21 ms·

Let me add some perspective here. This only became apparent to me fairly recently and it blows my mind. It's something I hadn't thought of before. Black holes

by cletus 6y ago

Let me add some perspective here. This only became apparent to me fairly recently and it blows my mind. It's something I hadn't thought of before. Black holes are relatively "simple". I mean that you can completely define a black hole with 3 properties, one of which isn't really relevant. The two most relevant properties are spin and mass. The last is electric charge. The reason this is somewhat irrelevant is because electric repulsion is about 60 orders of magnitude more than gravitational attraction so it's not expected black holes have a significant charge. Neutron stars OTOH are arguably the most complex objects in the Universe. Why? Because you're dealing with gravity, electric charges, nuclear forces and QCD such that there's no equation of state for describing dense nuclear matter. Probably my favourite variant of neutron stars is the extremely rare magnetar [1], the most powerful we've found has a magnetic field 100 trillion times that of Earth's [2]. This field is so strong it would flatten atoms and rip electrons from your body. So as much difficulty as we have of describing the nucleus of an atom (as referenced in this post), imagine a whole star of that stuff. [1]: https://en.wikipedia.org/wiki/Magnetar#:~:text=A%20magnetar%20is%20a%20type,X%2Drays%20and%20gamma%20rays https://en.wikipedia.org/wiki/Magnetar#:~:text=A%20magnetar%.... [2]: https://www.space.com/magnetar-eruptions-sculptor-galaxy#:~:text=The%20most%20powerful%20magnets%20in,13 https://www.space.com/magnetar-eruptions-sculptor-galaxy#:~:....

