14 ms·

What keeps earth from collapsing in on itself? (2010)

ncmncm 4y ago
Weird. Why would anybody expect Earth to collapse at all, or to wait billions of years to collapse, or to collapse, but Jupiter not collapse first? Or not wonder why their own head doesn't?
- chaps 4y ago
  Why wouldn't they expect it? It's a perfectly valid question to tease out curious aspects from our reality.
- erwincoumans 4y ago
  Why? Because * people need to be educated, and this article does a good job * different forces dominate at different sizes For a skull, gravitational forces of a human head are tiny. Collapse is prevented because of skull rigid structure that supports itself: inward forces are resisted by resistance to deformation and pressure (similar to semi-spherical cellars and rounded bridges) Earth has large gravitational forces, but resistance to compresson of its solid inner core and liquid iron outer core prevents collapse. Stars are much bigger, and the larger gravitational forces are resisted by an additional force, next to resistance of compression gasses: Nuclear reactions produce radiation in the form of photons that are streaming out from the star's interior creating outward pressure forces.
  - codeflo 4y ago
    To simplify even more, both the Earth and your head would eventually collapse due to gravity if it weren't for electromagnetic forces pushing the atoms apart. I would be in free fall towards the Earth's center right now if it weren't for the atoms in my couch pushing the atoms in my butt upwards.
    - ncmncm 4y ago
      All I can say is better them than me.
- mannykannot 4y ago
  Why ask 'why' at all, about anything? In particular, why did you ask this question? There is a plausible Darwinian story to be told about why generalized curiosity about causes abets fitness, but no-one would have come up with that explanation without asking quite a few questions about why things are as they are.
  - dcow 4y ago
    > There is a plausible Darwinian story to be told about why generalized curiosity about causes abets fitness… HN has served it’s purpose this morning I can now go about my day (first order, of course: feed the cats). Bravo.
- jrootabega 4y ago
  It's a kids'/popular science q&a site. I don't think it lines up well with the audience here, but it's a fine question for that site.
  - SiempreViernes 4y ago
    Yeah, the question might stem from someone overemphasising that stars don't live forever which lead to the generalisation that everything in astronomy collapses.
- croes 4y ago
  Matter is mostly empty space, so enough for a collapse.
- willis936 4y ago
  The Earth is the most dense celestial body in the solar system that weighs more than 10^20 kg.
jethkl 4y ago
Why is the earth's crust so stable? It has supported life for billions of years, yet it is just 12 mi thick [1] and floats on top of liquid rock that extends for thousands of miles -- the part of earth we are most familiar with is a tiny fraction of what our planet really is. You could imagine that turbulence in the liquid below would cause currents that blast through the crust with catastrophic consequences, and that this would happen regularly. But it doesn't -- we have a small number of (super) volcanos, but they are pretty rare. I find this unnerving and remarkable. Our perception of reality -- in this case the earth beneath us -- is skewed. [1] https://en.wikipedia.org/wiki/Structure_of_Earth https://en.wikipedia.org/wiki/Structure_of_Earth
- qbonnard 4y ago
  N. K. Jemisin wrote a triple Hugo winning trilogy[1] about what could happen to humanity with a sliiightly less stable crust, if you want some more unnerving ;) [1] https://en.wikipedia.org/wiki/N._K._Jemisin#Broken_Earth_series https://en.wikipedia.org/wiki/N._K._Jemisin#Broken_Earth_ser...
- adgjlsfhk1 4y ago
  something that is counter intuitive is that although the mantle is often described as liquid, that description is only valid on large scales (both space and time). for comparison, the mantle is significantly less liquid than cold asfault. it's just subject to huge pressures.
  - MrYellowP 4y ago
    > asfault asphalt?
- bell-cot 4y ago
  "Liquid" does not describe the Earth's mantle - https://en.wikipedia.org/wiki/Structure_of_Earth#Mantle https://en.wikipedia.org/wiki/Structure_of_Earth#Mantle It is more like cold pitch - https://en.wikipedia.org/wiki/Pitch_drop_experiment https://en.wikipedia.org/wiki/Pitch_drop_experiment
bell-cot 4y ago
Shorter answer, with simpler vocabulary: The Earth is basically a solid hunk of rock, with a core of dense metals like iron. Solid rock and iron just don't collapse under pressures or temperatures that are even slightly sane. (Unless they are hollow, have an empty space under them, or are falling down into something less dense - like an undersea landslide does.) Sure, the pressures and temperatures in the middle of the Earth are high - but we're pretty much talking pressures that some C-list college physics lab could maintain for days on end, and temperatures lower than an old arc welder you can buy on eBay could do forever. Stars that actually collapse - not just cool off, shrink, and fade away - have pressures and temperatures inside that are a million miles from sane. We're talking "a hundred-billion dollar atom smasher, that is 15 miles wide, could do that - but only to a speck of dust, and for a trillionth of a second". Vs. a star that is about to collapse has had millions of cubic miles of stuff under those pressures and temperatures, for years. Under those sorts of conditions, atoms get smashed. Really smashed. We're talking the difference between taking a box of packing peanuts and lightly patting 'em down (inside the Earth), and putting that box of packing peanuts into a big stamping press in a steel mill (inside the collapsing star).
