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This is not entirely true. We can imagine a civilization made up for very sturdy physicists, so tidal forces inside the black hole don't rip them apart immedia

by Maro 3y ago

This is not entirely true. We can imagine a civilization made up for very sturdy physicists, so tidal forces inside the black hole don't rip them apart immediately. This civilization can enter the event horizon of the black hole, and observe what happens inside, make measurements, new theories, write papers, upload them to pre-prints, go to conferences, etc. It is true that they cannot communicate with the outside world, but that may not bother them if there's enough of them that they can share their new discoveries with each other and have a society and satisfy their intellectual curiosity. According to classical general relativity there are no stable orbits inside the black hole, so eventually this society will get arbitrary close to the singularity (or, to extremely large curvatures), so eventually they all would die, irrespective of how sturdy they are. But this is also true outside the black hole, per our current best theories, we will all either get crushed in a big crunch (reverse of the big bang), or heat death as the Universe expands indefinitely. (Or, sooner, when the sun explodes, or sooner if an asteroid hits us, or global warming, or we nuke each other..)

corethree 3y ago
The weird thing about this is that according to the theory... nothing ever enters the black hole. Everything freezes at the event horizon because time slows down and eventually gets frozen at the horizon. This is what happens relative to the outside observer. The person entering the black hole does not perceive time freezing. How could he? Relative to himself he will enter the black hole but for him time outside of the black hole will accelerate at infinite speed well past the heat death of the universe forever in an instant. Then once the universe ends if there is an end, he will cross the threshold and move through the event horizon.
- Maro 3y ago
  No, this is false: "nothing ever enters the black hole". For the outside observer, it seems like nothing enters the event horizon. It seems like everything just gets infinitely close and redshifts and expands, and forms a giant low-energy redshifted enveloping pancake around the black hole. But, from the perspective of the object passing through the event horizon, none of this happens, she passes through just fine. Yes, relativity theory is weird as hell.
  - BoiledCabbage 3y ago
    > But the object passing the event horizon passes through just fine. Yes, but due to the extreme time dilation, will they observe/experience the heat death of the universe prior to entering the black hole? If so, does it make sense to say they actually enter it in any meaning full sense from the perspective of our existence? As in 'yes', they will enter the black hole, but they will enter it an infinite number of years from now when our universe "functionally" no longer exists. Isn't this just another form of a particle with constant acceleration, accelerating to the speed of light? Yes, from their perspective, they reach it, but from our perspective, it will take an infinite amount of time and so we say they never can reach it from either our perspective or theirs? I don't see how this can be any different. Gravity is a constant accelerator. (And note I'm calling out the constant acceleration case above for approaching 'C', not the increasing acceleration requiring 'exponentially increasing energy each second' case).
  - gnramires 3y ago
    Consider this argument: if you can see the person falling in for "infinitely long", then you can actually communicate with this person falling in. For example, through light or gestures. Since you can communicate, this means the image you see of the person falling in is not just an illusion or artifact of general relativity, you both must agree on reality, that the person still hasn't crossed the horizon.
    - corethree 3y ago
      Yeah, you're right. It's not an optical illusion. I think I'm wrong about the infinite acceleration part though. We never observe the person hitting the event horizon so time never actually freezes. It just gets really really slow and approaches the point of time freezing. The person falling into the black hole will have time in the outside universe accelerate relative to him. It will get faster and faster and when he hits the event horizon we don't know what happens as that's the singularity where the math no longer works. We can speculate that time actually freezes but that leads to paradoxes.
      - deleted 3y ago
- pontifier 3y ago
  Perhaps with that time dilation and the slow evaporation of the black hole, nothing ever enters the event horizon. The horizon would seem to retract away from you as you approached it until it was gone. Side note, I watched this almost B movie called "time trap" and I feel like falling into a black hole would be just like the end of that movie. It really made me want to jump in a black hole.
  - corethree 3y ago
    Hmm yeah you could be right. The black hole evaporates at a finite speed relative to the outside observer. So someone falling in will by logic see this evaporation speed accelerate. Before he touches the event horizon the black hole should have completely evaporated already so time never actually "freezes". That's an interesting solution and resolves the paradox. When the black hole evaporates the reference frames become consistent again.
- lavelganzu 3y ago
  I'm hoping for a happy coincidence: that expansion of space due to dark energy increases over time without bound. Then the person falling into a black hole will observe the outside universe passing by faster and faster until the expansion of space overcomes the black hole's gravitational pull. The person is thus rescued from crossing the event horizon ... though still torn apart by the expansion. Sure, there's no evidence for this (yet?). But it'd be a nice solution to the paradox.
  - corethree 3y ago
    This guy here has a good solution: https://news.ycombinator.com/item?id=38643347 https://news.ycombinator.com/item?id=38643347 Itm similar to science fiction where time loops resolve through circumstance. If you go back in time to stop your birth you will inevitably instigate your birth instead of creating a paradox. I'm this case if you try to freeze time by going into the black hole the black hole will inevitably be destroyed before you can get close enough to it to encounter the singularity.

