Sorry, why can this not be a coincidence? I understand that the universe is smooth across large spaces similar to how a fog is smooth on larger spaces, and coarse on smaller ones.
But even then, given a large universe, why would this be mathematically impossible? If galaxies formed evenly everywhere, couldn't this have happened by coincidence? Which theory is violated here?
Sorry my knowledge is a limited "The great courses Cosmology" course from 2009
It's not a hard violation, just that they are large enough and there are enough of them that you would not expect them to form in a universe that is otherwise described by the cosmological principle.
A random array of points can form a grid, but if you see a grid somewhere the natural assumption is that it wasn't formed by a random process.
Yet any arbitrary sequence (e.g. of bits) has an equal probability of occurring in a random bitstring. 111111 is equally likely as 100110 or 010101. Asked "which one is random?" most people would say the middle one (even people who know better, like me).
Personally I discount the likes of 111111 and 010101 because I know there are artificial processes which produce those sequences and so I discount them on that basis. Yet if you were training a machine to recognize "random" data you'd need to include one sample of each of the possible 2^6 sequences to train it on representative data.
There is another category of random / not random to be considered: self-similar data, where there is similar data in the same area or at different scales. Taken in total, all sequences in this "universe" may be nonetheless randomly distributed.
A taxonomy / review of sequences which we generate inordinately and what phenomena are affected is missing. Self-similar data always deserves a second look, although the cause can be a natural self-organizing principle (e.g. literal snowflakes).
This structure is too large in relation to our observable universe for it to be explainable by a mere coincidence. It's 1.3bn light years in diameter, while the observable universe is 93bn light years in diameter.
> This structure is too large in relation to our observable universe for it to be explainable by a mere coincidence. It's 1.3bn light years in diameter, while the observable universe is 93bn light years in diameter.
It should be possible to calculate them likelihood of distributions with a given degree of apparent structure. Not a given structure, but the degree of variance from a typical random distribution.
Not entirely sure if it applies to this two cases "Big Ring" and "Giant Arc", here, but other large "structures" have been found in the past and this paper "Seeing patterns in noise: gigaparsec-scale "structures" that do not violate homogeneity (2013)[0] addresses the possible randomness:
>In general when using an algorithmic approach to identify clusters of points in a distribution, one must employ some criterion in order to decide whether the results obtained correspond to ‘real’ structures in the Universe, or are merely artefacts of the algorithm. One possible criterion is theoretical: if there is a good reason to believe that the points in the cluster are in fact gravitationally bound, for instance, or if its properties match those of structures that are expected to exist in the real Universe, it may be regarded as real. Alternatively, to assess unusual clusters which do not conform to theoretical expectation, the relevant criterion is whether they are unlikely to have arisen purely from noise.
Since the linkage length used to identify the Huge-LQG is so large, there is no reason I know of to believe that it forms a gravitationally bound structure. Certainly no real structures of such size are expected in the standard cosmology. On the other hand, when using this linkage length the clustering algorithm often finds such extended structures even in pure Poisson noise. It therefore appears that the Huge-LQG fails to satisfy either criterion, and so its interpretation as a ‘structure’ is highly questionable. This conclusion is even more applicable to the other slightly smaller quasar groups whose existence has also been claimed.
Yes, I might be able encompass how a set of galaxies evolve into a ring structure but what process would end up with the galaxies in a coil configuration (viewed end on).
To my mind, the coil structure is the bigger headline, a bit buried in the BBC article.
I’ll try to get and read the AAS paper at the weekend, perhaps that will help me.
"Such large structures should not exist according to one of the guiding principles of astronomy, called the cosmological principle. This states that all matter is spread smoothly across the Universe."
This passage/article doesn't make intuitive sense to me here. What in this physical universe is smoothly spread? Only if you average or look at a massive aggregate level, sure. But at each "zoom level" there should be another non-smooth structure, while things at a smaller level smooth out.
It's more or less fractal all the way up and down.
I don't think this challenges our thinking on the cosmos?
