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I am highly curious about two questions that a physicist or a cosmologist could maybe answer... 1) What do we actually know about these "structures", and funda

I am highly curious about two questions that a physicist or a cosmologist could maybe answer... 1) What do we actually know about these "structures", and fundamentally how certain are we that they have any consequence whatsoever to our understanding of the universe? Is it possible that the patterns we notice are just us being humans noticing patterns in randomly generated white noise? 2) Could there be emergent behaviours at the super-astronomical scale where just like electrons and protons and other elementary particles combine to all sorts of emergent higher order behaviour in atoms and elements, could there be similar outcomes at the multi-galaxy-cluster scale that would be impossible to observe at the human scale?

root_axis 6y ago
Doesn't really seem like 2 could ever be ruled out in theory.
gnramires 6y ago
Not a physicist, but as far as 2 goes, galaxies are all atoms interacting after all. Filaments themselves are emergent structures formed from the interaction of large amounts of mass-energy at the largest scales. Forces have different ranges (scaling behavior) thus the behavior of matter changes as you change scales. At the largest scales it is mostly purely gravitational to my knowledge (plus dark energy which is also modeled gravitationally). When you play billiards you don't expect them to gravitate toward each other! If they were on the scale of planets though, you might (it depends on how you scale their velocities). Or if you waited extremely long times, and were not under the influence of Earth's gravity you also might notice in billiards.
- centimeter 6y ago
  Magnetic interaction is also relevant at large scales. Strange to think that magnetism has weaker asymptotics than electricity (only being found in the form of dipoles) and yet it can form much larger structures.
- bmitc 6y ago
  > as far as 2 goes, galaxies are all atoms interacting after all. Although, galaxies aren't just made of things only made out of atoms. Most of the important stuff is not simply composed of atoms: black holes, stars, neutron stars, pulsars, dark matter, etc.
- KhoomeiK 6y ago
  > At the largest scales it is mostly purely gravitational to my knowledge (plus dark energy which is also modeled gravitationally). I think what OP might've been alluding to is the idea that phenomena like dark energy could have a more elegant explanation that is the result of emergent behavior at large scales. Just like magnetism was originally seen almost like magic, but it was later realized that it's simply an emergent property of the electric force i.e. electromagnetism.
  - deanCommie 6y ago
    Exactly, thanks for clarifying that better than I did! i wonder if there is a possible way to measure that. It does seem not crazy that if the laws of physics are completely different at nanoscopic scales, they would also be different at gigascopic ones?
DiogenesKynikos 6y ago
1. I don't think there's much of a consequence of this particular "structure" for our understanding of the Universe. The theory that describes large-scale structure in the Universe is fairly well understood, and discovering this particular structure doesn't change the theory, as far as I can tell. 2. What happens at very large scales is actually quite simple, from a physical and mathematical point of view. That's because as you zoom out, the Universe eventually becomes smooth and homogeneous. You can model it as a constant-density fluid with slight density perturbations. General Relativity then gives you a set of equations to work with, which describe both how spacetime evolves and how the density perturbations grow over time. Things only get complicated once the perturbations grow large enough that the equations become non-linear. This happens on the scale of galaxies and galaxy clusters, but on the largest scales, things are still linear. Then, you can use numerical simulations to understand the formation of galaxies and galaxy clusters (these simulations do a really good job of reproducing what we see in the real Universe), or you can use heuristic arguments about how over-densities collapse (there are some heuristic arguments that get you pretty close to what the numerical simulations predict), or you can use perturbation theory to try to analyze the non-linear regime (this involves some pretty hard-core mathematical analysis, and it doesn't get you as accurate an answer as the numerical simulations, but it might help you understand what's going on). TL;DR: The title of this article is very click-baity. A lot of people will read it and think that this discovery overturns what we previously knew about cosmology. It doesn't, as far as I can tell. Cosmology predicts that structures like this should exist. Since the initial conditions of the Universe were random, cosmology doesn't predict where we'll find these structures. 1. A visualization of the formation of a galaxy cluster, from a numerical simulation called Illustris: The Next Generation: https://youtu.be/Rg12ub0PbeA https://youtu.be/Rg12ub0PbeA
- deanCommie 6y ago
  Thanks for that explanation, I have a dumb follow up. How can we possibly measure this at the scales you're talking about? I understand we can take a look at the scale of let's say background radiation across multiple galaxies, but how can we really infer anything about the universe at all other than to know that this is how things work at this exact moment in human-scale time?

