Why a galaxy rotates at a constant rate no matter how far from the center you measure. This violates the orbital formulas that Kepler created in studying the orbits of the planets around Sol.
Even if there were dark matter making a galaxy weight 6 times more than it should weigh, the speed of rotation should still vary with the distance from the center of the galaxy.
If dark matter existed, shouldn't the orbital speed of the solar systems outer planets be the same as the inner planets?
Does the gravity of dark matter only show its self over galactic distances and not the distances in our solar system?