Black hole is the densest .... in universe. We know that dimension of universe is 4D . So, what is the dimensions of black hole? Is string theory explains what is it's dimension?
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$\begingroup$ Not sure what you mean. In English "..." means a missing word or phrase. We don't know the Universe is 4D. Spacetime in general relativity is 4D, but that is not true in string theories. A "blackhole" is a region of spacetime. You could ask the same question of any region: "how many dimensions does your bedroom have?" Also, in English "what are the dimension of ..." means "how big is ...", though I think this is not what is meant. You should describe what research you have done, and why you think a blackhole might be different from any other region of spacetime. $\endgroup$– James KCommented Sep 2, 2017 at 14:30
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1$\begingroup$ Shakya I'm sorry, but this question isn't very clear. Please try to rephrase it to make it clearer. For now I would say the dimensions of a black hole are the same as the dimensions of a star, or your bedroom. And that no, string theory does not explain a black hole's dimensions. $\endgroup$– John DuffieldCommented Sep 2, 2017 at 17:51
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2 Answers
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The singularity itself is, by definition, zero dimensional (well...you could argue one dimensional as it exists over time, but it has zero spacelike dimensions).
The event horizon is a two dimensional sphere, just like the surface of a beach ball - whether it can be said to have any thickness is unknown, there might be a thickness down at the Planck scale, but that's currently unknown.
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I think, knowing that what dimension a black hole has depend on approach it with it's geometry.
When we discuss about a black hole and specially it's event horizon, we encounter to some geometry to study it. We should knowing the geometry of space-time and is space-times Flat and curved, if we use the geometry of Minkowski Space-time or other geometry. the Space-time structure is very important here.
In general relativity, it's unknown that what happens in GKP and with which manifold we must mathematically discuss about it!
I think this question that what is the dimensions of black hole, is physically vague and mathematically also.
