The Battle Between MOND and DM

[BeAChooser]

Here’s a quite fair and interesting article on MOND ...

https://physicsworld.com/a/cosmic-comba ... d-gravity/

The picture that dark matter forms is neat, but not quite neat enough for a small community of physicists and astronomers who have shunned dark-matter cosmology and adopted MOND instead. In fact, they have abundant evidence for their case. In 2016 Stacy McGaugh of Case Western Reserve University measured the rotation curves of 153 galaxies (Phys. Rev. Lett. 117 201101) and found, with an unprecedented accuracy, that their rotation curves are explained by MOND, without the need to resort to a halo of dark matter around each galaxy.

… snip …

“I would assert that MOND explains these things better than dark matter, and the reason for that is its predictive power,” says McGaugh – a former dark-matter researcher who is now a MOND advocate, following an epiphany that saw him switching sides. He is referring to the fact that if you know the visible mass (all its stars and gases) of a galaxy, then by applying MOND you can calculate what the rotation velocities are going to be. In the dark-matter paradigm, you can’t predict the velocities based on the presence of dark matter. Instead, you have to measure the galaxy’s rotation curve to infer how much dark matter is present. McGaugh argues that’s circular reasoning, and not proof of dark matter.

… snip …

MOND excels for individual galaxies, but depending on whom you speak to, it’s perhaps not doing so well in other environments. And one failure in particular has already turned one of MOND’s staunchest supporters against the theory.

Then the article goes on to explore data and MOND at other scales. For example …

An ideal laboratory in which to test MOND is one where dark matter would not be expected to be present in any great amounts, meaning any gravitational anomalies should just come from the laws of gravity themselves. Wide binary star systems are one such environment consisting of pairs of stars that are 500 AU or more apart (where one astronomical unit or AU is the mean distance between Earth and the Sun). At such huge separations, the gravitational field felt by each star is weak.

Thanks to the European Space Agency’s Gaia astrometric space mission, teams of MOND researchers have now been able to measure the motions of wide binaries in search of evidence of MOND. The results have been controversial and conflicting, in terms of the survival of MOND as a valid theory.

One team, led by Kyu-Hyun Chae of Sejong University in Seoul, carried out an exhaustive analysis of 26,500 wide binaries and found orbital motions that matched the predictions of MOND (ApJ 952 128). This was supported by earlier work from Xavier Hernandez of the Universidad Nacional Autónoma de México, who hailed how “exciting” Chae’s result were. But not everyone is convinced.

At the University of St Andrews in the UK, Indranil Banik was working on his own six-year project to measure MOND in wide binaries. … snip … “I obviously expected the MOND scenario to work,” he says. “So it was indeed a very major surprise when it didn’t.”

In a paper published in late 2023 Banik found no deviation from standard Newtonian gravity at all (Monthly Notices of the Royal Astronomical Society 10.1093/mnras/stad3393). The results were such a hammer blow to him that it shook Banik’s world, and he publicly declared that MOND was wrong – which caught him some flak.

It look like the verdict is out, though MOND seems to have 2 to 1 advantage.

At scales below a light year, however ...

It’s not just wide binaries where Banik sees MOND failing. He also cites the case of our own solar system. One of the central tenets of MOND is the phenomenon of the “external field effect”, whereby the overall gravitational field of the Milky Way galaxy is able to imprint itself on smaller systems, such as our solar system. We should see this imprint, particularly on the orbits of the outer planets. Searching for this effect through radio-tracking data from NASA’s Cassini spacecraft, which orbited Saturn between 2004 and 2017, has found no evidence for the external field effect on Saturn’s orbit.

Yet, at the scale of clusters, MOND looks to be in the running, at least as good as ACDM …

“It was claimed that the Bullet Cluster confirmed the existence of dark matter, which has been used to argue strongly against MOND,” says Pavel Kroupa, an astrophysicist at the University of Bonn. “Well, it turns out that the situation is exactly the opposite.”

