[oevi]

Black holes are an excellent example for so called "cognitive metaphors".

Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass.

This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the black hole".

I think it is really interesting how these cognitive metaphors can sometime limit our ability to think about a problem, because they often restrict the properties of the described thing to the properties of the analogy.

[dahart]

> Because we found no better analogy, we named them "holes"

Are you sure about that? This sounds specious. This requires knowing who named them and why. It sounds like a logical explanation, but history and human events don't follow logic and can't be derived.

> We talk about [...] "light cannot escape the black hole"

So, light not escaping certain "dark stars" was observed and was a concept before "black hole" was a term. "Dark stars" is one term they were called before the term "black hole".

http://curious.astro.cornell.edu/about-us/86-the-universe/bl...

Wikipedia says the name black hole was adopted because it was catchy, which is not because of the value of the analogy. "Dark star" might be a better analogy, and it existed before black hole.

https://en.m.wikipedia.org/wiki/Black_hole#Etymology

Having said that, black holes are actually black, and they are literally gravity holes in space. A hole in the ground on earth is only a hole because of gravity, it's a thing you can fall into. Because black holes are things you can fall into if you get too close, because it's doing the exact same thing as a hole in the ground, I'd argue that black hole is not a very good example of a cognitive metaphor.

Note also that the best way to demonstrate the intuitive effect of gravity is to show how it acts like a hole. A black hole visualized the same way is a very, very deep pit.

https://youtu.be/MTY1Kje0yLg

[InclinedPlane]

Neither dark star nor black hole are apt "models" for the objects. These are phenomena of space-time, not just of gravity. Light cannot escape a black hole because escaping a black hole is impossible. And it's impossible because the space-time inside an event horizon has no trajectories that go forward in time which go farther away from the singularity. Black holes are like pocket universes with one-way roads connecting them to our Universe, this is why light doesn't leave the inside of the event horizon, the path between there and here only goes one way, unlike the rest of space-time.

"Dark star" is also a misleading term in that it implies the object is a star or something physical at all. In fact to us it doesn't matter what the object is inside the black hole, and its structure is essentially unknown to us (at present), because we can't interact with it. We can only interact with the space-time phenomenon that it created, the event horizon.

[dahart]

Agree with all of this, and I appreciate the explanation, but "black hole" is just a name and not a model. We need a shortcut and not a thesis to talk about it efficiently, right? The name really only needs to identify, and not convey perfect and complete understanding, no? It's nice that the analogy is decent, but there is no name that could capture and communicate the complete meaning, that requires further explanation. True for most/all scientific subjects and physical phenomena, I think.

Given your description, "hole" still seems like a great and very literal analogy to me, if we had to pick a single word. It's capturing a sense of going in but not out, and it's also capturing a sense of darkness, and of going into or down via gravity as well. A one-way road that you can drive in but not out, and is downhill, and dark from the outside, sounds like a 'hole'.

We could call it a pocket universe, or a spacetime existence prison, or a one-way road to infinity, but I'd have to agree with John Wheeler, that "black hole" is brief and catchy, captures the essence of what we know about them in 9 letters, in a way that is accessible to non-physicists.

BTW, isn't gravity a phenomenon of spacetime? I don't understand your differentiation.

[coryfklein]

> escaping a black hole is impossible

Except for Hawking Radiation [1]

"black holes that do not gain mass through other means are expected to shrink and ultimately vanish. Micro black holes are predicted to be larger emitters of radiation than larger black holes and should shrink and dissipate faster."

[1] https://en.wikipedia.org/wiki/Hawking_radiation

[InclinedPlane]

Hawking Radiation comes from outside the event horizon.

[Retra]

Hawking radiation takes energy away from the inside of a black hole.

[InclinedPlane]

Certainly, but the radiation still comes from outside the event horizon.

[blackrock]

I would prefer if black holes were called "Dark Stars".

Because that really is what they are. A weird star that is so massive, its gravitational field distorted the fabric of its local space, that not even light can escape it.

