Data Analysis of the Cosmic Microwave Background

The early universe consisted of a dense, hot and ionised gas of
electrons, protons, neutrons, some light atomic nuclei and photons.
The universe at that time was optically thick as the photons could
not travel very far before being scattered on electrons in the
dense gas. The temperature was too hot for the electrons to combine
with the nuclei and form atoms. But as the universe expanded it
cooled. About 300 000 years after the Big Bang, the temperature of
the dense gas filling the universe was about 3000 degree Kelvin.
This temperature allowed the formation of the first atoms in the
universe. The electrons combined with the protons to form atoms.
The probability for a photon to scatter on a neutral atom is much
less than the probability to scatter on free electrons and protons.
For this reason it is said that the universe got transparent when
the electrons were bound to the protons. The photons continued
travelling in a straight line without being scattered. About 12
billion years later some of these photons hit a detector on the
planet called 'the earth'. And it provided scientists with valuable
information about the origin of the universe. This radiation which
has travelled more or less unchanged from the earliest times until
today is called the cosmic microwave background radiation, and is
the topic of this Ph.D. thesis.