Key words: 1. General relativity. 2. Black hole. 3. Relativity. 4. Cosmology. 5. Spinning black hole.
Note: Both females and males make competent observers. Ordinarily we treat as female any observer in free float (whether in orbit or plunging inward) as well as the remote observers called Schwarzschild and Kerr bookkeepers. (See the Glossary of Terms for definitions.) Male observers stand on spherical shells around a nonrotating black hole and ride on circular rings around a spinning black hole. In other settings we try to use gender-neutral language. Where this is not convenient we usually assign gender randomly.
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