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I have been trying to read Penrose diagram to understand what white hole can do, but can the white hole collapses into a black hole and if so then what kind of conditions would turn a white hole into a black hole? I know the event horizon of a white hole would repel everything including light but is there anything in GR that can turn white hole into black hole? I also understand that laws of thermodynamics prohibited the existence of white holes but I am fascinated by white holes

user6760
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  • Yes, according to the paper mentioned in this answer: https://physics.stackexchange.com/questions/513380/513497#513497 - but whether or not this paper makes any physical sense is a different question. – safesphere Jan 12 '24 at 02:55
  • A WH is a time reversed BH. The external metric is time symmetric and so is the same for both. This creates an impression that an astrophysical WH can exist as an observed attractive object just like a BH. However, this way geodesics are broken at the horizon (e.g the proper time of an infalling observer ends at the horizon). The correct time reversal is global, inside and outside (as in the maximally extended solution). This would make a WH a past state of the BH, but only if it has always existed in the infinitely old universe. So forget thermodynamics, real WHs are prohibited by geometry. – safesphere Jan 17 '24 at 06:04

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