If there’s no difference in the local spacetime geometry, is there anything to prevent a single object that behaves both ways at different times, or even simultaneously?
As far as I can see, if you’re able to switch the thermodynamic/cosmological arrow of time in the external universe, you could have a single structure act as a black hole for some of the time and a white hole for some of the time. The hole carries with it an enduring distinguished direction in time: the direction in time that accompanies outwards passage through the horizon. If the thermodynamic arrow associated with that direction in the external universe changed, then you’d be entitled to call the hole by different names in the different epochs. The “even simultaneously” is trickier; I think that depends on exactly where and when and in what coordinates you ask the question. The singularity inside a hole is actually spacelike — i.e. extended in a spatial direction, not in time — like the Big Bang or Big Crunch. When you fall into a BH, you don’t arrive at the singularity like you’re reaching the centre of the Earth; what you see is the space around you getting crushed to a point in t
As far as I can see, if you’re able to switch the thermodynamic/cosmological arrow of time in the external universe, you could have a single structure act as a black hole for some of the time and a white hole for some of the time. The hole carries with it an enduring distinguished direction in time: the direction in time that accompanies outwards passage through the horizon. If the thermodynamic arrow associated with that direction in the external universe changed, then you’d be entitled to call the hole by different names in the different epochs. The “even simultaneously” is trickier; I think that depends on exactly where and when and in what coordinates you ask the question. The singularity inside a hole is actually spacelike — i.e. extended in a spatial direction, not in time — like the Big Bang or Big Crunch. When you fall into a BH, you don’t arrive at the singularity like you’re reaching the centre of the Earth; what you see is the space around you getting crushed to a point in t
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