The first simulated image of a black hole, calculated with an IBM 7040 computer using 1960 punch cards and hand-plotted by French astrophysicist Jean-Pierre Luminet in 1978 Pro/Processed

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So many people I've talked to think they are actually holes.

Because they are. A black hole is where gravity is so high that it warps space around it such that it is cut off from the rest of space-time.

Gravity bends space-time. Like pulling on fabric of your sock. If you pull enough you end up with a hole in your sock where no threads pass through.

Saying "it would give off light if it wasn't for gravity" is like saying, your sock would be intact if not for the pulling that is holding the hole open.

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u/mindbleach Jan 16 '22

Only in the same sense as every other celestial object. "Gravity is the hole we are in."

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u/shouldbebabysitting Jan 16 '22

A bend is different from a discontinuity.

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u/mindbleach Jan 16 '22

The path into a black hole is the same bend as anything falling to Earth.

The only difference is that the slope gets too steep for anything to leave.

To my knowledge, it is possible for mundane matter and energy to exist inside a singularity - for a planet like Earth to develop deep within a black hole. Photons from the outside universe can pass the event horizon and reach it, possibly unmodified by the absurd forces acting upon them. But no photon from that planet can ever make the journey in reverse.

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u/shouldbebabysitting Jan 18 '22 edited Jan 18 '22

You have the event horizon confused with the black hole inside.

Edit:

But we don't have physics to understand the inside of a black hole. So could there be a planet inside? Maybe. Anything could be inside because we don't know.

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u/mindbleach Jan 18 '22

Only if you nitpick "inside a singularity" versus "past a singularity."

That event horizon is just the point of no return. It's the bit where the slope gets too steep to see as anything but an impassible cliff.

But things can still fall down a cliff. It's only impassible in one direction. (And a rough trip in the other.)

It's not discontinuous. It's not even undifferentiable. The problem is that speed has a hard upper limit, and you'd have to go faster than that to get out. It is the exact same situation as falling toward a planet, except for the part where rockets capable of escape velocity are allowed to exist.

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u/shouldbebabysitting Jan 18 '22

It is the exact same situation as falling toward a planet, except for the part where rockets capable of escape velocity are allowed to exist.

Which is why calling it a hole is more accurate than calling it a dark star.

You can walk down and back out a dip in the road. You fall into a black hole and you keep falling forever.

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u/mindbleach Jan 18 '22

One, if you agree it's differentiable, that no longer fits your sock analogy.

Two, putting aside any questions of what it means to experience falling into a black hole, the process is not eternal. The velocity at which you fall into a gravity well is not the same as escape velocity. For a black hole, it literally can't be. I don't think you even have to approach relativistic speeds.

If it were possible for a spacecraft to survive as it fell into a near-minimum-mass black hole, and it somehow had enough thrust to approach light speed, it would fall in slowly, at the delta of the above-C escape velocity and its below-C local speed.

Like falling into a hole whose steep sides you will never be able to run back up, it doesn't take forever, it just lasts forever. Being an inescapable pit you can mark on the map doesn't mean you cut a hole out of the map itself.

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u/shouldbebabysitting Jan 19 '22

One, if you agree it's differentiable, that no longer fits your sock analogy.

Singularities are not differentiable.

But it's not relevant because a donut is differentiable yet has a hole.

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u/mindbleach Jan 19 '22

Mathematical singularities are not differentiable. Black holes are not that kind of singularity. That's just a metaphor.

If you graph escape velocity for a celestial body, and pretend it's a dimensionless point mass, that graph will have a mathematical singularity at x = 0. But that's the only one. Outside of that, the graph shows near zero velocity toward infinite distance, and near infinite velocity toward zero distance, all following a smooth curve.

Most stuff in the universe is not dimensionless. (Barring a genuinely terrifying explanation for dark matter.) You can't get near x = 0, because the center of some rock is surrounded by... the rest of that rock.

The problem is that some heavy things are really really small. Being near x = 0 becomes possible. And there's a hard upper limit on velocity. There's a dashed line at y = c where the universe says "nope."

Where that line intersects the curve defines the singularity of a black hole. If a mass is compact enough to be treated as a point source, at that distance - that's an event horizon. We can never know anything that happens, closer than that, because it is fundamentally impossible for anything to go fast enough to come back out.

And yet: that space is the same as all the space around it. Some is more curved, some is less curved. There is an upper limit to how curved space can be, before light cannot climb up it... but there is no upper limit to how curved space can be.

(Also the hole in a donut is not like a black hole because you don't approach the event horizon and wind up behind yourself, but that is a whole other conversation.)

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u/BioTronic Jan 16 '22 edited Jan 16 '22

Because they are.

They're not, though.