It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot escape it. So, from the outside, the black hole appears dark. Hence, a dark star.

Perhaps if you are inside the Event Horizon of the black hole, then you can still see the light from the fusion of the star. But if you are outside of the Event Horizon, then you will only see the star as pitch black, since light can't even escape it.

[qubex]

The term “Dark Star” actually predates the term “Black Hole” by a very long margin (first recorded usage 1783) [0] for classical Newtonian objects whose mass is so large that the escape velocity at their surface exceeds the finite speed of light. Black Holes are very different beasts (self-sustaining concentrations of space-time curvature), despite their popular explanation as being “objects so massive space cannot escape”.

It’s extremely improbable that any “classical” (non exotic-quantum) processes are going on within the horizon because it’s very clear that the strength of the gravitational field would far exceed the hydrostatic pressure generated by fusion reactions. It far exceeds the degeneracy forces that prevent neutron stars from collapsing further under their own mass.

[0] https://en.wikipedia.org/wiki/Dark_star_(Newtonian_mechanics...

[Santosh83]

Gravitational collapse overwhelms fusion pressure much before the black hole stage is reached, i.e., neutron stars. Also general relativity seems to indicate unambiguously that the in-falling matter collapses to a singularity, which obviously cannot have any kind of structure or process inside it. I guess only a quantum theory of gravity can clear up this enigma.

[qubex]

(Not to mention that once one has crossed the Schartzchild Radius time dilation becomes infinite from the perspective of the outer universe, and time freezes, so any process becomes frozen in its tracks, at least from the perspective of external observers.)

[etskinner]

Why does the perspective of outside observers matter at that point? Aren't we talking about what happens inside?

[Santosh83]

True, for the in-falling person, the outside observer's perspective doesn't matter and vice versa. But what happens inside is, (and probably will always be), entirely theoretical, but we can observe the space just outside the event horizon.

[AnimalMuppet]

What happens in the Swartzchild Radius, stays in the Swartzchild Radius.

[BenMorganIO]

Yes, but that process is never truly reached since time has to slow down infinitely for that to happen.

[InclinedPlane]

This is untrue, gravitational collapse does not overwhelm fusion pressure, fusion stops, that's why neutron stars are created.

[4ad]

> It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot escape it.

No, it is not. In GR, once critical density is reached, gravitational collapse is inevitable: https://en.wikipedia.org/wiki/Penrose–Hawking_singularity_th....

It's possible this doesn't hold true in some theory of quantum gravity, but you'd get some exotic matter, not "stars still performing fusion, and emitting light and heat, like a regular star".

Please note that no fusion is happening in white dwarfs, nor in neutron stars.

[akvadrako]

> It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star.

I don't think that's a useful picture. It's closer to the truth to say that from the outside perspective, all the information and energy sits on the border and there is not even an inside to speak about. In other words, it's the edge of the universe and what's past the event horizon is another universe. Not like a star at all.

[blackrock]

To me, the concept that there is another universe, beyond the Event Horizon, is a little silly.

However, for fun, I once thought of a science fiction scenario for a novel.

I thought a Black Hole, can be used as the instrument for a wormhole in space. An Einstein-Rosen Bridge, that connects our universe to another universe, in the multiverse.

But there are a lot of plot holes in this idea. If light cannot escape the black hole, then you somehow need to go faster than light, to traverse the wormhole, and to escape it, when you cross over to the other side. So, once you exit the black hole, then you land at the other side, and there is a whole other universe there, with its own set of stars.

But, this will also allow other people from another universe, to cross into our universe, via this black hole.

Then how does such a black hole form?

It starts with a very massive star, more massive than a Neutron Star, that roams around our universe. Then, in an adjacent universe, another very massive star is wandering around also. Think of our universe as a bubble, and the adjacent universe is another bubble. These two massive stars, will distort the fabric of their bubbles, at the edges. The two stars will gravitationally attract each other, and they will basically punch a hole through each bubble. And when they collide, the mass from each star will form the structure of the wormhole. They won't explode on contact, but instead, it will now form a bridge between two universes.

