I understand the interest in a fifth force is to explain the dark matter/dark energy anomaly discovered by the astronomer Vera Rubin. The orbital velocities of

I understand the interest in a fifth force is to explain the dark matter/dark energy anomaly discovered by the astronomer Vera Rubin. The orbital velocities of stars at increasing radii (radiuses?) from the center can't be accounted for by the current understanding of gravity and visible matter.