The dark matter hypothesis is not perfect, but its alternative hypotheses are worse!

Maybe you don't like the hypothesis of dark matter, a hypothetical particle that makes up most of the mass in the universe. It is also true that this hypothesis has its shortcomings and of course, no particle of this matter has been discovered yet, but the truth is that the alternative hypotheses of dark matter are much worse.

BingMag.com The dark matter hypothesis is not perfect, but its alternative hypotheses are worse!

Maybe you don't like the hypothesis of dark matter, a hypothetical particle that makes up most of the mass in the universe. It is also true that this hypothesis has its shortcomings and of course, no particle of this matter has been discovered yet, but the truth is that the alternative hypotheses of dark matter are much worse.

In our universe there are many unexplained mysteries. There are, most of which are related to gravity. By examining the movement of stars around the center of galaxies, we find that if only the gravity of visible matter kept them in their current orbits, they would have to move much more slowly.

Also, the galaxies that go around galaxy clusters, according to the amount of visible mass. In clusters, they move very fast. On the other hand, these clusters bend the background light beyond the power of visible matter. Even large-scale structures in our universe should have formed much more slowly, without considering an additional source of mass.

Currently the best hypothesis scientists have to explain all these disparate observations is that a new type of particle There is something called dark matter in the universe, which is responsible for this cosmic arrangement. This particle is almost completely invisible, and that is why it is called dark. On the other hand, it does not interact with ordinary matter or rarely interacts.

This idea is not as far-fetched as it seems. Neutrinos are particles that have exactly such properties. They don't have enough mass to explain dark matter, but they show that such particles can exist.

  • The biggest cosmic structures are spinning and we don't know why.

However, the "dark matter" hypothesis is not complete. Computer simulations of galaxy growth show that galaxies dominated by dark matter must have extremely high densities at their centers. Observations of real galaxies also show a higher density in their cores, but not as much as the simulations predict.

Also, dark matter simulations predict that each galaxy should have hundreds of smaller galactic moons as the universe evolves. be, while observations do not show this number.

MOND hypothesis

Given that the dark matter hypothesis is not complete and there is no direct evidence for the existence of these particles We don't have a hypothesis, we can propose other options.

One of these options was introduced in the 1970s along with the main idea of dark matter and when the astronomer Vera Rubin (Vera Rubin) first identified the problem discovered the extremely fast motion of stars in galaxies.

But the alternative hypothesis is that instead of adding a new element like dark matter to the universe, by changing the way gravity works on a galactic scale. , explains the movements. This hypothesis is called "Modified Newtonian Dynamics" or "MOND". However, this name is also used for other theories derived from this main idea.

The MOND hypothesis states that Newtonian gravity works well on planetary scales or the dimensions of the solar system. Of course, except for the cases where exact calculations of gravity are needed and are explained by general relativity. But as soon as you go to a larger scale, the familiar relationship of Newton's second law (F=ma) does not apply completely, and the relationship between force and acceleration follows a different law.

Under the MOND hypothesis, there is no need for a particle to exist. There is no excess to explain the observations, and only a slight change in the gravitational force is sufficient. On the other hand, since this change of gravity under MOND is fully defined to explain the motion of stars in galaxies, it naturally does this well. And it doesn't need very dense galactic nuclei.

Major flaw

However, MOND also has major flaws. The changes that have been made to explain the motions of the stars in gravitational relations are deficient in explaining the motion of galaxies in clusters and the gravitational lensing of the background light.

Furthermore, while all modern theories of physics must be compatible with special relativity However, MOND is not a fully relativistic theory. A refinement on MOND is a theory called TeVeS, which can compete with general relativity but still has many shortcomings.

Modified gravity-based models explain the growth of cosmic structures, the properties of the cosmic microwave background, and more. They have fundamental problems, while dark matter does a good job of explaining all of this.

There is no theory based on MOND that can explain every single observation as well as dark matter. All of these kinds of theories fail in at least one test.

For example, while MOND may accurately explain the rotation diagrams of galaxies, there are enough observations to show that we need galaxies to be stable and In total being in the universe, still to We need dark matter.

Therefore, although the dark matter hypothesis is not perfect, there is no better scientific hypothesis either. When evaluating competing dark matter hypotheses, scientists can't just rely on gut feeling or choose the hypothesis that seems more interesting and simple, but rather see what the evidence shows.

Over the past 50 years or so, , no one has come up with a MOND-like theory that can explain the vast amount of information we have about the universe. This does not prove that MOND is wrong, but it does make it a much weaker alternative to the dark matter hypothesis.

Cover photo: The Small Magellanic Cloud, one of the Milky Way's moon galaxies, and its dark matter distribution in one half, which Shown graphically.
Credit: Dark matter, R. Caputo et al. 2016; background, Axel Mellinger, Central Michigan University

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