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Astronomy

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    $\begingroup$ related: astronomy.stackexchange.com/questions/32410/… $\endgroup$
    – Florin Andrei
    Commented Sep 5, 2019 at 7:46
  • $\begingroup$ Bear in mind that Alice and Bob rapidly fall towards the centres of their black holes, as do any photons they happen to emit. So you need SMBHs if you want them to last for more than a few milliseconds. But I'm not totally clear on what happens to the photon paths once the merging starts. $\endgroup$
    – PM 2Ring
    Commented Sep 5, 2019 at 16:56
  • $\begingroup$ FWIW, you can get the proper time of a freefalling body to reach the centre of a black hole, plus other interesting info, from the Hawking radiation calculator. $\endgroup$
    – PM 2Ring
    Commented Sep 5, 2019 at 16:59
  • $\begingroup$ Afaik there is some theorem saying that the total surface of the event horizons never decrease in any black hole configurations. $\endgroup$
    – peterh
    Commented Sep 5, 2019 at 18:00
  • $\begingroup$ @PM2Ring Right, but if I get the video below right, then once Alice crosses the EH of a blackhole, she can go at the speed of light (or so) right after having corssed it, and so, she will have "plenty" of time before reaching the singularity (she will reach it, but later [from her point of view] than if free falling)? Suppose Bob does the same after crossing his BH EH, and "then" the BH EH touches each other and start merging. Are now both Alice and Bob (or their "photons" since they are at almost the speed of light) "causaly" relatable? $\endgroup$
    – Xenos
    Commented Sep 6, 2019 at 7:31