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The second option is accurate. As you fall from the event horizon to the singularity, you see the entire future of the universe unfold since all arrows of time

The second option is accurate. As you fall from the event horizon to the singularity, you see the entire future of the universe unfold since all arrows of time now point toward the singularity so as you move along it, you are moving in time. This is one of the things shown in interstellar before he hits the tesseract and they go into pure speculative scifi. He gets bombarded with extremely energetic blue shifted particles as he moves through time while falling. Regarding what happens at the event horizon, your question is slightly inaccurate in that the photon is what you observe so it doesn't emit anything. If you assume, say, a torch falling in facing toward you, the reason that it feels delayed is ofc that it has to move out of the gravity well of the black hole. I haven't thought about the question myself, but basically think about the entire set of photons your torch emits and assume it is a magically resilient thing that never tears apart. Then it emits a fair few trillion packets of energy before it crosses the event horizon. Most of this is caught in the photon sphere and never makes it out (depends on incident angle and some other calculations I forget).But we will assume photons are ejected in one line out on some radius vector of the black hole. Then all photos ejected before the event horizon will eventually escape and you will see them. The last one is supposed to escape asymptotically as you approach the horizon but it is only constrained by how much energy it loses traversing that piece of space time from the event horizon to infinity (i.e. where the observer is located). So we can deduce that it gets emitted at some point in time. We assume infinity to make the math easier but real life is quantized so it'll likely be sooner than that. I can't do any better than that unfortunately.

colechristensen 5y ago
>As you fall from the event horizon to the singularity, you see the entire future of the universe unfold since all arrows of time now point toward the singularity so as you move along it, you are moving in time. This would suggest that as I see the entire future of the universe as I fall towards the event horizon I also see the entire future of the horizon itself... which means that I will never cross the horizon because it will at some point far in the future no longer exist. i.e. there is no spacetime path which ever crosses the event horizon I'm near the point where I'm going to have to learn some black hole math to convince myself otherwise. (I think I'm wrong but can't see why)
- hoten 5y ago
  Relevant discussion: https://physics.stackexchange.com/a/79086 https://physics.stackexchange.com/a/79086 > i.e. there is no spacetime path which ever crosses the event horizon As I understand it, there isn't, from the perspective of an observer external to the event horizon. (warning: I am only an avid watcher of PBS Spacetime)
  - pdonis 5y ago
    > As I understand it, there isn't, from the perspective of an observer external to the event horizon. This is not correct. An observer outside the horizon cannot see anything at or inside the horizon; but that doesn't mean he can't calculate that there is a region of spacetime inside the horizon, from observations he can make from the outside. He can.
  - colechristensen 5y ago
    As I understand it at this point... there is no round trip spacetime path to the horizon and back and best-case light which hits (or is arbitrarily close to hitting the event horizon) can get back to you the moment the black hole finally evaporates. However the first half of that trip is possible and happens in finite time.
pdonis 5y ago
> As you fall from the event horizon to the singularity, you see the entire future of the universe unfold No, you don't. Most of the universe will never be in your past light cone as you fall to the singularity. The fact that the singularity is unavoidably in your future when you are inside the hole, does not mean it is also to the future of everything outside the hole.
- lostmsu 5y ago
  This is unnecessarily pedantic. What parent meant is more akin to "if Earth would exist forever, and you would live forever on it, you'd see the entire future of the universe unfold". Obviously you won't see what happens on the moon when it is behind the horizon, but that was not the point.
  - pdonis 5y ago
    > What parent meant is more akin to "if Earth would exist forever, and you would live forever on it, you'd see the entire future of the universe unfold". No, that's not what the post I responded to meant. That post was specifically talking about what an observer falling into a black hole and hitting the singularity would see. That is not the same as existing forever outside the hole's horizon.
    - lostmsu 5y ago
      Why do you think the post did not refer to its author's understanding, that your experience would be the same as hanging forever just outside the horizon except in finite time from your perspective? This would be my default interpretation of their comment, and since you are successfully attacking a different stronger interpretation you should reconsider that this strong interpretation is the right way to interpret the comment. That's scenario is actually covered in HN discussion rules. To be fair until your comment I wrongly believed the moment you'd be crossing horizon you'd be hit by all light ever emitted toward that point of the horizon in the entirety of the future (assuming no hawking radiation of course).
- hnews_account_1 5y ago

colechristensen 5y ago

>As you fall from the event horizon to the singularity, you see the entire future of the universe unfold since all arrows of time now point toward the singularity so as you move along it, you are moving in time. This would suggest that as I see the entire future of the universe as I fall towards the event horizon I also see the entire future of the horizon itself... which means that I will never cross the horizon because it will at some point far in the future no longer exist. i.e. there is no spacetime path which ever crosses the event horizon I'm near the point where I'm going to have to learn some black hole math to convince myself otherwise. (I think I'm wrong but can't see why)

hoten 5y ago
Relevant discussion: https://physics.stackexchange.com/a/79086 https://physics.stackexchange.com/a/79086 > i.e. there is no spacetime path which ever crosses the event horizon As I understand it, there isn't, from the perspective of an observer external to the event horizon. (warning: I am only an avid watcher of PBS Spacetime)
- pdonis 5y ago
  > As I understand it, there isn't, from the perspective of an observer external to the event horizon. This is not correct. An observer outside the horizon cannot see anything at or inside the horizon; but that doesn't mean he can't calculate that there is a region of spacetime inside the horizon, from observations he can make from the outside. He can.
- colechristensen 5y ago
  As I understand it at this point... there is no round trip spacetime path to the horizon and back and best-case light which hits (or is arbitrarily close to hitting the event horizon) can get back to you the moment the black hole finally evaporates. However the first half of that trip is possible and happens in finite time.

pdonis 5y ago

> As you fall from the event horizon to the singularity, you see the entire future of the universe unfold No, you don't. Most of the universe will never be in your past light cone as you fall to the singularity. The fact that the singularity is unavoidably in your future when you are inside the hole, does not mean it is also to the future of everything outside the hole.

lostmsu 5y ago
This is unnecessarily pedantic. What parent meant is more akin to "if Earth would exist forever, and you would live forever on it, you'd see the entire future of the universe unfold". Obviously you won't see what happens on the moon when it is behind the horizon, but that was not the point.
- pdonis 5y ago
  > What parent meant is more akin to "if Earth would exist forever, and you would live forever on it, you'd see the entire future of the universe unfold". No, that's not what the post I responded to meant. That post was specifically talking about what an observer falling into a black hole and hitting the singularity would see. That is not the same as existing forever outside the hole's horizon.
  - lostmsu 5y ago
    Why do you think the post did not refer to its author's understanding, that your experience would be the same as hanging forever just outside the horizon except in finite time from your perspective? This would be my default interpretation of their comment, and since you are successfully attacking a different stronger interpretation you should reconsider that this strong interpretation is the right way to interpret the comment. That's scenario is actually covered in HN discussion rules. To be fair until your comment I wrongly believed the moment you'd be crossing horizon you'd be hit by all light ever emitted toward that point of the horizon in the entirety of the future (assuming no hawking radiation of course).
hnews_account_1 5y ago