Research Papers (JVN)
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Item Astronomy at the millennium(2002-03-27) Narlikar, J. V.This paper will highlight the important developments in astronomy in the last decade of the twentieth century and in the opening years of the twenty-first, On the observational front, the discovery of extra-solar planets, the detection of gamma- ray bursts and studies of the distances of extragalactic supernovae with implications for the expansion of the universe are the major developments highlighted here. On the theoretical front, the paper reports on the speculations in very high energy physics that have implications for cosmology, the role of the cosmological constant and the quasi-steady state cosmology proposed as an alternative to the big bang.Item Radiation backgrounds and their cosmologival implications(T.I.F.R., 1983-01-15) Narlikar, J. V.The information content of radiation backgrounds at wavelengths ranging from radio waves to gamma rays is reviewed, within the context of the standard big bang cosmology. It is shown that the various backgrounds provide useful inputs and constraints on the physical features of the universe such as the existence and growth of large scale inhomogeneities like galaxies, clusters and superclusters, the overall density of the universe, the photon to baryon ratio and the extent of antimatter in the universe, etc. It is argued that there are questions posed by the data which may require rethinking of some aspects of standard cosmology.Item Quantum cosmology as a cure of three ailments of classical cosmology(Astronomical Society of India, 1983-08-12) Padmanabhan, T.; Narlikar, J. V.The standard big bang models of classical cosmology are known to possess three defects. The oldest known defect is spacetime singularity whose existence seems inevitable within the classical framework. The second defect is the existence of a particle horizon which severely limits communications across the distant parts of the universe whose observed homogeneity therefore becomes inexplicable. Recently a third defect has been highlighted, viz., the required fine tuning of the early universe close to the flat spatial model in order to account for the present range of its mean density. We show before that the injection of quantum ideas holds out hope of a cure for all the three ailments described above. Using a simple path integral formalism for quantum cosmology we present arguments which suggest that (i) it is extremely unlikely that the universe evolved to the present state from quantum states of singularity and particles horizon;(ii) of all the possible Robertson-Walker models that could evolve our of quantum fluctuations of the empty Minkowski universe the flat model is overwhelmingly probable.Item Astro-particle physics in the quasi-steady state cosmology(Hadronic Press, 1997-06-25) Narlikar, J. V.This work highlights the conceptual and theoretical issues underlying the quasi- steady state cosmology which was proposed by the F. Hoyle, G. Burbidge and the author as an alternative to the standard big band cosmology. In particular, it is argued that this cosmology offers the high energy particle physicists several challenging problems on the cosmology-panicle physics frontier. To begin with it is shown with the help of a toy model how the problems of spacetime singularity and violation of the energy momentum conservation law that are present in the standard cosmology can be avoided by introducing a scalar field minimally coupled to gravity and having its sources in events where matter is created. It is then shown that matter creation preferentially occurs near collapsed massive objects and the scalar field created at such mini-creation events has a feedback on spacetime geometry causing the universe to have a steady expansion as in the de Sitter model but with periodic phases of expansion and contraction superposed on it. The parameters of the toy model can be empirically fixed in relation to the cosmological observations thus providing tests of the theory. Next it is argued that the toy model arises from a deeper theory which is Machian in origin with the inertia of a particle determined by the rest of the particles in the universe in a long range conformally invariant scalar interaction. The characteristic mass of a particle created is then the Planck mass. The Planck particle decays quickly to baryons. It is shown that the inertial effects produced by the Planck particles during their brief existence generate the scalar field of the toy model while the inertial effects of the stable baryonic particles give the more familiar Einstein equations of relativity. The baryons into which the Planck particle decays from an SU3 octet which, in the high density - high energy environment of mini-creation event finally forms the nuclei of hydrogen, heliu m and other elements of low atomic masses. These predicted abundances match those actually found. Finally it is shown that extending the theory to the most general confor- mally invariant form automatically leads to the cosmological