A dark matter remains one of the great mysteries of contemporary astrophysics. We know it exists because of its observed gravitational effects on galaxies, but we still don’t know what it’s made of.
The epic began in the 1930s, when Swiss astronomer Fritz Zwicky noticed that galaxies in clusters were moving too fast. In order for the cluster not to be decimated, with galaxies flying everywhere, there had to be an excess of matter there, generating enough gravity to keep the hurried ones trapped in the structure.
Unfortunately the work drew little attention at the time. It was only in the 1970s, when the great American astronomer Vera Rubin analyzed the movement of gas in galaxies like our own, that the dark matter hypothesis gained traction.
The discovery was similar to Zwicky’s: the gas was moving too fast, and the only explanation was some kind of invisible matter.
But Thiago —you would say—, isn’t it just some kind of atom that isn’t shining very brightly?
We’ve thought about this, but there really isn’t any kind of normal matter that would be invisible to all our instruments in this way. So it must really be some more exotic component, outside our standard understanding of the basic elements of the Universe.
We have several theories as to how this could be possible. Some have already been ruled out by experiments, others are more popular, like what we call supersymmetry.
The big problem is that we are designing increasingly complex experiments to try to find these strange elementary particles, without success. And we are reaching the limit of what nature allows us to study.
The difficulty brings to light alternative models, which have tried since the 1980s to explain the same phenomena without the need for the existence of dark matter.
Created by Mordehai Milgrom, the so-called modified Newtonian dynamics hypothesis, as its name indicates, is an update of Physics that alters the equations of motion at great distances, mathematically explaining the movement of bodies in the universe.
The work, although created “a posteriori” (that is, adjusted by hand to adapt to observations), is an elegant solution to the dark matter problem.
The big problem is that it is increasingly difficult to justify the use of modified Newtonian dynamics.
Science has come a long way since the 1980s, and the evidence for dark matter has multiplied.
The same exotic particle that would explain the movement of galaxies today is the basic principle to explain several phenomena in Astrophysics, from the bending of light beams around galaxy clusters to the number of clusters observed today in the Universe, passing even by the abundance itself. of hydrogen atoms today from its creation in the Big Bang.
All this today we only understand if we consider that about 25% of everything that exists in the Universe is made of dark matter (against only 4% of “normal” matter, made of ordinary atoms).
It is a simple explanation, which uniquely accounts for all of this at the same time.
Modified dynamics, on the other hand, have to unfold and become ever more complicated to explain these new discoveries. Not only the Newtonian dynamics, but the hypothesis itself must be more and more modified in order not to be discarded.
Does this mean that dark matter definitely exists?
We can’t say that definitively, but probably yes. After all, some of the advocates of modified dynamics are excellent researchers, not just denialists.
But they are also human. And this is what we need to understand: even in the exact sciences, researchers are people. With their own prejudices and ideologies, and even in technical and mathematical cases like dark matter, they may not necessarily be impartial in their positions.