- atty 4y ago
  The statement about particle colliders is not really correct. The relativistic heavy ion collider, where I used to work, is about 2.4 miles in circumference, and reaches temperatures in the 10s of trillions of degrees in its collisions. This is > 1000 times hotter than a supernova. The environment in these collisions is made to reproduce the state of the universe fractions of a second after the Big Bang, and aren’t really comparable to any normal stellar activity.
  - bell-cot 4y ago
    Any thought on what sort of hardware would actually be necessary to reproduce the temperatures / pressures / densities of a sleepy little 1.4 solar mass red supergiant pre-supernova iron core, for a full 10e-12 seconds, in the full volume of a visible speck of dust? (At least in Wikipedia's version of things, the temperature inside a nice, fresh hot-off-the-Collapse'O'Matic-grill neutron star is "from around 10e11 to 10e12 kelvins". Not quite your comfort zone, but far closer:)
rayiner 4y ago
Electron degeneracy pressure: https://en.wikipedia.org/wiki/Electron_degeneracy_pressure https://en.wikipedia.org/wiki/Electron_degeneracy_pressure Stars above 8 solar masses can turn into neutron stars or black holes because during their life they have two forces counteracting gravitational collapse: electron degeneracy pressure and thermal pressure from fusion. When the fusion stops you’re left with a massive body where the electron degeneracy pressure alone isn’t sufficient to counteract gravity. https://en.wikipedia.org/wiki/Chandrasekhar_limit https://en.wikipedia.org/wiki/Chandrasekhar_limit. You get a neutron star instead of a black hole when the gravitational collapse can be overcome by the strong force and neutron degeneracy pressure (the same forces that keep the nuclei of atoms from collapsing). See this more general description of the fundamental forces: https://en.wikipedia.org/wiki/Fundamental_interaction https://en.wikipedia.org/wiki/Fundamental_interaction
- vannevar 4y ago
  Interesting! I recall being taught that it was the electromagnetic repulsion between the electron shells of atoms, but that was probably in high school. I took quantum mechanics in college but don't remember touching on the particular question of stellar collapse. Somewhat surprising that this question wasn't really answered until the late 60s.
- changoplatanero 4y ago
  What allows neutron stars to overcome the degeneracy pressure? Does the electron get so close to the proton that it gets absorbed and then the pressure disappears?
  - deleted 4y ago
    [deleted]
  - rayiner 4y ago
    Yes, essentially. Degeneracy pressure arises as compression forces electrons into higher energy states to avoid being forced into the same quantum state (Pauli Exclusion principle). But at a certain point the gravitation pressure becomes so strong that protons capture electrons, producing a neutron and an electron neutrino, and relieving the electron degeneracy pressure. See: http://csep10.phys.utk.edu/OJTA2dev/ojta/c2c/neutron/neutronstars/degeneracy_tl.html http://csep10.phys.utk.edu/OJTA2dev/ojta/c2c/neutron/neutron...
grendelt 4y ago
Short answer, it's a solid hunk of rock. Stars are not. Stars are a mass of incandescent gasses; a gigantic nuclear furnace where hydrogen is smelt into helium at a temperature of millions of degrees. Gaseous planets and stars will collapse into something solid (or explode). Not all stars collapse to explode though. They have to be 1.4 times the size of our Sun to do that. https://en.wikipedia.org/wiki/Chandrasekhar_limit https://en.wikipedia.org/wiki/Chandrasekhar_limit
- Keyframe 4y ago
  Mass, not size.
  - grendelt 4y ago
    Trying to keep it simple for those who would ask the question in the first place and head off the follow-up: "What's the difference between size and mass?"
    - grayclhn 4y ago
      When discussing compression, the difference between size and mass is kind of important. :)
- marcosdumay 4y ago
  > Stars are not. Stars core pretty much are. Or rather, "solid" is a bad name because it is a specific name for material that is much more compressible than what is there.
- popularrecluse 4y ago
  Actually, the sun is a miasma of incandescent plasma. Forget what they told you before. https://tmbw.net/wiki/Why_Does_The_Sun_Really_Shine%3F https://tmbw.net/wiki/Why_Does_The_Sun_Really_Shine%3F
- sgtnoodle 4y ago
  Fascinating. Definitely very different environments. Stars are not places where we could live, but here on Earth there would be no life without the light our sun gives.
whoisthemachine 4y ago
My favorite new thing I learned from this was: > while larger stars will form neutron stars (which are essentially giant atomic nuclei) I had never heard that description before, and it's fascinating to think about!
- aardvark179 4y ago
  Neutron stars behave somewhat like giant nuclei, but only somewhat. We don’t even really good models of how their cores behave, maybe it’s a quark-gluon plasma, but we just don’t have a good enough model of matter to know.
rahimiali 4y ago
My take before reading the article was that “earth is already collapsed”. After reading the article, this still sounds like a fine explanation. Am I wrong?
RichardCA 4y ago
Since we're on this subject, one question I've never seen answered is why neutron stars have such intense magnetic fields. I mean in the normal universe we inhabit, certain chemical elements are magnetic while others are not. How can neutron star matter have magnetism when there are no electrons in orbitals anymore? I mean that seems like a good question, how a relatively well understood phenomenon like pulsars seems to depend on electromagnetic behavior that can't be explained by Maxwell's field equations.

