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> Woops. Yes, galaxies. Too late to edit. Not even galaxies, but massive galaxy clusters. The spatial smoothing used for the ring image is a 2D gaussian with a

> Woops. Yes, galaxies. Too late to edit. Not even galaxies, but massive galaxy clusters. The spatial smoothing used for the ring image is a 2D gaussian with an equivalent width of 11 Mpc, or 37 million light years, big enough to contain all the 2000 galaxies in the nearby Virgo cluster with room to spare. That's for each point in the ring (and that's why they all look so nice and round. These astronomers are playing a statistical game where a pixel combines information from trillions of stars) It's called the Big Ring for a reason. Our own Laniakea supercluster [1], whose dimensions are bigger than anyone imagined up to a few years ago, can be tiled inside the ring several times over. At that spatial scale, the Universe is supposed to be homogeneous. We do not have plausible mechanisms to generate structures on such a massive scale. Regarding your analogy with a constellation, yes you can always draw arbitrary squares and triangles among bright stars. But if you had 20+ stars arranged in a circle like that ring, no one would think it was a chance projection, you would demand a physical explanation. We do in fact have such a ring around us: the Gould Belt [2], made of young stars all around the Sun. It is difficult to recognize precisely because we are inside it, and its stars are spread all around the sky. And, of course, some kind of physical explanation is invoked for this ring as well. Moreover we do know it's an actual ring, and not some chance alignment, because we can derive the distance of each point from its redshift, and it turns out that they are all quite similar. The authors spend quite a few pages describing the 3D ring structure, showing that it's a ring only when seen from our direction, and how it would appear like an arc or a strange shape from other viewpoints. It would still be a kind of overdense structure, but maybe more difficult to recognize. BTW the mechanism used to detect the ring is quite clever: it's not a sky image, but rather an absorption map: thousands of background quasars provide a sort of uniform illumination, and they look where this light is removed by clumps of matter. [1] https://en.wikipedia.org/wiki/Laniakea_Supercluster https://en.wikipedia.org/wiki/Laniakea_Supercluster [2] https://en.wikipedia.org/wiki/Gould_Belt https://en.wikipedia.org/wiki/Gould_Belt

