Cosmological Thermodynamics Research Articles

Thermodynamics of scale-dependent Friedmann equations

In this work, the role of a time-varying Newton constant under the scale-dependent approach is investigated in the thermodynamics of the Friedman equations. In particular, we show that the extended Friedman equations can be derived either from equilibrium thermodynamics when the non-matter energy momentum tensor is interpreted as a fluid or from non-equilibrium thermodynamics when an entropy production term, which depends on the time-varying Newton constant, is included. Finally, a comparison between black hole and cosmological thermodynamics in the framework of scale-dependent gravity is briefly discussed.

Self-organized computational rewrite language L predicating an optimal thermodynamic cosmic birth-order automorphic evolution of intelligent life, and consciousness, as nature’s IT

This autonomous self-governed explanation of the cosmological thermodynamics of entirely novel states of matter (as in a renormalization group approach) includes the currently accepted fundamentals of physics, chemical valence, the periodic table and the basic neuroscience architecture/Nature’s IT of the sentient evolution of intelligent life; with notably, the DNA/RNA molecular biology of the genetic code, Standard Model elementary particle quantum physics, non-standard mathematical analysis and consciousness. Automorphic representations demonstrably have a’rest of the universe’ phenomenology which features: the zitterbewegung; the U1 unitary geometry of Standard model/chemical valence Lamb shift; the Aharonov-Bohm and Casimir effects; the single RNA and double DNA helices of biomolecular chemistry; the neuron/glial/microtubule//brain/mind/self. This anticipates the rewrite computation both of Turing and of L itself, in addition to mathematical analysis, natural semantic language capabilities and consciousness, as all inherent in the human genome/self, creating a new starting point for more of Nature’s IT wonders to come.

Analysing dissipative effects in the ΛCDM model

In the present paper, the effects of viscous dark matter are analysed within the ΛCDM model. Here we consider bulk viscosity through the Israel-Stewart theory approach, leading to an effective pressure term in the continuity equation that accomplishes for the dissipative effects of the dark matter fluid. Then, the corresponding equation for viscosity is solved and a general equation for the Hubble parameter is obtained with the presence of a cosmological constant. The existence of de Sitter solutions is discussed, where a wider range of solutions is found in comparison to the ΛCDM model. Also the conditions for the near thermodynamical equilibrium of the fluid is analysed. Finally, a qualitative analysis provides some constraints on the model by using Supernovae Ia data which reveals the possible importance of causal thermodynamics in cosmology.

Information entropy and dark energy evolution

Here, the information entropy is investigated in the context of early and late cosmology under the hypothesis that distinct phases of universe evolution are entangled between them. The approach is based on the entangled state ansatz, representing a coarse-grained definition of primordial dark temperature associated to an effective entangled energy density. The dark temperature definition comes from assuming either Von Neumann or linear entropy as sources of cosmological thermodynamics. We interpret the involved information entropies by means of probabilities of forming structures during cosmic evolution. Following this recipe, we propose that quantum entropy is simply associated to the thermodynamical entropy and we investigate the consequences of our approach using the adiabatic sound speed. As byproducts, we analyze two phases of universe evolution: the late and early stages. To do so, we first recover that dark energy reduces to a pure cosmological constant, as zero-order entanglement contribution, and second that inflation is well-described by means of an effective potential. In both cases, we infer numerical limits which are compatible with current observations.

Cosmological thermodynamics with Hawking temperature on the apparent horizon and Unruh temperature of the fluid: Some interesting consequences

Thermodynamics on the cosmological apparent horizon of a flat Friedmann-Lemaitre-Robertson-Walker metric has been investigated with Bekenstein entropy and Hawking temperature on the horizon, and Unruh temperature for the fluid inside the horizon. This temperature is experienced by a radial comoving observer infinitesimally close to the horizon due to the pressure exerted by the fluid bounded by the horizon. An expression for the entropy of the fluid has been obtained which is found to be proportional to the volume of the thermodynamic system which implies that the Unruh temperature of the fluid is inconsistent with the holographic principle. Further, we have been able to find an expression for the effective entropy of the system. Finally, assuming a barotropic equation of state (w constant) for the fluid, it has been shown that the generalized second law holds good for a non-phantom w, while thermodynamic equilibrium is never possible for such a scenario.

On the second law of thermodynamics in modified Gauss–Bonnet gravity

The second law and the generalized second law of thermodynamics in cosmology in the framework of the modified Gauss–Bonnet theory of gravity are investigated. The conditions under which these laws hold are derived and discussed.

Entropy and anisotropy

We address the problem of defining the concept of entropy for anisotropic cosmological models. In particular, we analyze for the Bianchi I and V models the entropy which follows from postulating the validity of the laws of standard thermodynamics in cosmology. Moreover, we analyze the Cardy–Verlinde construction of entropy and show that it cannot be associated with the one following from relativistic thermodynamics.

Cosmological thermodynamics and deflationary gas universe

We establish a general thermodynamic scheme for cosmic fluids with internal self-interactions and discuss equilibrium and non-equilibrium aspects of such systems in connection with (generalized) symmetry properties of the cosmological dynamics. As an example we construct an exactly solvable gas dynamical model of a ``deflationary'' transition from an initial de Sitter phase to a subsequent Friedmann-Lema\^{\i}tre-Robertson-Walker period. We demonstrate that this dynamics represents a manifestation of a conformal symmetry of an ``optical'' metric, characterized by a specific effective refraction index of the cosmic medium.

Generalized second law in cosmology from causal boundary entropy

A classical and quantum mechanical generalized second law of thermodynamics in cosmology implies constraints on the effective equation of state of the universe in the form of energy conditions, obeyed by many known cosmological solutions, forbids certain cosmological singularities, and is compatible with entropy bounds. This second law is based on the conjecture that causal boundaries and not only event horizons have geometric entropies proportional to their area. In string cosmology the second law provides new information about nonsingular solutions.