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$\begingroup$ That last sentence is important! It's not merely that you can't get enough speed or acceleration, the spacetime is curved so much that as you go forward in time you must travel towards the core. There are no paths away from the core, or even paths that keep the same distance. (The only way out is to go backwards in time, and as far as we know that's physically impossible). $\endgroup$
– PM 2Ring
Commented Apr 17, 2019 at 5:50
$\begingroup$ +1 for a good answer Florin, but that last sentence is wrong. You can plot gravitational potential by plotting the "coordinate" speed of light using a gedanken string of light clocks. The steeper the gradient in gravitational potential at some location, the stronger the gravity at that location. But at the event horizon, the coordinate speed of light is zero, and it can't go lower than that. So there's no more slope. $\endgroup$
– John Duffield
Commented Apr 17, 2019 at 12:51
$\begingroup$ @JohnDuffield Are you back with crackpot "theories" again? $\endgroup$
– Florin Andrei
Commented Apr 17, 2019 at 18:01
$\begingroup$ That's not crackpot, Florin. You really can plot gravitational potential with clocks. And see Einstein's 1939 paper on a stationary system with spherical symmetry consisting of many gravitating masses. He said this “g44 = (1 – μ/2r / 1 + μ/2r)² vanishes for r = μ/2. This means that a clock kept at this place would go at the rate zero". A clock can't go slower than that. Google on Oppenheimer frozen star. $\endgroup$
– John Duffield
Commented Apr 18, 2019 at 7:37
$\begingroup$ @Florin Andrei, how do the layers behind you that you leave behind pull you in the opposite direction? What's the physics behind that? $\endgroup$
– penguin99
Commented Apr 20, 2019 at 3:44

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