andyjohnson0 2y ago
Thank you for taking the time to write such an informative response.
deleted 2y ago
[deleted]
Retric 2y ago
> We do not have plausible mechanisms to generate structures on such a massive scale. Actual structure no. But, random chance can make things look like a structure on this scale. > But if you had 20+ stars arranged in a circle like that ring, no one would think it was a chance projection, you would demand a physical explanation. I would generally assume it to be random. In galaxies stars move around far to much for any structure from their initial formation to remain for long, and forming a ring long after creation would just be happenstance.
- pests 2y ago
  > I would generally assume it to be random. But its not, it has structure - it looks like ring or arc. The universe should be homologous at this scale.
  - Retric 2y ago
    Every formation of galaxies has structure. Random processes can appear to have meaningful structure, but that’s just because we value some outcomes more than others. > The universe should be homologous at this scale. That doesn’t mean we’re going to perceive it as homologous. A true random number generator spitting out 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 would be freaky as fuck to see, but that doesn’t make it non random.
    - jakeinspace 2y ago
      This is true, but at this scale, aren’t we looking at a moderate portion of the visible universe? This is hundreds of thousands or millions of galaxies appearing with some strong correlation, I believe. There are only a few trillion galaxies in the observable universe, so it’s not like we have 10^20 chances to observe random chance correlations like this. I’m just talking without actually having done a close reading or done the statistics for myself, so I could be quite wrong.
      - Retric 2y ago
        Check out the preprint: https://arxiv.org/pdf/2402.07591 https://arxiv.org/pdf/2402.07591 It’s less impressive when looking at the background data than how it’s described.
btilly 2y ago
Actually I do have a plausible mechanism whose numbers have been sanity checked by a couple of cosmologists, but has never been published. Here's the idea. The expansion of the universe is currently accelerating. If this continues indefinitely, we get the https://en.wikipedia.org/wiki/Big_Rip https://en.wikipedia.org/wiki/Big_Rip model. What happens if the Big Rip proceeds to the point where a lot of https://en.wikipedia.org/wiki/Vacuum_energy https://en.wikipedia.org/wiki/Vacuum_energy gets released, and that release stops the Rip by creating the next Big Bang? This could form a cycle since the next Bang creates cosmos that in turn will Rip. It doesn't sound entirely crazy to me. The Casimir effect shows that you should release vacuum energy when you constrain the volume that a particularly bit of space can interact with. The incredible expansion of a Rip should constrain such interactions. So a large release of vacuum energy seems expected. And who knows how releasing vacuum energy interacts with the acceleration of the expansion of the universe? Let's do a back of the envelope estimate. Theory estimates vacuum energy at something like 10^113 joules per cubic meter of vacuum energy. For comparison the visible universe is estimated at 10^53 kg. Using Einstein's E = mc^2, that's around 10^70 joules. Current cosmological models say that at the hottest part of the Big Bang, the universe must have already been larger than a cubic meter. Yes, there is a lot of energy not in the form of visible matter. Even so, there's a lot of room for a release of vacuum energy to explain the energy density needed at the beginning of a Big Bang. We at least pass the most basic sanity check. This would offer interesting answers to some key cosmological questions. Current Big Bang models struggle with how a large volume started out very uniform. Inflation has been proposed for this, but it has some problems. But in this model, extreme uniformity over a large volume is predicted. If you add in quantum fluctuations starting the vacuum release, that have spread out before we go from Rip to Bang, then you can also explain arbitrarily large structures in the universe. This also explains the arrow of time. How could we start off with such low entropy when entropy is always increasing? Well as the universe expands, entropy increases. But volume increases faster. We wind up with a giant universe filled with very low entropy/volume. When a small piece of that forms a new Big Bang, it again starts with very low entropy. Unfortunately, this involves an insane lack of conservation of energy. But GR provides no easy way to even state what conservation of energy means. At least not outside of limited classes of models. Which this is not one of. So the idea of energy not being conserved at cosmological scales is at least not entirely unprecedented by current theory.
stouset 2y ago
> But if you had 20+ stars arranged in a circle like that ring, no one would think it was a chance projection… Of course we would? This is absolutely backwards. A random plot of billions of points will have all sorts of coincidental shapes and clusterings. A uniform field might look more random but would actually demand explanation, as lacking those coincidental clusterings is strong evidence for structure. And as I understand the topic, the scales involved preclude those galaxies physically interacting and being able to form structure. So they should appear randomly distributed. Edit: To be clear I’m assuming my own ignorance here. I presume there is a reason this is significant, I just don’t understand it. But arguments like yours aren’t convincing to me because we should expect to see random structure, the same way a series of a billion coin flips is likely to have a giant run of alternating heads and tails.
venusenvy47 2y ago
I'm interested in the part about using quasars to illuminate the galaxies. Are quasars so common that they provide a uniform background to the whole universe? I always thought they were fairly sporadically distributed.

andyjohnson0 2y ago

Thank you for taking the time to write such an informative response.

deleted 2y ago

[deleted]

Retric 2y ago

> We do not have plausible mechanisms to generate structures on such a massive scale. Actual structure no. But, random chance can make things look like a structure on this scale. > But if you had 20+ stars arranged in a circle like that ring, no one would think it was a chance projection, you would demand a physical explanation. I would generally assume it to be random. In galaxies stars move around far to much for any structure from their initial formation to remain for long, and forming a ring long after creation would just be happenstance.