There's similarities to holes in the ground, in that they're basically a spot where you can get rid of things (protip: don't throw your garbage in a hole in the ground), but they're very different from those in other ways (if we ignore l'appel du vide, holes in the ground don't attract stuff, for one).

They're also similar to holes in the wall, in that there's basically a different "room" on the other side. Holes in walls let you travel both ways though, they let you see what's on the other side, and they're two-dimensional things, and finally they're not really things at all, just a lack of things.

The use of the word 'hole' in 'black hole' is confusing to some people because they think of it as that second type - a two-dimensional hole in spacetime that leads to another universe. If you know what a black hole is and have a decent understanding of the physics, the name is perfectly fine, but we're talking about how non-physicists react here.

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u/shouldbebabysitting Jan 16 '22

The use of the word 'hole' in 'black hole' is confusing to some people because they think of it as that second type - a two-dimensional hole in spacetime that leads to another universe.

It is 3d hole in space time. Whether it leads to something or not isn't part of the definition of a hole.

If you know what a black hole is and have a decent understanding of the physics, the name is perfectly fine, but we're talking about how non-physicists react here.

But it's still fine for non physicists because it conveys that it is different than a heavy object. A heavy object is still connected to space time. Beyond the event horizon isn't connected to the Universe.

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u/[deleted] Jan 16 '22

none of that says black holes are holes lol

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u/shouldbebabysitting Jan 16 '22

If you pull the edges of a fabric until there is a hole in the middle you don't call that a hole?

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u/DukeofVermont Jan 17 '22

Do they have mass? If they have mass then they are made up of matter. If they are made up of matter than they take up space in space.

They are not empty space that stuff falls into. They are objects of incredible density that stuff can hit.

You can fall through a hole in fabric.

If you fall into a black hole you will hit the black hole and become part of it.

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u/[deleted] Jan 17 '22 edited Jan 17 '22

The point he's making is time and space literally end at the event horizon, therefore, it's a hole because what we consider to be the real universe doesn't exist past the event horizon. Black holes do not have an interior in the sense that the concept of space/distance straight up does not exist.

It's simply not true that mass = matter in every case. If light is confined in a system, and you attempt to accelerate that system, the energy of the light will act as mass in terms of accelerating the system as a whole as energy = mass.

If you increase G (gravitational constant), black holes increase in diameter whereas traditional gravitating bodies decrease in diameter. What does that tell you about the nature of a black hole? My interpretation is that black holes are a surface, the increased gravity attempts to compress the matter on the surface further, finds that it can't because the matter is as compressed as possible, meaning the only possibility is to increase surface area.

If you hit a black hole, you are flattened at the surface, it's a hole the same way as the sock because the fabric of space as we know it doesn't exist in the interior of a black hole, similar to how the fabric of the sock doesn't exist where the hole is. You can only fall through the hole in the sock because the sock is embedded in a larger space allowing the concept of 'through the hole' to exist. This is not the case with black holes.

Source: astrophysicist

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u/[deleted] Jan 17 '22

yeah, i call that a hole. but that's not a black hole. that's a piece of fabric with a hole in it.

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u/shouldbebabysitting Jan 17 '22

A black hole is where space-time (both space and time) are bent such that there is an event horizon where the black hole mass exists (the edge of the fabric hole) and a volume inside the event horizon that isn't part of our universe because space (not outer space but the concept of distance between objects) itself doesn't exist inside the hole.

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u/[deleted] Jan 17 '22

"isn't part of our universe"? yeeeeeahhhhhh noooo that's not really how it works

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u/shouldbebabysitting Jan 17 '22

Our universe is defined by space and time. Inside the event horizon has no space or time.

Maybe in the future we will have a better understanding of black holes. But as of right now, inside of the event horizon is not part of our universe is as we understand it.

Again when I say there is no space inside, I'm not talking about outer space but the concept of distance itself.

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u/[deleted] Jan 17 '22 edited Jan 17 '22

It absolutely is, the inside of a black hole does not exist in our universe, time and space literally end at the event horizon. It's more like that everything that falls in is smashed together on what we perceive to be the surface.

A good thing to consider is that if you increase G, black holes increase in diameter. Idk about you but that sounds like gravity is trying to pull everything flatter on the surface, but since it's as compressed as possible it increases area instead, rather than being a solid body internally in contact with the rest of the universe.

Source: I'm an astrophysicist

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u/curly_redhead Jan 17 '22

Never heard about the surface area increasing thing before, what equations are involved?

