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A comment on What If Planet 9 Is a Primordial Black Hole?. Parent comment

Re:What If Planet 9 Is a Primordial Black Hole? by avar on Thursday September 26, 2019 @03:34AM (#21078995)
> everything near where it "touched down" would experience near zero-g as it approached[...] while the black hole was inside the earth, everything would be experiencing close to 2G, then zero G for a bit for the poor souls on the side of the earth where it exited.

All of these numbers are off by many orders of magnitude. You're fundamentally misunderstanding how gravity works.

If you were standing on the surface of the Earth and an Earth-mass black hole were magically stationary 1 km underneath your feet you wouldn't experience something close to 2G, you'd experience something closer to 40 million G.

Check out [1] for more details, and [2] for a calculator where you can play with the gravitational formula.

1. http://www.physbot.co.uk/gravity-fields-and-potentials.html

2. https://www.wolframalpha.com/input/?i=surface+gravity+calcul...

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Re:What If Planet 9 Is a Primordial Black Hole? by 0-_-0 on Thursday September 26, 2019 @04:31AM (#21079218)
I suspect by "while the black hole was inside the earth" he meant at the centre of the Earth
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Re:What If Planet 9 Is a Primordial Black Hole? by avar on Thursday September 26, 2019 @07:58AM (#21080092)
Then they wouldn't be saying that the people on the other side of the earth would experience zero-G as the black hole exited, they'd be "experiencing" some combination of being ripped apart by tidal forces and being buried under rapidly shifting rubble, and all of this would be happening at some G value in the range of millions.
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