root_axis 6y ago

Doesn't really seem like 2 could ever be ruled out in theory.

gnramires 6y ago

Not a physicist, but as far as 2 goes, galaxies are all atoms interacting after all. Filaments themselves are emergent structures formed from the interaction of large amounts of mass-energy at the largest scales. Forces have different ranges (scaling behavior) thus the behavior of matter changes as you change scales. At the largest scales it is mostly purely gravitational to my knowledge (plus dark energy which is also modeled gravitationally). When you play billiards you don't expect them to gravitate toward each other! If they were on the scale of planets though, you might (it depends on how you scale their velocities). Or if you waited extremely long times, and were not under the influence of Earth's gravity you also might notice in billiards.

centimeter 6y ago
Magnetic interaction is also relevant at large scales. Strange to think that magnetism has weaker asymptotics than electricity (only being found in the form of dipoles) and yet it can form much larger structures.
bmitc 6y ago
> as far as 2 goes, galaxies are all atoms interacting after all. Although, galaxies aren't just made of things only made out of atoms. Most of the important stuff is not simply composed of atoms: black holes, stars, neutron stars, pulsars, dark matter, etc.
KhoomeiK 6y ago
> At the largest scales it is mostly purely gravitational to my knowledge (plus dark energy which is also modeled gravitationally). I think what OP might've been alluding to is the idea that phenomena like dark energy could have a more elegant explanation that is the result of emergent behavior at large scales. Just like magnetism was originally seen almost like magic, but it was later realized that it's simply an emergent property of the electric force i.e. electromagnetism.
- deanCommie 6y ago
  Exactly, thanks for clarifying that better than I did! i wonder if there is a possible way to measure that. It does seem not crazy that if the laws of physics are completely different at nanoscopic scales, they would also be different at gigascopic ones?

DiogenesKynikos 6y ago

1. I don't think there's much of a consequence of this particular "structure" for our understanding of the Universe. The theory that describes large-scale structure in the Universe is fairly well understood, and discovering this particular structure doesn't change the theory, as far as I can tell. 2. What happens at very large scales is actually quite simple, from a physical and mathematical point of view. That's because as you zoom out, the Universe eventually becomes smooth and homogeneous. You can model it as a constant-density fluid with slight density perturbations. General Relativity then gives you a set of equations to work with, which describe both how spacetime evolves and how the density perturbations grow over time. Things only get complicated once the perturbations grow large enough that the equations become non-linear. This happens on the scale of galaxies and galaxy clusters, but on the largest scales, things are still linear. Then, you can use numerical simulations to understand the formation of galaxies and galaxy clusters (these simulations do a really good job of reproducing what we see in the real Universe), or you can use heuristic arguments about how over-densities collapse (there are some heuristic arguments that get you pretty close to what the numerical simulations predict), or you can use perturbation theory to try to analyze the non-linear regime (this involves some pretty hard-core mathematical analysis, and it doesn't get you as accurate an answer as the numerical simulations, but it might help you understand what's going on). TL;DR: The title of this article is very click-baity. A lot of people will read it and think that this discovery overturns what we previously knew about cosmology. It doesn't, as far as I can tell. Cosmology predicts that structures like this should exist. Since the initial conditions of the Universe were random, cosmology doesn't predict where we'll find these structures. 1. A visualization of the formation of a galaxy cluster, from a numerical simulation called Illustris: The Next Generation: https://youtu.be/Rg12ub0PbeA https://youtu.be/Rg12ub0PbeA

deanCommie 6y ago
Thanks for that explanation, I have a dumb follow up. How can we possibly measure this at the scales you're talking about? I understand we can take a look at the scale of let's say background radiation across multiple galaxies, but how can we really infer anything about the universe at all other than to know that this is how things work at this exact moment in human-scale time?