The cosmic microwave background (CMB) is electromagnetic radiation as
a remnant from an early stage of the universe in
Contents 1 Features 2 History 3 Relationship to the Big Bang 3.1 Primary anisotropy 3.2 Late time anisotropy 4 Polarization 4.1 E-modes 4.2 B-modes 4.2.1 Primordial gravitational waves 4.2.2 Gravitational lensing 5
6.1 CMBR dipole anisotropy 6.2 Low multipoles and other anomalies 7 Future evolution 8 Timeline of prediction, discovery and interpretation 8.1 Thermal (non-microwave background) temperature predictions
8.2
9 In popular culture 10 See also 11 References 12 Further reading 13 External links Features[edit] Graph of cosmic microwave background spectrum measured by the FIRAS instrument on the COBE, the most precisely measured black body spectrum in nature.[7] The error bars are too small to be seen even in an enlarged image, and it is impossible to distinguish the observed data from the theoretical curve. The cosmic microwave background radiation is an emission of uniform,
black body thermal energy coming from all parts of the sky. The
radiation is isotropic to roughly one part in 100,000: the root mean
square variations are only 18 µK,[8] after subtracting out a dipole
anisotropy from the
The
The 1948 results of Alpher and Herman were discussed in many physics
settings through about 1955, when both left the Applied Physics
Laboratory at Johns Hopkins University. The mainstream astronomical
community, however, was not intrigued at the time by cosmology. Alpher
and Herman's prediction was rediscovered by
view • discuss • edit -13 — – -12 — – -11 — – -10 — – -9 — – -8 — – -7 — – -6 — – -5 — – -4 — – -3 — – -2 — – -1 — – 0 — cosmic expansion Earliest light cosmic speed-up Solar System water Single-celled life photosynthesis Multicellular life Land life Earliest gravity Dark energy Dark matter ← Earliest universe (−13.80) ← Earliest stars ← Earliest galaxy ← Earliest quasar/sbh ←
←
←
←
← Earliest Earth (−4.54) ← Earliest life ← Earliest oxygen ← Atmospheric oxygen ← Earliest sexual reproduction ← Cambrian explosion ← Earliest humans L i f e P r i m o r d i a l Axis scale: billion years
Also see:
This section may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts, without removing the technical details. (September 2011) (Learn how and when to remove this template message) The cosmic microwave background radiation and the cosmological
redshift-distance relation are together regarded as the best available
evidence for the
Tr = 2.725(1 + z) For details about the reasoning that the radiation is evidence for the
Big Bang, see
The power spectrum of the cosmic microwave background radiation
temperature anisotropy in terms of the angular scale (or multipole
moment). The data shown comes from the
The anisotropy, or directional dependency, of the cosmic microwave background is divided into two types: primary anisotropy, due to effects that occur at the last scattering surface and before; and secondary anisotropy, due to effects such as interactions of the background radiation with hot gas or gravitational potentials, which occur between the last scattering surface and the observer. The structure of the cosmic microwave background anisotropies is principally determined by two effects: acoustic oscillations and diffusion damping (also called collisionless damping or Silk damping). The acoustic oscillations arise because of a conflict in the photon–baryon plasma in the early universe. The pressure of the photons tends to erase anisotropies, whereas the gravitational attraction of the baryons, moving at speeds much slower than light, makes them tend to collapse to form overdensities. These two effects compete to create acoustic oscillations, which give the microwave background its characteristic peak structure. The peaks correspond, roughly, to resonances in which the photons decouple when a particular mode is at its peak amplitude. The peaks contain interesting physical signatures. The angular scale of the first peak determines the curvature of the universe (but not the topology of the universe). The next peak—ratio of the odd peaks to the even peaks—determines the reduced baryon density.[53] The third peak can be used to get information about the dark-matter density.[54] The locations of the peaks also give important information about the nature of the primordial density perturbations. There are two fundamental types of density perturbations called adiabatic and isocurvature. A general density perturbation is a mixture of both, and different theories that purport to explain the primordial density perturbation spectrum predict different mixtures. Adiabatic density perturbations
In an adiabatic density perturbation, the fractional additional number
density of each type of particle (baryons, photons ...) is the same.
That is, if at one place there is a 1% higher number density of
baryons than average, then at that place there is also a 1% higher
number density of photons (and a 1% higher number density in
neutrinos) than average.
The
the increasing mean free path of the photons as the primordial plasma
becomes increasingly rarefied in an expanding universe,
the finite depth of the last scattering surface (LSS), which causes
the mean free path to increase rapidly during decoupling, even while
some
These effects contribute about equally to the suppression of
anisotropies at small scales and give rise to the characteristic
exponential damping tail seen in the very small angular scale
anisotropies.
The depth of the LSS refers to the fact that the decoupling of the
photons and baryons does not happen instantaneously, but instead
requires an appreciable fraction of the age of the universe up to that
era. One method of quantifying how long this process took uses the
photon visibility function (PVF). This function is defined so that,
denoting the PVF by P(t), the probability that a
Small scale anisotropies are erased. (Just as when looking at an object through fog, details of the object appear fuzzy.) The physics of how photons are scattered by free electrons (Thomson scattering) induces polarization anisotropies on large angular scales. This broad angle polarization is correlated with the broad angle temperature perturbation. Both of these effects have been observed by the
This artist's impression shows how light from the early universe is
deflected by the gravitational lensing effect of massive cosmic
structures forming
The cosmic microwave background is polarized at the level of a few
microkelvin. There are two types of polarization, called E-modes and
B-modes. This is in analogy to electrostatics, in which the electric
field (E-field) has a vanishing curl and the magnetic field (B-field)
has a vanishing divergence. The E-modes arise naturally from Thomson
scattering in a heterogeneous plasma. The
All-sky mollweide map of the CMB, created from 9 years of
Comparison of
In June 2001,
1896 –
1941 –
In popular culture[edit] In the Stargate
See also[edit] Wikimedia Commons has media related to Cosmic microwave background. Computational packages for Cosmologists
Cosmic neutrino background
Cosmic gravitational wave background
Cosmological perturbation theory
Axis of evil (cosmology)
References[edit] ^ a b Penzias, A. A.; Wilson, R. W. (1965). "A Measurement of Excess
Antenna Temperature at 4080 Mc/s". The Astrophysical Journal. 142 (1):
419–421. Bibcode:1965ApJ...142..419P. doi:10.1086/148307.
^ Smoot Group (28 March 1996). "The Cosmic
Further reading[edit] Balbi, Amedeo (2008). The music of the big bang : the cosmic
microwave background and the new cosmology. Berlin: Springer.
ISBN 3540787267.
Evans, Rhodri (2015). The Cosmic
External links[edit] Student Friendly Intro to the
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