The Cosmic Microwave Background Radiation
If the universe began in an infinitely hot, infinitely dense state:
- universe would have been opaque initially
- primordial light would have have had a continuous,
black body spectrum
- primordial light would have been very high energy
Expansion of the universe:
the wavelengths of the primordial photons
- does not change the shape of the spectrum
(i.e., remains a black body but with a different temperature than it
had early on)
- after roughly 14 billion years, the gamma rays will have stretched
so much that they will be microwave photons!
The Cosmic Microwave Background Radiation (CMBR)
appear as a (nearly) uniform "hiss" of microwave radiation on the sky and
it should have a black body spectrum.
Observations of the CMBR:
- discovered serendipitously
(i.e., by accident) in 1964 by Arno Penzias and
Bob Wilson (awarded Nobel Prize in Physics in 1978); were unable to measure
the shape of the spectrum
- in 1992 the Cosmic Background Explorer (COBE)
satellite measured the shape of the spectrum (a
nearly-perfect black body with a temperature of 2.73 K
) and detected extremely tiny "fluctuations"
in the temperature
(deviation of only 1 part in 100,000); low-resolution map of the temperature
on the sky (George Smoot and John Mather awarded Nobel Prize in Physics in 2006)
- from 2003 to 2005 the Wilkinson Microwave Anisotropy Probe (WMAP)
satellite made an extremely high-resolution map of the
temperature of the CMBR on the sky (see
Temperatures on the Earth (note the large range)
Temperature "Fluctuations" in the CMBR (Average Temp. = 2.73K)
blue = colder than average, red = hotter than average
Why should you care about the CMBR?
- direct confirmation of the "isotropy" of the universe (Cosmological
- direct confirmation of an initial hot, dense state of the universe
(Big Bang theory)
- without the "fluctuations" (lumps and bumps) in the temperature
of the CMBR WE WOULDN'T EXIST!!