ohazi 6y ago
Neutron stars seem like what you would see in a black hole if the interesting parts weren't shrouded by an event horizon. Although I suppose the event horizon does give you jets. But yeah, city-sized objects with the density of an atomic nucleus. Pretty mind-bending! (literally, I guess?)
- ramraj07 6y ago
  The “how to build a black hole” video from PBS space time says that’s how you do it - you start with a neutron star and keep adding more mass to it, which paradoxically makes it smaller until it becomes smaller than its swarzchild radius, becoming a black hole. Blew my mind and anyone else’s when I share the video with them! https://youtu.be/xx4562gesw0 https://youtu.be/xx4562gesw0
  - cletus 6y ago
    That depends on what size of black hole you want to make. It works for large black holes (you need sufficient mass for the gravitational forces to be sufficient) but those black holes aren’t that useful. Smaller black holes are harder to construct but way more useful.
    - willis936 6y ago
      It's simple, just deflate spacetime!
    - elseweather 6y ago
      I'm curious what useful applications we have for black holes of any size
      - jakeogh 6y ago
        It's assumed that little ones are the most efficient mass to energy converters, via Hawking radiation.
      - cletus 6y ago
        There are actually a lot of theoretical applications. Black holes are likely the most efficient form of power generation that we currently know of. Black hole propulsion may well be the best form of interstellar starship propulsion. Black holes may also be the ultimate computer. If the universe continues based on it current understanding then eventually all the stars will be dead and the universe will be a dark place. The Black hole era will last trillions of time as long but may well be the golden age of civilization. Each of these topics is a rabbit hole.
      - ThrustVectoring 6y ago
        The theoretical limit of how efficiently you can turn energy into useful work depends on how cold your energy sink is. The coldest energy sink in an ever-expanding universe gets colder over time as everything spreads out and the fixed amount of energy occupies more and more space. So the hypothetical optimal end-state of an extremely old civilization is hibernating a bunch of very stable mass until the extreme far future, at which point they can drip-feed it into a black hole to do some extremely efficient computation.
- ravi-delia 6y ago
  I was under the possibly incorrect impression that black holes result when the gravitational force is so great that it even overcomes Pauli's exclusion principle, collapsing the neutrons into an overlapping mass of staggering density. Now that I write that out, I'm a little more doubtful.
  - btilly 6y ago
    Close. Giant blue stars burn all of the way up to the most stable element of all, which is iron. And then collects an iron core. As the core grows, the star shrinks and the pressure in the middle grows. Once the pressure in the middle is high enough, it overcomes the Pauli exclusion principle and electrons merge with protons to become neutrons with a release of energy, which mostly comes out as neutrinos. Once a bit of that core disappears, the stuff around falls into the new gap, hits it, goes under way more pressure and the same thing happens. This starts a chain reaction that causes a supernova. The core collapses into a neutron star while the release of energy blows the outer shell out to eventually become a nebulae. If the initial star was big enough, the newly created neutron star is big enough to transform into a black hole. Otherwise it is left as a neutron star. If it forms a neutron star, the spin speeds up thanks to the collapse. Typical time to rotate can be anywhere from milliseconds to seconds. We can tell that because its magnetic field also gets trapped and forms a strong beam along the north and south magnetic poles. Since magnetic poles do not generally line up with the rotational poles, that beam becomes like a searchlight. If we're in the path of that beam, we see a pulsar, and the frequency of the pulsar is the rotational speed of the neutron star. This is probably way more than you wanted to know. :-) I probably also am going to get corrected on some details in 3, 2, 1...
    - hinkley 6y ago
      I was shocked to learn how long it takes a photon produced at the center of the sun by a fusion event to reach earth. The layers upon layers of subatomic particles that are all interacting in these tight quarters is simply astounding. I've heard this same theory on supernovas from a number of people in or around physics, but I always wonder how handwavy it is, whether we actually understand how that works yet, and how different (confusing) the real process is from the given one.
- CuriouslyC 6y ago
  Imagine if black holes were just neutron stars made of second or third generation quark "neutrons."
- hinkley 6y ago
  I remember the infinities of black holes being a challenge to explain to my artsy friends after reading A Brief History of Time. Correct me if I'm wrong, but isn't the curvature of space around - and within - a neutron star substantial enough that euclidean geometry doesn't really hold anymore? The volume of a basketball is the surface area x R/3, but is that true of a neutron star? I was under the impression that the difference between Euclid and actual was statistically significant, to the point that you get the wrong behavior if you don't account for it.
Groxx 6y ago
>In 2020, a fast radio burst (FRB) was detected from a magnetar.[⁷][⁸][⁹][¹⁰][¹¹][¹²][ᵉˣᶜᵉˢˢᶦᵛᵉ ᶜᶦᵗᵃᵗᶦᵒⁿˢ] Wikipedian humor at its finest. Because of course "excessive citations" looks like a citation.
- a1369209993 6y ago
  > [ᵉˣᶜᵉˢˢᶦᵛᵉ ᶜᶦᵗᵃᵗᶦᵒⁿˢ] FWIW, superscript i (contra ɪ) is at U+2071: [ᵉˣᶜᵉˢˢⁱᵛᵉ ᶜⁱᵗᵃᵗⁱᵒⁿˢ] I'm not seeing a superscript square bracket anywhere, unfortunately.
  - Groxx 6y ago
    ah, good, there is a `i`. that struck me as weird too. I just grabbed a random "write in superscript" site tbh :)
btilly 6y ago
Black holes are relatively "simple". I mean that you can completely define a black hole with 3 properties, one of which isn't really relevant. Classically, yes. But more recently we've discovered not. One of the major conundrums about black holes is how information gets lost in their creation. There is a lot more information in the stuff that creates a black hole than in the black hole itself. Which violates the third law of thermodynamics. This is called the Black Hole Information Paradox. But as https://blogs.scientificamerican.com/observations/have-we-solved-the-black-hole-information-paradox/ https://blogs.scientificamerican.com/observations/have-we-so... explains, the real state of a black hole includes all of the stuff that you can see in the process of falling in. (We never actually see anything hit the event horizon. And in theory something on its way there can still be retrieved a million years after it started falling.) When you track things carefully, a real black hole is a very complex thing indeed. With no information loss.
