Polarizable vacuum
Encyclopedia
In theoretical physics
, particularly fringe physics, polarizable vacuum (PV) and its associated theory refers to proposals by Harold Puthoff, Robert H. Dicke
, and others to develop an analogue of general relativity
to describe gravity and its relationship to electromagnetism
.
, εo and μo respectively by multiplying them by a scalar function, K:
arguing that this will affect the lengths of rulers made of ordinary matter, so that in the presence of a gravitational field the spacetime metric of Minkowski spacetime is replaced by
where
is the so-called "dielectric constant of the vacuum". This is a "diagonal" metric given in terms of a Cartesian chart and having the same stratified conformally flat form in the Watt-Misner theory of gravitation. However, according to Dicke and Puthoff, κ must satisfy a field equation which differs from the field equation of the Watt-Misner theory. In the case of a static spherically symmetric vacuum, this yields the asymptotically flat solution
The resulting Lorentzian spacetime happens to agree with the analogous solution in the Watt-Misner theory, and it has the same weak-field limit, and the same far-field, as the Schwarzschild vacuum
solution in general relativity, and it satisfies three of the four classical tests of relativistic gravitation (redshift, deflection of light, precession of the perihelion of Mercury) to within the limit of observational accuracy. However, as shown by Ibison (2003), it yields a different prediction for the inspiral of test particles due to gravitational radiation.
However, requiring stratified-conformally flat metrics rules out the possibility of recovering the weak-field Kerr metric
, and is certainly inconsistent with the claim that PV can give a general "approximation" of the general theory of relativity. In particular, this theory exhibits no frame-dragging
effects. Also, the effect of gravitational radiation on test particles differs profoundly between scalar theories and tensor theories of gravitation such as general relativity. LIGO
is not intended primarily as a test ruling out scalar theories, but is widely expected to do so as a side benefit once it detects unambiguous gravitational wave signals exhibiting the characteristics expected in general relativity.
Ibison has considered a "cosmological solution" of PV, analogous to the Friedmann dust solution with flat orthogonal hyperslices in general relativity, and argues that this model is inconsistent with various observational and theoretical constraints. He also finds a rate of inspiral disagreeing with observation. The latter result disagrees with that of Watt and Misner, whose Lorentzian manifold differs from PV in the case of cosmology.
It is widely accepted that no scalar theory of gravitation can reproduce all of general relativity's successes, contrary to Puthoff's claims. It might be noted that De Felice uses constitutive relations to obtain a susceptibility tensor which lives in spatial hyperslices; this provides extra degrees of freedom which help make up for the degree of freedom lacking in PV and other scalar theories.
Depp presents a PV Lagrangian field from which can be derived the exact Schwarzschild solution and the exact Reissner-Nordstrom solution. In addition it is also shown that electron charge renormalization can be obtained from the model that is in good agreement with QED.
PV has origins in more mainstream work by such physicists as Robert Dicke, but in current parlance the term does appear to be most closely associated with the speculations of Puthoff. The claims have not been accepted in mainstream physics.
Theoretical physics
Theoretical physics is a branch of physics which employs mathematical models and abstractions of physics to rationalize, explain and predict natural phenomena...
, particularly fringe physics, polarizable vacuum (PV) and its associated theory refers to proposals by Harold Puthoff, Robert H. Dicke
Robert H. Dicke
Robert Henry Dicke was an American physicist who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity.-Biography:...
, and others to develop an analogue 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...
to describe gravity and its relationship to electromagnetism
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
.
Description
In essence, Dicke and Puthoff proposed that the presence of mass alters the electric permittivity and the magnetic permeability of flat 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...
