The reason dark matter exists, is because Big Science has decided that instead of finding explanations using current theory, that it is more exciting to postulate something you cannot see. After all, careers are made not by finding logical explanations with know theories, but by postulating something that is not yet seen or detected and eventually finding it. This leads to Nobel Prizes and top positions at universities.
The postulation of dark matter comes from the observation that the velocities of stars on the edge of the galaxy move faster than what Kepler or Newton’s gravity would predict. The idea is that there is “dark” or “invisible” matter out there that is tugging on these stars in order to make them move faster than they should be. Critical thinkers however are always suspect of anything “dark” or “invisible” in physics because it often points to flaws in our theory, not to the mysterious or missing in the universe.
And as it turns out, Newton works just fine in describing the velocities of stars on the perimeter of the galaxy. It simply requires the simple fact that the gravitational field of galaxies are not uniform.
It is very common in physics and cosmology to treat a mass as a point. Newton did this. NASA still does this when calculating the gravitational forces of thousands of known objects in our solar system. The earth, the moon, the sun, the planets, and even galaxies are treated as point masses meaning, they concentrate all the mass of the galaxy into a point in the middle of the galaxy. For most calculations, this works fine because most objects in the heavens are spherical with a more or less uniform gravitational field. But when it comes to galaxies, this is not the case.
It turns out that most galaxies are not spherical. In fact, our galaxy is mostly flat and has spiral arms. It therefore certainly does not have a uniform gravitational field. Two critical thinkers, Bob de Hilster and Cameron Rebigsol have both addressed this point and have shown that in fact, the non-uniform gravitational field as described by Newton explains the faster velocities without the need of dark matter.
Gravitational Field Curve
Bob de Hilster saw something very simple yet striking in the curve of star velocities as a measure of the distance from the center of the galaxy. What he saw was the arms and spaces of the galaxy. In his paper “Dark Matter Versus G“, de Hilster shows how you can actually see the shape of the galaxy in the velocity curves for the Milky Way.
Here is Bob de Hilster’s talk at CNPS 2018 at the University of Connecticut.
Newtonian Calculations Show Speed Variations Without Dark Matter
Carmeron Rebigsol came up with a very simple model from which he calculated the gravitational fields using the notion that a galaxy was not uniform. He used a simply cross in order to make the calculations doable but the effect is the same: the calculations show that stars on the edge of galaxies will be whipped around faster at the ends of spiral arms.
This can be found in his paper “Newton’s Gravitational Law over Dark Matter” published in the CNPS 2016 Proceedings and presented at the University of Maryland.
Here is Cameron Rebigsol’s presentation of this work at CNPS 2016 at the University of Maryland.