For millions of years, they will dance around each other, until they finally find a stable orbit, where both are spinning around each other.

Think of this as a binary star system, where the two stars are rotating around each other, so fast, that it forms this virtual wall. This virtual wall, is the structure of the Einstein-Rosen bridge. And in the middle, it is gravitationally neutral.

And this wormhole structure, will now allow regular spacecraft, that can travel faster than light, to traverse the wormhole, and emerge on the other side.

Next, I just have to add the other parts of the story, like the bad guy, the love story and love triangle, and some good guy that is searching for himself. And with that, I'll have a blockbuster novel that I can turn into a live action movie.

[wruza]

Ah, that story when realistic physics happened and she loves him. First question, lasers or blasters? Second, is good guy’s dad bad guy?

Third, probably least interesting, how does one get into BH travelling FTL, if that makes you go back in time?

[pnut]

Lee Smolin proposed a really compelling concept in "Life of the Cosmos" - that the reason our universe has the universal constants that it does, is the product of natural selection at the cosmological level.

https://en.wikipedia.org/wiki/Lee_Smolin#Fecund_universes

His idea is that production of black holes is the universe producing offspring, and our perception that a black hole is constrained within a coordinate space in our own universe, is an illusion.

[trophycase]

I personally subscribe to this theory. I also think it's plausible that the development of intelligent life may be a part of the universe's reproductive process and may end up facilitating it in some way

[marcosdumay]

> From the outside perspective, all the information and energy sits on the border

Are you sure that's known? What kind of experiment would settle that?

[qubex]

Since at the event horizon (schardzchild radius) time dilation becomes infinite, essentially time ceases there. That's why it's called an “event horizon”: because events (four-dimensional coordinates) become disconnected there. As time is frozen (from an external observer's perspective) stuff ceases to move and just “piles up” there. From the in-falling matter's perspective, however, the transition occurs in finite proper time. Once it has crossed the horizon, it finds itself inside the hole where the direction of space pointing towards the horizon (inwards) becomes ‘timelike’ (in the sense that its flow cannot be arrested and it is unidirectional) and time becomes ‘spacelike’ (in the sense that it could be negotiated at will).

No experiment that I know of could confirm this because everything will depend on extrapolation from less extreme and finite scenarios.

[pault]

You could go into the black hole yourself but you'd need to communicate the results of your experiment by twitching the second hand on your daughter's watch who, conveniently, works for NASA.

[qubex]

Interstellar infuriated me worse than the average “space opera” Star Wars/Star Trek-type crap because it spread the pretence of being scientifically accurate and plausible.

Before we get to the black holes part... why didn't they have timestamped signals from the surface of that water-planet? Why didn't they go into a polar orbit (as opposed to equatorial orbit) around it so as to minimise the cumulative time dilation around the black hole it was orbiting? What kind of specific impulse were they supposed to have to be able to take off from it after they'd landed.

Oh, I cringed. I cringed so hard. Poor Kip Thorne.

[Sir_Cmpwn]

It's a lot more complicated than this and a lot of your assumptions are not true. So far as our universe is concerned, the inside of a black hole literally doesn't exist and events in there literally don't happen. Once you get inside, spacetime is warped so severely that a lot of our fundamental assumptions about how space and time work change. It's not reasonable to assume that normal processes observed outside of the event horizon are still happening inside (plus, black holes form from supernovas, which happen precisely because fusion ceased in the star (simplified explanation)).

[coryfklein]

> So far as our universe is concerned, the inside of a black hole literally doesn't exist and events in there literally don't happen.

Except our universe _is_ affected by what happens inside a black hole via Hawking Radiation [1], where energy from inside the black hole does make it out and interacts with the rest of the universe.

[1] https://en.wikipedia.org/wiki/Hawking_radiation

[Retra]

Obviously the inside of a black hole does exist on account of the fact that it is able to warp spacetime in an externally detectable manner. If the interiors of black holes didn't exist they would be indistinguishable from empty space, and not seem so remarkable as to be called "black holes."

