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?
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.
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.
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.
I've seen this vaguely referenced, but when I dig in I don't find support for it.
It's far from obvious that just because the event horizons (which is just a mathematical concept and a 3D area of space) should control the trajectory of the singularity.
With two identical blackholes, with a event horizon of radius R, why should a singularity 2R away be unable to escape?
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.
Right, but say you end up half way between two equal mass blackholes, under zero gravitational force. Are those two black holes definitely going to merge? If they were going near light speed in opposite directions could they not merge and free you as you stay equidistant from both?
Well, if you're halfway and outside of hte event horizon... I don't know. But you definitely can't escape an event horizon.
I don't know what would happen if two event horizons overlapped briefly, as two black holes passed by each other at significant speeds. That's definitely above my paygrade :P
Well imagine you are X distance from the singularity, and time dilation is hugely slowing down time from an external observer. As blackholes approach each other, the distance between the singularity and the event horizon significantly decreases. They become kidney shaped before the blackholes merge.
The trick is can a blackhole approach quickly enough to catch you as you keep dropping as you past horizon. Normally I'd say no, but the time dilation significantly complicates things.
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.
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.
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.
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.
> 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?
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.
Sort of, the red shift continues towards infinity, but since photos are quantitized there is a last photon.
Also don't forget even if you freeze forever as viewed by an external observer, the blackhole is growing, and will at some point consume everything that had previously fallen in.
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
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.
> 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
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.
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.
Won't this "long time" be only for the outside observer? Won't the person orbitting experience much less time and actually could get to watch the black hole evaporate?
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.
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.
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?
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.
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.
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.
All paths point singularity-way but a cone will also see a false image from in falling photons. That cone will get smaller the further in you fall. That doesn't mean you aren't pointed at the singularity, only that some photons are going faster than you. It's like saying that because some traffic on the highway is passing you, you're actually going backward.
All paths inside the event horizon lead to singularity. Full stop. This is reinforced by the Penrose diagrams you mention.
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.
“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.
> 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?
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.
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.
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.
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.
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?
Non-spinning and non-charged blackholes are called Schwarzschild or static black hole is a simple beast. You have a event horizon, a mass, and a slightly strange area near the event horizon where orbits are unstable, I believe within 1.5 times the event horizon distance.
Spinning blackholes (Kerr) of are quite complicated in comparison. They have an outer ergosphere, inner ergosphere, outer event horizon, and an inner event horizon. Also the singularity is no longer a point, but a ring.
A quote from the Ring_singularity link below:
An observer crossing the event horizon of a non-rotating and uncharged black hole (a Schwarzschild black hole) cannot avoid the central singularity
This is not necessarily true with a Kerr black hole. An observer falling into a Kerr black hole may be able to avoid the central singularity by making clever use of the inner event horizon associated with this class of black hole.
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.
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?
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.
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.
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.
The mentioned Hawking radiation is quite weak, weaker than we can currently measure, that's true. But for smalller black holes in the lab or for a black holes in our solar system (planet 9). It is very much possible (in the future) to detect the radiation and gain insights from it, maybe even within this century.
I would direct you to the holographic principle and the AdS/CFT correspondence. Because current theory suggest that the information that falls into a black hole is not lost and can be recovered (resolving the information paradox). Similar to as we can deduce the inner workings of the sun, from the information it emits, we could be able to deduce such information from hawking radiation in case of black holes.
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.
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…
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.
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.
> 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
> 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.
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
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.
> sufficiently close to a black hole it is impossible for particles to safely follow circular orbits.
Health and safety gone mad!
Weirdly, it's hard to actually find information about this using the phrase "plunging region", as if you search for it everyone is currently regurgitating the strange Oxford press release wording of "safely". Which is an ironic turn of phrase because the result of the plunge is falling into a black hole. Though I think they probably mean that the circular orbit itself would be safe, not that the particle is falling in deliberately to avoid orbiting in some unsafe manner within a circular orbit!
But the Wikipedia article is actually pretty clear: https://en.wikipedia.org/wiki/Innermost_stable_circular_orbi.... So closer than 3 Schwarzschild radii, you can in theory have an circular orbit instantaneously, at a speed lower than light (until the photon sphere at 1.5Rs, where you have to orbit at c). If it was Newtonian rules, you could just orbit here. But because spacetime is warped inwards, anything actually in such an orbit will tip off the circular orbit and into a lower orbit, where it tips inwards and so on, into an inward spiral.
It seems a bit like one of those coin spiral games/charity boxes where the coin spirals down a curved cone-like funnel into the central hole. Even a coin injected tangentially eventually falls in, because the continously curved inward slope of the surface always makes the coin turn inwards and resists a stable orbit (even if it had no friction or air resistance).
