Cosmic Microwave Background

In Cosmology , the cosmic microwave background radiation (most often abbreviated '''CMB''' but occasionally '''CMBR''', '''CBR''' or '''MBR''') is a form of Electromagnetic Radiation discovered in 1965 . It has a thermal Black-body spectrum which peaks in the Microwave range. Most cosmologists consider the cosmic microwave background radiation to be the best evidence for the Hot Big Bang model of the universe.

FEATURES

s and Error Bar s on this graph are obscured by the theoretical curve.]]

The cosmic microwave background is a 2.725 variations are only 18 µK.This ignores the Dipole anisotropy, which is due to the Doppler Shift of the microwave background radiation due to our Peculiar Velocity relative to the Comoving cosmic rest frame. This feature is consistent with the Earth moving at some 600 km/s towards the constellation Virgo . The Far-Infrared Absolute Spectrophotometer (FIRAS) instrument on the NASA COsmic Background Explorer (COBE) satellite has carefully measured the spectrum of the cosmic microwave background, which has made it the most precisely measured black body spectrum ever.D. J. Fixen ''et al.'', "The Cosmic Microwave Background Spectrum from the full COBE FIRAS data set", ''Astrophysical Journal'' 473, 576–587 (1996).

The cosmic microwave background is a prediction of the Big Bang . In the theory, the early universe was made up of a hot Plasma of Photon s, Electrons and Baryon s. The photons were constantly interacting with the plasma through Compton Scattering . As the universe expanded, the cosmological Redshift caused the plasma to cool until it became favorable for Electrons to combine with Hydrogen and Helium Nuclei and form atoms. This happened at around 3,000 K or when the universe was approximately 380,000 years old (z=1088). At this point, the photons did not scatter off of the now neutral atoms and begin to travel freely through space. This process is called Recombination or Decoupling .

The photons continued cooling until they reached their present 2.7 K temperature. Accordingly, the radiation from the sky we measure today comes from a spherical surface, called the surface of last scattering, from which the photons that decoupled from interaction with matter in the early universe, 13.7 billion years ago, are just now reaching observers on Earth. The big bang suggests that the cosmic microwave background fills all of observable space, and that most of the radiation energy in the universe is in the cosmic microwave background, which makes up a fraction of roughly 5×10^-5 of the total density of the universe.The energy density of a black-body spectrum is

\pi k_B^2T^4/15(\hbar c)^3

, where ''T'' is the temperature, ''k''_B is the Boltzmann constant,

\hbar

is the Planck constant and ''c'' is the speed of light. This can be related to the critical density of the universe using the parameters of the Lambda-CDM Model .

Two of the greatest successes of the big bang are its prediction of the exactly thermal spectrum and detailed prediction of the anisotropies of the cosmic microwave background. The recent model of the big bang. Some information, such as the Shape Of The Universe , can be obtained straightforwardly from the cosmic microwave background, while others, such as the Hubble Constant , are not constrained and must be inferred from other measurements.D. N. Spergel ''et al.'', "First-year Wilkinson Microwave Anisotropy Probe (WMAP) observations: determination of cosmological parameters", ''Astrophysical Journal Supplement'' 148, 175–194 (2003).

HISTORY

See Also: Discovery of cosmic microwave background radiation

The cosmic microwave background was predicted by George Gamow , Ralph Alpher , and Robert Hermann in 1948 . Moreover, Alpher and Herman were able to estimate the temperature of the cosmic microwave background to be 5 K.G. Gamow, "The Origin of Elements and the Separation of Galaxies," ''Physical Review'' 74 (1948), 505. G. Gamow, "The evolution of the universe", ''Nature'' '''162''' (1948), 680. R. A. Alpher and R. Herman, "On the Relative Abundance of the Elements," ''Physical Review'' 74 (1948), 1577. Although there were several

Information About

Cosmic Microwave Background