Radiation-Dominated Era
Encyclopedia
The radiation-dominated era refers to one of the three phases of the known universe, the other two being the matter-dominated era
and the dark-energy-dominated era. During this era, the dynamics of the universe
were set by radiation, which refers generally to the constituents of the universe which moved relativistically
. The radiation-dominated era occurred from the universe's creation until a cosmological redshift of approximately 3400, at which point the expansion of the universe caused the matter energy density to surpass the radiation energy density. Even though the matter energy density surpassed the radiation density at this point, the universe remained optically thick to radiation until a cosmological redshift of approximately 1100, when the universe was about 380,000 years old. This second moment in time, at which point the photons in that compose the cosmic microwave background radiation
were last scattered, is often mistaken as marking the end of the radiation era.
For a radiation-dominated universe the evolution of the scale factor
in the Friedmann–Lemaitre–Robertson–Walker metric is obtained solving the Friedmann equations
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Matter-Dominated Era
The matter-dominated era was the epoch in the evolution of the Universe that began after the radiation-dominated era ended, when the Universe was about 70,000 years old. Although it was often said that we still live in the matter-dominated era, it is more correct to say that when the Universe was...
and the dark-energy-dominated era. During this era, the dynamics of the universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
were set by radiation, which refers generally to the constituents of the universe which moved relativistically
Special relativity
Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...
. The radiation-dominated era occurred from the universe's creation until a cosmological redshift of approximately 3400, at which point the expansion of the universe caused the matter energy density to surpass the radiation energy density. Even though the matter energy density surpassed the radiation density at this point, the universe remained optically thick to radiation until a cosmological redshift of approximately 1100, when the universe was about 380,000 years old. This second moment in time, at which point the photons in that compose the cosmic microwave background radiation
Cosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
were last scattered, is often mistaken as marking the end of the radiation era.
For a radiation-dominated universe the evolution of the scale factor
Scale factor (Universe)
The scale factor or cosmic scale factor parameter of the Friedmann equations is a function of time which represents the relative expansion of the universe. It is sometimes called the Robertson-Walker scale factor...
in the Friedmann–Lemaitre–Robertson–Walker metric is obtained solving the Friedmann equations
Friedmann equations
The Friedmann equations are a set of equations in physical cosmology that govern the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity...
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