[HN Gopher] First proof that "plunging regions" exist around bla...
       ___________________________________________________________________
        
       First proof that "plunging regions" exist around black holes in
       space
        
       Author : carbocation
       Score  : 71 points
       Date   : 2024-05-18 03:15 UTC (19 hours ago)
        
 (HTM) web link (www.ox.ac.uk)
 (TXT) w3m dump (www.ox.ac.uk)
        
       | gigatexal wrote:
       | Still continues to amaze me that the more they look the more they
       | confirm Einstein. Yet we know -- or strongly suspect -- that at
       | the singularity and within the BH general relativity breaks down.
       | I hope we see a unification of GR and Quantum mechanics in my
       | lifetime. Would be really neat
        
         | cdchn wrote:
         | Not to bring the all pervasive AI topic into this discussion,
         | but I think the best hope we have for finding that unification
         | depends on an AI superintelligence. I wonder if we've reached
         | the limit of what a singular human mind can push.
        
           | klyrs wrote:
           | > I wonder if we've reached the limit of what a singular
           | human mind can push.
           | 
           | You people are becoming zombies. Get away from your computer
           | and interact with the world. Humans with profound intellect
           | are producing the content that LLMs regurgitate for you.
        
             | bisby wrote:
             | No one mentioned LLMs.
             | 
             | We know that there are things that computers can flat out
             | do better than humans, because there are limits to human
             | brains. If computers continue to grow in power, then the
             | fact that someday there might be an AI (actual AI, not LLM)
             | which can come up with novel solutions is totally
             | plausible. And if we go past that point and computers
             | continue to become more powerful, then it's likely that the
             | AI will continue to grow and become more powerful as well.
             | And if the AI eternally expands its thinking capabilities
             | with time, then it will inevitably surpass humans one day.
             | 
             | Do we need to get to that point to solve physics? Probably
             | not. We're not at the limits of human ingenuity yet. But
             | mentioning AI doesn't mean "I think LLMs in the next 3
             | months will solve everything!" either. No need to be so
             | defensive about someone wistfully pondering about the
             | limits of humanity.
        
               | card_zero wrote:
               | None of that is fact, or inevitable, or meaningful. What
               | are "thinking capabilities", what are they made of? More
               | RAM? A human can have more RAM, by installing it in the
               | human's computer. More parallelism? Maybe, but that's
               | like having more humans. More speed? It's not clear what
               | you'd do with it, since research tends to involve
               | interaction and the outside world has a pace of its own:
               | sitting in a cell on amphetamines does not make you
               | brilliant. More of some unknown component of the yet-to-
               | be-discovered formula for intelligence? Maybe, if it even
               | works that way, which is a massive assumption.
               | 
               | I'm sorry, I'm not buying "superintelligence", outside of
               | sci-fi plots. Even there it's kind of irritating deus ex
               | machina stuff.
        
               | Vampiero wrote:
               | I'd agree with what you're saying, but the jump to "not
               | believing in superintelligence" doesn't make sense
               | either. Are you implying that humans are the absolute
               | peak of intelligence or that computers can't ever achieve
               | something that is even just one iota better than human-
               | level intelligence?
               | 
               | There's one thing machines have that we don't: time. A
               | human-level AI would be better than a human because you
               | can ask it to solve a problem for years on end without
               | ever resting.
        
               | card_zero wrote:
               | I'm implying that intelligence doesn't have quantifiable
               | levels, so I disagree with "peak" and "better" as
               | concepts. I know we can become better at solving problems
               | in a domain, often with the assistance of tools. But I
               | think the bogeyman of "superintelligence" is just a human
               | with better tools. Perhaps including a synthetic brain. I
               | expect its smarts to be cultural, made of ideas,
               | _mediated_ by technology, as usual, and domain-dependent,
               | as usual, and not frighteningly  "super" for the culture
               | it exists in. I anticipate AGI as a development of us.
               | 
               | OK, so, maybe there are paradigm shifts to be reached
               | that way, and maybe technology (familiarity with tools)
               | will be crucial for these paradigm shifts which are the
               | only way to understand certain new things intuitively.
               | But, maybe this has been going on already, even before
               | there were computers.
        
