In cosmology, the equation of state of a perfect fluid is characterized by a In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement... dimensionless number w, equal to the ratio of its pressure p to its energy density ρ: w = p / ρ. It is closely related to the thermodynamic In physics and thermodynamics, an equation of state is a constitutive equation describing the state of matter under a given set of physical conditions. It provides a mathematical relationship between two or more state functions associated with the matter, such as its temperature, pressure, volume, or internal energy. Equations of... equation of state and The ideal gas law, or universal gas equation, is an equation of state of an ideal gas. It combines the three primitive gas laws derived from early physics researchers. Although roughly accurate for gases at low pressures and high temperatures, it becomes increasingly inaccurate at higher pressures and lower temperatures... ideal gas law. The equation of state is used to describe the evolution of a perfect fluid in a homogeneous isotropic universe, the The Friedmann-Lemaître-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. Depending on geographical/historical preferences, this may be referred to under the names of a preferred subset of the four scientists Alexander Friedmann, Georges Lemaître, Robertson and Walker, e.g. Friedmann-Robertson... Friedmann-Lemaître-Robertson-Walker universe. If a is the scale factor and t is the proper time, then they are related to the equation of state by and, if the fluid is the dominant form of matter in the universe, .

Finally, the equation of state is related to the acceleration or deceleration of the universe by

where G is Newton's constant and a is the The Friedmann-Lemaître-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. Depending on geographical/historical preferences, this may be referred to under the names of a preferred subset of the four scientists Alexander Friedmann, Georges Lemaître, Robertson and Walker, e.g. Friedmann-Robertson... scale factor and is the second Proper time is time measured when the clock is at rest relative to the observer. The distinction between proper time and the measured time is necessary because of the effects of time dilation, which is outlined in Einsteins theory of special relativity. To be more precise, proper time is... proper time derivative of the scale factor.

The equation of state of ordinary non- Albert Einsteins theory of relativity is a set of two theories in physics: special relativity and general relativity. These theories were conceived in order to explain the fact that electromagnetic waves do not conform to the Newtonian laws for motion. Electromagnetic waves were shown to move at a constant... relativistic matter (e.g. cold dust) is w = 0, which means that it is diluted as , where V is the volume. This means that the energy density This article is about the light phenomenon. For other uses of the phrase Red Shift, see Red Shift Redshift describes a change in the wavelength of light, in which the wavelength is longer than when it was emitted at the source. This can happen when the source moves away from... red-shifts as the volume, which is natural for matter. The equation of state of ultra- Albert Einsteins theory of relativity is a set of two theories in physics: special relativity and general relativity. These theories were conceived in order to explain the fact that electromagnetic waves do not conform to the Newtonian laws for motion. Electromagnetic waves were shown to move at a constant... relativistic matter (e.g. radiation, but also matter in the very early universe) is w = 1 / 3 which means that it is diluted as a ^{− 4}. In an expanding universe, the energy density decreases more quickly than the volume expansion, because radiation has In physics, momentum is a physical quantity related to the velocity and mass of an object. Momentum is the Noether charge of translational invariance. As such, even fields as well as other things can have momentum, not just particles. However, in curved spacetime which is not asymptotically Minkowski, momentum isn... momentum which is This article is about the light phenomenon. For other uses of the phrase Red Shift, see Red Shift Redshift describes a change in the wavelength of light, in which the wavelength is longer than when it was emitted at the source. This can happen when the source moves away from... red-shifted.

