Research Papers (JVN)

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    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.
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    Black hole physics in globally hyperbolic space-times
    (Indian Academy of Sciences, 1982-02-16) Joshi, P. S.; Narlikar, J. V.
    The usual definition of a black hole is modified to make it applicable in a globally hyperbolic space-time. It is shown that in a closed globally hyperbolic universe the surface area of a black hole must eventually decrease. The implications of this breakdown of the black hole area theorem are discussed in the context of thermodynamics and cosmology. A modified definition of surface gravity is also given for non-stationary universes. The limitations of these concepts are illustrated by the explicit example of the Kerr-Vaidya metric.
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    Black holes as detectors of tachyons
    (General Relativity and Gravation, 1978-01-17) Narlikar, J. V.; Dhurandhar, Sanjeev
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    Tachyon trajectories in Schwarzschild's space-time
    (Springer, 1976-03-15) Narlikar, J. V.; Dhurandhar, Sanjeev
    The motion of a tachyon in the empty Schwarzschild solution outside a mass m i~ discussea. It is shown that a tachyon falling radially inwards never reaches the space-time singularity at the origin. Instead, it is bounced back at a point inside the Schwarzschild radius. The causal and non-causal aspects of such a bounce are considered. It is shown that a tachyon dropped from a radial co- ol'dinate < 2.56 m always aarives before it went in whereas a tachyon dropped from a radial co-ordinate >3.27 m always arrives later than its starting time. The more general case of a tachyon with a finite angular momentum is also analyzed. The possible astrophysical consequence7 of the presence of tachyons near condensed or collapsing objects and black holes are qualitathely discussed.
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    Schwarzschild solution: some conceptual difficulties
    (Springer, 1987-04-27) Narlikar, J. V.; Padmanabhan, T.
    It is shown that inconsistencies arise when we look upon the Schwarzschild solution as the space-time arising from a localized point singularity. The notion of black holes is critically examined, and it is argued that, since black hole formation never takes place within the past light cone of a typical external observer, the discussion of physical behavior of black holes, classical or quantum, is only of academic interest. It is suggested that problems related to the source could be avoided if the event horizon did not form and that the universe only contained quasi-black holes.