10 ms·

How does one descr blackhole to a non-physicist without losing much accuracy? I just it of a very-dense-object.

by dekdrop 1mo ago

icepush 1mo ago
A one-way door in space.
crooked-v 1mo ago
The problem there is that not even the physicists completely agree on the details, because we know black holes definitely exist, but every explanation breaks one rule or another that should apply from different disciplines. It's part of why they get so much ongoing attention.
- lazide 1mo ago
  Black holes are essentially where our knowledge of spacetime breaks, and we can’t even see into it. It’s hard to really concretely know much about it directly.
pantulis 1mo ago
It's a region of space from where not even light can scape. You can get a region like that by squashing a lot of mass in a small space, like happens when a star collapses under its own gravity. So here the intuition of "high density" makes sense. But at the center of galaxies you have the so called "supermassive black holes" which are more or less comparable in size to the solar system and yes, they have a lot of mass but they are not very dense, a pop-sci trope is comparing it's density to cotton candy or even the air we're breathing right now. So it's a matter of how you distribute mass/energy in a given diameter, not exactly of density.
ben_w 1mo ago
Normally people think of gravity as pulling on objects. You can instead think of it as pulling on the space those objects are in. A black hole happens when there is enough gravity that space gets pulled inwards somewhere, at at least the speed of light. Gravity falls off with distance, and the distance where space is being pulled inwards at exactly the speed of light is called the "event horizon". It has this name because speed of light is the speed of causality: events that happen further in, are "over the horizon" for you, they cannot causally influence you.
- 0x20cowboy 1mo ago
  > Normally people think of gravity as pulling on objects. You can instead think of it as pulling on the space those objects are in. (Very uneducated person here) I’ve always wondered if large objects caused gravity, or if maybe large objects form in the places where there is a lot of gravity. This is probably elementary, but I’ve never looked in to it. Maybe today is the day!
  - ben_w 1mo ago
    Dark matter is mysterious enough to be compatible with both at the same time, I think. (Is a collisionless gas really even an "object"?)
    - zelphirkalt 1mo ago
      I tend to believe that dark matter is a name for something we don't understand better yet. I don't necessarily mean MOND or anything specifically, but dark matter is just a little too mysterious and convenient for my taste. Maybe in 100y we will laugh about the notion of something like an aether named dark matter, and see it as simply a model which was necessary, because we didn't get what really is going on.
  - lopsotronic 1mo ago
    If you want to take a very large-scale - if poetic - view of things, you could also (very arguably) say something like "Mass is Fate". Mass represents a zone where probabilities want to be. The more that aggregate, the more they make other things want to glom on. With a high enough density, nothing that's nearby can glom to literally anywhere else, and there's your black hole. The Great Inevitable. In this space, there are no other possibilities. Very Demiurge-y.
    - 0x20cowboy 1mo ago
      That’s amazing
  - rcxdude 1mo ago
bell-cot 1mo ago
"A really interesting and cool thing for astronomers to talk about...but you might want to pray that not one of 'em ever comes within a million trillion miles of the Earth."
- misnome 1mo ago
  Unfortunately, there is a rather large one not one sixth of that distance away (a million trillion miles is actually rather large - 170 kly - approximately double the size of our galaxy)
  - bell-cot 1mo ago
    Yes - I took the grandparent comment's "descr to a non-physicist" as "describe to someone who really isn't into math or hard sciences". Those folks will hear "million trillion" as "a really Really REALLY REALLY big number". Not as "1 x 10^18".
    - Dylan16807 1mo ago
      I guess, but "light year" is easy to say, easy to understand, and much less likely to mislead. And most black holes would probably be safe at that distance. Though the issue of small black holes is worth bringing up. If you scrunch up one cubic kilometer of stone into a black hole, that's heavy to be stable for trillions of years, but light enough to pass between the Earth and the moon without causing serious problems. And we really have no idea what the smallest existing black hole is.
      - sfn42 1mo ago
        You'd be surprised how may people don't even understand that a light year is a measure of distance.
        Dylan16807 1mo ago
        Hmm. Well even then I think a million million miles will suffice, that's over ten thousand AU, .17 light years.
altairprime 1mo ago
Consider a balloon. I don’t imagine in visuals but if you do, either a solid color or a patterned balloon works. Let’s say it’s a cow print design. Deflate it, then stretch the balloon over a vacuum cleaner tube and put on a rubber band to keep it in place. If you pour sand on it, you can only get a small bump of sand and then it’ll run off the sides. Reasonable, logical, normal behavior. Clearly it’s a surface — it’s holding sand, it’s pouring sand in different directions over the edge, the sand is not all compacted into a single grain. Turn on the vacuum cleaner. Assume a balloon stretchier than the strongest vacuum cleaner in the universe. What happens? Several things, each of which are perfectly reasonable: 1) The end of the tube is still a circle, and the balloon is still attached and covering the tube, so it’s still a two-dimensional circle. 2) A single grain of sand can’t block the vacuum tube, so it clearly hasn’t collapsed to a point. 3) The covered end of the vacuum cleaner tube is still the same circle, with the same diameter, as it was before you turned on the vacuum. 4) You can pour buckets more of sand onto that stretched circle of balloon than the handful you could before. 5) If you pour enough sand onto the circle, it’ll behave just like it did before: the sand will form a small mound and then newly-poured sand will run off whichever side the sand was poured on. 6) The rubber band is going to catch some of the overflowing grains of sand and hold onto them (‘accretion’), near but just outside the circle. Next: Consider a more powerful vacuum cleaner. How much more? Lots. The most. An atomic Dyson powered by nuclear fusion. (This is a bit unrealistic, but that’s astrophysics for you.) How much sand can you pour onto that two-dimensional, circular, balloon surface? Lots. The most. Some of it will spill around the edges and get caught in the accretion band, but somehow that circle, that’s still the same size and clearly still blocking the vacuum tube, can hold an entire universe of sand. That’s how black holes work :) ps. For those who dislike the crudity of my teaching analogy and want to pop the spherical cow balloon: Topologically, the surface covering the vacuum tube is always a circle, even if you have an infinitely-powerful vacuum cleaner. At no point — pun intended — can a vacuum cleaner apply a transformation applied that reduces the dimensionality of the surface, thus it must remain, topologically, a circle. pps. So clearly I must choose the circle in front of me! Hahaha! Aaaahahahah! ppps. dies
inigyou 1mo ago
Why not just say it's something with such strong gravity you can't escape even if you go at the speed of light? Maybe that loses too much accuracy for you?

