Research Publications

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    Secret Life of the Spacetime
    (World scientific, 2012-03-28) Padmanabhan, T.
    Just as the thermal properties of normal matterdemandsthe existence of microscopic degrees of freedom, the thermal properties of null surfaces — perceived as local Rindler horizons by accelerated observers — demands the existence of microscopic degrees of freedom to spacetime. The distortion of the null surfaces, just like the deformation of an elastic solid, costs entropy. I show how, just like in the case of an elastic solid, one can describe the dynamics of thespacetime solid by introducing an entropy density to the distortion of null surfaces in the spacetime.
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    Conformal quantization and space-time singularity
    (World Scientific Publishing group, 1986-06-06) Joshi, P. S.; Narlikar, J. V.
    This work generalizes earlier results of conformal quantization that within the full range of space-times conformal to any singular space-time satisfying Einstein's field equations for minimally coupled matter, the singular solutions form a set of zero-probability measure. A wider definition of space-time singularity that includes the curvature singularity assumed in the earlier work (op. cit.) is adapted and it is shown that the previous conclusion stands even when the present state of the universe is defined by wave functionals that are not necessarily wave packets. Within the present framework of quantum gravity therefore it seems extremely unlikely that the universe had a singular origin.
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    Quantum fluctuations near the classical spacetime singularity
    (World Scientific, 1984-01-18) Narlikar, J. V.
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    Vanishing likelihood of spacetime singularity in quantum conformal cosmology
    (Springer, 1984-01-06) Narlikar, J. V.
    A general formalism is developed for studying the behavior of quant&ed conformal fluctuations near the space-time singularity of classical relativistic cosmology. It is shown that if the material contents of space-time are made of massive particles which obey the principle of asymptotic freedom and interact only gravitationally, then it is possible to estimate the quantum mechanical probability that, of the various possible conformal transforms of the classical Einstein solution, the actual model had a singularity in the past. This probability turns out to be vanishingly small, thus indicating that within the regime of quantum conformal cosmology it is extremely unlikely that the universe originated out of a space-time singularity.
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    Quantum conformal fluctuations in a singular spacetime
    (Nature Publishing Group, 1982-02-25) Padmanabhan, T.; Narlikar, J. V.
    The cosmological solutions of Einstein's general relativistic equations lead inevitably to space-time singularities. However, general relativity is only an approximation to a fully quantized theory of gravity and we need to consider whether singularity persists in the quantum domain. Although a full quantum theory of gravity has not yet been developed, we show here that the above question can be tackled in a simplified model where only the conformal degree of freedom is quantized. Previous applications of this technique had shown that in specific cases the quantum conformai fluctuations (QCF) from the classical solutions diverge at the classical singularity, thus rendering the classical solution physically meaningless. Recently one of us (J.V.N. ref. 4) has generalized this result to cover all dust cosmologies. Here we show that this conclusion is applicable to even more general types of cosmological singularities.
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    Quantum fluctuations in the conformally flat and the Schwarzschild spacetimes
    (Springer, 1981-01-12) Padmanabhan, T.; Narlikar, J. V.
    A general technique is described for dealing with the quantum fluctuations between conformally flat space-times. The second part of the paper deals with the Schwarzschild spacetime. It is shown there that this space-time is stable against fluctuations of mass, but transitions between two space-times of different masses can be obtained via conformal fluctuations. Purely conformal fluctuations of the Schwarzschild metric are, however, damped at the event horizon. Similar conclusions are drawn about the Reissner-Nordstrom space-time.
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    Quantum conformal fluctuations near the classical spacetime singularity
    (Springer, 1981-01-15) Narlikar, J. V.
    This paper investigates the behavior of conformal fluctuations of space-time geometry that are admissible under the quantized version of Einstein's general relativity. The approach to quantum gravity is via path integrals. It is shown that considerable simplification results when only the conformal degrees of freedom are considered under this scheme, so much so that it is possible to write down a formal kernel in the most general case where the space-time contains arbitrary distributions of particles with no other interaction except gravity. The behavior of this kernel near the classical space-time singularity then shows that quantum fluctuations inevitably diverge near the singularity. It is shown further that the root cause of this divergence lies in the fact that the Green's function for the conformally invariant scalar wave equation diverges at the singularity. The limitations on the validity of classical general relativity near the space-time singularity are discussed and it is argued that the notion of singularity itself needs to be radically modified once the quantum effects are taken into account.
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    Biscalar and bivector green's functions in de sitter space time
    (National academy, 1970-03-15) Narlikar, J. V.
    Biscalar and bivector Green's functions of wave equations are calculated explicitly in de Sitter space time. The calculation is performed by considering the electromagnetic field generated by the spontaneous creation of an electric charge.
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    Time asymmetry in electrodynamics and cosmology
    (-, 1970-03-10) Narlikar, J. V.
    The concept of the barrow of time' is discussed in relation to thermodynamics, electrodynamics and cosmology Time symmetric electrodynamics, the absorber theory of radiation and quantum transitions receive attention to develop a working theory applicable to a universe with a perfect future absorber and an imperfect past absorber, such as the steady state cosmological model. It is stated that the approach adopted herein establishes a strong connection between the electrodynamic and cosmological arrows of time, and points a way towards linking these arrows with the thermodynamic one.
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    What can classical gravity tell us about quantum structure of spacetime?
    (IOP Publishing, 2011-09-12) Padmanabhan, T.
    Several features of classical gravity, combined with the existence of Davies-Unruh temperature of horizon s, support the following paradigm: Gravitational field equations in a wide class of theories, including Einstein ’s theory, should be viewed as describing the thermodynamic limit of the statistical mechanics of (as yet unknown) atoms of spacetime. I present the conceptual evidence for this emergent paradigm and discuss several facets of this approach.