- jihadjihad 6y ago
  > Which violates the third law of thermodynamics Wouldn't this be a violation of the second law rather than the third?
  - willis936 6y ago
    It's not quite Maxwell's demon because the event horizon is a one-way causal ticket. The information might not be destroyed but it is totally inaccessible on this side of the horizon.
  - btilly 6y ago
    I just looked it up, and it is a violation of the fact that the laws of physics should be reversible. So from the wave function at any point of time you should be able to reconstruct the wave at any other. My bad for having stuck thermodynamics in there at all. :-(
- colechristensen 6y ago
  This brings up a question I have had for a while: what is the life story of a photon shot at a black hole? From an outside observer, presumably you shoot a laser at a black hole and if your photons don't hit anything on the way to the horizon, they never hit it either but just approach asymptotically as time goes to infinity. As, a photon though, you don't "notice" crossing the horizon and in a measurable amount of time you go from being emitted to hitting the singularity. Black holes don't last until infinity though, they evaporate in a large but measurable time. (let's say 10^100 years, it depends on time and how the universe dies and how big the black hole is, but whatever, presuming it happens it is some extraordinarily large number of years) So... as something falling into a black hole an outside observer will watch you infinitely slowly approaching a growing horizon until at some point the growth goes negative and you watch the horizon falling away from your friend the photon until at last the horizon disappears entirely and releases the photon to go about its merry way to hit something sometime around the heat death of the universe. In other words, if you are a conscious very resilient little particle doomed to fall into a black hole... do you really appear from the outside to be falling in until the black hole evaporates? Do you experience going through the event horizon like it's nothing and hit the singularity in a few hours by your own watch... Or is a black hole sort of a time machine to the end of the universe where in the short process of falling in you get to watch the whole history of existence pass you by and you come out at the end having never crossed the horizon in what was for you a very short ride. Or is there some third option where from the outside it takes an infinite amount of time for you to fall in, but that infinity "for math reasons" actually takes place and passes in a Zeno's paradox kind of way at some distinct point in your timeline and you meanwhile pass the horizon and hit the singularity in short order and are no more? I don't really know anything but these are questions and vague thoughts I have had. The central question is reconciling the outside apparent infinite time to watch something cross an event horizon with the finite lifespan of evaporating black holes.
jayd16 6y ago
>The reason this is somewhat irrelevant is because electric repulsion is about 60 orders of magnitude more than gravitational attraction so it's not expected black holes have a significant charge. I hadn't thought about it but I guess that means protons or electrons have a maximum resting density. A group of those will never collapse from gravity?
- Tagbert 6y ago
  If that were true, you would not get a neutron star where the electrons and protons are collapsed into neutrons. Not sure how that stands to the overall strength question, though.
- throwaway2568 6y ago
  Protons and electrons are both Fermions, which means they can not have identical quantum numbers (have to obey the Pauli exclusion principle as mentioned elsewhere in the thread). In the case of a very dense system, like the sun, this can lead to an effect known as degeneracy pressure (which acts against gravity). Essentially you have filled all the lower quantum numbers and then adding an extra proton/electron to the system requires a certain amount of energy. It's quite handwavy but the degeneracy pressure of electrons is mostly what keeps a white dwarf from contracting, whereas in the case of a neutron star it is the degeneracy pressure of neutrons (plus repulsive strong force and other effects as indicated in the OP). This kind of high level discussion is often covered in first year astronomy courses auditing a MOOC like the following may be of interest (https://www.edx.org/course/astrophysics-the-violent-universe https://www.edx.org/course/astrophysics-the-violent-universe)
yongjik 6y ago
> This field is so strong it would flatten atoms and rip electrons from your body. ...which is underselling it a bit. :) (As quoted in Wikipedia) the field is so strong that pure vacuum itself has ~10,000 times the density of lead, due to the energy contained in the field. Imagine that.
detritus 6y ago
> Neutron stars OTOH are arguably the most complex objects in the Universe. In OUR universe, at least. If a black hole ends in a white hole, Gosh only knows how complex things will end up at the other end. Witness, for example, our entire reality.
o_p 6y ago
A black hole is just a very heavy object
Tomminn 6y ago
I really like this take, but on a weird philosophical way I gotta disagree. The surface of the earth has by a long shot the most difficult physics in the universe we know about. Try to imagine a model that predicts the things going on there. At least the neutron star probably has some scale at which it starts to looks homogeneous. This, btw, is a pretty good marketing strategy for condensed matter physics (and indeed, biology and chemistry [1]): "The most interesting physics in the universe takes place on the surface of earth." [1] Biology and Chemistry are literally subdisciplines of physics so large we call them different names. And they're subdisciplines which are only so large because the surface the earth exists. Without the surface of the earth as part of the universe, as far as we know biology wouldn't exist, and chemistry would probably still be nothing more than a medium-sized subdiscipline of physics.
- fggg444 6y ago
  if free will is to be believed, then it can't be modeled, right?
  - Tomminn 6y ago
    I mean, free will isn't to be believed. But if you wanna, be my guest. If quantum mechanics is to be believed, then the model is certainly probabilistic at best, so you'll have enough wiggle room for it.
    - stevenhuang 6y ago
      Even granting the weirdness of quantum mechanics there may not be any wiggle room, as random will is not free will.
      - Tomminn 6y ago
        Oh don't you know that acts of free will only take place in the subset of chains of cause and effect that can be traced to the (decoherence-induced) collapse of a quantum state, and also just happen to turn out to be perfectly randomly distributed samples of the particular distribution quantum physics predicts for that situation? Free will of the gaps lives on [1]. [1] https://en.wikipedia.org/wiki/God_of_the_gaps https://en.wikipedia.org/wiki/God_of_the_gaps

