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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