Re: black hole radius question please

Faye Kane wrote:
In a different post, someone said that black holes are macroscopic and
not subject to quantum effects.

One must be careful to keep the theoretical context clear, and to be sure to discuss only one thing at a time -- it seems to me you are confusing several discussions of different aspects of black holes.


I thought the radius decreased continually due to
unending collapse. (I am not talking about the radius of the event
horizon). If a black hole continues to shrink, won't it become
smaller than a quark or a string? How long will that take? And if
not, what keeps it from shrinking further?

In General Relativity, which is a classical theory (i.e. not quantum), the collapse of a star to become a black hole cannot be stopped once it starts, and the outer surface of the star will collapse all the way into a singularity in a finite proper time; this singularity has no meaningful size, but speaking loosely it goes to zero size. Note that GR has no concept of quarks or strings -- they belong to other theoretical contexts (ones that are incommensurate with GR). While the surface of the star shrinks through the event horizon and decreases toward the eventual singularity, the event horizon itself remains fixed once the surface passes through it (assuming nothing else falls in).


I know that space is bent almost 90 degrees next to a mass this dense,

Hmmm. You are confused. The suggestion to read Geroch's book is a good one.


but I would think that the definition of the spatial extent of a black
hole would still have some meaning.

When we say "black hole", we mean the region inside and including the event horizon. In GR, as long as nothing falls into the black hole, its size remains constant. The "radius" of a black hole (i.e. of its event horizon) is not well defined, but the area of the horizon is well defined.


Tom Roberts
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