[HN Gopher] What keeps earth from collapsing in on itself? (2010)
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What keeps earth from collapsing in on itself? (2010)
Author : gigglesupstairs
Score : 49 points
Date : 2022-04-30 08:29 UTC (14 hours ago)
(HTM) web link (scienceline.ucsb.edu)
(TXT) w3m dump (scienceline.ucsb.edu)
| rayiner wrote:
| 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.
|
| 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
| criticaltinker wrote:
| This is a thoughtful comment but IMO your phrasing is too
| strong and potentially misleading.
|
| As far as science is concerned, the jury is still out on
| stellar nucleosynthesis. The leading _theory_ - that
| gravitational collapse causes fusion near the core - may be
| entirely incorrect, and there is mounting evidence suggesting
| so including a plethora of modern observations that the theory
| fails to explain.
|
| For example the so-called 'coronal heating' problem has existed
| for 75 years, since the solar corona was first demonstrated to
| contain plasma with temperatures of 1 million degrees kelvin
| and above, much higher than the photospheric surface
| temperature of approximately 6000 K [1].
|
| As another stunning counterexample, current gravitational
| models do not explain observed properties of the solar wind
| like spatial variation and periodicity in time (thanks voyager
| 1 & 2), among many other things.
|
| See [2] for a dense intro to more unresolved problems in solar
| physics.
|
| Alternative (non mainstream) theories like "plasma cosmology"
| are gaining traction in the scientific community for this
| reason. Note though that many papers do not use that particular
| phrase to describe their work.
|
| Unfortunately (for intellectually curious folks), the
| contributors to Wikipedia pages on these physics topics are
| extremely ... biased. Reading [3] may leave you with the
| impression that "plasma cosmology" has been completely debunked
| by the scientific community, when in fact nothing could be
| further from the truth ([4][5] are examples to support this
| claim).
|
| [1]
| https://royalsocietypublishing.org/doi/full/10.1098/rsta.201...
|
| [2]
| https://www.ias.ac.in/article/fulltext/joaa/029/01-02/0003-0...
|
| [3] https://en.m.wikipedia.org/wiki/Plasma_cosmology
|
| [4] https://link.springer.com/article/10.1007/s00159-013-0062-7
|
| [5]
| https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.102...
| rayiner wrote:
| I'm certainly no physicist. I'm just recounting the
| explanation I remember from high school quantum mechanics.
| vannevar wrote:
| 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.
| zackmorris wrote:
| I was going to say the same thing about neutron degeneracy
| pressure, so I'll add a thought experiment that I haven't seen
| discussed or answered yet online. This is probably a really old
| debate, and is maybe settled, but not in layman's terms:
|
| **
|
| Imagine we have a neutron star that's 1 atom away from
| collapsing into a black hole. What does that mean? There are 2
| edge cases of interest: 1) when an event horizon begins forming
| at the core, and 2) when it swallows the surface.
|
| 1) Starting with the core event horizon, we can imagine
| dropping an atom on the surface of the star, and pressure
| passing the neutron degeneracy pressure limit at its center. A
| tiny black hole appears in the core, roughly the width of a
| neutron, and all of the neutrons start slipping down the drain
| into it, making the horizon bigger and bigger until the star is
| eventually swallowed.
|
| Except that time passes more slowly in a deep gravity well. It
| crawls almost to a halt at the center of a neutron star, and
| halts completely when the event horizon at the core forms. Time
| may even seem to be running backwards inside the event horizon
| from our frame of reference.
|
| So my feeling is that this is the point where quantum mechanics
| stops and relativity takes over. We can treat the event horizon
| as a black box trying to evaporate outwards with Hawking
| radiation as hard as the star is trying to collapse into it. In
| other words, the event horizon feels solid to the star around
| it.
|
| The test of this is to see how Hawking radiation for the
| smallest black hole compares to the pressure at the center of a
| neutron star at the brink of collapse. I'd predict them to
| either be off by orders of magnitude or exactly equal.
|
| 2) Carrying that idea forward, as we add more atoms, the event
| horizon grows bigger and bigger until it finally covers the
| surface and we see the star red shift redder and redder until
| it approaches black.
|
| What happens when we pass the tipping point and 1 final atom
| causes the event horizon to surround the entire star? Is it
| like a one-way door, where the black hole stays that way
| forever?
|
| Well, we can test that by waiting for as much Hawking radiation
| energy to evaporate as the mass of 1 atom.
