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OK, I see what’s troubling you.
The horizon isn’t really a “place”: it’s traced out by null rays in spacetime, rather than timelike rays. For a black hole, the horizon has a constant area, which makes it seem like a thing that’s standing still in some sense, but it’s generated, geometrically, by light rays, so it’s moving at the speed of light.
For two people who cross the horizon at different times, the latter one will see the former one when they are both crossing the horizon, but that doesn’t imply that they bump into each other.
Bob’s notion of his distance from *the horizon* (in the sense of the distance to a spacetime event that lies on the horizon “right now”, in his reference frame and with his notion of simultaneity) goes from being fixed to being monotically decreasing when he jumps out of the ship.
But his notion of his distance *from Alice* when she emitted the light with which he is currently seeing her starts *increasing*.
That’s not a contradiction, because these are two different things.
Greg Egan /
npub1qq…j5nhv
2024-11-24 16:05:50
in reply to nevent1q…ra9e
Author Public Key
npub1qqm7nu2qf25xd3mw6y6cyp4v2wr7ktf43ymp5wqz4u8jvz76ymtsjj5nhvPublished at
2024-11-24 16:05:50Event JSON
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