Either way, we do not know what processes occur inside because we lack any theory which could describe it. This certainly doesn't mean nothing happens in there or nothing exists in there.

[Sir_Cmpwn]

From my earlier comment:

>So far as our universe is concerned, the inside of a black hole literally doesn't exist and events in there literally don't happen.

It would probably be easier to get this across if I substituted "So far as our universe is concerned" with "From our perspective outside of the event horizon". Remember that a singularity doesn't just "pull" light so hard that it can't escape - they warp spacetime around them, so much so that the space and time within the event horizon ceases to be meaningful from our reference frame. The only way to go is down - literally. If you turn 360 degrees in a black hole you will never face the outside.

Also, we definitely have theories that describe what could happen inside an event horizon. General relativity, for example. It's from these that we can establish that space and time "switch" within, for example. We can solve general relativity for the conditions within an event horizon and make some pretty strong predictions about it (it's from these predictions that I conclude elsewhre in this discussion that fusion is unlikely).

[qubex]

The inside of a black hole doesn’t exist as far as our universe is concerned. Even the ‘gravity’ isn’t ‘emanated’ by the mass ‘inside’ the event horizon; rather it is a ‘recursively’ generated field (remember: gravity is generated by mass-energy curving space-time, gravity is a form of energy, and so gravity begets gravity in an entirely self-sustaining manner).

[thathappened]

This is a misconception of spacetime. The object exists, it just consumes faster than it dissipates mater. Just because there's no discoverable interaction between the consumed matter doesn't mean it doesn't happen, which is all time really illustrates.

[Sir_Cmpwn]

From our external perspective, they never happen. The time they use to happen in doesn't exist.

[wruza]

So, in our reference frame, black holes never grow from original collapse and remain in that same state, tiny mass and size, no matter what falls into it. Wait, no. It loses mass through particle emission, which is assumed to actually happen. This puzzle was worth investigating when I learned this topic (not sure I understood all math and concepts correctly though).

[Sir_Cmpwn]

I mean, the real answer is "black holes are very complicated" and a full explanation is out of scope for a HN comment. Hawking radiation requires a lot of background knowledge to understand (and I have to admit I still don't fully understand it). The pop-sci explanation of particle/anti-particle pairs appearing on either side of the event horizon is incorrect.

[whyever]

I would argue that calling them "dark stars" is just as misleading and "limiting thinking". In fact, I think you are a victim of this in your post: you incorrectly ascribe nuclear fusion (which is typical for many stars) to a black hole.

[Moodles]

I believe the term "frozen star" was also used for a time to describe black holes. I'm no physicist but I'm not sure this is an appropriate term either: blackholes are supposed to be really cold inside but really hot from the outside.

[Santosh83]

I think frozen star refers to the fact that from an outside observer's perspective, the star seems to stop collapsing at the last possible moment, suspended in time as it were, because light from the moment of black hole formation takes an infinite amount of time to reach the observer.

[JumpCrisscross]

> then you will only see the star as pitch black, since light can't even escape it

Would it be black? Right above the event horizon is flaming relativistic matter.

[chopin]

That's true but afaik time dilation makes it rather dim infrared radiation.

[Retra]

On the inner-most layer, yes. But outside of that, it will be less dim and less infrared.

[hackerman12345]

It is my understanding that black holes create new stars. It's also my understanding that small mass will eventually be drawn towards bigger mass. Does this mean the eventual "heat death of the universe" won't actually happen as stray light/heat/RF/particles/whatever will always get drawn in back towards a mass like a blackhole and reformed?

[kazagistar]

> small mass will eventually be drawn towards bigger mass

Common misunderstanding. All mass has acceleration from gravity, but stuff like orbits can still happen due to existing velocity.

More importantly, even if objects were to be pulled together, there space expanding means they might still be futher apart, if the space between objects grows faster then they move togeather. So the heat death looks like it will happen anyways.

[dsacco]

> Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass.

