Cosmic Microwave Background

The Cosmic Microwave Background (CMB) is a form of electromagnetic radiation dating from an early stage of the universe. is a faint afterglow of the Big Bang, a relic from the very early universe.

  • The CMB is the oldest known form of radiation and is considered to be evidence for the Big Bang theory of the formation of the Universe.
  • With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope can detect the CMB as a faint glow that is not associated with any star, galaxy, or other object.
  • The CMB was initially composed of extremely high-energy gamma rays. However, as the universe expanded and cooled, these gamma rays have been redshifted, meaning that their wavelengths have been stretched. Today, the CMB appears as microwave radiation.
  • The CMB is detected as a faint glow of uniform thermal energy coming from all parts of the sky.
  • The CMB is a relic of the Big Bang, dating back to about 13.8 billion years ago in look-back time.
    • The phrase look-back time refers to the time it takes for light to travel from its point of origin to our here-and-now.
    • This means that the radiation that we see today from the CMB was emitted from a point in time that is 13.8 billion light-years away.
    • However, the light from the CMB may have taken far longer than 13.8 billion years to reach us, because we believe that the universe is expanding.
    • However, we do not know the exact rate of expansion of the universe during the time since the CMB was emitted.
    • It is therefore not possible to know for sure how long the light has taken to reach us or for that matter, the distance it has travelled.