What is Hoyle–Narlikar theory of gravity?

The Hoyle–Narlikar theory of gravity, proposed by Fred Hoyle and Jayant Narlikar in the 1960s, is an alternative gravitational theory that seeks to address some of the limitations associated with general relativity, particularly regarding cosmology and the dynamics of the universe. In this theory, gravity is treated as a field that influences matter and energy in a manner that differs from how it is understood in Einstein's general relativity. One of the key aspects of the Hoyle–Narlikar theory is the incorporation of a "creation of matter" mechanism, which allows for the continuous generation of matter as the universe expands. This idea was introduced to explain the observed uniformity of the universe while avoiding the need for a singular beginning, such as the Big Bang. The theory also emphasizes the concept of "action at a distance," suggesting that the gravitational influence of an object can extend beyond the influence described by the curvature of spacetime in general relativity. The Hoyle–Narlikar theory has implications for the understanding of cosmological phenomena and seeks to provide insights into the large-scale structure of the universe. However, despite its attempts to explain certain cosmological observations, the Hoyle–Narlikar theory did not gain widespread acceptance and has largely been supplanted by the standard model of cosmology based on general relativity and the Big Bang theory. Nevertheless, it remains a notable effort to explore alternative frameworks for understanding gravity and the cosmos.