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Here's what I've never understood. From an outside perspective the black hole will evaporate before the thing falls in. Thus a thing can never fall in. From its

Here's what I've never understood. From an outside perspective the black hole will evaporate before the thing falls in. Thus a thing can never fall in. From its perspective the hole will emit more and more intense radiation and finally evaporate just before it hits the horizon. If true, I think you can go even further and say no black hole can completely form; the collapsing matter just gets exponentially closer to being fully black until the effect of the Hawking radiation outweighs the gravitation, but it all evaporates before going fully black. No? (This latter part assumes there's some Hawking radiation or equivalent from pre-black holes as well). Now, I assume the pre-Hawking radiation would be unitary, since the only reason Hawking radiation is not unitary is because BHs don't have information, but pre-black holes are not black holes. So doesn't that solve the info paradox? Without resorting to holographs and whatnot? Where's the error?

PaulHoule 5y ago
See https://en.wikipedia.org/wiki/Firewall_(physics) https://en.wikipedia.org/wiki/Firewall_(physics) vs https://en.wikipedia.org/wiki/Black_hole_complementarity https://en.wikipedia.org/wiki/Black_hole_complementarity
- daxfohl 5y ago
  Sure, but the paradoxes listed on those pages go away because the black hole never fully exists. The mass inside any volume is always just short of what would be required to make a black hole. And so of course we can expect to see crazy quantum effects at the boundaries, just like any other massively dense celestial object. However it's hidden behind insane time dilation to anyone outside. Going a bit further, it could even explain dark energy (Granted, I'm way out of my depth here): One outcome of General Relativity is that a large enough object of any density is a black hole (a black hole the size of Saturn's orbit need only be the density of water). Thus if we assume the universe is infinite and self similar, mass would have to constantly expand in order to avoid black holing.
  - peterburkimsher 5y ago
    Could a black hole exist in the same universe as a magnetic monopole? https://en.wikipedia.org/wiki/Magnetic_monopole https://en.wikipedia.org/wiki/Magnetic_monopole If energy is related to matter by E=mc², then the electromagnetic field of the monopole would also be diminished by a black hole, if one truly exists. But there might only be a single monopole. "Standard models of inflation solve the “monopole problem” by arguing that the seed from which our entire visible Universe grew was a quantum fluctuation so small that it contained only one monopole." https://www.newscientist.com/article/mg14419512-600-do-we-live-in-a-magnetic-monopole/ https://www.newscientist.com/article/mg14419512-600-do-we-li... Scientifically I'm way out of my depth, but perhaps there's a perfect universe on the other side of the black hole/white hole/wormhole. Or perhaps the perfect design is already here, and when we find bugs, we should be working to improve the world around us to make it better over time. I know I can't do that alone, but by some miracle, technology seems to be helping.
  - TheOtherHobbes 5y ago
    Some predictions suggest particle-sized black holes are a possible outcome of very energetic collisions. If they didn't evaporate, they'd be relatively common because the universe is quite an energetic place. This suggests either that particle-sized black holes don't exist, or that they evaporate very quickly. This is a good thing. Because some predictions imply they could be created at the energies CERN generates. And if they didn't evaporate they'd end up in or around the earth, with very unfortunate consequences. None of this solves the information paradox. But if microscopic black holes turned out to be a thing, it would make it slightly - not much, but a little - easier to consider that it might be possible to experiment on them directly.
    - mr_toad 5y ago
      > with very unfortunate consequences Less than you might suppose. A micro black hole that the LHD could generate is a tiny tiny hole, and you can only cram a tiny amount of matter down it at once. An extreme lower bound on the time such a black hole might take to grow large enough to destroy the Earth is on the order of 10,000 years. More likely it would take longer than the lifetime of the Earth. https://s3.cern.ch/inspire-prod-files-8/836037ce600a972222901517045a5412 https://s3.cern.ch/inspire-prod-files-8/836037ce600a97222290...
deleted 5y ago
[deleted]
Blammar 5y ago
I had a similar issue. This is my tl;dr understanding now. The thing to realize is that the view from outside shows the object falling in and getting dimmer and dimmer and more and more red shifted. You never actually see the object disappear. From the viewpoint sitting on the object, you fall right through the event horizon and get turned into mush, pretty quickly. So, black holes can be created as the matter can clearly fall past the event horizon and add to the black hole mass.
- syrrim 5y ago
