Whitehead's theory of gravitation
Encyclopedia
In theoretical physics
, Whitehead's theory of gravitation was introduced by the distinguished mathematician and philosopher Alfred North Whitehead
in 1922.
(as defined by the metric
determined from geometrical measurements and timing experiments), while gravitational waves propagate along null geodesics of a flat background represented by the metric tensor of Minkowski spacetime. The gravitational potential can be expressed entirely in terms of waves retarded along the background metric, like the Liénard–Wiechert potential in electromagnetic theory.
A cosmological constant
can be introduced by changing the background metric to a de Sitter
or anti de Sitter
metric. This was first suggested by G. Temple in 1923. Temple's suggestions on how to do this were criticized by C. B. Rayner in 1955.
), and was regarded as a viable competitor of general relativity for several decades. Clifford M. Will
claims that the theory makes predictions concerning ordinary ocean tides
on Earth which are in violent disagreement with observation (specifically, the theory predicts a "sidereal tide", induced by the gravitational field of the Milky Way, which is hundreds of times stronger than the solar and lunar tides) which immediately nullified this theory.
In 1989, a new interpretation of Whitehead's theory was proposed that eliminated the unobserved sidereal tide effects. However, the new interpretation did not satisfy another observed effect, called the "Nordtvedt Effect
."
Theoretical physics
Theoretical physics is a branch of physics which employs mathematical models and abstractions of physics to rationalize, explain and predict natural phenomena...
, Whitehead's theory of gravitation was introduced by the distinguished mathematician and philosopher Alfred North Whitehead
Alfred North Whitehead
Alfred North Whitehead, OM FRS was an English mathematician who became a philosopher. He wrote on algebra, logic, foundations of mathematics, philosophy of science, physics, metaphysics, and education...
in 1922.
Principal features of the theory
Whitehead's theory is said to feature a prior geometry. It has the curious feature that electromagnetic waves propagate along null geodesics of the physical spacetimeSpacetime
In physics, spacetime is any mathematical model that combines space and time into a single continuum. Spacetime is usually interpreted with space as being three-dimensional and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions...
(as defined by the metric
Metric tensor
In the mathematical field of differential geometry, a metric tensor is a type of function defined on a manifold which takes as input a pair of tangent vectors v and w and produces a real number g in a way that generalizes many of the familiar properties of the dot product of vectors in Euclidean...
determined from geometrical measurements and timing experiments), while gravitational waves propagate along null geodesics of a flat background represented by the metric tensor of Minkowski spacetime. The gravitational potential can be expressed entirely in terms of waves retarded along the background metric, like the Liénard–Wiechert potential in electromagnetic theory.
A cosmological constant
Cosmological constant
In physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...
can be introduced by changing the background metric to a de Sitter
De Sitter space
In mathematics and physics, a de Sitter space is the analog in Minkowski space, or spacetime, of a sphere in ordinary, Euclidean space. The n-dimensional de Sitter space , denoted dS_n, is the Lorentzian manifold analog of an n-sphere ; it is maximally symmetric, has constant positive curvature,...
or anti de Sitter
Anti de Sitter space
In mathematics and physics, n-dimensional anti de Sitter space, sometimes written AdS_n, is a maximally symmetric Lorentzian manifold with constant negative scalar curvature...
metric. This was first suggested by G. Temple in 1923. Temple's suggestions on how to do this were criticized by C. B. Rayner in 1955.
Tests of Whitehead's theory
Whitehead's theory makes the same predictions as general relativity regarding the four classical solar system tests (gravitational red shift, light bending, perihelion shift, Shapiro time delayShapiro delay
The Shapiro time delay effect, or gravitational time delay effect, is one of the four classic solar system tests of general relativity. Radar signals passing near a massive object take slightly longer to travel to a target and longer to return than it would if the mass of the object were not...
), and was regarded as a viable competitor of general relativity for several decades. Clifford M. Will
Clifford Martin Will
Clifford Martin Will is a Canadian born mathematical physicist who is well known for his contributions to the theory of general relativity....
claims that the theory makes predictions concerning ordinary ocean tides
Physical oceanography
Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.Physical oceanography is one of several sub-domains into which oceanography is divided...
on Earth which are in violent disagreement with observation (specifically, the theory predicts a "sidereal tide", induced by the gravitational field of the Milky Way, which is hundreds of times stronger than the solar and lunar tides) which immediately nullified this theory.
In 1989, a new interpretation of Whitehead's theory was proposed that eliminated the unobserved sidereal tide effects. However, the new interpretation did not satisfy another observed effect, called the "Nordtvedt Effect
Nordtvedt effect
In theoretical astrophysics, the Nordtvedt effect refers to the relative motion between the Earth and the Moon which would be observed if the gravitational self-energy of a body contributed to its gravitational mass but not its inertial mass...
."