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The following images attempt to describe Cosmic Microwave Background Radiation (CBR)
Nine-year Wilkinson Microwave Anisotropy Probe heat map of temperature fluctuations in the cosmic microwave background
As the Universe appears to have expanded, the radiation shifted toward wavelengths longer than those of visible light, through what is known as the Doppler effect. The radiation is now in the form of microwaves.
In 1965 Penzias and Wilson were attempting to build a radio receiver and wanted to identify the source of "noise" in their signal. They inadvertently discovered the CMB remnant of the Big Bang
An illustration of the cosmic radiation background at various redshifts in the Universe. Note that the CMB isn't just a surface that comes from one point, but rather is a bath of radiation that exists everywhere at once.EARTH: NASA/BLUEEARTH; MILKY WAY: ESO/S. BRUNIER; CMB: NASA/WMAP
Diagram comparing the surface of last scattering in the Universe and in the Earth's atmosphere. The cosmic microwave background Radiation's "surface of last scatter" is analogous to the light coming through the clouds to our eye on a cloudy day. We can only see the surface of the cloud where light was last scattered. Credit: NASA / WMAP
This weird cold spot, located in the constellation of Eridanus in our Southern Hemisphere sky, is baffling. The insets show the environment of this anomalous patch, with its angular diameter marked by the white circles; it spans a mind-blowing 1.8 billion light-years. Credit: Gergő Kránicz ESA Planck Collaboration
The Big Bang and CMB
The Big Bang and CMB
A summary of the almost 14 billion year history of the Universe, showing in particular the events that contributed to the Cosmic Microwave Background, or CMB.
The timeline in the upper part of the illustration shows an artistic view of the evolution of the cosmos on large scales. The processes depicted range from inflation, the brief era of accelerated expansion that the Universe underwent when it was a tiny fraction of a second old, to the release of the CMB, the oldest light in our Universe, imprinted on the sky when the cosmos was just 380 000 years old; and from the ‘Dark Ages’ to the birth of the first stars and galaxies, which reionised the Universe when it was a few hundred million years old, all the way to the present time.
Tiny quantum fluctuations generated during the inflationary epoch are the seeds of future structure: the stars and galaxies of today. After the end of inflation, dark matter particles started to clump around these cosmic seeds, slowly building a cosmic web of structures. Later, after the release of the CMB, normal matter started to fall into these structures, eventually giving rise to stars and galaxies.
The inserts below show a zoomed-in view on some of the microscopic processes taking place during cosmic history: from the tiny fluctuations generated during inflation, to the dense soup of light and particles that filled the early Universe; from the last scattering of light off electrons, which gave rise to the CMB and its polarisation, to the reionisation of the Universe, caused by the first stars and galaxies, which induced additional polarisation on the CMB.
CREDIT: ESA
LICENCE: ESA Standard Licence
Tools to Measure the CMBR
Tools to Measure the CMBR
Wien's Law and Temp of Background Radiation
Wien's Law and Temp of Background Radiation
Astronomers were able to use data concerning the Big Bang expansion of the universe to predict its average temperature to be 2.76 K.
We know that all objects emit radiation which is characteristic of their temperature. Using Wien's law (λMax T = 2.9 × 10-3 mK), we can determine the value of the wavelength at which radiation intensity is maximized for a temperature of 2.76 K: 2max = 1.1 × 10-3 m, which is in the microwave section of the electromagnetic spectrum.
Describing the characteristics of CMB radiation
Describing the characteristics of CMB radiation
This figure shows the spectrum at 2.76K from any object which approximates to a black body. This radiation was found to be arriving at Earth (and by implication, anywhere else) equally from all directions (isotropic).
Tiny variations were discovered many years later and are considered to be of great importance. These variations are called ANISOTROPIES (structural property of non-uniformity in different directions). They are fluctuations in the slight variation of temperature of the CMBR and is not constant in all different directions. These fluctuations can also be described as differences in peak wavelength (related to temperatures) or intensity of the CMBR.