               | actionfromafar wrote:
               | Humans do that too, ie research institutes.
        
             | redundantly wrote:
             | I read their comment more as a nod to The Last Question
             | than speaking about the recent "AI" in the news.
             | 
             | https://archive.org/details/Science_Fiction_Quarterly_New_S
             | e...
             | 
             | https://en.wikipedia.org/wiki/The_Last_Question
        
               | Sakos wrote:
               | Then they should've made an explicit reference. As is, I
               | don't see any indication that they're even aware that The
               | Last Question exists and it sounds like every other LLM
               | fanatic.
        
               | redundantly wrote:
               | The term AI has been around a heckuva lot longer than the
               | current LLM hype. It's not unreasonable to make that
               | assumption, to link it along the lines of what AI really
               | means vs how the term has been used as of late.
        
               | cdchn wrote:
               | Yes, it was more along the lines of The Last Question,
               | wasn't even thinking about LLM.
        
             | MeImCounting wrote:
             | Yes the LLM hype can be annoying.
             | 
             | Equally if not more annoying is the smug disdain of those
             | who criticize it.
             | 
             | Even more annoying than that is people too caught up in
             | "the world" and "serious matters" to read some sci-fi.
        
               | klyrs wrote:
               | Don't get me wrong, I love reading and watching sci-fi!
               | And actually, that's a great source of inspiration to
               | keep my mind sharp; a superintelligence unleashed on our
               | world today, with pathetically insecure networked
               | listening devices in all of our pockets, a populace
               | demonstrably manipulable through social media, etc;
               | humanity has nothing but literal prayer to protect itself
               | from actual superintelligence. Which isn't an actual
               | defense, but hope feels nice.
               | 
               | Let's be clear: what we have today is LLMs. Not
               | superintelligence. When people drool over the promise of
               | superintelligence, to the exclusion of curiosity about
               | the problems we intelligent humans can solve, they've
               | bought into a thought-terminating utopian fantasy. That's
               | a dead brain, that will not help humanity progress.
               | Zombies.
               | 
               | Superintelligence, should it ever arise, is my enemy. The
               | disdain that I have for its adherents is born of self-
               | preservation.
               | 
               | edit to add clarity regarding my admonition to experience
               | "the world": whoever receives all of their knowledge from
               | computer sources is readily replaced by an automaton with
               | access to the same. Those of us who are curious about the
               | world around us are capable of making observations yet to
               | be recorded in electronic form. Be curious, my friend, or
               | succumb to zombiehood.
        
               | MeImCounting wrote:
               | At the risk of repeating myself, yes the LLM hype is
               | quite overdone and annoying. What you say is true people
               | have bought into a fantasy which is wholly unrealistic.
               | 
               | Unfortunately your view is altogether tiresome and much
               | harder to scroll past than the juvenile LLM excitement
               | because it could actually do some real harm in the long
               | term. No 'The Terminator" was not a documentary, nor was
               | "The Matrix" nor even is your favorite episode of "Black
               | Mirror".
               | 
               | Watts is far more eloquent than I could ever be on this
               | subject matter. I highly recommend this article in The
               | Atlantic by him and if you havent picked up any of his
               | work I highly recommend pretty much anything hes ever
               | written.
               | 
               | https://www.theatlantic.com/ideas/archive/2024/03/ai-
               | conscio...
        
               | klyrs wrote:
               | I was cured of blind techno-optimism years ago. The race
               | for superintelligence is between ad-slinging megacorps
               | and authoritarian governments. Whoever wins, we humans
               | lose.
        
               | MeImCounting wrote:
               | I Feel like were having two different conversations here.
               | Who said anything about optimism? Are those the two
               | options now optimism or doomerism? No space left for
               | anything approaching realism?
               | 
               | I criticize blind techno-doomerism for its use of clanky
               | old worn out cliches from the sci-fi of last century. I
               | criticize LLM bros for being naive and blinded by
               | advertising. Both groups completely misunderstood the
               | relevant sci-fi from this century, if they actually
               | bothered to read any.
               | 
               | Sometimes between the rabid hype-bros and the holier-
               | than-thou doomers you can find actual conversation about
               | the nature of human interaction with theoretical future
               | machine intelligence, how LLMs relate to that and the
               | technical aspects of creating such a thing. Its rare but
               | it is out there.
        
