3.33 Sspd_chapter 1_part 13_ constituent particles of solid state  (Page 13/14)

When neutral atoms were formed the interaction between neutral atoms and photon stopped. Radiation got decoupled. This decoupled radiation today 13.7 Gy after is seen as the Blackbody Radiation at 2.77K. This 2.77K black body radiation appears as Cosmic Microwave Background Radiation.

In 1960’s AT&T, Bell Lab used a radiometer in a telescope that would track the early communication satellites namely Echo-1 and Telster. This radiometer was being tested by Arno A. Penzias and Robert W. Wilson. In course of this testing they detected a background noise in microwave spectrum. It corresponded to 2.776K Cosmic Microwave Background Radiation(CMBR). They were led to this idea by the news that Robert H. Dick had suggested in 1940 that a radiometer would detect this CMBR.

The discovery firmly established the Big Bang Theory. In 1978 the Nobel Prize in Physics was awarded to Arno A Penzias (American), Robert Woodrow Wilson (American) and P.L. Kepiteza (Russian) for the discovery of Cosmic Microwave Background Radiation.

For 300,000 years this relic radiation was coupled with matter through Compton Scattering and temperature of Black Body Radiation and temperature of Matter are equal though they have different adiabatic indices. Because of Compton Scattering, radiation should have the same density distribution as the matter density distribution. After 300,000 years when temperature fell below 4000K, the matter and radiation decoupled because matter had recombined and neutralized. Since then the two cooled independently. T(matter) α 1/R ² and T(Radiation) α 1/R but Black Body Radiation continues to carry the imprint of Mass Distribution at the time of decoupling.

Since then Matter has evolved in a very differentiated and non-homogeneous system of super-clusters, clusters, galaxies and solar systems hence at 300,000 year after the Big Bang, matter density distribution should have contained ripples of correct size which could eventually evolve in today’s variegated structure. Hence by studing the relic radiation and its ripples we can ascertain if indeed such a coupling existed 300,000 years ago.

Following are the stages through which the matter density ripples must have evolved: matter must have first segregated into super clusters, super clusters evolved into clusters of galaxies, clusters further sub-divided into galaxies. The turbulence within the galaxies gave birth to the stars and some stars had their solar systems too.

If matter density distribution would have had density ripples then radiation density distribution should have had similar ripples of the correct size and these ripples should be observable today also.

In 1990, a satellite called COBE ( Cosmic Background Explorer) measured the spectrum and temperature variations in the radiation pattern. The spectrum was exactly as expected for 2.7K Black Body radiator. The temperature variation was 1 in 100,000. Till then CMB radiation had appeared as perfectly isotropic and isotropic radiation pattern cannot explain the galaxies, clusters and super-clusters formation. Therefore the achievement of COBE marked the correctness of the Big Bang Theory.