… snip …

“Galaxy cluster collisions are in complete disagreement with ΛCDM while being in rather natural agreement with MOND,” says Kroupa. Despite Kroupa’s enthusiasm, McGaugh isn’t so sure. In fact, he thinks galaxy clusters are a real problem for both ΛCDM and MOND.

“It’s a mess,” he concedes. “For dark matter, the collision velocities are much too high. Dark-matter people have gone back and forth, arguing are the velocities too fast, or not? For MOND, it is that galaxy clusters show a mass discrepancy even after you apply MOND. Clusters concern me because I just don’t see a nice way out of that.”

But as the article points out ...

Clusters and wide binaries can be debated ad infinitum until one side or the other admits defeat. But perhaps the most serious criticism levelled at MOND has been its outright lack of a workable cosmological model. It’s all well and good trying to replace dark matter with modified gravity in galaxies, but for the theory to ultimately be successful it must explain everything that dark matter can and more.

Sorry but that’s the same criticism leveled at Plasma Cosmology ... that it doesn't have a workable model. Of course that criticism simply ignores all the *surprises* that the dark matter modelers have encountered in the development of their theory over five decades. They didn’t start out with a completely workable model either and they've modified it countless times since then. Plus, it’s taken MASSIVE funding to get to where they are now … and they still have no real proof of dark matter's/dark energy's existence and they're finding more *surprises* nearly every day. If MOND (or plasma cosmology) had been given the same funding they've been given, perhaps there would be a workable model and no more surprises right now. Perhaps the mainstream's FAITH in the DM/DE gnome has lost human civilization a great opportunity?

Continuing from the article …

This means it [MOND] needs to be a rival to ΛCDM in explaining what we see in the cosmic microwave background (CMB) – the primordial microwave radiation that fills the universe.

… snip …

MOND was devised to explain galaxy rotation curves by riffing on Newton, not Einstein. It took another 20 years for Bekenstein to come up with a relativistic model of MOND that could be applied to modern cosmology. Called Tensor–Vector–Scalar (TeVeS) gravity, it proved unpopular, struggling to explain the size of the third acoustic peak in the anisotropies that in the standard model is attributable to dark matter, as well as limitations in modelling gravitational lensing and gravitational waves.

Many people thought that the problem of a relativistic model of MOND was so difficult that it wasn’t possible. … snip … But in 2021 Constantinos Skordis and Tom Złośnik [of the Czech Academy of Sciences] created a MOND-inspired model that matches the Planck data just as well as dark-matter models. … snip … The Skordis and Złośnik model is not perfect. Like TeVeS, it struggles to explain the amount of gravitational lensing we observe in the universe.

… snip …

Baker echoes these concerns. “While it was a good step forward for MOND to be able to do that,” he says, “I don’t think it was enough to bring MOND back into the mainstream. The reason being [Skordis and Złośnik] have added a lot of extra fields to it, a lot of bells and whistles, and it really loses elegance. It works with the CMB, but it seems very unnatural.”

As if Dark Matter and Dark Energy seem natural.

And then the author makes another key observation that could be applied to plasma cosmology as well …

Perhaps we’re putting undue weight onto the model’s shoulders. It could be viewed as just a beginning, a proof of concept. “Whether this is the final theory, or even down the right path, I don’t know,” says McGaugh. “But people have been saying that it can’t be done, and what Skordis and Złośnik have shown is that it can be done, and that’s an important step forward.”

MOND continues to fascinate, frustrate and foster disdain from dark matter’s disciples. There’s still a long way to go for the scientific community to consider it a heavyweight rival to ΛCDM, and it’s certainly hampered by having relatively few people working on it, meaning that progress is slow.

If MOND has fewer people working on it, Plasma Cosmology has even fewer ... with far less funding. Just saying ...

I look forward to seeing part 2 of this 3 part series which will explore DM’s success and challenges. I'll post it here if I see it

By the way, it's too bad the author, Keith Cooper, can't be induced to write an article on PC/EU. He might do a much better job than that flake, Sarah Scoles, who came to the forum a few years ago asking for information then wrote nothing but a biased hit piece.