In Section 16.3, it was explained that the same cosmic microwave background (CMB) radiation coming from all directions was evidence of an average temperature of 2.76 K and therefore evidence of the Big Bang.
However, there are some very small fluctuations in the CMB.
What do the ovals represent?
What do the ovals represent?
These ovals are all maps of the entire celestial sphere in an equal-area. The image at right shows a topographical map of the Earth in this projection. Note that there is no part of the Earth that is not included in the oval, and thus there is nothing "outside" the WMAP map.
It is known that some 24% of the universe is helium, however calculations show that fusion within stars alone cannot account for this large amount of helium
This suggests that there must have been conditions early on in the universe suitable for fusion to produce the excess helium we see.
This map shows a range of 0.0005 K from the coldest (blue) to the hottest (red) parts of the sky.
The universe did not become transparent for radiation until it was about 400000 years old. It was at this time that the CMB radiation was emitted.
The COBE, WMAP and Planck Space Observatories have provided information about anisotropies, the latest estimates for the critical density and age of the universe, plus estimates of the proportions of observable mass, dark matter and dark energy in the universe.
These slight fluctuations may have resulted from:
quantum fluctuations that have expanded.
During the metamorphosis of quantum fluctuations into CMB anisotropies and then into galaxies, primordial quantum fluctuations of a scalar field get amplified and evolve to become classical seed perturbations and eventually large scale structure. Primordial quantum fluctuations are initial conditions.
density perturbations that resulted in galaxies and clusters of galaxies.
These anisotropies in the temperature map correspond to areas of varying density fluctuations in the early universe. Eventually, gravity would draw the high-density fluctuations into even denser and more pronounced ones. After billions of years, these little ripples in the early universe evolved, through gravitational attraction, into the planets, stars, galaxies, and clusters of galaxies that we see today.
dipole distortion due to the motion of the Earth
as the Earth moves through the CMBR there is a Doppler shift due to our motion. The Earth travels at 367 km/s through the CMBR resulting in the
CMB and support of Dark Matter
CMB and support of Dark Matter
Among other things, these variations in the CMB tell us how matter was distributed (density perturbations that resulted in galaxies and clusters of galaxies) throughout space in the early universe. Because dark matter began clumping under the influence of gravity earlier than normal matter did, its influence can be seen in numerous small hot and cold patches, each covering an angle in the sky of 0.25 degrees or so.
The pattern of these spots even allows us to determine how much dark matter must be present. It turns out that for every gram of stuff that we can see in the cosmos there must be 4 or 5 grams that we can’t. That doesn’t even include another, perhaps even more mysterious, substance whose existence can be inferred from the CMB: dark energy, a force that seems to be causing our universe to expand ever faster. Totting up all the mass and energy in the universe, dark energy trumps normal matter and dark matter combined by a factor of almost 3 to 1.
CMB Problems
CMB Problems
Calculate the peak wavelength that most of the CMB photons have. Ans: 1.1x10-3 m
Taking the temperature of the universe at decoupling to be 3000K, determine the red shift of the surface of last scattering at which decoupling occurred. Ans: z = 0.99908
Redshift: Doppler or Cosmic Expansion?
Redshift: Doppler or Cosmic Expansion?
During the first 380000 years after the Big Bang, the universe was so hot that all matter existed as plasma. During this time, photons could not travel undisturbed through the plasma because they interacted constantly with the charged electrons and baryons, in a phenomenon known as Thompson Scattering. As a result, the universe was opaque.
As the universe expanded and cooled, electrons began to bind to nuclei, forming atoms. The introduction of neutral matter allowed light to pass freely without scattering. This separation of light and matter is known as decoupling. The light first radiated from this process is what we now see as the Cosmic Microwave Background.
The CMB is a perfect example of redshift. Originally, CMB photons had much shorter wavelengths with high associated energy, corresponding to a temperature of about 3000K. As the universe expanded, the light was stretched into longer and less energetic wavelengths. By the time the light reaches us, 14 billion years later, we observe it as low-energy microwaves at a frigid 2.7K. This is why CMB is so cold now.
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