Cosmic microwave background radiation (CMB) refers to a faint, uniform radiation pervading the universe in the form of electromagnetic waves. It is a remnant of the early universe, originating approximately 380,000 years after the Big Bang, when the universe transitioned from being too hot and dense to allow the formation of neutral atoms, into a state where atoms could finally form. At this epoch, protons, electrons, and photons existed in a plasma state.
The CMB consists mainly of photons that have been traveling freely through space ever since that time, which was about 13.8 billion years ago. As the universe continued to expand, the wavelengths of these photons stretched and cooled, resulting in the characteristic microwave radiation we observe today. This radiation is now evenly distributed throughout the cosmos, with a near-uniform temperature of approximately 2.7 Kelvin (or about -270.45 degrees Celsius).
The discovery and detailed analysis of the CMB provided strong evidence for the Big Bang theory of the universe's origin. It played a crucial role in confirming several key predictions, such as the isotropy (uniformity) of the radiation and its black body spectrum. Further examination of the CMB has also revealed intricate patterns and fluctuations, providing insights into the composition, geometry, and evolution of the universe.
In summary, cosmic microwave background radiation refers to the faint microwave radiation originating from the early universe and currently permeating throughout space, offering valuable information about the universe's origins, properties, and evolution.