  >From the viewpoint sitting on the object, you fall right through the event horizon and get turned into mush, pretty quickly. Do you? From an outside perspective you never fall in, and from an outside perspective the black hole eventually evaporates. From your perspective, as you fall in, the black hole evaporates in front of you.
  - deleted 5y ago
    [deleted]
  - zamadatix 5y ago
    Outsider perspective is about not being under significant influence of the black hole, not simply being outside the event horizon. As you fall in your perspective no longer follows that of a simple outside perspective.
    - GoblinSlayer 5y ago
      You mean black hole is created from your perspective, but not from outside perspective?
      - zamadatix 5y ago
        A black hole is black because you can't observe it, observing things falling past the region you can't observe isn't a requirement for it to be black it's actually an anti-requirement. The outside perspective still sees a black hole, as in a region of space it can't observe anything from, it just can't observe what's happening to a perspective at or beyond the event horizon.
djenendik 5y ago
you can always start by performing a mass/energy balance...
zamadatix 5y ago
> From its perspective the hole will Which "its"?
_8j50 5y ago
Question/ELI5 for anyone still reading this thread: What if blackholes form a worm-whole emto elsewhere, possibly to other blackholes, they would have enough energy to sustain a large enough wormwhole where They start acting like one or two way tunnels for information across great distances and maybe even galaxies? Also:The wiki for hawking radiation lead me to the Unruh effect, can the heat from this effect be used to generate even more acceleration? As in, a spaceship only needs enough energy to accelerate to a point where the unruh effect radiation is sufficient to maintain acceleration, after that point it can continue to accelerate without needing to use any fuel?
- raattgift 5y ago
  Taking your "Also" first: The accelerations required for reasonably measurable Unruh temperatures will rip apart any structure we know of, so at present we only have hope for accelerating charged leptons. However even still we are probably only able to sustain the accelerations for on the order of nanoseconds, which poses seriously difficult engineering challenges to the detector-side of a measurement experiment. That's the problem with Unruh radiation: acceleration has to be powered by something, and it's hard to separate the power source from the accelerated object. And if your object is accelerating strongly enough, it will pancake/disintegrate/explode. So we must use an outside power source, like in linear particle accelerators, to drive the extreme acceleration (at least many billions of billions of "g") of a particle that can survive it (or a stream of them), and try to work out the detection difficulties. This idea dates to J.S. Bell in 1983, who probably correctly summarized that the temperature changes would be "... too small for real experiments in linear accerators." Wormholes in General Relativity are weird. They are not forbidden, but they make a mess of trying to extract good (as in compatible with everyday experience) behaviour from dust, gas, stars, and so forth populating the universe as we know it. Worse, once you allow them, it's hard to suppress them, and we can be pretty confident (by virtue of actually being alive and seeing a reliable relationship between a running engine and the fuel it consumes) that they are not popping up everywhere willy-nilly like they would without some unknown suppression mechanism. In order to allow them in the first place, one needs some "exotic" matter (exotic in the sense of undiscovered, unknown, and very different from ordinary matter and even any plausible form of dark matter). Introducing that can give you wormholes, but then you have to be very careful about where and when you introduce the exotic stuff. Otherwise, wormholes everywhere, eating through ordinary matter structures. Depositing energy into discharged batteries, draining non-leaking fuel tanks. Or worse doing that in your cardiovascular system or brain. Also alien brains, stars, clouds of interstellar dust... (Pervasive wormholes has been embraced by some name-brand theoreticians, but they then rely upon some unknown scale suppression mechanism: there are wormholes all over the place but they are always very very very tiny compared to atoms, so the effects on e.g. AAA-batteries and stars are undetectably small. In this approach you are already riddled with wormholes connecting subatomic bits of you to subatomic bits of e.g. our galaxy's central black hole, but alas, you remain unable to travel faster than light). We can of course say, "well General Relativity could be wrong", and explore the consequences of a theory wherein we can build usefully-traversable wormholes without unknown matter. That theory, however, is virtually certain to be wrong on details about the orbits of bodies in our solar system and the difference at Earth-bound receivers from test signals sent across the solar system originating in our space probes like MESSENGER.