How does one descr blackhole to a non-physicist without losing much accuracy? I just it of a very-dense-object.

by dekdrop 1mo ago

How does one descr blackhole to a non-physicist without losing much accuracy? I just it of a very-dense-object.

icepush 1mo ago

A one-way door in space.

crooked-v 1mo ago

The problem there is that not even the physicists completely agree on the details, because we know black holes definitely exist, but every explanation breaks one rule or another that should apply from different disciplines. It's part of why they get so much ongoing attention.

lazide 1mo ago
Black holes are essentially where our knowledge of spacetime breaks, and we can’t even see into it. It’s hard to really concretely know much about it directly.

pantulis 1mo ago

It's a region of space from where not even light can scape. You can get a region like that by squashing a lot of mass in a small space, like happens when a star collapses under its own gravity. So here the intuition of "high density" makes sense. But at the center of galaxies you have the so called "supermassive black holes" which are more or less comparable in size to the solar system and yes, they have a lot of mass but they are not very dense, a pop-sci trope is comparing it's density to cotton candy or even the air we're breathing right now. So it's a matter of how you distribute mass/energy in a given diameter, not exactly of density.

ben_w 1mo ago

Normally people think of gravity as pulling on objects. You can instead think of it as pulling on the space those objects are in. A black hole happens when there is enough gravity that space gets pulled inwards somewhere, at at least the speed of light. Gravity falls off with distance, and the distance where space is being pulled inwards at exactly the speed of light is called the "event horizon". It has this name because speed of light is the speed of causality: events that happen further in, are "over the horizon" for you, they cannot causally influence you.