|
| Then the neutron star red shifts less and comes back into view.
| In other words, time gets faster again, the event horizon
| retreats, and the star blue shifts back into being visible. The
| longer we wait, and the more Hawking radiation is emitted, the
| smaller the event horizon gets until it finally disappears
| completely and the star goes back to being a neutron star.
|
| By this logic, with time running slower and slower, then faster
| and faster, is it more likely that the neutrons within the
| event horizon suddenly turn into pure energy and collapse into
| each other to a singularity? Or is it more likely that they
| stay how they are, frozen in time, then go back to how they
| were when the energy representing their mass leaks out in
| Hawking radiation and then back into the form of a neutron?
|
| This is the central question not being adequately addressed
| IMHO.
|
| **
|
| Now, I don't think that I have broken any rules of physics
| talking about black hole formation this way. But I'd vote for
| the latter case where nothing happens to the neutrons, the
| event horizon just moves outwards and inwards within the
| neutron star as it gains and loses mass. This may happen in
| real life when they suck in mass from a neighboring star.
|
| What happens if a white dwarf or neutron star gains a lot of
| mass this way quickly? Any potential energy remaining in atoms
| which haven't been reduced to neutrons yet quickly falls
| beneath the electron degeneracy pressure, goes through the
| high-pressure slowed space on and within the neutron star,
| fuses instantly and explodes. Which is called a nova.
|
| So even in the center of an ordinary star like our sun, the
| high-pressure slowed space presses atoms close enough together
| to fuse. The rate of fusion is proportional to how slow that
| space is. The slower the space, the faster the fusion.
|
| Going beyond edge case 2, if we add a lot of matter and it
| falls beneath the event horizon, it's going to take a long time
| to evaporate back out, potentially trillions of years. Which is
| why most black holes that formed naturally probably have so
| much mass that we'll never see them blue shift back to our
| frame of reference.
|
| But, I'm probably wrong. Another interpretation is that the
| slower space at the center of a neutron star is actually
| longer. So we can imagine the distance to the core getting
| further away as the star gains mass. When the event horizon
| forms, the space there starts falling in away from us faster
| than the speed of light. Meaning that Hawking radiation may not
| be strong enough to hold the neutrons out. The gravity gradient
| passes 90 degrees and they fall straight in as if nothing is
| beneath them.
|
| If that's the case, then the neutrons fall through that pin
| prick rip in spacetime, maybe turning into pure energy. Their
| energy comes out the other side where time is running backwards
| from our frame of reference, so space is ballooning out at the
| speed of light, possibly with one less spatial dimension,
| although my gut feeling is that the z axis is just flipped so
| the number of dimensions probably stays constant.
|
| This would be a white hole and look very much like the birth of
| our universe in the big bang. Inflation would be the period
| when spacetime is still flowing faster than the speed of light
| within the event horizon, until it reaches the radius of the
| event horizon in that frame of reference and slows below the
| speed of light again.
|
| The child universe within the black hole would last until the
| parent black hole evaporates. Inside, it would look like
| there's an outward pressure causing the child universe to
| expand (dark energy), powered by the Hawking radiation of the
| parent black hole. This would push matter outside the child
| universe's visible universe, whose radius is equal to parent
| black hole's event horizon radius from our frame of reference,
| causing the rate of expansion to increase. Eventually more and
| more matter would escape, lowering the mass of the child
| universe until the edge of the universe rushes in, pulling an
| observer in the child universe apart in reverse
| spaghettification as it gets pulled back into our universe when
| the parent black hole evaporates completely and explodes. Which
| might be our universe's fate in trillions of years.
|
| Again, I'm probably wrong about this stuff. But I'm approaching
| it as a software developer who just thinks of the problem as a
| bunch of edge cases to test. It would be helpful to know the
| improper steps in my thought process so that a working solution
| can be found.
|
| Sorry this got so long, it might have been better to put it on
| a wiki somewhere.
|
| Edit: added speculation about the source of dark energy.
|
| Edit 2: the time direction in the white hole paragraphs doesn't
| seem quite right. For example, if time is running backwards
| inside, then I might have the inflation and reverse
| spaghettification timestamps reversed.
| snowwrestler wrote:
| The event horizon does not expand until it consumes the
| neutron star, because the Schwarzchild radius is smaller than
| the radius of the neutron star. The neutron star collapses
| into the smaller black hole.
|
| The matter cannot be considered neutrons anymore at that
| point, because it is too dense. Once neutron degeneracy
| pressure is overcome, they're not individual neutrons
| anymore.