No, they actually are holes. We don’t need analogies or metaphors to describe black holes. Their mathematical properties are quite complicated to define and we have to reason about what happens around or inside them using figurative thought experiments, but their action does correspond to our intuitive sense of what a hole is.

In particular, a black hole consists of an event horizon, around which various stable and unstable orbits are possible, and within which is a theoretical singularity. The event horizon perfectly corresponds to the mathematical concept of a hole, which is a pure abstraction of our common sense of a hole, not a metaphor. A hole is a lack of points in a dimensional space, which means everything inside the event horizon is as much a hole as a manhole in a street is a hole (information theoretically speaking, the inside of a black hole is nothing). To say a black hole is a hole is not a cognitive metaphor, because space around the event horizon actually does curve down to something that is a physical hole. Instead, here are two examples of cognitive metaphors:

1. A donut is a 3-dimensional space with a topological hole in the middle of it. Suppose I define the mathematical properties of taste and equip it as the only sense you have for investigation. Then the hole of a donut tastes like nothing because it is nothing, in the same sense that we can know nothing about the inside of a black hole because it is nothing.

2. Roll a quarter at an angle down a spherical curvature with a hole in the center. The quarter will gradually descend down the curvature, with each revolution about the center happening faster and faster. Finally, it will simply drop it. This is analogous to deteriorating your orbit around a black hole, until you enter various unstable orbits and finally fall into the event horizon.

Obviously these cognitive metaphors, while instructive, are imperfect. For instance, we can see a quarter drop into the hole, but we’d never actually see a shuttle fall into the event horizon. On the other hand, the event horizon is a hole in the same sense that a manhole is a hole. Comparing it to a manhole is another cognitive metaphor; calling it a hole isn’t, because it is one.

[nikofeyn]

does it make sense to you that a "hole" has mass, electric charge, and angular momentum and is completely characterized by these properties?

[4ad]

Notice how an electron hole also has all those properties. That's because those properties are due to specific symmetries of various fields (in space), or symmetries of space itself. Those properties are not "in" the particle, they do not belong to it, rather they are constraints over what kind of interactions can happen in all space that is causally-connected.

[chrisweekly]

Great comment -- but while I agree w/ your point about metaphors, I respectfully mildly disagree about this one in particular. For context, I associate it with the popular analogy of timespace as an elastic "sheet" of sorts, with marble-like objects resting on (and sinking into) its surface, with their mass dictating how "deep" their gravity "well" is. With that metaphor in mind, black holes really do approximate holes in the sheet.

[thathappened]

But even how we illustrate a sheet of spacetime we show it dip when it should stay flat and pinch, closing the gap between atoms as they get more dense.

All of these inaccurate descriptions assume we have the concept already in mind to recursively look up. Describing more accurately let's the reader get a clearer picture and thats where real concepts get conceived.

I like heavy/dark star/planet for a vague description. I also think the fact that humans rely on visuals now and we can't get more than a single angle of one of these we can show anyone a 3D view of how it's not just nothing.

[nsxwolf]

I don't like the elastic sheet analogy because it doesn't work without gravity, the very thing it's attempting to explain.

[chias]

I like it because it isn't quite as self-referential as it at first seems: the notion of gravity that it requires is not the notion of gravity it is explaining: it uses the colloquial and accessible idea of gravity (i.e. "things fall downwards") to describe a more precise idea of gravity (i.e. "things fall towards each other in accordance with mass").

[atilaneves]

This has always bothered me as well, and I'm surprised that this is the first time I've seen anyone else mention it!

[westoncb]

I think this is something that deserves much greater general awareness. I think by default we're pretty unaware of the kind of analogizing/metaphoring that takes place when we conceptualize anything—but it's completely pervasive. I see it as a kind of subtle 'dust on the lens' of the microscope which we use to observe things generally. It's an (in a certain sense) inescapable artifact due to the fact the we conceptualize with a definite thing with its own properties and quirks and limitations, which is the human brain. Anyway, I see it as a kind of 'bias' (best I can think of atm, but that term isn't really broad enough to capture the idea) which we could watch for and in doing so make gains in objectivity.

