Big Things in the Universe
About a year ago I wrote a couple of articles (here and here) in response to the discovery of a very large structure (“The Big Ring“) and claims that this structure and others – such as a Giant Arc – were inconsistent with the standard model of cosmology; the work concerned was later submitted as a preprint to arXiv. In my first post on the Big Ring I wrote
To assess the significance of the Big Ring or other structures in a proper scientific fashion, one has to calculate how probable that structure is given a model. We have a standard model that can be used for this purpose, but to simulate very structures is not straightforward because it requires a lot of computing power even to simulate just the mass distribution. In this case one also has to understand how to embed Magnesium absorption too, something which may turn out to trace the mass in a very biased way. Moreover, one has to simulate the observational selection process too, so one is doing a fair comparison between observations and predictions.
Well on today’s arXiv there is a preprint by Sawala et al. with the title aims to assess the significance of structures comparable to the Giant Arc. The title of the paper is The Emperor’s New Arc: gigaparsec patterns abound in a ΛCDM universe from which you can guess the conclusions. The abstract is
Recent discoveries of apparent large-scale features in the structure of the universe, extending over many hundreds of megaparsecs, have been claimed to contradict the large-scale isotropy and homogeneity foundational to the standard (ΛCDM) cosmological model. We explicitly test and refute this conjecture using FLAMINGO-10K, a new and very large cosmological simulation of the growth of structure in a ΛCDM context. Applying the same methods used in the observations, we show that patterns like the “Giant Arc”, supposedly in tension with the standard model, are, in fact, common and expected in a ΛCDM universe. We also show that their reported significant overdensities are an algorithmic artefact and unlikely to reflect any underlying structure.
arXiv:2502.03515
Here’s a picture of a large structure (a “Giant Arc”) taken from a gallery of such objects found in the simulations
I quote from the conclusions:
We hope that our results will dispel the misconception that no inhomogeneity can be found in the standard model Universe beyond some finite size. Instead, any given realisation of the isotropic universe comprises a time- and scale-dependent population of structures from which patterns can be identified on any scale.
I have nothing to add.
#arXiv250203515 #BigRing #Cosmology #GiantArc #LambdaCDM
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