Grand anneau

[Liet Kynes]

Une découverte qui semble intéressante en cosmologie : https://trustmyscience.com/decouvert...eorie-univers/
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[yves95210]

Bonsoir,

un peu de lecture (sur le blog du cosmologiste Peter Coles):

So is this structure “so big it challenges our understanding of the universe”?

Based on the available information it is impossible to say. The large-scale structure of the Universe comprises a complex network of walls and filaments known as the cosmic web which I have written about numerous times on this blog. This structure is so vast and complicated that it is very easy to find strange shapes in it but very hard to determine whether or not they indicate anything other than an over-active imagination.

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.

I have seen no evidence that this has been done in this case. When it is, I’ll comment on the details. I’m not optimistic however, as the description given in the media accounts contains numerous falsehoods. For example, quoting the lead author:

The Cosmological Principle assumes that the part of the universe we can see is viewed as a ‘fair sample’ of what we expect the rest of the universe to be like. We expect matter to be evenly distributed everywhere in space when we view the universe on a large scale, so there should be no noticeable irregularities above a certain size.
https://www.uclan.ac.uk/news/big-ring-in-the-sky

This just isn’t correct. The standard cosmology has fluctuations on all scales. Although the fluctuation amplitude decreases with scale, there is no scale at which the Universe is completely smooth. See the discussion, for example, here. We can see correlations on very large angular scales in the cosmic microwave background which would be absent if the Universe were completely smooth on those scales. The observed structure is about 400 Mpc in size, which does not seem to be to be particularly impressive.

I suspect that the 5.2σ figure mentioned above comes from some sort of comparison between the observed structure and a completely uniform background, in which case it is meaningless.

My main comment on this episode is that I think it’s very poor practice to go hunting headlines when there isn’t even a preprint describing the results. That’s not the sort of thing PhD supervisors should be allowing their PhD students to do. As I have mentioned before on this blog, there is an increasing tendency for university press offices to see themselves entirely as marketing agencies instead of informing and/or educating the public. Press releases about scientific research nowadays rarely make any attempt at accuracy – they are just designed to get the institution concerned into the headlines. In other words, research is just a marketing tool.

In the long run, this kind of media circus, driven by hype rather than science, does nobody any good.

P.S. I was going to joke that ring-like structures can be easily explained by circular reasoning, but decided not to.

[Liet Kynes]

Ah ben pour le coup cela remet les pendules à l'heure

[Juzo]

Bonsoir, à priori trustmyscience (source donnée dans le 1er message) n'est pas un site fiable.
Dans un autre article il affirme par exemple qu'une sonde extraterrestre est probablement arrivée sur Terre, et il y a de nombreuses plaintes sur internet.

[A voir en vidéo sur Futura]

[Liet Kynes]

J'ai mis ce lien car le même article sur futura est un quasi copié collé...

[Juzo]

Bonjour, finalement comment explique-t-on que ces deux structures plutôt exceptionnelles (le grand anneau et le grand arc) aient été découvertes dans des zones aussi proches du ciel ?