Edit: also, another way of looking at it is: when we express any concepts in some concrete form, the particular representation we choose (and we have to choose something) brings its own baggage along with it. And, subsequently, we end up reasoning off of the baggage rather than the thing in itself.

[dalbasal]

One that I think comes up often is the robots/automation metaphor. Technology has reduced 90% or more of farm labour needs, multiplied industrial output many times, etc. We've seen a lot of automation, but it's been vague economics.

When we think back on these things, we see technology, tools, & machines like tractors and looms. When we look forward we see robots and automation.

Practically this has 2 effects. First, we come back with a Jetsons lime picture, everything is the same as a regular hotel but the maid is a robot, the front desk is an ATM, the barman is a robot arm and the resteraunt is a Japanese conveyor belt. Robots are human shaped metaphors for technology, placeholders for unknowns.

Second, we think in terms of replacement. In reality, it's really more like efficiency. A tractor still uses a farmer, but requires a lot less time and effort to get a field ploughed. Again, there's a difference in how we think when looking back or forward.

[dragonwriter]

> Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass.

Strictly speaking, the defining character is enormous density, not mass. And the black hole is arguably a name for an effect of the object, not the object itself; the object itself is (or is in the process of becoming; verb tenses get weird when time gets weird) infinitesimally small, but the “black hole” generally refers to the space bounded by the event horizon.

[Santosh83]

A black hole can literally be considered severely warped spacetime. The high gravity is a consequence of the severe warping, and as for the internal contents, they don't matter to external observers and physics (so far) has very little to say about it.

[4ad]

No, black holes are topological holes. It's a mathematical abstraction, not merely a cognitive metaphor.

[akvadrako]

I'm pretty sure every "mathematical abstraction" is a "cognitive metaphor".

[leetcrew]

if you are unaware, this is extremely controversial.

https://en.wikipedia.org/wiki/Philosophy_of_mathematics#Math...

[dsacco]

No, not really. Symmetries of an n-gon (a 2-dimensional figure with n sides) are just permutations of the n numbers representing the sides. A cognitive metaphor is to call certain types of symmetries “rotations” or “reflections”, because we can’t really describe all symmetries through a metaphor like that. The symmetries are not literally operated by picking up your figure and flipping it over.

On the other hand, mathematical abstractions of dimensionality not cognitive metaphors. A “hole” is a meaningful topological abstraction in various dimensions that corresponds to what we consider a colloquial “hole” in 3-dimensional space. If I tell you a Klein bottle is a bottle that has only one surface (no inside or outside) without any “hole”, I’m not making a metaphor, I’m describing a 4-dimensional object as closely as I can describe a mug or a vase in 3-dimensional space. Just because I’m not defining it through pure mathematics and we can’t immediately visualize it (in entirety) doesn’t mean it is a cognitive metaphor, because it perfectly corresponds to the actual concept of dimensionality (instead of being a clever figurative description of it).

Similarly, if we geometrically represent a black hole we can clearly see the curvature of space (from one angle), leading down to an event horizon, within which is a singularity. This representation corresponds to rolling a coin at an angle down a curvature, watching it spin at the bottom a bunch of times, then fall in. In fact, a shuttle falling out of orbit down to the event horizon would look just like this as it entered the whirl zoom of a black hole, before the unstable orbit failed and it just fell in.

Even further, there is a very cogent, topological sense of what “within” means here. Just as you can fall into a manhole in the middle of the street, you can fall into the event horizon of a black hole. If we represent a street as a 2-dimensional plane, a manhole in the street is the topological space in the plane that has no points - a mathematical hole. In three dimensions, a jelly donut has a topological hole, and the hole is also 3-dimensional (the missing points would be representable as 3-dimensional vectors). Information theoretically speaking, the inside of a black hole’s event horizon does not exist - it’s strictly an absence that we can only reason about heuristically. It would be a cognitive metaphor for me to say that we can only reason about the inside of the event horizon in the same way we can reason about the middle of a donut that tastes like nothing because there is “no donut”. But it is not a cognitive metaphor to call the black hole a “hole”, because fundamentally and literally it acts like one. The singularity inside the black hole is not a hole, but that’s different.

