Thermodynamics of spacetime: The Einstein equation of state.
TLDR
The Einstein equation is derived from the form of black hole entropy together with the fundamental relation $\delta Q=TdS$ connecting heat, entropy, and temperature, and its validity is seen to depend on the existence of local equilibrium conditions.Abstract:
The Einstein equation is derived from the proportionality of entropy and the horizon area together with the fundamental relation $\ensuremath{\delta}Q\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}T\mathrm{dS}$. The key idea is to demand that this relation hold for all the local Rindler causal horizons through each spacetime point, with $\ensuremath{\delta}Q$ and $T$ interpreted as the energy flux and Unruh temperature seen by an accelerated observer just inside the horizon. This requires that gravitational lensing by matter energy distorts the causal structure of spacetime so that the Einstein equation holds. Viewed in this way, the Einstein equation is an equation of state.read more
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f(R) theories
TL;DR: Various applications of f(R) theories to cosmology and gravity — such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds are reviewed.
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The Holographic principle
TL;DR: The holographic principle as mentioned in this paper asserts that the fundamental degrees of freedom involved in a unified description of spacetime and matter must be manifest in an underlying quantum theory of gravity, and it has yet to be explained.
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On the origin of gravity and the laws of Newton
TL;DR: In this article, the authors present a heuristic argument that shows that Newton's law of gravitation naturally arises in a theory in which space emerges through a holographic scenario and gravity is identified with an entropic force caused by changes in the information associated with the positions of material bodies.
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Dark energy cosmology: the equivalent description via different theoretical models and cosmography tests
TL;DR: In this paper, a review of different dark energy cosmologies for different fluids is presented, and their properties are also explored, and special attention is paid to the equivalence of different models.
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Dark energy cosmology: the equivalent description via different theoretical models and cosmography tests
TL;DR: In this article, a review of different dark energy cosmologies is presented, including the Lambda$CDM cosmology, Little Rip and Pseudo-Rip universes, the phantom and quintessence cosmology with Type I, II, III and IV finite-time future singularities and non-singular dark energy universes.
References
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The world as a hologram
TL;DR: In this article, the effects of particle growth with momentum on information spreading near black hole horizons were investigated. But the authors only considered the earliest times of the propagation of information near the horizon.
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Increase of black hole entropy in higher curvature gravity.
TL;DR: Within a class of higher curvature theories where the Lagrangian consists of a polynomial in the Ricci scalar, a conformally equivalent theory is used to establish that stationary black hole solutions with a Killing horizon satisfy the Zeroth Law, and that the Second Law holds in general for any dynamical process.