               | klyrs wrote:
               | You called me annoying because I don't read sci-fi. Now I
               | stand accused of reading the wrong the wrong sci-fi?
               | Whatever.
               | 
               | Hope for the best, prepare for the worst.
        
             | cdchn wrote:
             | The idea for me comes less from AI than the slowdown, I
             | think, of really ground breaking science. We're still
             | proving Einstein's ideas, we haven't really moved much
             | beyond Einstein.
        
             | cdchn wrote:
             | Thats the distinction I think between an LLM and a real
             | AGI. One is a stochastic parrot, the other can come up with
             | new ideas.
        
           | kitd wrote:
           | It takes a singularity to comprehend a singularity?
        
           | af78 wrote:
           | AI or not, if a machine finds an answer so complex that no
           | human can understand it, how useful is it?
        
             | rthnbgrredf wrote:
             | Depends on whether we can instruct the AI to make something
             | useful out of it. Today we have complex systems like CPUs
             | that most humans don't understand.
        
             | DonHopkins wrote:
             | Or an answer so simple: 42.
        
             | ben_w wrote:
             | I don't see that as being an important objection, because
             | from the point of view of any single human... that's
             | already true for the expertise found only in other humans.
             | 
             | I don't know the chemistry necessary to turn crude oil into
             | any plastic, I don't know how to use a Lagrangian, I tried
             | and failed to learn group theory (I've only got the basics,
             | and I'm not confident about them), and I've still only got
             | a toy model of special relativity (which is supposed to be
             | the easier one) -- and yet, not only are those all still
             | useful, the four colour theorem is useful even though it's
             | a non-surveyable proof: https://en.wikipedia.org/wiki/Non-
             | surveyable_proof
        
             | cdchn wrote:
             | Abstractions are a thing. We use devices all the time that
             | we don't understand entirely the workings of.
        
           | z3phyr wrote:
           | Please touch grass sir!
        
           | tbrownaw wrote:
           | > _I wonder if we 've reached the limit of what a singular
           | human mind can push._
           | 
           | We passed that limit ages ago. The underlying technology used
           | to do so is called "writing", which is what allows for things
           | like libraries and letters / email and personal scratchpad
           | notes.
        
         | vbezhenar wrote:
         | Is it even scientific to claim anything about black hole
         | insides? AFAIU it's impossible by definition for any
         | information to escape black hole insides. Any observation or
         | experiment is not possible. Any assumption can't be confirmed
         | or rebuted. Basically it can't be falsified, so it's not a
         | science according to Popper.
        
           | chungy wrote:
           | We can hypothesize, but there is no known way to ever test
           | it. At least not with the information getting out of the
           | black hole.
        
             | kelseyfrog wrote:
             | Without being able to test, the insides of blackholes are
             | outside the realm of falsifiability and thus forever beyond
             | science.
        
           | disconcision wrote:
           | > AFAIU it's impossible by definition for any information to
           | escape black hole insides. Any observation or experiment is
           | not possible
           | 
           | this doesnt precisely follow. observation or experiment is
           | possible from within the event horizon, although this might
           | limit plausible venues for publication
        
             | jl6 wrote:
             | Publish _and_ perish.
        
               | sliken wrote:
               | No need to perish, current theories explain that the
               | innermost region of a spinning black hole (all real world
               | black holes spin) has a low gravity region where
               | arbitrary navigation is possible. You can't escape, but
               | you also don't have a death date with the singularity.
        
               | knodi123 wrote:
               | Uh... But how do you _get_ there? My understanding as a
               | lay-person is that you can 't get past the event horizon
               | without getting spaghettified, and cooked by high-energy
               | blue-shifted radiation.
        
