Brans Dicke Theory
Brans-Dicke Theory
The Brans-Dicke theory of gravitation, sometimes referred to as the Jordan-Brans-Dicke theory, is a significant competitor to Einstein's general theory of relativity. This theory represents a category within scalar-tensor theories, which are theories of gravitation involving both a scalar field and a tensor field.
Historical Background
The Brans-Dicke theory was developed in 1961 by Robert H. Dicke and Carl H. Brans. Their work was built on the foundation of earlier research conducted by Pascual Jordan in 1959. This collaborative effort emerged as a response to the quest for alternatives to Einstein's formulation of gravitation.
Core Concepts
Scalar-Tensor Theory
In general, scalar-tensor theories of gravity propose that the gravitational interaction is mediated by both a scalar field, which is a single-valued field throughout spacetime, and the tensor field of general relativity. The scalar field in the Brans-Dicke theory can vary throughout the universe, influencing gravitational strength.
Gravitational Interaction
The gravitational field in the Brans-Dicke framework is influenced by the stress-energy tensor, just like in general relativity. However, the immediate presence of mass-energy affects the gravitational field differently than in general relativity. The theory posits that, in addition to the metric—a rank two tensor field—there is a dynamic scalar field that also plays a crucial role in determining the gravitational interaction.
Implications and Observations
The Brans-Dicke theory aligns with many observations that also support general relativity. Both theories predict gravitational phenomena such as the gravitational redshift effect, where light or other electromagnetic radiation from an object is increased in wavelength, or shifted to the red end of the spectrum, in the presence of a gravitational field.
Mach's Principle and Cosmology
The development of the Brans-Dicke theory was partially inspired by Mach's principle, which suggests that local inertial frames are influenced by the large-scale structure of the universe. This connection aligns with the cosmological considerations that Robert H. Dicke explored with Jim Peebles, re-deriving concepts pertinent to the early universe.
Related Theories
The Brans-Dicke theory is part of a broader spectrum of alternative gravity theories, including:
These theories explore various modifications and extensions to the gravitational framework established by Einstein, each with their own unique implications for cosmology and astrophysics.