0x20cowboy 1mo ago
> Normally people think of gravity as pulling on objects. You can instead think of it as pulling on the space those objects are in. (Very uneducated person here) I’ve always wondered if large objects caused gravity, or if maybe large objects form in the places where there is a lot of gravity. This is probably elementary, but I’ve never looked in to it. Maybe today is the day!
- ben_w 1mo ago
  Dark matter is mysterious enough to be compatible with both at the same time, I think. (Is a collisionless gas really even an "object"?)
  - zelphirkalt 1mo ago
    I tend to believe that dark matter is a name for something we don't understand better yet. I don't necessarily mean MOND or anything specifically, but dark matter is just a little too mysterious and convenient for my taste. Maybe in 100y we will laugh about the notion of something like an aether named dark matter, and see it as simply a model which was necessary, because we didn't get what really is going on.
- lopsotronic 1mo ago
  If you want to take a very large-scale - if poetic - view of things, you could also (very arguably) say something like "Mass is Fate". Mass represents a zone where probabilities want to be. The more that aggregate, the more they make other things want to glom on. With a high enough density, nothing that's nearby can glom to literally anywhere else, and there's your black hole. The Great Inevitable. In this space, there are no other possibilities. Very Demiurge-y.
  - 0x20cowboy 1mo ago
    That’s amazing
- rcxdude 1mo ago

bell-cot 1mo ago

"A really interesting and cool thing for astronomers to talk about...but you might want to pray that not one of 'em ever comes within a million trillion miles of the Earth."

misnome 1mo ago
Unfortunately, there is a rather large one not one sixth of that distance away (a million trillion miles is actually rather large - 170 kly - approximately double the size of our galaxy)
- bell-cot 1mo ago
  Yes - I took the grandparent comment's "descr to a non-physicist" as "describe to someone who really isn't into math or hard sciences". Those folks will hear "million trillion" as "a really Really REALLY REALLY big number". Not as "1 x 10^18".
  - Dylan16807 1mo ago
    I guess, but "light year" is easy to say, easy to understand, and much less likely to mislead. And most black holes would probably be safe at that distance. Though the issue of small black holes is worth bringing up. If you scrunch up one cubic kilometer of stone into a black hole, that's heavy to be stable for trillions of years, but light enough to pass between the Earth and the moon without causing serious problems. And we really have no idea what the smallest existing black hole is.
    - sfn42 1mo ago
      You'd be surprised how may people don't even understand that a light year is a measure of distance.
      - Dylan16807 1mo ago
        Hmm. Well even then I think a million million miles will suffice, that's over ten thousand AU, .17 light years.

altairprime 1mo ago

Consider a balloon. I don’t imagine in visuals but if you do, either a solid color or a patterned balloon works. Let’s say it’s a cow print design. Deflate it, then stretch the balloon over a vacuum cleaner tube and put on a rubber band to keep it in place. If you pour sand on it, you can only get a small bump of sand and then it’ll run off the sides. Reasonable, logical, normal behavior. Clearly it’s a surface — it’s holding sand, it’s pouring sand in different directions over the edge, the sand is not all compacted into a single grain. Turn on the vacuum cleaner. Assume a balloon stretchier than the strongest vacuum cleaner in the universe. What happens? Several things, each of which are perfectly reasonable: 1) The end of the tube is still a circle, and the balloon is still attached and covering the tube, so it’s still a two-dimensional circle. 2) A single grain of sand can’t block the vacuum tube, so it clearly hasn’t collapsed to a point. 3) The covered end of the vacuum cleaner tube is still the same circle, with the same diameter, as it was before you turned on the vacuum. 4) You can pour buckets more of sand onto that stretched circle of balloon than the handful you could before. 5) If you pour enough sand onto the circle, it’ll behave just like it did before: the sand will form a small mound and then newly-poured sand will run off whichever side the sand was poured on. 6) The rubber band is going to catch some of the overflowing grains of sand and hold onto them (‘accretion’), near but just outside the circle. Next: Consider a more powerful vacuum cleaner. How much more? Lots. The most. An atomic Dyson powered by nuclear fusion. (This is a bit unrealistic, but that’s astrophysics for you.) How much sand can you pour onto that two-dimensional, circular, balloon surface? Lots. The most. Some of it will spill around the edges and get caught in the accretion band, but somehow that circle, that’s still the same size and clearly still blocking the vacuum tube, can hold an entire universe of sand. That’s how black holes work :) ps. For those who dislike the crudity of my teaching analogy and want to pop the spherical cow balloon: Topologically, the surface covering the vacuum tube is always a circle, even if you have an infinitely-powerful vacuum cleaner. At no point — pun intended — can a vacuum cleaner apply a transformation applied that reduces the dimensionality of the surface, thus it must remain, topologically, a circle. pps. So clearly I must choose the circle in front of me! Hahaha! Aaaahahahah! ppps. dies

inigyou 1mo ago

Why not just say it's something with such strong gravity you can't escape even if you go at the speed of light? Maybe that loses too much accuracy for you?