               | sliken wrote:
               | Getting past the event horizon of a small blackhole is
               | tough, the gravitational gradient causes
               | spaghetification. However larger blackholes lessen the
               | gradient at the event horizon, so it's not a problem.
               | 
               | Not sure about the inner horizon, just saw a discussion
               | of the paper for a spinning black hole recently, it
               | described three distinct regions.
        
               | vikingerik wrote:
               | Most lay-person discussion of black holes just ignores
               | the spaghettification and radiation problems. Those don't
               | really have anything to do with space-time or information
               | propagation or cosmology or such, those are just
               | limitations of material strength and biology.
               | 
               | The discussion is more like, if we had infinitely
               | resilient materials or biology, what could they observe
               | and experience.
        
               | knodi123 wrote:
               | > what could they observe and experience
               | 
               | Observe? Nothing, once you're inside the event horizon,
               | right? The event horizon isn't a solid wall, it's just
               | the point at which light can only move further inward,
               | never outward. So even inside the event horizon, we still
               | can't observe anything further in.
        
               | db48x wrote:
               | "Spaghettification" only happens to large enough objects
               | near small enough gravitational sources. If the Moon got
               | too close to the Earth, closer than the Roche Limit, then
               | it would break up into a ring of debris. But a
               | communications satellite can exist at that same distance
               | with no ill effects.
               | 
               | The same is true for black holes. A rocket or a human
               | diving into a stellar mass non-spinning black hole would
               | be "spaghettified"; they would be broken up into a thin
               | stream of debris as they crossed the Roche Limit before
               | they crossed the event horizon. But they could cross the
               | event horizon of a much larger black hole, such as a
               | supermassive black hole at the center of a galaxy.
               | 
               | In fact, if the black hole were massive enough then the
               | gravitational field near the event horizon would be so
               | mild as to be Earth-like. If you were to stuff all of the
               | mass of three or four Milky Way-type galaxies into one
               | black hole, you could build an actively-stabilized
               | structure around the black hole to create a livable
               | environment of truly insane proportions with Earth-normal
               | gravity. Look up Birch Worlds sometime.
        
               | knodi123 wrote:
               | > you could build an actively-stabilized structure around
               | the black hole to create a livable environment of truly
               | insane proportions with Earth-normal gravity
               | 
               | Which was also a rocketship into the future, moving you
               | super fast towards the heat death of the universe?
        
               | db48x wrote:
               | Not exactly. Time does run more slowly near a strong
               | gravitational source, and if you are near the event
               | horizon of a stellar-mass black hole this effect can be
               | extreme. However, the larger the black hole is, the
               | flatter the space around it. Furthermore, "near" is
               | relative. A Birch world would be built around a black
               | hole which is approximately a light-year in diameter. The
               | structure would be "near" the black hole's event horizon
               | in relative terms but in absolute terms it would still be
               | pretty far away, perhaps a quarter of a light year.
               | Expect a time dilation of just 2:1, meaning that for
               | every year on the Birch world two years pass for the rest
               | of the universe.
               | 
               | It might seem like this costs you a lot, since it halves
               | the amount of time you can live near your black hole.
               | However, the lifetime of that black hole will be
               | somewhere between 10100 and 10106 years, which is pretty
               | insane even if you only get to use half of them.
               | Furthermore, this is many orders of magnitude longer than
               | the lifetime of a galaxy, so your civilization could
               | potentially outlive everything else in the universe.
               | Large stars burn out the quickest, but with black holes
               | it is the other way around: small black holes evaporate
               | the soonest. You might think that storing hydrogen in
               | brown dwarf planets for use in fusion reactors would
               | power a civilization for a long time, but fusion reactors
               | are surprisingly inefficient. A civilization built around
               | a rotating supermassive black hole can take advantage of
               | the Penrose process to extract more usable energy from
               | the same mass than the fusion reactors would.
        
               | squrky wrote:
               | My layperson understanding is that collision with the
               | singularity (if that even exists) is mathematically
               | inevitable for an object that has crossed the event
               | horizon. I think your scenario of hanging out within the
               | event horizon and safely away from the singularity for
               | indefinite time would require infinite fuel to counteract
               | the gravitational gradient, or for even more fundamental
               | reasons.
        
