astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...

and

cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in ...

, dark fluid theories attempt to explain

dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...

and

dark energy In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univer ...

in a single framework. The theory proposes that dark matter and dark energy are not separate physical phenomena, nor do they have separate origins, but that they are strongly linked together and can be considered as two facets of a single fluid. At galactic scales, the dark fluid behaves like dark matter, and at larger scales its behavior becomes similar to dark energy. In 2018 astrophysicist Jamie Farnes proposed that a dark fluid with

negative mass In theoretical physics, negative mass is a type of exotic matter whose mass is of opposite sign to the mass of normal matter, e.g. −1 kg. Such matter would violate one or more energy conditions and show some strange properties such as the ...

would have the properties required to explain both dark matter and dark energy.

Overview

Dark fluid is hypothesized to be a specific kind of fluid whose attractive and repulsive behaviors depend on the local energy density. In this theory, the dark fluid behaves like dark matter in the regions of space where the baryon density is high. The idea is that when the dark fluid is in the presence of matter, it slows down and coagulates around it; this then attracts more dark fluid to coagulate around it, thus amplifying the force of gravity near it. The effect is always present but only becomes noticeable in the presence of a very large mass such as a galaxy. This description is similar to theories of

, and a special case of the equations of dark fluid reproduces dark matter. On the other hand, in places where there is relatively little matter, as in the

voids Void may refer to: Science, engineering, and technology * Void (astronomy), the spaces between galaxy filaments that contain no galaxies * Void (composites), a pore that remains unoccupied in a composite material * Void, synonym for vacuum, a s ...

between galactic superclusters, this hypothesis predicts that the dark fluid relaxes and acquires a negative pressure. Thus dark fluid becomes a repulsive force, with an effect similar to that of

. Dark fluid goes beyond dark matter and dark energy in that it predicts a continuous range of attractive and repulsive qualities under various matter density cases. Indeed, special cases of various other gravitational theories are reproduced by dark fluid, e.g.

inflation In economics, inflation is an increase in the general price level of goods and services in an economy. When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation corresponds to a reductio ...

, quintessence, k-essence, f(R), Generalized Einstein-Aether f(K),

MOND Modified Newtonian dynamics (MOND) is a hypothesis that proposes a modification of Newton's law of universal gravitation to account for observed properties of galaxies. It is an alternative to the hypothesis of dark matter in terms of explaining ...

, TeVeS, BSTV, etc. Dark fluid theory also suggests new models, such as a certain f(K+R) model that suggests interesting corrections to MOND that depend on redshift and density.

Simplifying assumptions

Dark fluid is not analyzed like a standard

fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics of fluids ( liquids, gases, and plasmas) and the forces on them. It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical and bio ...

model, because the complete equations in fluid mechanics are as yet too difficult to solve. A formalized fluid mechanical approach, like the generalized Chaplygin gas model, would be an ideal method for modeling dark fluid, but it currently requires too many observational data points for the computations to be feasible, and not enough data points are available to cosmologists. A simplification step was undertaken by modeling the hypothesis through scalar field models instead, as is done in other alternative approaches to dark energy and dark matter.

References

External links

* * * * {{Portal bar, Physics, Space Dark matter Astrophysics Physical cosmology Theoretical physics Dark concepts in astrophysics