Is Modified Gravity a Viable Alternative to Dark Matter?

The Standard Model of cosmology, ΛCDM, explains the observations well, but with a major caveat: it assumes that about 95% of the Universe is undetected dark matter. This loose assumption prompts us to look for alternative explanations.

One of them is modified gravity (MOG), a well-developed theory that can account for various phenomena without dark matter. It weakly explains the masses of galaxy clusters, the rotation curves of galaxies, the velocity dispersions of satellite galaxies, and the globular clusters.

But it also agrees with key cosmological observations, such as the cosmic microwave background (CMB), the power spectrum of matter (galaxies), and the luminosity-distance relation, which are consistent with the data without dark matter or cosmological constant.

MOG is based on a different principle of physical action, where relativistic effects are explained by scalar, tensor, and vector fields. A new entity, a massive vector field, is needed for the emergence of repulsive gravitational modification at short distances.

MOG is not the only alternative theory of gravity, but it is one of the most promising candidates to challenge the Standard Model.