               | ben_w wrote:
               | > or for even more fundamental reasons.
               | 
               | Even more fundamental: you'd need infinite fuel to hang
               | out forever _just outside_ the event horizon -- once you
               | 're inside, the direction of the singularity is "future"
               | not "forwards", so you can't resist getting there with
               | any form of propulsion any more than you can resist
               | getting to next Thursday with any form of propulsion.
        
               | hirsin wrote:
               | This may be hopelessly naive but isn't the idea of GR
               | that with sufficient fuel (and I suppose breaking some
               | laws of physics) I can effectively postpone my
               | experiencing next Thursday (here on earth) by moving away
               | from earth at one lightsecond/second?
        
               | ben_w wrote:
               | Other way around, the more you accelerate, the less time
               | you experience between now and then.
        
               | ykonstant wrote:
               | And to emphasize the above point, it doesn't matter which
               | "direction" you accelerate towards; the singularity is in
               | the future, and you are approaching the future faster the
               | more you accelerate.
        
               | BurningFrog wrote:
               | You can orbit a black hole like any other gravity source,
               | without spending fuel.
               | 
               | I don't know how near the event horizon a safe orbit can
               | be?
        
               | idiotsecant wrote:
               | That's kind of the definition of the event horizon. You
               | cannot be 'safe' once you're inside. All paths lead to
               | the event horizon. No matter which direction you point,
               | you're pointed at it.
        
               | lambdaxyzw wrote:
               | I am not too knowledgeable about black hole physics, but
               | it was my understanding that there's nothing locally
               | interesting about event horizon: it's just the point of
               | no return that doesn't change much for the local
               | observer. Your definition of the event horizon make it
               | sound more locally important.
               | 
               | In fact, I know that as a local observer falling into a
               | black hole you can still see some of the outside world
               | after falling into the event horizon (by looking "behind
               | you"), you just can't send anything back. This also seem
               | to contradict the statement that all paths point inside
               | (or I may misunderstanding something).
               | 
               | Edit again: I did some research and it looks like that
               | while parent's comment may be true for simplified model
               | of a black hole, it is conjured to be possible for
               | rotating black holes where you can stay inside. Also
               | Google "penrose diagram kerr black hole" for some weird
               | physic if you want to follow this rabbit hole. Keep in
               | mind that I'm not a physicist and this is my
               | understanding after 40 minutes of watching YouTube and
               | Wikipedia.
        
               | U1F984 wrote:
               | I can't find anything about these low gravity regions
               | (Google redirects me to your post) but they sound
               | interesting. Can you share some reading material?
        
               | jameshart wrote:
               | The entry point is probably looking at how Penrose
               | Diagrams describe black holes.
               | 
               | Recent Veritasium video:
               | https://www.youtube.com/watch?v=6akmv1bsz1M
               | 
               | Wiki: https://en.wikipedia.org/wiki/Penrose_diagram
        
               | golem14 wrote:
               | I always wondered if you can orbit inside the event
               | horizon of a large black hole and wait until its hawking
               | radiation shrinks the event horizon so that you find
               | yourself outside. You would have to wait a long time I
               | guess.
        
             | exe34 wrote:
             | Cartan Null?
        
           | card_zero wrote:
           | But we can have an explanation, which can be falsified by
           | arguments, without needing to directly test the inside of
           | black holes with instruments.
           | 
           | > Now my reply to instrumentalism consists in showing that
           | there are profound differences between "pure" theories and
           | technological computation rules, and that instrumentalism can
           | give a perfect description of these rules but is quite unable
           | to account for the difference between them and the theories.
           | 
           | I _think_ that 's the right quote, Popper often lets me down
           | when I want something terse and uncomplicated.
        
           | Sakos wrote:
           | This is such a weird statement. A lot of currently
           | established science was only theorized during the early 20th
           | century, long before we had the tools so they could be
           | "proven" with real-world experiments. It was still science at
           | the time.
        
           | rthnbgrredf wrote:
           | We have Hawking radiation and gravitational waves and the
           | future potential to experiment with microscopic black holes
           | in the lab, along with the hypothesis that Planet 9 might be
           | a primordial black hole in our solar system, there is a
           | wealth of opportunities to explore and learn more about black
           | holes experimentally, without entering one physically.
        
