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The MOND alternative to dark matter is wrong

What next for cosmology?

21st November 2023
| Research fellow in Galaxy Dynamics, University of St Andrews, investigating modified theories of gravity and the need for postulating the existence of dark matter.
2,003 words
Read time: approx. 10 mins

Dark matter is a central but contentious part of the dominant model of cosmology. It has never been observed directly and is seen as an arbitrary add-on to Einstein's theory of gravity, just to make the data fit. MOND has for a long time been considered the most credible alternative theory of gravity, doing away with the need to postulate dark matter. But a recent study lead by Dr Indranil Banik, a past supporter of MOND, demonstrates that the theory is in fact wrong. The search for a more credible alternative continues.

 

According to the dominant paradigm in cosmology, the majority of the stuff that makes up our universe is not the ordinary matter we see around us, but something called dark matter. According to this standard model of cosmology, dark matter has a gravitational effect at large scales in the universe, effects that are not observable at smaller scales like our Solar System. The only problem is, no one has ever observed dark matter directly – its existence is only postulated by its supposed gravitational effect at large scales. I have been a critic of the dark matter hypothesis, and in the past have expressed an interest in its main alternative –Milgromian dynamics, or MOND for short. MOND has been heralded as making better sense of the data astronomers gather, and as having made accurate predictions, whereas dark matter theory has to retrospectively adjust to make sense of new data. But according to a recent paper I published along with colleagues, I show that MOND is in fact wrong. That leaves cosmology without an accurate or complete theory of gravity, opening up the prospect for a paradigm shift in our understanding of gravity.

Indranil Banik
21st November 2023

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Bud Rapanault 26 November 2023

Quite apart from the central but still open question regarding the efficacy of MOND with respect to wide binaries, the author makes numerous dubious assertions regarding cosmology that are not supported by their preferred conclusion to that open question. In particular MOND is repeatedly contrasted with ΛCDM, the standard model of cosmology, and the author maintains two distinct falsification standards, one for MOND and quite another for ΛCDM and for the standard gravitational models of Newtonian Dynamics and General Relativity:

"Correct predictions do not confirm a theory, but a clear falsification means we can be sure that it is wrong, at least as presently formulated. This is definitely the case for MOND, which completely fails when tested on even slightly smaller or larger scales than those for which it was designed. ΛCDM also fails, but it can be extended much further from the infant Universe where its parameters are usually calibrated."

Comparing and contrasting MOND and ΛCDM represents a categorical error; since MOND is a gravitational model and ΛCDM is a cosmological model comparing them doesn't produce much useful insight. It's like comparing bicycles to rocket ships - you can do it but so what? MOND should be compared to the two standard gravitational models - particularly since MOND represents a direct modification of Newtonian Dynamics.

The author criticizes MOND correctly when saying it "completely fails when tested on even slightly smaller or larger scales than those for which it was designed." The scale for which it was designed was of course that of galaxies. What the author does not note is that the exact same criticism can be leveled at Newtonian Dynamics and General Relativity - they only work on the scale for which they were designed - that of the solar system.

So how is it then that MOND is falsified but ND and GR are not? I guess you can call it a kind of mathematicist miracle otherwise known as ΛCDM. Λ stands for dark energy while CDM represents cold dark matter both of which are components of the standard model that bears their name, but neither of which are found in physical reality - their supposed existence has been repeatedly falsified by all attempts to directly detect them. The falsification standard for the standard model is in essence non-existent.

The standard model requires their existence so Λ & CDM must exist because ND & GR are universal laws - says so right there in the textbooks. Circular reasoning cannot get any tighter or more illogical. Whatever the outcome of the MOND - wide binary tests controversy the entire matter is a tempest in a teapot. Modern cosmology is an unscientific mess. Until it reverts to being a science, so it will remain. As with the situation in the time of Copernicus and Kepler when the only way forward was to discard the Geocentric model, the only way to return cosmology to a scientific endeavor is to discard the bankrupt Expanding Universe model that has distorted cosmology into a caricature of itself. The tenor of this article gives little hope that the necessary adjustment will be arriving any time soon.

Steve Maricic 23 November 2023

From the article: "As long as dark matter is not directly detected, we should keep an open mind to any completely new ideas about cosmology..."
OK, here's one (from a non-scientist):

Gravitational waves emanating from every atom sometimes add to each other, and sometimes subtract from each other -- just as all types of waves do. The result is that the attractive force of gravity sometimes increases and sometimes decreases.

Inside each galaxy, the tendency is for gravity to increase; outside of each galaxy, the tendency is for gravity to decrease.

There is no dark matter holding galaxies together; there is no dark energy forcing each galaxy away from its neighbors.

If the above is true, how does each atom keep pumping out gravitational energy? Well, all atoms take in electromagnetic radiation from the stars. Possibly, each atom converts some small part of that "positive" electromagnetic energy into the "negative" energy of gravitational waves. Analogies don't always work, and this one might not, but I think of waves coming into a beach, and undertow pulling one swimmer out -- they call that "rip current"; but fifty yards to the north, a return current pulls another swimmer in.