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u/[deleted] Jan 17 '22 edited Jan 17 '22

Check out the equation for the Schwartzchild radius of a gravitating body. Practically, this tells you the size to which you need to compress an object in order for it to become a black hole. You'll see that G is in the numerator of the fraction, meaning that as G increases the radius increases, blew my mind when it was first pointed out to me as well :)

It's also possible that black holes are holographic, in the sense that they hold all of the 3D information of the matter that falls in as a 2D surface (scrambled as fuck of course). Somewhat similar how you can get those cards that appear to have perspective when you tilt them. However, this is really cutting-edge theoretical stuff that I'm not qualified to talk about in detail.

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u/[deleted] Jan 17 '22

[deleted]

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u/shouldbebabysitting Jan 17 '22

They are not empty space that stuff falls into.

In so far as spacetime is distorted such that the middle of the distortion is outside of space time, nothing else describes it as well as the word hole.

That is there is no space inside the event horizon, there is no time inside the event horizon.

Here's an example but it isn't a black hole because there is no gravity: Imagine if there was a spot in your room that you couldn't go. As you approach you were bent around the spot. Nothing in the universe would let you go to that spot because space itself was bent around it. What do you call a defined spot that as far as all current scientific knowledge is defined, is outside of the universe?

If you fall into a black hole you will hit the black hole and become part of it.

That's the event horizon. But there's "space" inside the event horizon. That's the hole.

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u/[deleted] Feb 12 '22

You do not "hit" or touch a black hole, the black you see is just the outermost "shell" of where light can still orbit, any closer and light doesnt continue, but its still an empty spot, one that you fall into, dont reach a bottom, and the fabric of the universe bends downwards into, which is best described as a hole

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u/[deleted] Feb 12 '22

[deleted]

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u/[deleted] Feb 12 '22

The reason black holes create their intense mass is because they are dense, density is what creates gravity, TON has 66×10⁹ solar mass but the thing that makes it a black hole is that all of that mass is condensed into a point smaller than a city. This extreme density of mass is what increases its gravity, which is what increases the distance at which light is pulled in, the event horizon. The event horizon that you observe as a black ball is a measure of distance, its not the black hole, and it doesnt take up any space, objects fall straight through it with no resistance

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u/[deleted] Feb 12 '22

Does you deleting half your replies mean weve come to an understanding or...?

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u/DukeofVermont Feb 12 '22

It means that I'm so done arguing about what is purely theoretical with someone that clearly thinks we have an absolute understanding of something which we can not view, test, or experiment on or in, in any way shape or form.

EVERYTHING past the event horizon of a black hole is 100% unknown as all we can do is view a black holes impact outside of that radius.

If you want to argue the math side it's pretty irrelevant. It might be correct, it might not be but there is literally no way of knowing.

And then my god man the volume thing, when dealing with a singularity (a point at which a function takes an infinite value) than normal definitions don't even really matter anymore. But again, we cannot see past the event horizon so there is literally no way to know.

Basically this whole argument is like two people arguing what dark matter is or isn't. Truth is we just have no idea.

My literally only point I was trying to make a month ago was this:

The name makes people visualize something that is different from what it is, and I personally prefer a different name because I feel it helps people better visualize that it (or at least it's event horizon) takes up space/volume in space.

That's literally it! Dude I had multiple people try to argue with me that a black hole is like a hole in a sheet of paper! I had people argue that they are just empty places in space that stuff falls into.

I NEVER wanted to get into the highly theoretical PhD level discussion about what the interior of a black hole may or may not be like.

Literally just was stating my preference!

It's like I said that I like the name Dwarf Planet over large asteroid and now I've had people telling me how wrong I am with 50% of them citing JJ Abrams Star Trek as a source.

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u/[deleted] Feb 12 '22

No bro you went from

I don't know why everyone keeps wanting to argue without even the simplest of google searches.

To

"well its just theoretical and we dont really know so im just choosing to believe my preference"

If youre argument from the start was "we just dont know" you wouldve said that, but you cited videos,you quoted sources, you very obviously attempted to present your "preference" as real data as though it was fact, not once did you talk about how its all theoretical, you were attempting a real debate in order to convince me that Black Holes are physical objects and not empty space. Only after having your sources fundamentally pulled apart did you suddenly back track to "nah bro its all subjective i was just stating my opinion man, i never tried to debate with you at all" like actually bullshit dude no

"no one really knows what a black hole is"

Unless youre trying to argue philisophical "truth doesnt exist" then no, people do know what a Black Hole is, and you had several astrophysicists explain to you exactly why a Black Hole is best defined as a Hole, its literally just you who doesnt know what a black hole is, and refuses to listen to everyone trying to explain it to you, so you can understand that yes, a point at which space-time is warped at an extreme downward path toward a volume-less and light-less center is best described as a hole, not a "dark star" that is a disengenous and misleading name for what the thing is

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u/patchouli_cthulhu Jan 17 '22

I do fun shit with the hole in my sock