pests 2y ago
> I would generally assume it to be random. But its not, it has structure - it looks like ring or arc. The universe should be homologous at this scale.
- Retric 2y ago
  Every formation of galaxies has structure. Random processes can appear to have meaningful structure, but that’s just because we value some outcomes more than others. > The universe should be homologous at this scale. That doesn’t mean we’re going to perceive it as homologous. A true random number generator spitting out 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 would be freaky as fuck to see, but that doesn’t make it non random.
  - jakeinspace 2y ago
    This is true, but at this scale, aren’t we looking at a moderate portion of the visible universe? This is hundreds of thousands or millions of galaxies appearing with some strong correlation, I believe. There are only a few trillion galaxies in the observable universe, so it’s not like we have 10^20 chances to observe random chance correlations like this. I’m just talking without actually having done a close reading or done the statistics for myself, so I could be quite wrong.
    - Retric 2y ago
      Check out the preprint: https://arxiv.org/pdf/2402.07591 https://arxiv.org/pdf/2402.07591 It’s less impressive when looking at the background data than how it’s described.

btilly 2y ago

Actually I do have a plausible mechanism whose numbers have been sanity checked by a couple of cosmologists, but has never been published. Here's the idea. The expansion of the universe is currently accelerating. If this continues indefinitely, we get the https://en.wikipedia.org/wiki/Big_Rip https://en.wikipedia.org/wiki/Big_Rip model. What happens if the Big Rip proceeds to the point where a lot of https://en.wikipedia.org/wiki/Vacuum_energy https://en.wikipedia.org/wiki/Vacuum_energy gets released, and that release stops the Rip by creating the next Big Bang? This could form a cycle since the next Bang creates cosmos that in turn will Rip. It doesn't sound entirely crazy to me. The Casimir effect shows that you should release vacuum energy when you constrain the volume that a particularly bit of space can interact with. The incredible expansion of a Rip should constrain such interactions. So a large release of vacuum energy seems expected. And who knows how releasing vacuum energy interacts with the acceleration of the expansion of the universe? Let's do a back of the envelope estimate. Theory estimates vacuum energy at something like 10^113 joules per cubic meter of vacuum energy. For comparison the visible universe is estimated at 10^53 kg. Using Einstein's E = mc^2, that's around 10^70 joules. Current cosmological models say that at the hottest part of the Big Bang, the universe must have already been larger than a cubic meter. Yes, there is a lot of energy not in the form of visible matter. Even so, there's a lot of room for a release of vacuum energy to explain the energy density needed at the beginning of a Big Bang. We at least pass the most basic sanity check. This would offer interesting answers to some key cosmological questions. Current Big Bang models struggle with how a large volume started out very uniform. Inflation has been proposed for this, but it has some problems. But in this model, extreme uniformity over a large volume is predicted. If you add in quantum fluctuations starting the vacuum release, that have spread out before we go from Rip to Bang, then you can also explain arbitrarily large structures in the universe. This also explains the arrow of time. How could we start off with such low entropy when entropy is always increasing? Well as the universe expands, entropy increases. But volume increases faster. We wind up with a giant universe filled with very low entropy/volume. When a small piece of that forms a new Big Bang, it again starts with very low entropy. Unfortunately, this involves an insane lack of conservation of energy. But GR provides no easy way to even state what conservation of energy means. At least not outside of limited classes of models. Which this is not one of. So the idea of energy not being conserved at cosmological scales is at least not entirely unprecedented by current theory.

stouset 2y ago

> But if you had 20+ stars arranged in a circle like that ring, no one would think it was a chance projection… Of course we would? This is absolutely backwards. A random plot of billions of points will have all sorts of coincidental shapes and clusterings. A uniform field might look more random but would actually demand explanation, as lacking those coincidental clusterings is strong evidence for structure. And as I understand the topic, the scales involved preclude those galaxies physically interacting and being able to form structure. So they should appear randomly distributed. Edit: To be clear I’m assuming my own ignorance here. I presume there is a reason this is significant, I just don’t understand it. But arguments like yours aren’t convincing to me because we should expect to see random structure, the same way a series of a billion coin flips is likely to have a giant run of alternating heads and tails.

venusenvy47 2y ago

I'm interested in the part about using quasars to illuminate the galaxies. Are quasars so common that they provide a uniform background to the whole universe? I always thought they were fairly sporadically distributed.