concentrated into truly infinitesimal volumes on the way to becoming a sizezero singularity. A smallish correction: You said "1 dimensional" above but I assume you meant "zerodimensional"; a onedimensional singularity would be a line not a point. 


#4
Sep2513, 03:40 PM

P: 326

Geometry of a black hole



#5
Sep2513, 04:11 PM

C. Spirit
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P: 5,661

Kerr black holes have 1D singularities (ring).



#6
Sep2713, 11:46 AM

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#7
Sep2713, 02:00 PM

P: 371




#8
Sep2713, 02:34 PM

PF Gold
P: 6,506




#9
Sep2713, 03:56 PM

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PF Gold
P: 9,488

The singularities in a Kerr black hole are coordinate singularities. They can be resolved by changing the coordinate system. There is a strong belief a similar solution is possible to eliminate the singularity in a Schwarzschild black hole, although it remains to be demonstrated.



#10
Sep2713, 04:55 PM

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#11
Sep2713, 09:30 PM

Sci Advisor
PF Gold
P: 9,488

See http://arxiv.org/abs/grqc/9803087 for discussion.



#12
Oct513, 01:59 AM

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#13
Oct513, 04:26 PM

Sci Advisor
PF Gold
P: 9,488

Agreed. Coordinate transforms do not resolve point singularities as they suffer from infinite curvature, which produces other infinities. Efforts to remove this infinite curvature are being attempted in LQG and AdS/CFT. The Kerr central singularity is rather unique in that there are trajectories that need not pass through a region of infinite curvature. The lure of adding extra dimensions to resolve this singularity, such as in AdS/CFT, is undeniably tempting. Here is a paper some may find of interest: 'Infinities as a measure of our ignorance', http://arxiv.org/abs/1305.2358.



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