Ambitwistor: Myria: But doesn't the concept of escape speed not apply if you have propulsion the whole time? See "Misconception" in Wikipedia's article on escape speed/velocity.Yes. This is why escape from a black hole is different from "escape velocity" in Newtonian gravity. You could escape a "Newtonian black hole" (an object whose surface gravity is great enough that its escape velocity is greater than the speed of light) by accelerating hard enough. But you can't escape an Einsteinian black hole with any acceleration, because spacetime curves inward upon itself to deflect all trajectories toward the interior singularity. The only way to escape an Einsteinian black hole is to go faster than light, but in relativity there's no acceleration or amount of energy that will let you do that.
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