, εo and μo respectively by multiplying them by a scalar function, K:
εo→ε = Kεo, μo→μ = Kμo
arguing that this will affect the lengths of rulers made of ordinary matter, so that in the presence of a gravitational field the spacetime metric of Minkowski spacetime is replaced by
where
is the so-called "dielectric constant of the vacuum". This is a "diagonal" metric given in terms of a Cartesian chart and having the same stratified conformally flat form in the Watt-Misner theory of gravitation. However, according to Dicke and Puthoff, κ must satisfy a field equation which differs from the field equation of the Watt-Misner theory. In the case of a static spherically symmetric vacuum, this yields the asymptotically flat solutionThe resulting Lorentzian spacetime happens to agree with the analogous solution in the Watt-Misner theory, and it has the same weak-field limit, and the same far-field, as the Schwarzschild vacuum
Schwarzschild metric
In Einstein's theory of general relativity, the Schwarzschild solution describes the gravitational field outside a spherical, uncharged, non-rotating mass such as a star, planet, or black hole. It is also a good approximation to the gravitational field of a slowly rotating body like the Earth or...
solution in general relativity, and it satisfies three of the four classical tests of relativistic gravitation (redshift, deflection of light, precession of the perihelion of Mercury) to within the limit of observational accuracy. However, as shown by Ibison (2003), it yields a different prediction for the inspiral of test particles due to gravitational radiation.
However, requiring stratified-conformally flat metrics rules out the possibility of recovering the weak-field Kerr metric
Kerr metric
The Kerr metric describes the geometry of empty spacetime around an uncharged axially-symmetric black-hole with an event horizon which is topologically a sphere. The Kerr metric is an exact solution of the Einstein field equations of general relativity; these equations are highly non-linear, which...
, and is certainly inconsistent with the claim that PV can give a general "approximation" of the general theory of relativity. In particular, this theory exhibits no frame-dragging
Frame-dragging
Einstein's general theory of relativity predicts that non-static, stationary mass-energy distributions affect spacetime in a peculiar way giving rise to a phenomenon usually known as frame-dragging...
effects. Also, the effect of gravitational radiation on test particles differs profoundly between scalar theories and tensor theories of gravitation such as general relativity. LIGO
LIGO
LIGO, which stands for the Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. Cofounded in 1992 by Kip Thorne and Ronald Drever of Caltech and Rainer Weiss of MIT, LIGO is a joint project between scientists at MIT,...
is not intended primarily as a test ruling out scalar theories, but is widely expected to do so as a side benefit once it detects unambiguous gravitational wave signals exhibiting the characteristics expected in general relativity.
Ibison has considered a "cosmological solution" of PV, analogous to the Friedmann dust solution with flat orthogonal hyperslices in general relativity, and argues that this model is inconsistent with various observational and theoretical constraints. He also finds a rate of inspiral disagreeing with observation. The latter result disagrees with that of Watt and Misner, whose Lorentzian manifold differs from PV in the case of cosmology.
It is widely accepted that no scalar theory of gravitation can reproduce all of general relativity's successes, contrary to Puthoff's claims. It might be noted that De Felice uses constitutive relations to obtain a susceptibility tensor which lives in spatial hyperslices; this provides extra degrees of freedom which help make up for the degree of freedom lacking in PV and other scalar theories.
Modified PV Model
In 2005 Depp proposed a modification to the original PV work of Dicke that addresses many of the objections above. The revised model is not a replacement for general relativity but is meant to provide insight into the possible underlying physics of general relativity.Depp presents a PV Lagrangian field from which can be derived the exact Schwarzschild solution and the exact Reissner-Nordstrom solution. In addition it is also shown that electron charge renormalization can be obtained from the model that is in good agreement with QED.
Generalization
Puthoff himself has apparently offered various characterizations of his proposal, which has been variously characterized as- an attempt to reformulate general relativity in terms of a purely formal analogy with the propagation of light through an optical medium,
- an attempt to replace general relativity with a scalar theory of gravitation featuring formal analogies with Maxwell's theory of electromagnetism,
- an attempt to unify gravitation and electromagnetism in a theory of electrogravity,
- an attempt to provide a physical mechanism for how spacetime gets curved in general relativity, which suggests (to Puthoff) the possibility of "metric engineering" for such purposes as spacecraft propulsion (see Breakthrough Propulsion Physics ProgramBreakthrough Propulsion Physics ProgramThe Breakthrough Propulsion Physics Project was a research project funded by NASA from 1996 through 2002, to study various proposals for "revolutionary" methods of spacecraft propulsion which would require breakthroughs in physics before they could be realized, hence the name...
