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> The instant you entered the black hole, reality would split in two. From the 3rd paragraph. However, yes the alternate universe comes into existence when you

> The instant you entered the black hole, reality would split in two. From the 3rd paragraph. However, yes the alternate universe comes into existence when you reach the singularity. Still, if you can exist both inside and outside, then your ashes can exist in both places alongside living you without causing a paradox because you simply will not exist in the same space as you ashes that will arrive very much later anyway as time slows at the edge of the black hole. You are more likely, having read the article, to have a post-life crises knowing that outside the black hole you are dead.

repsilat 11y ago
>> The instant you entered the black hole, reality would split in two. Ah, I'd assumed this meant that "you" would split in two, both copies being "in the same universe". I don't know enough about the physics to know which is meant.
logfromblammo 11y ago
Reality only splits in two in the sense that the observer-dependent reality of the person falling into the black hole and the observer-dependent reality of the person remaining outside of it can no longer exchange information anywhere except inside of the black hole's event horizon. The half of your light cone that extends into the future remains entirely within that event horizon. The outside observer's cone can remain outside of it only as long as she avoids crossing the event horizon. Even if the outside observer decide to jump in just seconds after you, it is possible that the physics inside the event horizon would prevent her from ever catching up with you to compare notes, or even sending you a message. You could send a message with modulated x-rays, and she might pick them up with a VLF antenna. She might reply with a deep infrared laser and accidentally cook your brains with cosmic rays. Assuming a steep spacetime gradient as you approach the singularity, everything sent inward would be severely blueshifted, and everything sent outward severely redshifted. There might even be a sort of Zeno's Paradox inside, where once you cross the event horizon, there's another event horizon beyond that, such that anything that much closer to the singularity than you are can never communicate with you, in the same way that you can never communicate with the universe outside the first event horizon.
- dragonwriter 11y ago
  > There might even be a sort of Zeno's Paradox inside, where once you cross the event horizon, there's another event horizon beyond that, such that anything that much closer to the singularity than you are can never communicate with you, in the same way that you can never communicate with the universe outside the first event horizon. Isn't every step in from the event horizon effectively an event horizon? If all the mass of a black hole is effectively at the singularity in the center, and escape velocity is the speed of light at the event horizon, won't there be no point within the event horizon where escape velocity is less than the speed of light, such that at any point within the event horizon, no point farther from the event horizon is within the future light cone of that point.
  - repsilat 11y ago
    I don't think that's quite what they meant by that. In silly "outside universe coordinates", inside the black hole you can define a "minimum inwards speed" as a function of distance from the singularity. This is how fast a photon will go towards the singularity if fired directly away from it. It's zero at the event horizon, and it increases as you go in. Now, what (I think) logfromblammo was saying was, "If I'm at the event horizon, can there be someone close enough to the singularity that I can never catch up?" Communication isn't much of a problem for two people falling into a black hole one after another if they're close enough. The messages from the person lower down don't "go up", they just go down more slowly than the person higher up. If they're too far apart, though, this might not work.
    - logfromblammo 11y ago
      The distance between fallers determines the energy requirements for communication. The lower person will also experience slower time than the higher. The analogy is as follows: Two BASE jumpers leap from the top of an infinitely tall radio mast in a vacuum, one after the other. They are in free-fall, so do not directly experience the effects of gravity, but the increase in the gravitational field as the distance to the singularity decreases will be detectable as a pseudoforce in that reference frame. The first jumper writes a note on a baseball and throws it at the second. The second also writes a note on a baseball and throws it at the first. The concern for the first jumper is not whether the baseball can be thrown back to the top of the radio mast, but whether it can be thrown hard enough and accurately enough for the second to ever reach it. The concern for the second is whether the first can catch his ball without exploding like a paper sack full of wet spaghetti. The other thing to consider is that both fallers will "see" multiple images of the other, and of themselves, because there is a direct light path, the light path that twists around once, the light path that twists around twice, and so on. Images further away will be lower, slower, and older. If you aimed correctly, you could send messages to your older self, but I'm not entirely certain if your older self could reply.

repsilat 11y ago

>> The instant you entered the black hole, reality would split in two. Ah, I'd assumed this meant that "you" would split in two, both copies being "in the same universe". I don't know enough about the physics to know which is meant.

logfromblammo 11y ago

Reality only splits in two in the sense that the observer-dependent reality of the person falling into the black hole and the observer-dependent reality of the person remaining outside of it can no longer exchange information anywhere except inside of the black hole's event horizon. The half of your light cone that extends into the future remains entirely within that event horizon. The outside observer's cone can remain outside of it only as long as she avoids crossing the event horizon. Even if the outside observer decide to jump in just seconds after you, it is possible that the physics inside the event horizon would prevent her from ever catching up with you to compare notes, or even sending you a message. You could send a message with modulated x-rays, and she might pick them up with a VLF antenna. She might reply with a deep infrared laser and accidentally cook your brains with cosmic rays. Assuming a steep spacetime gradient as you approach the singularity, everything sent inward would be severely blueshifted, and everything sent outward severely redshifted. There might even be a sort of Zeno's Paradox inside, where once you cross the event horizon, there's another event horizon beyond that, such that anything that much closer to the singularity than you are can never communicate with you, in the same way that you can never communicate with the universe outside the first event horizon.

dragonwriter 11y ago
> There might even be a sort of Zeno's Paradox inside, where once you cross the event horizon, there's another event horizon beyond that, such that anything that much closer to the singularity than you are can never communicate with you, in the same way that you can never communicate with the universe outside the first event horizon. Isn't every step in from the event horizon effectively an event horizon? If all the mass of a black hole is effectively at the singularity in the center, and escape velocity is the speed of light at the event horizon, won't there be no point within the event horizon where escape velocity is less than the speed of light, such that at any point within the event horizon, no point farther from the event horizon is within the future light cone of that point.
- repsilat 11y ago
  I don't think that's quite what they meant by that. In silly "outside universe coordinates", inside the black hole you can define a "minimum inwards speed" as a function of distance from the singularity. This is how fast a photon will go towards the singularity if fired directly away from it. It's zero at the event horizon, and it increases as you go in. Now, what (I think) logfromblammo was saying was, "If I'm at the event horizon, can there be someone close enough to the singularity that I can never catch up?" Communication isn't much of a problem for two people falling into a black hole one after another if they're close enough. The messages from the person lower down don't "go up", they just go down more slowly than the person higher up. If they're too far apart, though, this might not work.
  - logfromblammo 11y ago
    The distance between fallers determines the energy requirements for communication. The lower person will also experience slower time than the higher. The analogy is as follows: Two BASE jumpers leap from the top of an infinitely tall radio mast in a vacuum, one after the other. They are in free-fall, so do not directly experience the effects of gravity, but the increase in the gravitational field as the distance to the singularity decreases will be detectable as a pseudoforce in that reference frame. The first jumper writes a note on a baseball and throws it at the second. The second also writes a note on a baseball and throws it at the first. The concern for the first jumper is not whether the baseball can be thrown back to the top of the radio mast, but whether it can be thrown hard enough and accurately enough for the second to ever reach it. The concern for the second is whether the first can catch his ball without exploding like a paper sack full of wet spaghetti. The other thing to consider is that both fallers will "see" multiple images of the other, and of themselves, because there is a direct light path, the light path that twists around once, the light path that twists around twice, and so on. Images further away will be lower, slower, and older. If you aimed correctly, you could send messages to your older self, but I'm not entirely certain if your older self could reply.