|
| Once the black hole forms, the original matter never comes
| out again, even if it loses mass to Hawking radiation. The
| neutron star never comes back into view.
| zackmorris wrote:
| Apologies for replying to my own post, but I should have
| included sources. Here is the best stuff I've found so far:
|
| https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g
|
| https://www.youtube.com/playlist?list=PL39_ud5aKSvkl_wj5BIkR.
| ..
|
| https://jila.colorado.edu/~ajsh/insidebh/waterfall.html
|
| There is an episode of How the Universe Works (I think) where
| they talk about the multiverse looking like an infinite block
| of swiss cheese, and each black hole having a child universe
| inside with its own physics, sealed off from the parent
| universes. So we're in the black hole where the rules of
| physics allow us to exist to realize it. In other words, the
| multiverse used black holes to evolve the rules of physics
| until consciousness could exist. It's another interpretation
| of the anthropic principle so isn't really testable, but I
| thought it was elegant. Wish I could find it.
|
| Edit: some places to start:
|
| https://www.youtube.com/watch?v=KePNhUJ2reI
|
| https://www.youtube.com/watch?v=3DhDSjgw3j8
| wrycoder wrote:
| Lee Smolin's 1997 book, "The Life of the Cosmos" was where
| I first learned about the idea of universes evolving
| through black holes. I don't recollect if it was his idea,
| but it is certainly creative.
| changoplatanero wrote:
| 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]
| rayiner wrote:
| 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/neutron...
| chaps wrote:
| What happens to the neutrino at that point? Does it stay
| with the neutron star?
| monus21 wrote:
| Yes but after exceeding ~2 solar masses (Tolman-
| Oppenheimer-Volkoff limit) the neutron star will undergo
| further collapse to form a black hole.
| rayiner wrote:
| Initially they're trapped but they play a major role in
| the supernova explosion that accompanies stellar
| collapse: https://indico.cern.ch/event/657167/contributio
| ns/2677895/at...
| rahimiali wrote:
| 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?
| jethkl wrote:
| 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
| qbonnard wrote:
| 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_ser...
| adgjlsfhk1 wrote:
| 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 wrote:
| > asfault
|
| asphalt?
| bell-cot wrote:
| "Liquid" does not describe the Earth's mantle -
| https://en.wikipedia.org/wiki/Structure_of_Earth#Mantle It is
| more like cold pitch -
| https://en.wikipedia.org/wiki/Pitch_drop_experiment
| jethkl wrote:
| Agree that "rock made weak and ductile under intense heat and
| pressure" would probably be better than "liquid", but common
| language and daily experience do not apply. Whatever the
| dynamic processes are doing, they must have symmetry and be
| stable -- hot plumes of stuff don't punch through the
| contents in random locations.
| [deleted]
| deepsun wrote:
| Yet it's thankfully not that stable as is Venus's crust,
| otherwise we'd have much more carbon in atmosphere, so
| persistent hothouse effect and surface temperatures of 100+
| Celsius.
| ncmncm wrote:
| 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 wrote:
| Why wouldn't they expect it? It's a perfectly valid question to
| tease out curious aspects from our reality.
| mannykannot wrote:
| 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 wrote:
| > 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.
| croes wrote:
| Matter is mostly empty space, so enough for a collapse.
| jrootabega wrote:
| 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 wrote:
| Yeah, the question might stem from someone overemphasising
| that stars don't live forever which lead to the
| generalisation that everything in astronomy collapses.
| erwincoumans wrote:
| 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 wrote:
| 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 wrote:
| All I can say is better them than me.
| willis936 wrote:
| The Earth is the most dense celestial body in the solar system
| that weighs more than 10^20 kg.
| whoisthemachine wrote:
| 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 wrote:
| 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.
| grendelt wrote:
| 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
| marcosdumay wrote:
| > 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.
| sgtnoodle wrote:
| 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.
| popularrecluse wrote:
| 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
| Keyframe wrote:
| Mass, not size.
| grendelt wrote:
| 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 wrote:
| When discussing compression, the difference between size
| and mass is kind of important. :)
| nanomonkey wrote:
| I see what you did there.
|
| https://www.youtube.com/watch?v=3JdWlSF195Y [They Might be
| Giants - Why does the sun shine?]
| bell-cot wrote:
| 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 wrote:
| 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 wrote:
| 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:)
| RichardCA wrote:
| 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.
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