Weird. Why would anybody expect Earth to collapse at all, or to wait billions of years to collapse, or to collapse, but Jupiter not collapse first? Or not wonder why their own head doesn't?

chaps 4y ago
Why wouldn't they expect it? It's a perfectly valid question to tease out curious aspects from our reality.
erwincoumans 4y ago
Why? Because * people need to be educated, and this article does a good job * different forces dominate at different sizes For a skull, gravitational forces of a human head are tiny. Collapse is prevented because of skull rigid structure that supports itself: inward forces are resisted by resistance to deformation and pressure (similar to semi-spherical cellars and rounded bridges) Earth has large gravitational forces, but resistance to compresson of its solid inner core and liquid iron outer core prevents collapse. Stars are much bigger, and the larger gravitational forces are resisted by an additional force, next to resistance of compression gasses: Nuclear reactions produce radiation in the form of photons that are streaming out from the star's interior creating outward pressure forces.
- codeflo 4y ago
  To simplify even more, both the Earth and your head would eventually collapse due to gravity if it weren't for electromagnetic forces pushing the atoms apart. I would be in free fall towards the Earth's center right now if it weren't for the atoms in my couch pushing the atoms in my butt upwards.
  - ncmncm 4y ago
    All I can say is better them than me.
mannykannot 4y ago
Why ask 'why' at all, about anything? In particular, why did you ask this question? There is a plausible Darwinian story to be told about why generalized curiosity about causes abets fitness, but no-one would have come up with that explanation without asking quite a few questions about why things are as they are.
- dcow 4y ago
  > There is a plausible Darwinian story to be told about why generalized curiosity about causes abets fitness… HN has served it’s purpose this morning I can now go about my day (first order, of course: feed the cats). Bravo.
jrootabega 4y ago
It's a kids'/popular science q&a site. I don't think it lines up well with the audience here, but it's a fine question for that site.
- SiempreViernes 4y ago
  Yeah, the question might stem from someone overemphasising that stars don't live forever which lead to the generalisation that everything in astronomy collapses.
croes 4y ago
Matter is mostly empty space, so enough for a collapse.
willis936 4y ago
The Earth is the most dense celestial body in the solar system that weighs more than 10^20 kg.

