3 ms·

Am I understanding this right by thinking - if I was walking toward the black hole past the event horizon, and then I turned around, I would still be walking to

Am I understanding this right by thinking - if I was walking toward the black hole past the event horizon, and then I turned around, I would still be walking toward the black hole?

aqfamnzc 1mo ago
Sounds like that would be true if you were inside any closed surface.
- XorNot 1mo ago
  Not quite: inside a closed surface you can't escape, but things can repeat. You can avoid a coordinate, for example by choosing not to go there, or revisit another one repeatedly. A black hole on the other hand doesn't have that: you cannot revisit old locations - attempting to do so moves you closer to the singularity.
  - inigyou 1mo ago
    Unless it's a spinning black hole, which contains closed timelike curves that can be reached from and can escape back to the outside universe?
    - XorNot 1mo ago
      None of those proposed time machines has ever turned out to be theoretically workable when the details are investigated more closely by physicists.
    - pdonis 1mo ago
      Kerr spacetime contains closed timelike curves inside the inner horizon. You can reach them from the outside universe, but you can't escape back out. Also, the region inside the inner horizon of Kerr spacetime is widely considered to be not physically reasonable, not just because of the closed timelike curves, but because the inner horizon itself is unstable--there is an infinite blueshift there which, it is believed, would cause it to be destroyed by the first tiny bit of incoming matter or radiation.
HappMacDonald 1mo ago
Once you pass the event horizon, every direction leads to the singularity in your future. Directions "away" from the singularity may still visibly show what things looked like outside of the event horizon before you fell in, but that is from your past. Heading in that direction will not get you back there anymore, you will only find the singularity along that path in your future.
pdonis 1mo ago
> if I was walking toward the black hole past the event horizon, and then I turned around Note that, once you're inside the horizon, you can't "turn around" and go back outside again. You're inside the hole for good. And once you're inside the hole, yes, no matter which direction in space you move, you're moving "towards" the singularity. But a better way to look at it is that the singularity is a moment of time, not a place in space. You're moving "towards" the singularity in the same sense as you're moving "towards" next Tuesday. You can't stop moving towards next Tuesday by changing which direction in space you move. The same is true for the singularity once you're inside the hole's horizon.
shepardrtc 1mo ago
You can't turn around though. Everything goes toward the black hole. If you turned around, atoms would be moving away from, or at the least changing their direction in respect to the black hole. And that's not possible. You wouldn't even see anything because all light is going toward the center, and it wouldn't go into your eyes. Unless you went in butt-first, but the path of the photons would have changed and would now be going toward the black hole, and everything would look probably all smushed together.

Am I understanding this right by thinking - if I was walking toward the black hole past the event horizon, and then I turned around, I would still be walking toward the black hole?

aqfamnzc 1mo ago

Sounds like that would be true if you were inside any closed surface.

XorNot 1mo ago
Not quite: inside a closed surface you can't escape, but things can repeat. You can avoid a coordinate, for example by choosing not to go there, or revisit another one repeatedly. A black hole on the other hand doesn't have that: you cannot revisit old locations - attempting to do so moves you closer to the singularity.
- inigyou 1mo ago
  Unless it's a spinning black hole, which contains closed timelike curves that can be reached from and can escape back to the outside universe?
  - XorNot 1mo ago
    None of those proposed time machines has ever turned out to be theoretically workable when the details are investigated more closely by physicists.
  - pdonis 1mo ago
    Kerr spacetime contains closed timelike curves inside the inner horizon. You can reach them from the outside universe, but you can't escape back out. Also, the region inside the inner horizon of Kerr spacetime is widely considered to be not physically reasonable, not just because of the closed timelike curves, but because the inner horizon itself is unstable--there is an infinite blueshift there which, it is believed, would cause it to be destroyed by the first tiny bit of incoming matter or radiation.

HappMacDonald 1mo ago

Once you pass the event horizon, every direction leads to the singularity in your future. Directions "away" from the singularity may still visibly show what things looked like outside of the event horizon before you fell in, but that is from your past. Heading in that direction will not get you back there anymore, you will only find the singularity along that path in your future.

pdonis 1mo ago

> if I was walking toward the black hole past the event horizon, and then I turned around Note that, once you're inside the horizon, you can't "turn around" and go back outside again. You're inside the hole for good. And once you're inside the hole, yes, no matter which direction in space you move, you're moving "towards" the singularity. But a better way to look at it is that the singularity is a moment of time, not a place in space. You're moving "towards" the singularity in the same sense as you're moving "towards" next Tuesday. You can't stop moving towards next Tuesday by changing which direction in space you move. The same is true for the singularity once you're inside the hole's horizon.

shepardrtc 1mo ago

You can't turn around though. Everything goes toward the black hole. If you turned around, atoms would be moving away from, or at the least changing their direction in respect to the black hole. And that's not possible. You wouldn't even see anything because all light is going toward the center, and it wouldn't go into your eyes. Unless you went in butt-first, but the path of the photons would have changed and would now be going toward the black hole, and everything would look probably all smushed together.