Hoyle–Narlikar theory of gravity

The Hoyle–Narlikar theory of gravity, developed by Fred Hoyle and Jayant Narlikar in the early 1960s, is an alternative to Einstein's general theory of relativity. This theory emerged as part of their broader attempts to formulate a cosmological model that incorporates the creation of matter and addresses certain observed phenomena that are difficult to explain with the standard model of cosmology. Key features of the Hoyle–Narlikar theory include: 1. **Creation of Matter**: One of the central tenets of this theory is the idea that new matter can be created in the universe, which allows for a dynamic universe that can evolve over time without violating conservation of energy. This concept was particularly appealing during a time when the steady-state model of the universe was a subject of serious consideration. 2. **Gravitational Interaction**: The theory posits a modified form of gravitational interaction that differs from Einstein's formulation. Hoyle and Narlikar proposed that gravitational forces might not be invariant and could depend on the local density of matter. 3. **Inclusion of Time**: The theory takes time into account not just as a parameter but as an integral part of the interaction between gravity and matter. This allows for the possibility of evolving gravitational influences and changes in the gravitational field over cosmic time scales. 4. **Quantum Aspects**: The Hoyle–Narlikar theory also attempts to bridge concepts from quantum mechanics with classical gravitational theory, proposing that gravity might possess quantum properties that are not accounted for in general relativity. Although the Hoyle–Narlikar theory presents interesting ideas, it has not gained widespread acceptance in the scientific community compared to general relativity. Observational evidence, such as the cosmic microwave background radiation and the expansion of the universe, has strongly supported the Big Bang model and general relativity over the steady-state model. However, Hoyle–Narlikar and similar alternative theories often provoke discussions and explorations in theoretical physics, contributing to the plurality of ideas in efforts to understand gravity and the universe.