jethkl 4y ago

Why is the earth's crust so stable? It has supported life for billions of years, yet it is just 12 mi thick [1] and floats on top of liquid rock that extends for thousands of miles -- the part of earth we are most familiar with is a tiny fraction of what our planet really is. You could imagine that turbulence in the liquid below would cause currents that blast through the crust with catastrophic consequences, and that this would happen regularly. But it doesn't -- we have a small number of (super) volcanos, but they are pretty rare. I find this unnerving and remarkable. Our perception of reality -- in this case the earth beneath us -- is skewed. [1] https://en.wikipedia.org/wiki/Structure_of_Earth https://en.wikipedia.org/wiki/Structure_of_Earth

qbonnard 4y ago
N. K. Jemisin wrote a triple Hugo winning trilogy[1] about what could happen to humanity with a sliiightly less stable crust, if you want some more unnerving ;) [1] https://en.wikipedia.org/wiki/N._K._Jemisin#Broken_Earth_series https://en.wikipedia.org/wiki/N._K._Jemisin#Broken_Earth_ser...
adgjlsfhk1 4y ago
something that is counter intuitive is that although the mantle is often described as liquid, that description is only valid on large scales (both space and time). for comparison, the mantle is significantly less liquid than cold asfault. it's just subject to huge pressures.
- MrYellowP 4y ago
  > asfault asphalt?
bell-cot 4y ago
"Liquid" does not describe the Earth's mantle - https://en.wikipedia.org/wiki/Structure_of_Earth#Mantle https://en.wikipedia.org/wiki/Structure_of_Earth#Mantle It is more like cold pitch - https://en.wikipedia.org/wiki/Pitch_drop_experiment https://en.wikipedia.org/wiki/Pitch_drop_experiment

bell-cot 4y ago

Shorter answer, with simpler vocabulary: The Earth is basically a solid hunk of rock, with a core of dense metals like iron. Solid rock and iron just don't collapse under pressures or temperatures that are even slightly sane. (Unless they are hollow, have an empty space under them, or are falling down into something less dense - like an undersea landslide does.) Sure, the pressures and temperatures in the middle of the Earth are high - but we're pretty much talking pressures that some C-list college physics lab could maintain for days on end, and temperatures lower than an old arc welder you can buy on eBay could do forever. Stars that actually collapse - not just cool off, shrink, and fade away - have pressures and temperatures inside that are a million miles from sane. We're talking "a hundred-billion dollar atom smasher, that is 15 miles wide, could do that - but only to a speck of dust, and for a trillionth of a second". Vs. a star that is about to collapse has had millions of cubic miles of stuff under those pressures and temperatures, for years. Under those sorts of conditions, atoms get smashed. Really smashed. We're talking the difference between taking a box of packing peanuts and lightly patting 'em down (inside the Earth), and putting that box of packing peanuts into a big stamping press in a steel mill (inside the collapsing star).

atty 4y ago
The statement about particle colliders is not really correct. The relativistic heavy ion collider, where I used to work, is about 2.4 miles in circumference, and reaches temperatures in the 10s of trillions of degrees in its collisions. This is > 1000 times hotter than a supernova. The environment in these collisions is made to reproduce the state of the universe fractions of a second after the Big Bang, and aren’t really comparable to any normal stellar activity.
- bell-cot 4y ago
  Any thought on what sort of hardware would actually be necessary to reproduce the temperatures / pressures / densities of a sleepy little 1.4 solar mass red supergiant pre-supernova iron core, for a full 10e-12 seconds, in the full volume of a visible speck of dust? (At least in Wikipedia's version of things, the temperature inside a nice, fresh hot-off-the-Collapse'O'Matic-grill neutron star is "from around 10e11 to 10e12 kelvins". Not quite your comfort zone, but far closer:)