To put it crudely, it's about how it started vs how it's going - initial distribution is expected to have been uniform with small fluctuations that over time were exacerbated by gravity resulting in the Universe we see today. A ring of galaxies implies some unexpected very early structure - like seeing shapes in an explosion.
Maybe the matter is still spread smoothly across the whole cosmos, but the observable universe is tiny enough so that it is not completely smooth and some we see some local artifacts, which would have been smoothed out / insignificant if we saw way more of it inside our viewport.
> While the Big Ring appears as an almost perfect ring on the sky, analysis by Ms Lopez suggests it has more of a coil shape - like a corkscrew - with its face aligned with Earth.
I wonder if there are other structures, but we can’t (easily?) tell because of how they are aligned with Earth.
I don’t find the part, explaining why they think it is a structure and not say an optical illusion? Are all these galaxies of the same-ish distances to us? Are they gravitationally bound together or how should we understand the term “structure” here?
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But even then, given a large universe, why would this be mathematically impossible? If galaxies formed evenly everywhere, couldn't this have happened by coincidence? Which theory is violated here?
Sorry my knowledge is a limited "The great courses Cosmology" course from 2009
A random array of points can form a grid, but if you see a grid somewhere the natural assumption is that it wasn't formed by a random process.
Personally I discount the likes of 111111 and 010101 because I know there are artificial processes which produce those sequences and so I discount them on that basis. Yet if you were training a machine to recognize "random" data you'd need to include one sample of each of the possible 2^6 sequences to train it on representative data.
There is another category of random / not random to be considered: self-similar data, where there is similar data in the same area or at different scales. Taken in total, all sequences in this "universe" may be nonetheless randomly distributed.
A taxonomy / review of sequences which we generate inordinately and what phenomena are affected is missing. Self-similar data always deserves a second look, although the cause can be a natural self-organizing principle (e.g. literal snowflakes).
If random processes can give birth to structure, then one can also argue that maybe this ring is a fluke.
Remember that randomness is not necessarily uniformity
This is also not the only such structure found, some other examples are even larger: https://en.wikipedia.org/wiki/List_of_largest_cosmic_structu...
Why is that important?
>In general when using an algorithmic approach to identify clusters of points in a distribution, one must employ some criterion in order to decide whether the results obtained correspond to ‘real’ structures in the Universe, or are merely artefacts of the algorithm. One possible criterion is theoretical: if there is a good reason to believe that the points in the cluster are in fact gravitationally bound, for instance, or if its properties match those of structures that are expected to exist in the real Universe, it may be regarded as real. Alternatively, to assess unusual clusters which do not conform to theoretical expectation, the relevant criterion is whether they are unlikely to have arisen purely from noise.
Since the linkage length used to identify the Huge-LQG is so large, there is no reason I know of to believe that it forms a gravitationally bound structure. Certainly no real structures of such size are expected in the standard cosmology. On the other hand, when using this linkage length the clustering algorithm often finds such extended structures even in pure Poisson noise. It therefore appears that the Huge-LQG fails to satisfy either criterion, and so its interpretation as a ‘structure’ is highly questionable. This conclusion is even more applicable to the other slightly smaller quasar groups whose existence has also been claimed.
[0]https://academic.oup.com/mnras/article/434/1/398/997865
This is seen as a ring, but likely a coil aligned with our viewpoint.
I don't know much about astronomy, but that fact changed how I played with the idea in my head.
To my mind, the coil structure is the bigger headline, a bit buried in the BBC article.
I’ll try to get and read the AAS paper at the weekend, perhaps that will help me.
Something that has both a linear and an angular momentum or spin while pushing things (galaxies in this case) away?
I’m not a physicist in any way, so I might use terms incorrectly, but I hope the point got across.
This passage/article doesn't make intuitive sense to me here. What in this physical universe is smoothly spread? Only if you average or look at a massive aggregate level, sure. But at each "zoom level" there should be another non-smooth structure, while things at a smaller level smooth out.
It's more or less fractal all the way up and down.
I don't think this challenges our thinking on the cosmos?
That would still be a valuable find, though.
I wonder if there are other structures, but we can’t (easily?) tell because of how they are aligned with Earth.