Inflation is the idea—first proposed by Alan Guth (1981)—that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. This expansion can be modelled by a non-zero cosmological constant. As a direct... Cosmic inflation and the Accelerating universe is a term for the idea that our universe is undergoing divergent rapid expansion. In the late 1990s, observations of supernovae (type Ia) produced the unexpected result that the expansion of the universe appears to be accelerating. These observations appear more firm as new data have appeared. This... accelerated expansion of the universe can be characterized by the equation of state of In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has negative pressure resulting in an effective repulsive gravitational force. (Michael Turner coined the term dark energy.) Adding dark energy to the standard theory of cosmology (i.e. FLRW metric) is currently the most... dark energy. In the simplest case, the equation of state of the The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) occurs in Einsteins theory of general relativity. The units of Λ are 1/second2. The constant is proportional to the energy density of the vacuum ρ: where: π is pi G is the gravitational constant c is... cosmological constant is w = − 1. In this case, the above expression for the scale factor is not valid and , where the constant H is the Hubbles law is the statement in astronomy that the redshift in light coming from distant galaxies is proportional to their distance. The law was first formulated by Edwin Hubble in 1929. If one assumes that this redshift is caused by Doppler effect while galaxies move away from us then... Hubble parameter. More generally, the universe is accelerating for any equation of state w < − 1 / 3. Wikipedia does not yet have an article with this exact name. Start the Phantom energy article If you have created this page in the past few minutes and it has not yet appeared, it may not be visible due to a delay in updating the database. Please wait and check... Phantom energy has equation of state , and causes a The Big Rip is a cosmological hypothesis about the ultimate fate of the Universe. The hypothesis relies crucially on the type of dark energy in the universe. The key value is the equation of state w, the ratio between the dark energy pressure and its energy density. At w <... Big Rip.

In an expanding universe, fluids with larger equations of state disappear more quickly than those with smaller equations of state. This is the origin of the The flatness problem is a cosmological problem with the Big Bang theory, which is solved by hypothesising an inflationary universe. In an expanding universe, the gravity field created by the matter within the universe will tend to slow down its expansion. If there is enough matter, the expansion will eventually... flatness and In physics, magnetic monopole is a term describing a hypothetical particle that could be quickly clarified to a person familiar with magnets but not electromagnetic theory as a magnet with only one pole. In more accurate terms, it would have net magnetic charge. Interest in the concept stems from particle... monopole problems of the According to the Big Bang theory, the universe originated in an infinitely dense and physically paradoxical singularity. Space has expanded with the passage of time, objects being moved farther away from each other. In cosmology, the Big Bang is the scientific theory that describes the early development and shape of... big bang: Curvature is the amount by which a geometric object deviates from being flat. The word flat might have very different meanings depending on the objects considered (for curves it is a straight line and for surfaces it is a Euclidean plane). In this article we consider the most basic examples... curvature has w = − 1 / 3 and monopoles have w = 0, so if they were around at the time of the early big bang, they should still be visible today. These problems are solved by Inflation is the idea—first proposed by Alan Guth (1981)—that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. This expansion can be modelled by a non-zero cosmological constant. As a direct... cosmic inflation which has . Measuring the equation of state of In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has negative pressure resulting in an effective repulsive gravitational force. (Michael Turner coined the term dark energy.) Adding dark energy to the standard theory of cosmology (i.e. FLRW metric) is currently the most... dark energy is one of the largest efforts of observational Cosmology is the study of the large-scale structure and history of the universe. In particular, it deals with subjects regarding its origin and evolution. It is studied by Astronomy, Philosophy, and Religion. See also cosmogony. Subjects in cosmology include: Physical cosmology The Big Bang The Friedmann-Lemaître-Robertson... cosmology. By accurately measuring w, it is hoped that the The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) occurs in Einsteins theory of general relativity. The units of Λ are 1/second2. The constant is proportional to the energy density of the vacuum ρ: where: π is pi G is the gravitational constant c is... cosmological constant could be distinguished from In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. Quintessence is a scalar field which has an equation of state w (relating its pressure pq and density q) of pq = wq which is less than -1/3. Quintessence is... quintessence which has .

A In mathematics and physics, a scalar field associates a single number (or scalar) to every point in space. Scalar fields are often used in physics, for instance to indicate the temperature distribution throughout space, or the air pressure. Definition A scalar field is a function or The scalar field can... scalar field φ can be viewed as a sort of perfect fluid with equation of state

where is the time-derivative of φ and V(φ) is the potential energy. A free (V = 0) scalar field has w = 1, and one with vanishing kinetic energy is equivalent to a cosmological constant: w = − 1. Any equation of state in between is acheivable, which makes In mathematics and physics, a scalar field associates a single number (or scalar) to every point in space. Scalar fields are often used in physics, for instance to indicate the temperature distribution throughout space, or the air pressure. Definition A scalar field is a function or The scalar field can... scalar fields useful models for many phenomena in cosmology.