Our common sense of what it means to be a hole is literally described by the mathematical abstraction of a hole. When mathematical abstractions are actually just literal abstractions of what we already understand, they’re not cognitive metaphors. If you’d like an example of a cognitive metaphor insead of a pure abstraction, look at string theory. While our common sense of a hole literally corresponds to its 3-dimensional topological abstraction, our common sense of what we call a “string” has no precise mathematical correspondence. A string in the common sense of the word is a 3-dimensional object that is very long and thin. A string in the mathematical/physical sense is a one dimensional object, like a line. To call it a string is to invoke an intuition of something like a small thread that in some sense seems “barely” 3-dimensional.

[westoncb]

> Information theoretically speaking, the inside of a black hole’s event horizon does not exist

There's your metaphor. If you didn't need to qualify it that way, you could perhaps get away with saying otherwise—but with the qualification, your telling us about a different domain in which something has the same 'structure' as a (physical) hole. That's exactly how analogies/metaphors work: two things which are analogous share the same structure but have representations of those structures in differing domains.

There's a simpler way of seeing that it's metaphor still, though. You have chosen some characteristics of holes and arbitrarily decided that they are the ones which define it—but if we want to say it's literally a hole and not metaphorically, then all the attributes which familiar physical holes have should apply. For instance, there should be an interior surface, and things inserted into it should be retractable. Your description treats the singularity and event horizon as two distinct objects, which provides a kind of solution to the second—but it seems like those two things aren't as readily separable as, for instance, if we had a hole in the ground and it was filled with a powerful acid: in that case it's clear which is hole and which is thing filling it. Perhaps I'm mistaken, but I'd bet that the way in which the singularity 'fills' a black hole cannot be anything more than metaphorically.

[dsacco]

> There's your metaphor.

No, it’s not. That’s the definition, much like information theoretic death is death. Here is a metaphor: from our perspective on a street, we cannot perceive anything within a manhole, just like from outside a black hole we cannot perceive anything inside it.

Here is not a metaphor: a black hole is a hole in space, with a singularity inside of it.

[westoncb]

> That’s the definition, much like information theoretic death is death

Information theoretic 'death' implies actual death (assuming I understand your 'death' metaphor in 'information theoretic death' ), but that's not the same as being it.

> Here is not a metaphor: a black hole is a hole in space, with a singularity inside of it.

No, you've just removed the linguistic cues for introducing a metaphor, while still making as heavy use of metaphor as ever.

[4ad]

I don't know what a cognitive metaphor is and whether it's applicable to mathematical abstractions. I was responding to the claim that:

> Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite

Which is false.

[mrleiter]

Very true.

Although not specifically in this context, Ludwig Wittgenstein said:"The limits of my language mean the limits of my world."

[Sir_Cmpwn]

"Hole" is accurate. The "object" with enormous mass would be the singularity, whereas "black hole" refers to the nature of spacetime near the singularity, for which "hole" is an apt name from our reference frame. Also, we don't talk about "spitting things out of the black hole".

[qubex]

On the topic of how languages and metaphors affect (and might even form the fundamental substrate of) our thinking, I highly recommend Douglas Hofstadter (he of Godel, Escher, Bach fame) 's book Surfaces and Essences (2010).

[pvg]

Is it really an [excellent] example of that? We don't use much of the language we use for holes in general for 'black holes'. The term may have been influenced by 'Black hole of Calcutta', itself a metaphorical use.

[zrb05293]

So for example is it more accurate to say that things fall...on to...rather than in to a black hole? That’s fascinating!

[colechristensen]

Eh, that's taking it too far as the parent does.

"Hole" and "in" are pretty good metaphors for what a black hole is. It's hard to have any particularly accurate metaphors for what a black hole is because time dilation, the speed of light, curved space, etc. just aren't a part of life for any humans.