).
PV has origins in more mainstream work by such physicists as Robert Dicke, but in current parlance the term does appear to be most closely associated with the speculations of Puthoff. The claims have not been accepted in mainstream physics.
Not a unified field theory?
Mainstream physicists agree that PV is- not viable as a unification of gravitation and electromagnetism
- not a "reformulation" of general relativity,
- not a viable theory of gravitation, since it violates observational and theoretical requirements.
Related work
Antecedents of PV and more recent related proposals include the following:- A proposal in 1921 by H. A. Wilson to reduce gravitation to electromagnetism by pursuing the formal analogy between "light bending" in metric theories of gravitationClassical theories of gravitationThe current Gold Standard Theory of Gravitation is the general theory of relativity. This is a classical, relativistic field theory of gravitation...
and propagation of light through an optical medium having a spatially varying refractive indexRefractive indexIn optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
. Wilson's approach to a unified field theoryUnified field theoryIn physics, a unified field theory, occasionally referred to as a uniform field theory, is a type of field theory that allows all that is usually thought of as fundamental forces and elementary particles to be written in terms of a single field. There is no accepted unified field theory, and thus...
is not considered viable today. - An attempt (roughly 1960-1970) by Robert Dicke and Fernando de Felice to resurrect and improve Wilson's idea of an optical analogue of gravitational effects. If interpreted conservatively as an attempt to provide an alternative approach to gtr, rather than as work toward a theory unifying electromagnetism and gravitation, this is not an unreasonable approach, although most likely of rather limited utility.
- The 1967 proposal of Andrei SakharovAndrei SakharovAndrei Dmitrievich Sakharov was a Soviet nuclear physicist, dissident and human rights activist. He earned renown as the designer of the Soviet Union's Third Idea, a codename for Soviet development of thermonuclear weapons. Sakharov was an advocate of civil liberties and civil reforms in the...
that gravitation might arise from underlying quantum field theoryQuantum field theoryQuantum field theory provides a theoretical framework for constructing quantum mechanical models of systems classically parametrized by an infinite number of dynamical degrees of freedom, that is, fields and many-body systems. It is the natural and quantitative language of particle physics and...
effects, in a manner somewhat analogous to the way that the (simple) classical theory of elasticity arises from (complicated) particle physics. This work is generally regarded as mainstream and not entirely implausible, but highly speculative, and most physicists seem to feel that little progress has been made. - In a series of papers, Bernard HaischBernard HaischBernard Haisch is a German-born American astrophysicist who has done research in solar-stellar astrophysics and stochastic electrodynamics. He has developed with Alfonso Rueda a speculative theory that the non-zero lowest energy state of the vacuum, as predicted by quantum mechanics, might provide...
and Alfonso Rueda have proposed that the inertiaInertiaInertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...
of massive objects arises as a "electromagnetic reaction force", due to interaction with the so-called zero point field. According to mainstream physics, their claims rest upon incorrect computations using quantum field theoryQuantum field theoryQuantum field theory provides a theoretical framework for constructing quantum mechanical models of systems classically parametrized by an infinite number of dynamical degrees of freedom, that is, fields and many-body systems. It is the natural and quantitative language of particle physics and...
. - Recent work, motivated in large part by the discoveries of the Unruh effectUnruh effectThe Unruh effect , was first described by Stephen Fulling in 1973, Paul Davies in 1975 and Bill Unruh in 1976. It is the prediction that an accelerating observer will observe black-body radiation where an inertial observer would observe none...