PaulHoule 5y ago

See https://en.wikipedia.org/wiki/Firewall_(physics) https://en.wikipedia.org/wiki/Firewall_(physics) vs https://en.wikipedia.org/wiki/Black_hole_complementarity https://en.wikipedia.org/wiki/Black_hole_complementarity

daxfohl 5y ago
Sure, but the paradoxes listed on those pages go away because the black hole never fully exists. The mass inside any volume is always just short of what would be required to make a black hole. And so of course we can expect to see crazy quantum effects at the boundaries, just like any other massively dense celestial object. However it's hidden behind insane time dilation to anyone outside. Going a bit further, it could even explain dark energy (Granted, I'm way out of my depth here): One outcome of General Relativity is that a large enough object of any density is a black hole (a black hole the size of Saturn's orbit need only be the density of water). Thus if we assume the universe is infinite and self similar, mass would have to constantly expand in order to avoid black holing.
- peterburkimsher 5y ago
  Could a black hole exist in the same universe as a magnetic monopole? https://en.wikipedia.org/wiki/Magnetic_monopole https://en.wikipedia.org/wiki/Magnetic_monopole If energy is related to matter by E=mc², then the electromagnetic field of the monopole would also be diminished by a black hole, if one truly exists. But there might only be a single monopole. "Standard models of inflation solve the “monopole problem” by arguing that the seed from which our entire visible Universe grew was a quantum fluctuation so small that it contained only one monopole." https://www.newscientist.com/article/mg14419512-600-do-we-live-in-a-magnetic-monopole/ https://www.newscientist.com/article/mg14419512-600-do-we-li... Scientifically I'm way out of my depth, but perhaps there's a perfect universe on the other side of the black hole/white hole/wormhole. Or perhaps the perfect design is already here, and when we find bugs, we should be working to improve the world around us to make it better over time. I know I can't do that alone, but by some miracle, technology seems to be helping.
- TheOtherHobbes 5y ago
  Some predictions suggest particle-sized black holes are a possible outcome of very energetic collisions. If they didn't evaporate, they'd be relatively common because the universe is quite an energetic place. This suggests either that particle-sized black holes don't exist, or that they evaporate very quickly. This is a good thing. Because some predictions imply they could be created at the energies CERN generates. And if they didn't evaporate they'd end up in or around the earth, with very unfortunate consequences. None of this solves the information paradox. But if microscopic black holes turned out to be a thing, it would make it slightly - not much, but a little - easier to consider that it might be possible to experiment on them directly.
  - mr_toad 5y ago
    > with very unfortunate consequences Less than you might suppose. A micro black hole that the LHD could generate is a tiny tiny hole, and you can only cram a tiny amount of matter down it at once. An extreme lower bound on the time such a black hole might take to grow large enough to destroy the Earth is on the order of 10,000 years. More likely it would take longer than the lifetime of the Earth. https://s3.cern.ch/inspire-prod-files-8/836037ce600a972222901517045a5412 https://s3.cern.ch/inspire-prod-files-8/836037ce600a97222290...

deleted 5y ago

[deleted]

Blammar 5y ago

I had a similar issue. This is my tl;dr understanding now. The thing to realize is that the view from outside shows the object falling in and getting dimmer and dimmer and more and more red shifted. You never actually see the object disappear. From the viewpoint sitting on the object, you fall right through the event horizon and get turned into mush, pretty quickly. So, black holes can be created as the matter can clearly fall past the event horizon and add to the black hole mass.

