18-03 Cosmic Microwave Background Radiation and the Big Bang


  • The discovery of CMB
     
    [The antenna at Bell Lab ]

    [The 2.725 +- 0.001 K CMB spectrum]

     
  • The Big Bang hypothesis
     
    [The idea of the big bang ]

    A rough estimate of the age of the universe ~ 1/H0 = 1010 h-1 yr
     
  • The Great Attractor

    [The dipole moment in CMB, an excess of 0.00337 K in the direction of Leo ]

    Our solar system is moving toward Leo at 371 km/sec. The whole Local Group is heading (at 620 km/sec) toward Hydra-Centaurus supercluster. So are many other galaxies. This Great Attractor is about 50 Mpc away.
     
  • Density of radiation and matter
     
    • Density of radiation
      rr = u/c2 = 4s T4/c3
      where s = 5.67 x 10-5 erg/sec/m2/K4 is the Stefan-Boltzmann constant.
      for T = 2.725 K
      rr = 4.6 x 10-34 g/cm3
       
    • Average density of matter
      Difficult to estimate, but one can measure halo gas temperature of galaxy clusters to count mass, which includes dark matter:
      rm = 2.4 x 10-30 g/cm3
      (The density of luminous matter is about only 10% of that.)
       
    • At present, it is a matter-dominated universe (later you will see it is actually a 'dark-energy-dominated universe'), but in earlier days it was a radiation-dominated universe.
      The transition occurred at about 24,000 years after the Big Bang, corresponding to a redshift of z = 5200; so temperature is about 2.725K x 5200 = 14000 K.
       
  • The last scattering surface - Era of recombination
    at t = 380,000 years, z = 1100 (T ~ 2.725 K x 1100 = 3000 K).

    [Era of recombination, after which the universe became transparent. ]
     
  • Anisotropy of CMB
    At the scale of one degree or so, there are fluctuations less than 300 mK, i.e. < 10-4

    [COBE map with resolution of about 7 degrees (1992)]

    [BOOMERANG at the Antarctica]

    [A patch of sky mapped by BOOMERANG (1998)]

    [WMAP map with resolution of about 0.3 degrees (2003); new and more accurate results are coming ... Check the LAMBDA site at NASA and also the PLANCK mission (launched 2009) at ESA.]

    [The power spectrum of CMB anisotropy (from WMAP)]

     
  • Polarization of CMB; gravitational waves beyond the last scattering surface