Research Papers (TP)

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1982 - 19878

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End date: 1999Subject: search.filters.subject.Quantum gravity

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    Inflation from quantum gravity
    (Elsevier Science Publishers, 1984-08-27) Padmanabhan, T.
    A model for inflation based on a quantum gravity scenario is presented. The process allows inflation of a Planck size bubble to the observed universe.
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    Limitations on the operational definition of spacetime events and quantum gravity
    (IOP Publishing, 1987-01-12) Padmanabhan, T.
    Using simple arguments from general relativity and quantum theory we show that it is not possible to devise experiments (or operational procedures) which will measure the position of a particle to an accuracy better than the Planck length (Gh/c3) = cm. It is also impossible to synchronise clocks to a precision better than Planck time. The implications of the result are discussed.
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    Quantum cosmology and stationary states
    (Spinger, 1982-06-04) Padmanabhan, T.
    A model for quantum gravity, in which the conformal part of the metric is quantized using the path integral formalism, is presented. Einstein's equations can be suitably modified to take into account the effects of quantum conformal fluctuations. A closed Friedman model can be described in terms of well-defined stationary states. The "ground states" sets a lower bound (at Plank length) to the scale factor preventing the collapse. A possible explanation for matter creation and quantum nature of matter is suggested.
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    Quantum stationary geometries and avoidance of singularities
    (IOP Publications, 1983-09-26) Padmanabhan, T.
    A recent approach to quantum gravity leading to the concept of quantum stationary geometries is reviewed. A stationary states equation is presented for: (a)homogeneous relativistic cosmologies of the various Bianchi types; (b) a Friedmann universe filled with a massless scalar field. The equation is solved near the singularity to show that stationary states avoid the singularity. The result is discussed and compared with other approaches.
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    Quantum gravity and the "flatness problem" of standard big bang cosmology
    (Elsevier Science Publishers, 1983-06-13) Padmanabhan, T.
    It is shown that, if the universe originated through quantum conformal fluctuations from the empty Minkowski space, then it is most likely to be spatially flat.
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    Quantum Conformal Fluctuations and Stationary States
    (Plenum Publishing Corporation, 1982-04-07) Padmanabhan, T.
    Conformal fluctuations serve as a powerful tool to study the nature of quantum gravity. They lead, in a natural fashion, to the concept of stationary states for the quantum geometry. We attempt to incorporate the effect of conformal fluctuations into the background metric and matter. A modified set of equations, including the effect of conformal fluctuations, is presented and the solutions are discussed. It is shown that matter-free vacuum is unstable to conformal fluctuations. A scenario for creation of matter is indicated.
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    Physical Significance of Planck Length
    (Elsevier Science Publishers, 1984-08-14) Padmanabhan, T.
    The significance of Planck length in a quantum gravity model is investigated by concentrating on the conformal degree of freedom. It is shown that Planck length is a lower bound to physical proper length in any space-time. It is impossible to construct an apparatus which will measure length scales smaller than Planck length. These effects exist even in flat space-time because of vacuum fluctuations of gravity. It is shown that these fluctuations lead to a high energy cut-off in flat space field theories, thereby removing the divergence problem. The oneloop corrections to a self interacting scalar field is computed and shown to be finite.
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    Approach to quantum gravity
    (American Physical Society, 1983-08-15) Padmanabhan, T.
    A model for quantum gravity is presented by treating the light-cone structure of space time as classical and the conformal factor as a quantum degree of freedom. The motivation and the details of the formalism are discussed. The approach is used to discuss the question of singularities in the cosmological models. It is shown that one can introduce the concept of stationary states for the quantum geometry, in analogy with the stationary states of simple quantum systems. The quantum stationary geometries QSG's)avoid the classical singularities. The light-cone structure is determined by a set of equations involving the expectations values in the QSG concerned. The cosmological implication of the formalism, especially to matter creation, flatness, etc. are discussed. The theory is conformally invariant in the quantum level.