by cletus 6y ago

ohazi 6y ago

Neutron stars seem like what you would see in a black hole if the interesting parts weren't shrouded by an event horizon. Although I suppose the event horizon does give you jets. But yeah, city-sized objects with the density of an atomic nucleus. Pretty mind-bending! (literally, I guess?)

ramraj07 6y ago
The “how to build a black hole” video from PBS space time says that’s how you do it - you start with a neutron star and keep adding more mass to it, which paradoxically makes it smaller until it becomes smaller than its swarzchild radius, becoming a black hole. Blew my mind and anyone else’s when I share the video with them! https://youtu.be/xx4562gesw0 https://youtu.be/xx4562gesw0
- cletus 6y ago
  That depends on what size of black hole you want to make. It works for large black holes (you need sufficient mass for the gravitational forces to be sufficient) but those black holes aren’t that useful. Smaller black holes are harder to construct but way more useful.
  - willis936 6y ago
    It's simple, just deflate spacetime!
  - elseweather 6y ago
    I'm curious what useful applications we have for black holes of any size
    - jakeogh 6y ago
      It's assumed that little ones are the most efficient mass to energy converters, via Hawking radiation.
    - cletus 6y ago
      There are actually a lot of theoretical applications. Black holes are likely the most efficient form of power generation that we currently know of. Black hole propulsion may well be the best form of interstellar starship propulsion. Black holes may also be the ultimate computer. If the universe continues based on it current understanding then eventually all the stars will be dead and the universe will be a dark place. The Black hole era will last trillions of time as long but may well be the golden age of civilization. Each of these topics is a rabbit hole.
    - ThrustVectoring 6y ago
      The theoretical limit of how efficiently you can turn energy into useful work depends on how cold your energy sink is. The coldest energy sink in an ever-expanding universe gets colder over time as everything spreads out and the fixed amount of energy occupies more and more space. So the hypothetical optimal end-state of an extremely old civilization is hibernating a bunch of very stable mass until the extreme far future, at which point they can drip-feed it into a black hole to do some extremely efficient computation.
ravi-delia 6y ago
I was under the possibly incorrect impression that black holes result when the gravitational force is so great that it even overcomes Pauli's exclusion principle, collapsing the neutrons into an overlapping mass of staggering density. Now that I write that out, I'm a little more doubtful.
- btilly 6y ago
  Close. Giant blue stars burn all of the way up to the most stable element of all, which is iron. And then collects an iron core. As the core grows, the star shrinks and the pressure in the middle grows. Once the pressure in the middle is high enough, it overcomes the Pauli exclusion principle and electrons merge with protons to become neutrons with a release of energy, which mostly comes out as neutrinos. Once a bit of that core disappears, the stuff around falls into the new gap, hits it, goes under way more pressure and the same thing happens. This starts a chain reaction that causes a supernova. The core collapses into a neutron star while the release of energy blows the outer shell out to eventually become a nebulae. If the initial star was big enough, the newly created neutron star is big enough to transform into a black hole. Otherwise it is left as a neutron star. If it forms a neutron star, the spin speeds up thanks to the collapse. Typical time to rotate can be anywhere from milliseconds to seconds. We can tell that because its magnetic field also gets trapped and forms a strong beam along the north and south magnetic poles. Since magnetic poles do not generally line up with the rotational poles, that beam becomes like a searchlight. If we're in the path of that beam, we see a pulsar, and the frequency of the pulsar is the rotational speed of the neutron star. This is probably way more than you wanted to know. :-) I probably also am going to get corrected on some details in 3, 2, 1...
  - hinkley 6y ago
    I was shocked to learn how long it takes a photon produced at the center of the sun by a fusion event to reach earth. The layers upon layers of subatomic particles that are all interacting in these tight quarters is simply astounding. I've heard this same theory on supernovas from a number of people in or around physics, but I always wonder how handwavy it is, whether we actually understand how that works yet, and how different (confusing) the real process is from the given one.
CuriouslyC 6y ago
Imagine if black holes were just neutron stars made of second or third generation quark "neutrons."
hinkley 6y ago
I remember the infinities of black holes being a challenge to explain to my artsy friends after reading A Brief History of Time. Correct me if I'm wrong, but isn't the curvature of space around - and within - a neutron star substantial enough that euclidean geometry doesn't really hold anymore? The volume of a basketball is the surface area x R/3, but is that true of a neutron star? I was under the impression that the difference between Euclid and actual was statistically significant, to the point that you get the wrong behavior if you don't account for it.