constant whose sign and magnitude are of the right cosmological order.Item Alternative cosmology(Korean Astronomical Society, 1996-06-18) Narlikar, J. V.Recent discussions of observational constraints on the standard hot big bang model are reviewed and it is argued that now there is room for considering alternative cosmologies. The quasi-steady state cosmology is briefly described. This model seems to explain most of the observed features of the universe, including the m-z relation, radio source count, the light nuclear abundances and the microwave background.Item Alternative to big bang cosmology(World Scientific Publishing Company, 1995-03-15) Narlikar, J. V.Item Basic theory underlying the quasi-steady state cosmology(Royal Society Publishing, 1995-02-08) Hoyle, F.; Burbidge, G.; Narlikar, J. V.Outside cosmology, the procedure normally followed in science requires the inte- gration of hyperbolic partial differential equations subject to initial data given on a free surface, which is usually taken to be a time section of spacetime. The initial data are determined in experimental science from observation and the re- sults of the integrations are also checked by observations. Friedmann (Big Bang) cosmology suffers, however, from the fact that the observations cannot determine initial conditions. Thus in that theory the initial conditions have only the weak status of guesses. There is also some question whether the correct equations are being used, since the gravitational equations of that cosmology are not scale invariant, a situation unlike the rest of physics. Since matter exists in what is supposed to be a space of finite temporal duration its origin should be explained, working from a suitable lagrangian and action. Otherwise the origin is placed outside science. This is what is done in Big Bang cosmology. In this paper we depart from the standard procedure by first deriving grav- itational equations that are scale invariant, whence it is shown that in a scale invariant gravitational theory particles have the property that the two lengths associated with them, the Compton wavelength and gravitational radius, must be comparable, i.e. they are Planck particles. It is then shown that the theory has the scope to explain the genesis of the so-called cosmological constant, and the usually required magnitude of the cosmological constant is derived. When interactions other than gravitation are included, Planck particles are un- stable. The effect of instability on newly created Planck particles is to introduce terms into the gravitational equations additional to those of general relativity. In particular, there are negative pressure terms which act to expand the universe. The energy terms are such as to suggest that particle creation must be of an ex- plosive nature and that it must occur in the neighbourhoods of highly compacted bodies, a property which appears to provide a connection between cosmological theory and high-energy astrophysics.Item Quasi-steady state cosmology(University of South Africa, 1994-01-22) Narlikar, J. V.Because of a number of unsatisfactory features of the standard hot big bang cosmology, it is argued that there is a case for exploring alternative approaches to cosmology. The approach described here attempts to relate the large scale features of the universe to the basic phenomenon of creation of matter. This theory, called the quasi steady state cosmology (QSSC), begins with a field heoretic description of matter creation within the framework of general relativity. A scalar field C of zero restmass but negative energy and stresses interacts with matter at the instants of creation thereby preserving the law of conservation of the universe expanding at an overall exponential rate along with cycles of expansion and contraction with shorter time scales. It is argued that such a solution arises from mini-creation events taking place near the event horizons of highly collapsed massive objects. The now familiar phe- nomena like QSOs, AGN , radio sources, etc. are the manifestations of matter creation in such events. These events arc cophased and the oscillations occur because of feedback between the creation process and the expansion of space. In this way he cosmology is seen to be related to high energy astrophysics in a very direct way. The QSSC can explain the abundances of light nuclei and the microwave background, the observed large scale features of the universe like the m — z relation, the source count, the angular size-redshift relation, as well as the observed distribution of the ages of galaxies. This work gives a brief review of these properties of the quasi steady state cosmology.Item Alternative cosmology(P.C. Vaidya Sanman Nidhi Trust, 1993-03-29) Narlikar, J. V.Item Extragalactic universe: an alternative view(Nature Publishing Group, 1990-08-30) Narlikar, J. V.; Arp, H. C.; Burbidge, G.; et al.We discuss evidence to show that the generally accepted view of the Big Bang model for the origin of the Universe is unsatisfactory. We suggest an alternative model that satisfies the constraints better.