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
The last scattering surface - Era of recombination
- Density of radiation
rr = u/c2 =
where s = 5.67 x 10-5
erg/sec/m2/K4 is the Stefan-Boltzmann constant.
for T = 2.725 K
= 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:
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
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.
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)
[The power spectrum of CMB anisotropy (from WMAP)]
Polarization of CMB; gravitational waves beyond the last scattering surface