             | santoshalper wrote:
             | Yes, but definitionally, none of those experiments can tell
             | us anything about what is inside the black hole.
        
               | rthnbgrredf wrote:
               | Well, we have a pretty good understanding of how our sun
               | works internally just by observing it from the outside,
               | without ever digging a hole into it to observe it from
               | the inside.
        
               | idiotsecant wrote:
               | That's because the sun emits a great deal of information.
               | Black holes by definition emit none (on human time
               | scales)
        
           | thriftwy wrote:
           | Yes, it is scientific. For example, Kruskal-Szekeres
           | coordinates precisely describe movement inside the black
           | hole.
           | 
           | https://en.m.wikipedia.org/wiki/Kruskal-Szekeres_coordinates
        
           | csomar wrote:
           | Maybe if you can create nano-blackholes and explode them
           | later in a controlled fashion?
        
           | cjfd wrote:
           | It looks like they are mostly making statements about what is
           | happening outside the Schwarzschild radius. These are
           | testable statements.
        
           | gigatexal wrote:
           | Given our best theories we speculate what the inside of a
           | black hole might be like. Of course we can't know. But that's
           | how scientific things go: the cutting edge of human
           | understanding is used to make predictions. Particular to the
           | inside of a black hole, though, it's impossible to test what
           | we see or what happens when something passes the event
           | horizon. I guess unless we wait basically an eternity
           | capturing all the hawking radiation to rebuild what was sent
           | in...
        
           | dotnet00 wrote:
           | From my understanding, that invokes the black hole
           | information paradox. There should be some way in which the
           | information of what went into a black hole is retained, a
           | possible answer being with the Hawking radiation.
           | 
           | We just don't know enough about black holes to say for sure
           | that the insides can not be studied in some manner. That's
           | kind of why a theory of quantum gravity is so relevant,
           | without it, the inaccessibility of the inside of a black hole
           | remains at odds with key components of quantum physics.
           | 
           | Eg The current theory is that black holes release Hawking
           | radiation, and studying that over the lifetime of the black
           | hole might reveal information about the matter that went in.
           | Understanding how this information is encoded could reveal
           | things about the inside. Other possible explanations are that
           | near the point of evaporation, when the black hole shrinks
           | down to a size where quantum effects dominate, the
           | information within becomes accessible, which could again
           | allow potentially studying the inside.
        
             | bongodongobob wrote:
             | Using information from Hawking Radiation to understand what
             | went in: while it might be possible, isn't this on the same
             | practical level of unscrambling an egg? Sure we could do it
             | with nanobots but is that really a possibility or just a
             | mathematical curiosity?
        
               | dotnet00 wrote:
               | Given the amount of mass typically involved, probably
               | just a mathematical curiosity, but if that's the only way
               | we can figure out to try to understand the inside, maybe
               | we'll eventually be able to generate microblackholes from
               | tiny amounts of matter, collect the hawking radiation and
               | study those in this manner (they'd evaporate pretty
               | quickly).
               | 
               | Edit: I forgot to add in my original post that there's
               | also just the possibility that the mechanism by which
               | this paradox is resolved still hides the inside.
        
       | legohead wrote:
       | And the graphic on the page is the opposite of what they are
       | describing...
        
         | SiempreViernes wrote:
         | No, the inner most stable orbit is just not very large which
         | the graphics illustrate by the central black region around the
         | black hole.
        
       | ganzuul wrote:
       | Why is it that some experts say stuff falls into the center of a
       | black hole while others say it slows down and never passes the
       | event horizon? Is it just semantics?
        
         | anal_reactor wrote:
         | The closer you are to the black hole the slower the time
         | passes.
        
         | pests wrote:
         | Frame of reference. The object falling in experiences time as
         | normal and actually falls in.
         | 
         | From an outside observer they never cross the event horizon,
         | due to the time dilation mentioned by the other comment.
        