Groxx 6y ago

>In 2020, a fast radio burst (FRB) was detected from a magnetar.[⁷][⁸][⁹][¹⁰][¹¹][¹²][ᵉˣᶜᵉˢˢᶦᵛᵉ ᶜᶦᵗᵃᵗᶦᵒⁿˢ] Wikipedian humor at its finest. Because of course "excessive citations" looks like a citation.

a1369209993 6y ago
> [ᵉˣᶜᵉˢˢᶦᵛᵉ ᶜᶦᵗᵃᵗᶦᵒⁿˢ] FWIW, superscript i (contra ɪ) is at U+2071: [ᵉˣᶜᵉˢˢⁱᵛᵉ ᶜⁱᵗᵃᵗⁱᵒⁿˢ] I'm not seeing a superscript square bracket anywhere, unfortunately.
- Groxx 6y ago
  ah, good, there is a `i`. that struck me as weird too. I just grabbed a random "write in superscript" site tbh :)

btilly 6y ago

Black holes are relatively "simple". I mean that you can completely define a black hole with 3 properties, one of which isn't really relevant. Classically, yes. But more recently we've discovered not. One of the major conundrums about black holes is how information gets lost in their creation. There is a lot more information in the stuff that creates a black hole than in the black hole itself. Which violates the third law of thermodynamics. This is called the Black Hole Information Paradox. But as https://blogs.scientificamerican.com/observations/have-we-solved-the-black-hole-information-paradox/ https://blogs.scientificamerican.com/observations/have-we-so... explains, the real state of a black hole includes all of the stuff that you can see in the process of falling in. (We never actually see anything hit the event horizon. And in theory something on its way there can still be retrieved a million years after it started falling.) When you track things carefully, a real black hole is a very complex thing indeed. With no information loss.

jihadjihad 6y ago
> Which violates the third law of thermodynamics Wouldn't this be a violation of the second law rather than the third?
- willis936 6y ago
  It's not quite Maxwell's demon because the event horizon is a one-way causal ticket. The information might not be destroyed but it is totally inaccessible on this side of the horizon.
- btilly 6y ago
  I just looked it up, and it is a violation of the fact that the laws of physics should be reversible. So from the wave function at any point of time you should be able to reconstruct the wave at any other. My bad for having stuck thermodynamics in there at all. :-(
colechristensen 6y ago
This brings up a question I have had for a while: what is the life story of a photon shot at a black hole? From an outside observer, presumably you shoot a laser at a black hole and if your photons don't hit anything on the way to the horizon, they never hit it either but just approach asymptotically as time goes to infinity. As, a photon though, you don't "notice" crossing the horizon and in a measurable amount of time you go from being emitted to hitting the singularity. Black holes don't last until infinity though, they evaporate in a large but measurable time. (let's say 10^100 years, it depends on time and how the universe dies and how big the black hole is, but whatever, presuming it happens it is some extraordinarily large number of years) So... as something falling into a black hole an outside observer will watch you infinitely slowly approaching a growing horizon until at some point the growth goes negative and you watch the horizon falling away from your friend the photon until at last the horizon disappears entirely and releases the photon to go about its merry way to hit something sometime around the heat death of the universe. In other words, if you are a conscious very resilient little particle doomed to fall into a black hole... do you really appear from the outside to be falling in until the black hole evaporates? Do you experience going through the event horizon like it's nothing and hit the singularity in a few hours by your own watch... Or is a black hole sort of a time machine to the end of the universe where in the short process of falling in you get to watch the whole history of existence pass you by and you come out at the end having never crossed the horizon in what was for you a very short ride. Or is there some third option where from the outside it takes an infinite amount of time for you to fall in, but that infinity "for math reasons" actually takes place and passes in a Zeno's paradox kind of way at some distinct point in your timeline and you meanwhile pass the horizon and hit the singularity in short order and are no more? I don't really know anything but these are questions and vague thoughts I have had. The central question is reconciling the outside apparent infinite time to watch something cross an event horizon with the finite lifespan of evaporating black holes.

