Alternative Gravitational Theories

Abstract

There have been many proposed modifications of gravitational theory, beginning with Einstein’s general relativity, modifying Newtonian gravity, and Weyl’s attempt at unifying gravity and electromagnetism. The standard model of cosmology, the Lambda CDM model, requires dark matter and dark energy to fit experimental data. There is a lack of direct evidence for dark matter and dark energy. An alternative theory called modified gravity (MOG) seeks to fit the observational data for the dynamics of galaxies and clusters of galaxies without dark matter. The MOG gravitational theory has a solution for a black hole that modifies the Schwarzschild and Kerr solutions, and can be tested using the data collected on supermassive black holes by the Event Horizon Telescope. There are many modified gravity theories proposed to explain the accelerating expansion of the universe, generally ascribed to dark energy. However, Einstein’s cosmological constant is the simplest explanation for the accelerating expansion.