           | knodi123 wrote:
           | > From an outside observer they never cross the event
           | horizon, due to the time dilation mentioned by the other
           | comment.
           | 
           | Doesn't that imply that if we look at a black hole from a
           | safe distance, the event horizon will appear to be a
           | cluttered frozen motionless ring, full of all the stuff that
           | is in the process of falling in but which from out point of
           | view, never will?
        
             | pests wrote:
             | Almost, another detail is the closer the object gets to the
             | event horizon, the more it's light redshifts - until it's
             | no longer in the visible spectrum at all. You can think of
             | the black hole's gravity as stealing energy from the light,
             | shifting it into a lower energy spectrum.
        
         | ghighighighilo wrote:
         | I think only the last photons at the event horizon of you never
         | escape the event horizon. So as you're falling toward the
         | horizon you're colour shifting as the photons move slower and
         | slower until you cross the event horizon at which point your
         | last reflected photons outward speed matches their inward
         | gravity and they freeze, balanced on the edge. You actually
         | keep falling toward the singularity but no one will ever see
         | you after the horizon because any reflected photons can't
         | escape the gravity well.
         | 
         | You won't actually see the frozen photons though, just the ones
         | before it. Once you see them, though, the image on the horizon
         | is gone.
        
         | ben_w wrote:
         | IIRC, it depends on the frame of the observer.
         | 
         | An outsider will see in-falling objects slow down, redshift,
         | and never cross the horizon; but if you're falling in, this
         | happens in finite time, you don't get to see the universe
         | rapidly age, the black hole doesn't evaporate from Hawking
         | radiation before you reach it.
        
         | sliken wrote:
         | From the external view you never enter, just get dimmer as you
         | approach the speed of light and the time dilation keeps
         | increasing.
         | 
         | From the viewpoint of the one falling in, you just fall in and
         | cross the horizon without noticing.
         | 
         | Does make you wonder if time dilation gets so extreme, could
         | another black hole wonder by, offset the gravity of the black
         | hole, and let you escape. Even if it takes a billion years.
        
           | rthnbgrredf wrote:
           | > Does make you wonder if time dilation gets so extreme,
           | could another black hole wonder by, ... Even if it takes a
           | billion years.
           | 
           | This could even be the most likley scenario, since ultra
           | massive black holes eats vast amounts of smaller over the
           | course of billion years.
        
           | pavel_lishin wrote:
           | Once you've crossed the horizon from your point of view,
           | there is no escape. If another, larger black hole passes by,
           | at best you'd be within a larger event horizon comprised of
           | both, I think.
        
           | evo wrote:
           | I suspect that would fall under the rule that if two black
           | holes' respective event horizons ever cross, they merge and
           | initiate the eventual merger of the two respective black
           | holes.
        
           | Filligree wrote:
           | The time dilation does not act in that way. You will not
           | experience the outside universe speeding up, at least not by
           | very much; the reason for this "paradox" is primarily that
           | photons coming off you take longer and longer to climb out,
           | and the ones from right when you crossed the event horizon
           | never will.
        
         | willis936 wrote:
         | PBS SpaceTime had a recent episode that helps with this
         | apparent paradox.
         | 
         | Really their entire playlist on black holes (and entire catalog
         | for that matter) is worth a watch.
         | 
         | https://youtu.be/Rogm_lpVZYU
        
         | x3n0ph3n3 wrote:
         | I believe there is nothing actually inside a black hole -- to
         | us, it appears as a giant sphere, where all of the matter is at
         | the surface, but there is no "inside." It' s like a giant shell
         | with no interior because spacetime breaks down. All matter on
         | the shell is at zero distance from all the other matter on the
         | shell.
        
         | woopsn wrote:
         | There is also a theory that as you approach the horizon you'll
         | be incinerated by a kind of hidden firewall. This apparently
         | contradicts GR - but on the other hand if you're allowed to
         | fall in it seemingly contradicts QM.
        
       | SiempreViernes wrote:
       | Here's the paper:
       | https://academic.oup.com/mnras/article/531/1/366/7671518
       | 
       | X-ray astronomers, how weird is it that they show their fits in
       | physical space and not in instrument space?
        
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