Comment by thicktarget
19 days ago
Let me start by saying there are a lot of false claims in the dark matter section. It's also filled with self contradiction, announcing that DM as wrong, and later pronouncing LCDM as unfalsifiable. The pillars of modem cosmology are the ability to quantitatively describe and predict large-scale structure, the expansion history of the universe, the CMB and primordial nucleosynthesis. Can this "model" calculate any of those things? No. What the author has here is some ideas, not a model.
To demonstrate you can even reproduce the Cosmic Web you have to actually run some calculations, or simulations. How do you know AGN bubbles produce a universe that looks anything like ours? The author dismisses simulations as "not science", while paradoxically using them as the only representation of the cosmic web in the article. These simulations have a lot of value, they demonstrate that standard cosmology and normal gravity has no problem forming voids and filaments. These simulations have been compared to countless new observations, which this model cannot because it's purely qualitative. The article says these simulations are worthless because they don't work from first principles, this is a practical limitation that you cannot simulate galaxies down to the resolution of atoms on any existing computer. You have to make some simplifications. The structure of the cosmic web is seen in all of them, even going back to very early simulations, it doesn't depend on these assumptions.
And at the end of the article we go back to the problem of dark matter, and find out the author has no explanation for rotation curves or other classical tests of DM. So despite bashing DM cosmology, this model explains none of the pillars of evidence for dark matter. At some point in developing an idea like this you need to actually start applying physics, either with calculations or simulations. Every new hypothesis is perfect before it has been subjected to rigor and analysis.
I agree with most of what you've said here, particularly the following line which I'm copying for emphasis because I think it's incredibly important.
> These simulations have a lot of value, they demonstrate that standard cosmology and normal gravity has no problem forming voids and filaments.
That being said, I think the author intends for this article to be more of a call to action than an actual result. Simulations aren't cheap, somebody needs to actually do the work. The point that there aren't any simulations without dark matter is an important one too.
One can do simple simulations on a laptop which show the cosmic web. It's not really an excuse for not having tried. There are lots of claims in the article which need to be justified, and in science that comes before making big claims.
https://alvinng4.github.io/grav_sim/examples/cosmic_structur...
These simulations take their simple initial conditions from the Cosmic Microwave Background fluctuations, but models without dark matter fail to match the observed CMB. There are no major baryon-only simulations because cosmology doesn't work without DM, and you have nothing to start from. You need a quantitative model which works on some level to even begin, people have tried with modified gravity models.
We need a model that includes electromagnetism. The author isn't the only one making this claim. When we do magnetohydrodynamic cosmological sims we consistently find surprising effects. The recent simulation showing that black hole accretion disks are supported by magnetism comes to mind.[0][1]
Apologies, I know this is typically considered bad form, but have you gotten to the following section in the article?[2] It appears to directly contradict your claims.
> MOND’s also been around since the early 1980s, but, in 2021, it finally developed a model – the Aether-Scalar-Tensor framework, or AeST – which ALSO maps perfectly onto the acoustic peaks revealed by WMAP and Planck. (It does it by proposing a new vector field and scalar field that duplicate the effects of Cold Dark Matter in the early universe...
[0] https://astro.theoj.org/article/93065-an-analytic-model-for-...
[1] https://www.caltech.edu/about/news/cosmic-simulation-reveals...
[2] https://theeggandtherock.com/i/158515951/more-matter-or-less...
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I think the point is that for filaments to form in simulations you have to assume dark matter to be so abundant that it stops explaining other things that are explained with it. Basically you can adjust dark matter parameters to explain everything but you can't find a single set of parameter values to explain all the things at the same time.
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