Live data from Hacker News

Most images of black holes are illustrations. Here’s what our telescopes capture

vox.com

81–90 of 167 posts

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#81
post #24

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 b…

> 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

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#82
post #72
post #67

Earlier quoted context omitted.

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 p…

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.

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.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#83

Earlier quoted context omitted.

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…

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 t…

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.

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#84
post #24

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 b…

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 hol…

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

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#85
post #32

Earlier quoted context omitted.

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

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

if you are unaware, this is extremely controversial.

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

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#86

Earlier quoted context omitted.

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 t…

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.

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

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#88
post #17
post #14

Earlier quoted context omitted.

I'll take your comment in good faith, but there are very good reasons to believe black holes exist and that, for instance, the center of our galaxy contains a very massive black hole and not a neutron star. This is basic general relativity, which only has (physical and theoretical) evidence in support of it. While quantum gravity is still very much uncertain, that would (most likely) only have to do with understandin…

You skipped a step. Yes, the general relativity prediction of a black hole is solid once it exists . But you have to construct that black hole in the first place. And it's that part that's on shaky ground.

This seem to be a contrarian view. Do you have any sources you can share with us?

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#89
post #84

Earlier quoted context omitted.

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 hol…

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

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").

Re: Most images of black holes are illustrations. Here’s what our telescopes capture

#90
post #32

Earlier quoted context omitted.

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

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

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.

Post reply on HN