Why a variableG?

Since a possible time variability ofG has received renewed attention (Wesson and Goodson, 1981), we think it is important to stress a conceptual aspect so far not sufficiently appreciated and which puts the variability ofG in a much wider context. VariableG is a popular but incomplete representation of a much deeper problem:Is the Strong Equivalence Principle (SEP) valid?     

Viscous fluid in a kaluza-klein metric

Exact solutions are obtained in a five-dimensional space-time with an energy-momentum tensor containing a viscous fluid, assuming either an equation of state or a special form for the viscous term in line with the assumption of Belinskii and Khalatnikov (1977). The solutions are, in fact, generalizations of an earlier work by Grøn for a perfect fluid in the 5D rest-mass varying theory of gravity proposed recently by Wesson. It is found that dimensional reduction of the extra space takes place in some of the cases such that the 5-dimensional universe naturally evolves into an effective 4-dimensional one. A huge amount of entropy can be produced following this shrinkage of extra-dimension which may account for the very large value of entropy per baryon observed in our 4D world. Moreover, the observed constancy of the rest-mass in the present era is also interpreted.     

Five-dimensional cosmological model with a time-dependent equation of state in Wesson’s theory

Exact solution for a homogeneous cosmological model in 5D space-time-mass gravity theory proposed by Wesson (Astron. Astrophys. 119:145, 1983) is obtained by assuming the time-dependent equation of state. The behavior of the solution is discussed for the two cases k<0 and k=0. It is found that the observed constancy of the rest mass of an isolated particle in the present era may be interpreted as a consequence of the decreasing rate of change of rest mass with time. Moreover, a spontaneous compactification-like phenomenon of an extra dimension takes place in the case of k=0. It is also found that with decrease in extra space the observable three-dimensional space entropy increases, thus accounting for the large value of entropy observable at present.     

Scale invariant theory for Bianchi Type VIII and IX space-times with perfect fluid

In this paper we have taken an attempt to study the feasibility of scale invariant theory (Wesson, 1981a,b) in Bianchi type VIII and IX space-times with a time dependent gauge function (Dirac Gauge i.e. βα )and a matter field in the form of a perfect fluid. It is found that Bianchi type VIII (δ=1) space-time is feasible in this theory whereas Bianchi type IX (δ=-1) space-time is not feasible. In this feasible case a radiating model is constructed and its physical behaviour is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cosmological models with viscous fluid and time- dependent equation of state in Wesson’s theory

Assuming the time-dependent equation of state p=λ(t)ρ, five dimensional cosmological models with viscous fluid for an open universe (k=−1) and flat universe (k=0) are presented. Exact solutions in the context of the rest mass varying theory of gravity proposed by Wesson (Astron. Astrophys. 119, 145, 1983) are obtained. It is found that the phenomenon of isotropisation takes place in this theory, i.e. the mass scale factor A(t) which characterizes the rest mass of a typical particle is evolving with cosmic time just as the spatial scale factor R(t). It is further found that rest mass is approximately constant in the present universe.     

Self-similar space-times

An exact solution of Einstein's field equations is given representing an inhomogeneous sphere of matter in static isothermal equilibrium with a density profile of the form R ^–2. A perturbation analysis shows that initial small density inhomogeneities grow self-similarly in a non-extreme configuration for which general relativistic effects are important. The perturbed configuration develops asymptotically like the expanding solution to Einstein's equations considered previously by Henriksen and Wesson, and the present solution is therefore identified as the initial stage of that evolving model. As a cosmology, the solutions in tandem provide an expanding cosmology that did not begin as a Big Bang, but evolved from an inhomogeneous primeval atom, tending at late epochs to a model with homogeneous density. The new static solution has applications also in other branches of astrophysics.     

The number of information bits related to the minimum quantum and gravitational masses in a vacuum dominated universe

Wesson obtained a limit on quantum and gravitational mass in the universe by combining the cosmological constant Λ, Planck’s constant ?, the speed of light c, and also the gravitational constant G. The corresponding masses are 2.0×10^?62 kg and 2.3×10⁵⁴ kg respectively, and in general can be obtained with the help of a generic dimensional analysis, or from an analysis where the cosmological constant appears in a four dimensional space-time and as a result of a higher dimensional reduction. In this paper our goal is to establish a relation for both quantum and gravitational mass as function of the information number bit N. For this reason, we first derive an expression for the cosmological constant as a function of information bit, since both masses depend on it, and then various resulting relations are explored, in relation to information number of bits N. Fractional information bits imply no information extraction is possible. We see, that the order of magnitude of the various parameters as well as their ratios involve the large number 10¹²², that is produced naturally from the fundamental parameters of modern cosmology. Finally, we propose that in a complete quantum gravity theory the idea of information the might have to be included, with the quantum bits of information (q-bits) as one of its fundamental parameters, resulting thus to a more complete understanding of the universe, its laws, and its evolution.     

General-relativistic hierarchical cosmology: An exact model

An exact solution of Einstein's equation is stated in which the density (), pressure (p), scale factorS and metric coefficients are functions of only one dimensionless self-similar variable,ct/R, wheret is cosmic time andR is a co-moving radial coordinate. The solution represents a cosmology that begins as a static sphere having R ^–2 and evolves into an expanding model which is pressure-free and has a hierarchical type of density law ( R ^–, approximately, with =a number, 02). It is suggested that this model should supersede the previous models of Wesson and other workers, since it appears to be the simplest cosmology for a hierarchy.     

