According to our review, it should be abandoned in favour of a new theory of gravity.

Using Newton's laws of physics, we can simulate the motions of the planets in the Solar System quite precisely. But in the early 1970s, researchers discovered that this was incorrect because stars in disc galaxies, which are far from the gravitational pull of all the matter at their centres, were moving much more quickly than predicted by Newton's theory.

This led physicists to postulate that extra gravitational attraction from "dark matter," an invisible substance, was forcing the stars to accelerate. This idea has now gained enormous popularity. However, in a recent analysis, my coworkers and I argue that the Milgromian dynamics or Mond, an alternative theory of gravity put forth by Israeli physicist Mordehai Milgrom in 1982 and needing no invisible matter, provides a much better explanation for evidence at a wide range of scales.

Mond's major hypothesis is that gravity begins to behave differently from Newtonian physics when it becomes extremely weak, as happens at the edge of galaxies. This explains why stars, planets, and gas near the periphery of over 150 galaxies rotate more quickly than would be predicted from just their apparent mass. But Mond not only explains such rotation curves, it frequently predicts them as well.

Scientists have suggested that Mond is preferable than the conventional cosmological model, which holds that there is more dark matter than visible matter in the universe, because to his ability to anticipate the future.

This is due to the fact that the dark matter content of galaxies is predicted by this model to be highly unknown and dependent on the galaxy's formation history, which is not always known. As a result, the rate at which galaxies should rotate is unpredictable. But with Mond, such forecasts are common, and they have thus far come true.

Consider a scenario in which we are aware of the galaxy's observable mass distribution but not its rotational speed. Only on the periphery could it be reasonably predicted in the conventional cosmological model that the rotation speed will fall between 100 km/s and 300 km/s. Mond predicts with greater certainty that the rotation speed must fall between 180 and 190 km/s.

Both ideas can explain data that later show a rotation speed of 188 km/s, but Mond is definitely the more likely candidate. In this instance, we should explain observations with as few "free parameters" as feasible. This is a modern interpretation of Occam's razor, which states that the simplest solution is preferable to more complex ones.

To encapsulate the basic principle of Occam's razor—that a theory with more free parameters is consistent with a wider range of evidence, making it more complex—we proposed the concept of "theoretical flexibility." This idea was employed in our review to compare the mainstream cosmological model and Mond to a number of astronomical phenomena, including galaxy rotation and motions inside galaxy clusters.

We also gave each model a score based on how well it explained the data, with +2 denoting great agreement and -2 designating data that blatantly contradicted the theory. The theoretical flexibility score is then subtracted from the score for agreement with observations because while being able to fit any data is excellent, it is negative to be able to fit everything.

The mainstream cosmological model received an average of -0.25 over 32 tests, while Mond received an average of +1.69 across 29 tests. The results for the traditional cosmological model and Mond, respectively, in a variety of tests are displayed in figures 1 and 2 below.

The problems with dark matter

Galaxies frequently contain "galaxy bars" in their central regions, which are rod-shaped brilliant patches comprised of stars. This is one of the conventional cosmological model's most obvious shortcomings (see lead image). Over time, the bars turn. If galaxies were surrounded by large dark matter haloes, their bars would move more slowly. However, the majority of observed galaxy bars—if not all—are swift.

This strongly suggests that the mainstream cosmological model is false.Another issue is that the original models that showed galaxies contain dark matter halos made a serious error by assuming that the dark matter particles gave gravity to the surrounding matter while being unaffected by the gravity of the regular matter. Calculations were made simpler, but reality was not reflected.

It became evident that dark matter halos around galaxies do not consistently explain their properties when this was taken into consideration in later simulations.We came to the conclusion that Mond is highly supported by the available observations because of the enormous advantage it had over the conventional cosmological model in our investigation. Even if we can not assert that Mond is faultless, we believe it captures the overall picture accurately: galaxies actually do not contain dark matter.