, Hawking radiationHawking radiationHawking radiation is a thermal radiation with a black body spectrum predicted to be emitted by black holes due to quantum effects. It is named after the physicist Stephen Hawking, who provided a theoretical argument for its existence in 1974, and sometimes also after the physicist Jacob Bekenstein...
, and black hole thermodynamicsBlack hole thermodynamicsIn physics, black hole thermodynamics is the area of study that seeks to reconcile the laws of thermodynamics with the existence of black hole event horizons...
, to work out a complete theory of physical analogues such as optical black holes. This is not work toward a unified field theory, but in another sense can be regarded as work towards an even more ambitious unification, in which some of the most famous effects usually ascribed to general relativity (but actually common to many metric theories of gravitation) would be seen as essentially thermodynamical effects, not specifically gravitational effects. This work has excited great interest because it might enable experimental verification of the basic concept of Hawking radiation, which is widely regarded as one of the most revolutionary proposals in twentieth century physics, but which in its gravitational incarnation seems to be impossible to verify in experiments in earthly laboratories. - The 1999 proposal by Keith Watt and Charles W. MisnerCharles W. MisnerCharles W. Misner is an American physicist and one of the authors of Gravitation. His specialties include general relativity and cosmology. His work has also provided early foundations for studies of quantum gravity and numerical relativity....
of a scalar theory of gravitationScalar theories of gravitationScalar theories of gravitation are field theories of gravitation in which the gravitational field is described using a scalar field, which is required to satisfy some field equation....
which postulates a stratified conformally flat metric of the form
, given with respect to a Cartesian chart, where φ satisfies a certain partial differential equationPartial differential equationIn mathematics, partial differential equations are a type of differential equation, i.e., a relation involving an unknown function of several independent variables and their partial derivatives with respect to those variables...
which reduces in a vacuum region to the flat spacetime wave equationWave equationThe wave equation is an important second-order linear partial differential equation for the description of waves – as they occur in physics – such as sound waves, light waves and water waves. It arises in fields like acoustics, electromagnetics, and fluid dynamics...
. This is a "toy theory", not a fully fledged theory of gravitation, since as Watt and Misner pointed out, while this theory does have the correct Newtonian limitNewtonian limitIn physics, the Newtonian limit refers to physical systems without significantly intense gravitation, in the sense that Newton's law of universal gravitation may be used to obtain values that are correct to a high order...
, it disagrees with the result of certain observations.
See also
- Induced gravityInduced gravityInduced gravity is an idea in quantum gravity that space-time background emerges asa mean field approximation of underlying microscopic degrees of freedom, similar to the fluid mechanics approximation of Bose–Einstein condensates...
(for Sakharov's proposal) - Stochastic electrodynamicsStochastic electrodynamicsIn theoretical physics, Stochastic Electrodynamics is a variant of Classical Electrodynamics which posits the existence of a classical Lorentz Invariant radiation field having statistical properties similar to that of the electromagnetic zero-point field of Quantum Electrodynamics...
- Bernard HaischBernard HaischBernard Haisch is a German-born American astrophysicist who has done research in solar-stellar astrophysics and stochastic electrodynamics. He has developed with Alfonso Rueda a speculative theory that the non-zero lowest energy state of the vacuum, as predicted by quantum mechanics, might provide...
- Maxwell's equations in curved spacetimeMaxwell's equations in curved spacetimeIn physics, Maxwell's equations in curved spacetime govern the dynamics of the electromagnetic field in curved spacetime or where one uses an arbitrary coordinate system...
- Electromagnetic stress-energy tensor
External links
- H. E. Puthoff, M. Ibison, Polarizable Vacuum "Metric Engineering" Approach to GR-Type Effects, MITRE Conference, McLean, VA, May 8, 2003. From the website of EarthTech, a company founded by Puthoff.
- H. E. Puthoff, S. R. Little, M. Ibison, Engineering the Zero-Point Field and Polarizable Vacuum For Interstellar Flight, Institute for Advanced Studies, Austin, Texas, January 2001.