Books and Multimedia Reviews

Book reviewed in this article: Shoemaker by Levy: The Man who Made an Impact by David H. Levy Impact Stratigraphy: The Italian Record by Alessandro Montanari and Christian Koeberl The Odessa Meteorite Craters and Their Geological Implications by Glen L. Evans and Charles E. Mear Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature by Ewen A. Whitaker Impacts and the Early Earth edited by Iain Gilmour and Christian Koeberl     

Books and Multimedia Reviews

Book reviewed in this article: Our Universe: The Thrill of Extragalactic Exploration as Told by Leading Experts edited by S. Alan Stern. Solar System Dynamics by C. D. Murray and S. F. Dermott. Astrobiology by Monica Grady. Moon Lander by Thomas J. Kelly. Noble Gas Geochemistry by Minoru Ozima and Frank A. Podosek.     

Adaptive optics for large telescopes

The performance of large telescopes is determined both by their angular resolution and by their collection area. It is, therefore, important to achieve as high an angular resolution as possible by site selection, by avoiding image deterioration by the telescope and its environment, and by real time image restoration by adaptive optics. We summarize the principles of adaptive optics, their predicted performance and the current programs underway to implement adaptive optics for astronomical purposes.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.     

Pancake cyclones and anti-cyclones in the ionosphere

The formation of pancake cyclones and anticyclones in the E-region of the Earth's ionosphere is considered. It is shown that the vortices can be maintained by the neutral winds or by chemical reactions including the energy release caused by the triple collisions of atomic oxygen with neutrals. It is found that the variations of the magnetic fields induced by the vortices are not localized and decrease slowly far from the vortex core. They can be easily detected by ground based magnetometers or by facilities on board the low-orbiting satellites.     

Book Reviews

Book Revieweds in this article: Victor Moritz Goldschmidt: Father of Modern Geochemistry by Brian Mason Meteorites: The Key to Our Existence by Robert Hutchison and Andrew Graham From Mantle to Meteorites edited by K. Gopalan, Vinod K. Gaur, B. L. K. Somayajulu and J. D. Macdougall Our Universe: An Armchair Guide by Michael Rowan-Robinson. W. H. Freeman Comets: A Chronological History of Observation, Science, Myth, and Folklore by Donald K. Yeomans Dictionary of Minor Planet Names by Lutz D. Schmadel.     

The light curve analysis of MM Herculis

The photoelectric light curves of MM Her obtained in 1983 and 1984 by Evren (1985, 1987) were analyzed by two different methods. Firsly, the effects of the wave-like distortions on the observations were removed from the observed magnitudes by obtaining its mathematical expression. The remaining light curves were analyzed by using Wood's approach. Later, the light curves of the same years were treated by the method of Wilson-Devinney and distortions seen in the light curves were thought to be explained by locating the spots on the surface of the cooler component. The results obtained by two different approaches are in good agreement.     

Book and Multimedia Reviews

Book reviewed in this article: Encyclopedia of Mineral Names by William H. Blackburn and William H. Dennen. Radiogenic Isotope Geology by A. P. Dickin Evolution of Hydrothermal Ecosystems on Earth (and Mars?) edited by Gregory R. Bock and Jamie A. Goode The Strange Case of Mrs. Hudson's Cat: And Other Science Mysteries Solved by Sherlock Holmes by Colin Bruce Astrophysical Implications of the Laboratory Study of PreSolar Materials edited by Thomas Bernatowicz and Ernst Zinner     

Book Reviews

Book Revieweds in this article: The Shadows of Creation by Michael Riordon and David Schramm. W.H. Freeman From Stone to Star by Claude Allègre GPS Satellite Surveying by Alfred Leick Le Fer de Dieu by Théodore Monod and Brigitte Zanda Meteoritter, nøglen til Jordens Fortid by Vagn F. Buchwald     

Books and Multimedia Reviews

Book reviewed in this article: Evolutionary Catastrophes: The Science of Mass Extinction by Vincent Courtillot. Brother Astronomer: Adventures of a Vatican Scientist by Brother Guy Consolmagno SJ. Photochemistry of Planetary Atmospheres by Yuk L. Yung and William B. DeMore. Looking for Earths: The Race to Find New Solar Systems by Alan Boss. Venus Revealed: A New Look Below the Clouds of our Mysterious Twin Planet by David H. Grinspoon.     

Nonresonant generation of MHD disturbances during supernova explosions in an inhomogeneous interstellar medium

We analyze the nonresonant generation of large-scale magnetic inhomogeneities near a shock front by accelerated particles. The MHD disturbances are generated by the electric current excited by relativistic particles in the preshock medium in the presence of weak large-scale density inhomogeneities. The MHD modes considered can be amplified by other resonant and nonresonant mechanisms related to the presence of relativistic particles. We estimate the magnetic fields and the energies to which charged particles can be accelerated in different phases of the interstellar medium by taking into account the random magnetic fields generated by the mechanism considered.     

Books and Multimedia Reviews

Book reviewed in this article: Fault-Related Rocks: A Photographic Atlas edited by A. W. Snoke, J. Tullis, and V. R. Todd. The Search for Life on Other Planets by Bruce Jakosky. The Search for Extraterrestrial Life: Essays on Science and Technology edited by Peter Day Cosmic Bullets: High Energy Particles in Astrophysics by Roger Clay and Bruce Dawson. Pluto and Charon edited by S. Alan Stern and David J. Tholen. Fanfare for Earth by Harry McSween, Jr. St.