Suppose a cloud of dust of sufficient mass and density collapses to form a black hole. As this mass falls within the event horizon, to an outside observer it enters an area of infinite time dilation. (time stops) So within the mass's frame of reference it will continue to collapse into a singularity, to an outside observer this will only happen at an infinite time in the future. So are black holes singularities or not. Secondly, how could an outside observer tell if the mass within the event horizon still occupied say 90% of that volume, or had already become a singularity. It seems to me that as we have only gravitational evidence, it would be impossible to tell. Perhaps most black holes still haven't become singularities.
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That's true, in the frame of the outside observer the gravitational time dilation prevents the matter from collapsing to a point, in that frame the matter distribution stays at least an infinitesimal larger than the horizon. – Yukterez Dec 31 '23 at 18:02
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Also relevant: How can anything ever fall into a black hole as seen from an outside observer? – John Rennie Dec 31 '23 at 18:08
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“As this mass falls within the event horizon, to an outside observer it enters an area of infinite time dilation. (time stops)” - This is incorrect in 3 parts. (1) As observed from outside, nothing ever crosses the horizon, because (2) the infinite time dilation is at the horizon, not at the singularity. (3) There is no volume inside the black hole, it is zero. A black hole is not a “ball” with a volume inside, but a complex 4-dimensional spacetime structure (rapidly shrinking spherinder) that evolves “after” the eternity of the cosmological time of the universe. – safesphere Jan 01 '24 at 06:33