by Maro 3y ago

corethree 3y ago

The weird thing about this is that according to the theory... nothing ever enters the black hole. Everything freezes at the event horizon because time slows down and eventually gets frozen at the horizon. This is what happens relative to the outside observer. The person entering the black hole does not perceive time freezing. How could he? Relative to himself he will enter the black hole but for him time outside of the black hole will accelerate at infinite speed well past the heat death of the universe forever in an instant. Then once the universe ends if there is an end, he will cross the threshold and move through the event horizon.

Maro 3y ago
No, this is false: "nothing ever enters the black hole". For the outside observer, it seems like nothing enters the event horizon. It seems like everything just gets infinitely close and redshifts and expands, and forms a giant low-energy redshifted enveloping pancake around the black hole. But, from the perspective of the object passing through the event horizon, none of this happens, she passes through just fine. Yes, relativity theory is weird as hell.
- BoiledCabbage 3y ago
  > But the object passing the event horizon passes through just fine. Yes, but due to the extreme time dilation, will they observe/experience the heat death of the universe prior to entering the black hole? If so, does it make sense to say they actually enter it in any meaning full sense from the perspective of our existence? As in 'yes', they will enter the black hole, but they will enter it an infinite number of years from now when our universe "functionally" no longer exists. Isn't this just another form of a particle with constant acceleration, accelerating to the speed of light? Yes, from their perspective, they reach it, but from our perspective, it will take an infinite amount of time and so we say they never can reach it from either our perspective or theirs? I don't see how this can be any different. Gravity is a constant accelerator. (And note I'm calling out the constant acceleration case above for approaching 'C', not the increasing acceleration requiring 'exponentially increasing energy each second' case).
- gnramires 3y ago
  Consider this argument: if you can see the person falling in for "infinitely long", then you can actually communicate with this person falling in. For example, through light or gestures. Since you can communicate, this means the image you see of the person falling in is not just an illusion or artifact of general relativity, you both must agree on reality, that the person still hasn't crossed the horizon.
  - corethree 3y ago
    Yeah, you're right. It's not an optical illusion. I think I'm wrong about the infinite acceleration part though. We never observe the person hitting the event horizon so time never actually freezes. It just gets really really slow and approaches the point of time freezing. The person falling into the black hole will have time in the outside universe accelerate relative to him. It will get faster and faster and when he hits the event horizon we don't know what happens as that's the singularity where the math no longer works. We can speculate that time actually freezes but that leads to paradoxes.
    - deleted 3y ago
pontifier 3y ago
Perhaps with that time dilation and the slow evaporation of the black hole, nothing ever enters the event horizon. The horizon would seem to retract away from you as you approached it until it was gone. Side note, I watched this almost B movie called "time trap" and I feel like falling into a black hole would be just like the end of that movie. It really made me want to jump in a black hole.
- corethree 3y ago
  Hmm yeah you could be right. The black hole evaporates at a finite speed relative to the outside observer. So someone falling in will by logic see this evaporation speed accelerate. Before he touches the event horizon the black hole should have completely evaporated already so time never actually "freezes". That's an interesting solution and resolves the paradox. When the black hole evaporates the reference frames become consistent again.
lavelganzu 3y ago
I'm hoping for a happy coincidence: that expansion of space due to dark energy increases over time without bound. Then the person falling into a black hole will observe the outside universe passing by faster and faster until the expansion of space overcomes the black hole's gravitational pull. The person is thus rescued from crossing the event horizon ... though still torn apart by the expansion. Sure, there's no evidence for this (yet?). But it'd be a nice solution to the paradox.
- corethree 3y ago
  This guy here has a good solution: https://news.ycombinator.com/item?id=38643347 https://news.ycombinator.com/item?id=38643347 Itm similar to science fiction where time loops resolve through circumstance. If you go back in time to stop your birth you will inevitably instigate your birth instead of creating a paradox. I'm this case if you try to freeze time by going into the black hole the black hole will inevitably be destroyed before you can get close enough to it to encounter the singularity.