syrrim 5y ago
>From the viewpoint sitting on the object, you fall right through the event horizon and get turned into mush, pretty quickly. Do you? From an outside perspective you never fall in, and from an outside perspective the black hole eventually evaporates. From your perspective, as you fall in, the black hole evaporates in front of you.
- deleted 5y ago
  [deleted]
- zamadatix 5y ago
  Outsider perspective is about not being under significant influence of the black hole, not simply being outside the event horizon. As you fall in your perspective no longer follows that of a simple outside perspective.
  - GoblinSlayer 5y ago
    You mean black hole is created from your perspective, but not from outside perspective?
    - zamadatix 5y ago
      A black hole is black because you can't observe it, observing things falling past the region you can't observe isn't a requirement for it to be black it's actually an anti-requirement. The outside perspective still sees a black hole, as in a region of space it can't observe anything from, it just can't observe what's happening to a perspective at or beyond the event horizon.

djenendik 5y ago

you can always start by performing a mass/energy balance...

zamadatix 5y ago

> From its perspective the hole will Which "its"?

_8j50 5y ago

Question/ELI5 for anyone still reading this thread: What if blackholes form a worm-whole emto elsewhere, possibly to other blackholes, they would have enough energy to sustain a large enough wormwhole where They start acting like one or two way tunnels for information across great distances and maybe even galaxies? Also:The wiki for hawking radiation lead me to the Unruh effect, can the heat from this effect be used to generate even more acceleration? As in, a spaceship only needs enough energy to accelerate to a point where the unruh effect radiation is sufficient to maintain acceleration, after that point it can continue to accelerate without needing to use any fuel?

raattgift 5y ago
Taking your "Also" first: The accelerations required for reasonably measurable Unruh temperatures will rip apart any structure we know of, so at present we only have hope for accelerating charged leptons. However even still we are probably only able to sustain the accelerations for on the order of nanoseconds, which poses seriously difficult engineering challenges to the detector-side of a measurement experiment. That's the problem with Unruh radiation: acceleration has to be powered by something, and it's hard to separate the power source from the accelerated object. And if your object is accelerating strongly enough, it will pancake/disintegrate/explode. So we must use an outside power source, like in linear particle accelerators, to drive the extreme acceleration (at least many billions of billions of "g") of a particle that can survive it (or a stream of them), and try to work out the detection difficulties. This idea dates to J.S. Bell in 1983, who probably correctly summarized that the temperature changes would be "... too small for real experiments in linear accerators." Wormholes in General Relativity are weird. They are not forbidden, but they make a mess of trying to extract good (as in compatible with everyday experience) behaviour from dust, gas, stars, and so forth populating the universe as we know it. Worse, once you allow them, it's hard to suppress them, and we can be pretty confident (by virtue of actually being alive and seeing a reliable relationship between a running engine and the fuel it consumes) that they are not popping up everywhere willy-nilly like they would without some unknown suppression mechanism. In order to allow them in the first place, one needs some "exotic" matter (exotic in the sense of undiscovered, unknown, and very different from ordinary matter and even any plausible form of dark matter). Introducing that can give you wormholes, but then you have to be very careful about where and when you introduce the exotic stuff. Otherwise, wormholes everywhere, eating through ordinary matter structures. Depositing energy into discharged batteries, draining non-leaking fuel tanks. Or worse doing that in your cardiovascular system or brain. Also alien brains, stars, clouds of interstellar dust... (Pervasive wormholes has been embraced by some name-brand theoreticians, but they then rely upon some unknown scale suppression mechanism: there are wormholes all over the place but they are always very very very tiny compared to atoms, so the effects on e.g. AAA-batteries and stars are undetectably small. In this approach you are already riddled with wormholes connecting subatomic bits of you to subatomic bits of e.g. our galaxy's central black hole, but alas, you remain unable to travel faster than light). We can of course say, "well General Relativity could be wrong", and explore the consequences of a theory wherein we can build usefully-traversable wormholes without unknown matter. That theory, however, is virtually certain to be wrong on details about the orbits of bodies in our solar system and the difference at Earth-bound receivers from test signals sent across the solar system originating in our space probes like MESSENGER.