Scalar–tensor–vector gravity (STVG) is a modified theory of
gravity
In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...
developed by
John Moffat, a researcher at the
Perimeter Institute for Theoretical Physics
Perimeter Institute for Theoretical Physics (PI, Perimeter, PITP) is an independent research centre in foundational theoretical physics located in Waterloo, Ontario, Canada. It was founded in 1999. The institute's founding and major benefactor i ...
in
Waterloo, Ontario
Waterloo is a city in the Canadian province of Ontario. It is one of three cities in the Regional Municipality of Waterloo (formerly Waterloo County). Waterloo is situated about west-southwest of Toronto. Due to the close proximity of the ci ...
. The theory is also often referred to by the acronym MOG (''MO''dified ''G''ravity).
Overview
Scalar–tensor–vector gravity theory,
also known as MOdified Gravity (MOG), is based on an
action principle and postulates the existence of a
vector field, while elevating the three constants of the theory to
scalar fields. In the
weak-field approximation
In the theory of general relativity, linearized gravity is the application of perturbation theory to the Metric tensor (general relativity), metric tensor that describes the geometry of spacetime. As a consequence, linearized gravity is an effect ...
, STVG produces a
Yukawa-like modification of the gravitational force due to a point source. Intuitively, this result can be described as follows: far from a source gravity is stronger than the Newtonian prediction, but at shorter distances, it is counteracted by a repulsive
fifth force due to the vector field.
STVG has been used successfully to explain
galaxy rotation curves,
the mass profiles of galaxy clusters,
gravitational lensing in the
Bullet Cluster,
and cosmological observations
without the need for
dark matter
Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not a ...
. On a smaller scale, in the Solar System, STVG predicts no observable deviation from general relativity.
The theory may also offer an explanation for the origin of
inertia
Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...
.
Mathematical details
STVG is formulated using the action principle. In the following discussion, a
metric
Metric or metrical may refer to:
* Metric system, an internationally adopted decimal system of measurement
* An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement
Mathematics
In mathem ...
signature of