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A comment on Simple Rules ‘Bootstrap’ the Laws of Physics. Parent comment

Re:Simple Rules ‘Bootstrap’ the Laws of Physics by chongli on Monday December 09, 2019 @01:24PM (#21744975)
It's totally counterintuitive. Classical angular momentum requires a choice of origin. All angular momentum is then relative to that origin. Any point particle lying at the origin should not be able to have any angular momentum.

Imagining the classic "figure skater experiment", the figure skater speeds up as she draws her arms inward, due to conservation of angular momentum. If she could shrink down to a point, her angular speed would tend to infinity. This is what I imagine happening to a black hole.

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Re:Simple Rules ‘Bootstrap’ the Laws of Physics by ISL on Monday December 09, 2019 @11:57PM (#21749719)
You need not worry about infinity in the black-hole case. Known physics ends at the black hole's event horizon, for an external observer. Black holes of a given mass can only have so much angular momentum.

As a rule of thumb, that angular momentum corresponds to that at which the equator of the black hole is moving at the speed of light.

This has important consequences for the mergers of two high-spin black holes that have aligned spins. The merger is actually delayed for a little while, just before merger, as the binary dumps angular momentum through gravitational radiation.

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