Yilmaz theory of gravitation
Encyclopedia
The Yilmaz theory of gravitation is an attempt by Huseyin Yilmaz (Turkish: Hüseyin Yılmaz) and his coworkers to formulate a classical field theory of gravitation which is similar to general relativity
in weak-field conditions, but in which event horizon
s cannot appear.
Yilmaz's work has been criticized on various grounds, including the claims that
Yilmaz disputes these criticisms. He claims that his critics have misunderstood him, but it has been suggested that his papers are too murky in crucial places to admit a single clear interpretation.
It is well known that naive attempts to quantize general relativity along the same lines which lead from Maxwell's classical field theory of electromagnetism to quantum electrodynamics fail, and that it has proven very difficult to construct a theory of quantum gravity
which goes over to general relativity in an appropriate limit. Yilmaz has claimed that, in contrast, his theory is in some sense 'compatible with quantum mechanics
'. He suggests that it might be an alternative to superstring theory
.
To understand one of the most basic criticisms of Yilmaz's work, one needs to be familiar with
With this background in hand, one can say that Yilmaz apparently wishes to keep the left hand side of the Einstein field equation (namely the Einstein tensor
, which is well-defined for any Lorentzian manifold, independent of general relativity) but to modify the right hand side, the stress-energy tensor
, by adding a kind of gravitational contribution. According to Yilmaz's critics, this additional term is not well-defined, and cannot be made well defined.
No astronomers have tested his ideas, although some have tested competitors of general relativity; see :Category:Tests of general relativity.
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...
in weak-field conditions, but in which event horizon
Event horizon
In general relativity, an event horizon is a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms it is defined as "the point of no return" i.e. the point at which the gravitational pull becomes so great as to make escape impossible. The most common case...
s cannot appear.
Yilmaz's work has been criticized on various grounds, including the claims that
- his proposed field equationField equationA field equation is an equation in a physical theory that describes how a fundamental force interacts with matter...
is ill-defined, - event horizons can occur in weak field situations according to the general theory of relativity, in the case of a supermassive black holeBlack holeA black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...
. - the theory is consistent only with either a completely empty universe or a negative energy vacuum
Yilmaz disputes these criticisms. He claims that his critics have misunderstood him, but it has been suggested that his papers are too murky in crucial places to admit a single clear interpretation.
It is well known that naive attempts to quantize general relativity along the same lines which lead from Maxwell's classical field theory of electromagnetism to quantum electrodynamics fail, and that it has proven very difficult to construct a theory of quantum gravity
Quantum gravity
Quantum gravity is the field of theoretical physics which attempts to develop scientific models that unify quantum mechanics with general relativity...
which goes over to general relativity in an appropriate limit. Yilmaz has claimed that, in contrast, his theory is in some sense 'compatible with quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
'. He suggests that it might be an alternative to superstring theory
Superstring theory
Superstring theory is an attempt to explain all of the particles and fundamental forces of nature in one theory by modelling them as vibrations of tiny supersymmetric strings...
.
To understand one of the most basic criticisms of Yilmaz's work, one needs to be familiar with
- the statement of the Einstein field equation,
- the distinction between coordinate dependent and coordinate independent quantities,
- facts concerning integration in curved spacetimeSpacetimeIn 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...
s, - facts concerning gravitational energy-momentum pseudotensorPseudotensorIn physics and mathematics, a pseudotensor is usually a quantity that transforms like a tensor under an orientation preserving coordinate transformation , but gains an additional sign flip under an orientation reversing coordinate transformation In physics and mathematics, a pseudotensor is usually...
s in general relativity.
With this background in hand, one can say that Yilmaz apparently wishes to keep the left hand side of the Einstein field equation (namely the Einstein tensor
Einstein tensor
In differential geometry, the Einstein tensor , named after Albert Einstein, is used to express the curvature of a Riemannian manifold...
, which is well-defined for any Lorentzian manifold, independent of general relativity) but to modify the right hand side, the stress-energy tensor
Stress-energy tensor
The stress–energy tensor is a tensor quantity in physics that describes the density and flux of energy and momentum in spacetime, generalizing the stress tensor of Newtonian physics. It is an attribute of matter, radiation, and non-gravitational force fields...
, by adding a kind of gravitational contribution. According to Yilmaz's critics, this additional term is not well-defined, and cannot be made well defined.
No astronomers have tested his ideas, although some have tested competitors of general relativity; see :Category:Tests of general relativity.
External links
- One page in the website Relativity on the World Wide Web (archived link) lists some apparent misstatements by Yilmaz concerning the general theory of relativity, similar to those discussed by Fackerell.