rayiner 4y ago

Electron degeneracy pressure: https://en.wikipedia.org/wiki/Electron_degeneracy_pressure https://en.wikipedia.org/wiki/Electron_degeneracy_pressure Stars above 8 solar masses can turn into neutron stars or black holes because during their life they have two forces counteracting gravitational collapse: electron degeneracy pressure and thermal pressure from fusion. When the fusion stops you’re left with a massive body where the electron degeneracy pressure alone isn’t sufficient to counteract gravity. https://en.wikipedia.org/wiki/Chandrasekhar_limit https://en.wikipedia.org/wiki/Chandrasekhar_limit. You get a neutron star instead of a black hole when the gravitational collapse can be overcome by the strong force and neutron degeneracy pressure (the same forces that keep the nuclei of atoms from collapsing). See this more general description of the fundamental forces: https://en.wikipedia.org/wiki/Fundamental_interaction https://en.wikipedia.org/wiki/Fundamental_interaction

vannevar 4y ago
Interesting! I recall being taught that it was the electromagnetic repulsion between the electron shells of atoms, but that was probably in high school. I took quantum mechanics in college but don't remember touching on the particular question of stellar collapse. Somewhat surprising that this question wasn't really answered until the late 60s.
changoplatanero 4y ago
What allows neutron stars to overcome the degeneracy pressure? Does the electron get so close to the proton that it gets absorbed and then the pressure disappears?
- deleted 4y ago
  [deleted]
- rayiner 4y ago
  Yes, essentially. Degeneracy pressure arises as compression forces electrons into higher energy states to avoid being forced into the same quantum state (Pauli Exclusion principle). But at a certain point the gravitation pressure becomes so strong that protons capture electrons, producing a neutron and an electron neutrino, and relieving the electron degeneracy pressure. See: http://csep10.phys.utk.edu/OJTA2dev/ojta/c2c/neutron/neutronstars/degeneracy_tl.html http://csep10.phys.utk.edu/OJTA2dev/ojta/c2c/neutron/neutron...

grendelt 4y ago

Short answer, it's a solid hunk of rock. Stars are not. Stars are a mass of incandescent gasses; a gigantic nuclear furnace where hydrogen is smelt into helium at a temperature of millions of degrees. Gaseous planets and stars will collapse into something solid (or explode). Not all stars collapse to explode though. They have to be 1.4 times the size of our Sun to do that. https://en.wikipedia.org/wiki/Chandrasekhar_limit https://en.wikipedia.org/wiki/Chandrasekhar_limit

Keyframe 4y ago
Mass, not size.
- grendelt 4y ago
  Trying to keep it simple for those who would ask the question in the first place and head off the follow-up: "What's the difference between size and mass?"
  - grayclhn 4y ago
    When discussing compression, the difference between size and mass is kind of important. :)
marcosdumay 4y ago
> Stars are not. Stars core pretty much are. Or rather, "solid" is a bad name because it is a specific name for material that is much more compressible than what is there.
popularrecluse 4y ago
Actually, the sun is a miasma of incandescent plasma. Forget what they told you before. https://tmbw.net/wiki/Why_Does_The_Sun_Really_Shine%3F https://tmbw.net/wiki/Why_Does_The_Sun_Really_Shine%3F
sgtnoodle 4y ago
Fascinating. Definitely very different environments. Stars are not places where we could live, but here on Earth there would be no life without the light our sun gives.

whoisthemachine 4y ago

My favorite new thing I learned from this was: > while larger stars will form neutron stars (which are essentially giant atomic nuclei) I had never heard that description before, and it's fascinating to think about!

aardvark179 4y ago
Neutron stars behave somewhat like giant nuclei, but only somewhat. We don’t even really good models of how their cores behave, maybe it’s a quark-gluon plasma, but we just don’t have a good enough model of matter to know.

rahimiali 4y ago

My take before reading the article was that “earth is already collapsed”. After reading the article, this still sounds like a fine explanation. Am I wrong?

RichardCA 4y ago

Since we're on this subject, one question I've never seen answered is why neutron stars have such intense magnetic fields. I mean in the normal universe we inhabit, certain chemical elements are magnetic while others are not. How can neutron star matter have magnetism when there are no electrons in orbitals anymore? I mean that seems like a good question, how a relatively well understood phenomenon like pulsars seems to depend on electromagnetic behavior that can't be explained by Maxwell's field equations.