Fluids in Cosmology

Abstract

We review the role of fluids in cosmology by first introducing them in General Relativity and then by applying them to a FRW Universe's model. We describe how relativistic and non-relativistic components evolve in the background dynamics. We also introduce scalar fields to show that they are able to yield an inflationary dynamics at very early times (inflation) and late times (quintessence). Then, we proceed to study the thermodynamical properties of the fluids and, lastly, its perturbed kinematics. We make emphasis in the constrictions of parameters by recent cosmological probes.

On the theory and applications of modern cosmography

“…In order to achieve this, we first assume that the energy budget of the universe is built up from a set of perfect fluids [17]. In a homogeneous and isotropic universe 2 , this leads to the Friedmann equations 3 :…”

“…In cases where this is not true, the Mayer relation does not necessarily have to hold and the specific heats become more complicated. Consequently the thermodynamic quantities are not forced to be negative 17 .…”

Fluid Model of Spacetime Curvature and Galactic Dynamics

“…Fluid mechanics is a branch of physics that studies the behavior of liquids and gases under various conditions [3]. This discipline analyzes how fluids flow under different forces and in different environments, applying principles such as mass conservation, momentum conservation, and fluid dynamics.…”

“…In terrestrial contexts, these principles allow for an understanding of everything from the movement of oceans and the atmosphere to the design of aerodynamic vehicles. By applying these principles to the cosmic context, intriguing parallels can be found [3]. In this model, galaxies, instead of being seen as isolated entities, are considered analogous to particles in a fluid, moving and interacting within the "membrane" of spacetime.…”

“…The central proposal of the model is as follows: galaxies, like particles in a viscous fluid, move influenced by the tension of the spacetime membrane. This idea is based on concepts discussed in the work of Cervantes-Cota and Klapp [3]. This tension, similar to the surface tension in a liquid, could dictate how galaxies move along spacetime curvatures.…”