jayd16 6y ago

>The reason this is somewhat irrelevant is because electric repulsion is about 60 orders of magnitude more than gravitational attraction so it's not expected black holes have a significant charge. I hadn't thought about it but I guess that means protons or electrons have a maximum resting density. A group of those will never collapse from gravity?

Tagbert 6y ago
If that were true, you would not get a neutron star where the electrons and protons are collapsed into neutrons. Not sure how that stands to the overall strength question, though.
throwaway2568 6y ago
Protons and electrons are both Fermions, which means they can not have identical quantum numbers (have to obey the Pauli exclusion principle as mentioned elsewhere in the thread). In the case of a very dense system, like the sun, this can lead to an effect known as degeneracy pressure (which acts against gravity). Essentially you have filled all the lower quantum numbers and then adding an extra proton/electron to the system requires a certain amount of energy. It's quite handwavy but the degeneracy pressure of electrons is mostly what keeps a white dwarf from contracting, whereas in the case of a neutron star it is the degeneracy pressure of neutrons (plus repulsive strong force and other effects as indicated in the OP). This kind of high level discussion is often covered in first year astronomy courses auditing a MOOC like the following may be of interest (https://www.edx.org/course/astrophysics-the-violent-universe https://www.edx.org/course/astrophysics-the-violent-universe)

yongjik 6y ago

> This field is so strong it would flatten atoms and rip electrons from your body. ...which is underselling it a bit. :) (As quoted in Wikipedia) the field is so strong that pure vacuum itself has ~10,000 times the density of lead, due to the energy contained in the field. Imagine that.

detritus 6y ago

> Neutron stars OTOH are arguably the most complex objects in the Universe. In OUR universe, at least. If a black hole ends in a white hole, Gosh only knows how complex things will end up at the other end. Witness, for example, our entire reality.

o_p 6y ago

A black hole is just a very heavy object

Tomminn 6y ago

I really like this take, but on a weird philosophical way I gotta disagree. The surface of the earth has by a long shot the most difficult physics in the universe we know about. Try to imagine a model that predicts the things going on there. At least the neutron star probably has some scale at which it starts to looks homogeneous. This, btw, is a pretty good marketing strategy for condensed matter physics (and indeed, biology and chemistry [1]): "The most interesting physics in the universe takes place on the surface of earth." [1] Biology and Chemistry are literally subdisciplines of physics so large we call them different names. And they're subdisciplines which are only so large because the surface the earth exists. Without the surface of the earth as part of the universe, as far as we know biology wouldn't exist, and chemistry would probably still be nothing more than a medium-sized subdiscipline of physics.

fggg444 6y ago
if free will is to be believed, then it can't be modeled, right?
- Tomminn 6y ago
  I mean, free will isn't to be believed. But if you wanna, be my guest. If quantum mechanics is to be believed, then the model is certainly probabilistic at best, so you'll have enough wiggle room for it.
  - stevenhuang 6y ago
    Even granting the weirdness of quantum mechanics there may not be any wiggle room, as random will is not free will.
    - Tomminn 6y ago
      Oh don't you know that acts of free will only take place in the subset of chains of cause and effect that can be traced to the (decoherence-induced) collapse of a quantum state, and also just happen to turn out to be perfectly randomly distributed samples of the particular distribution quantum physics predicts for that situation? Free will of the gaps lives on [1]. [1] https://en.wikipedia.org/wiki/God_of_the_gaps https://en.wikipedia.org/wiki/God_of_the_gaps