8 Cosmic Microwave Background
In this chapter we shall meet several important observational discoveries. The cosmic
microwave background (CMB), which is a consequence of the hot Big Bang and the
following radiation-dominated epoch, was discovered in 1964. We discuss this discov-
ery in Section 8.1.
The hot Big Bang also predicts that the CMB radiation should have a blackbody
spectrum. Inflation predicts that the mean temperature of the CMB should exhibit
minute perturbations across the sky. These predictions were verified by a 1990 satellite
experiment, theCosmic Background Explorer (COBE). The COBE observations veri-
fied the existence of a nearly scale-invariant spectrum of primordial fluctuations on
angular scales larger than 7∘. Many experiments have since then extended the range,
in particular the Wilkinson Microwave Anisotropy ProbeWMAP. Most recently the
third-generation space missionPlanckhas made observations of temperature and
polarization anisotropies with much improved precision and statistics at different
angular scales. These measurements will be discussed in the rest of this chapter.
In Section 8.2 we shall discuss the method of analyzing the temperature per-
turbations which are expected to be associated with the even smaller polarization
variations, due to Thomson scattering at the LSS. These were first observed by the
ground-based Degree Angular Scale Interferometer (DASI) in late 2002 and by in early
- We discuss this in Section 8.3.
The CMB contains a wealth of information about the dynamical parameters of
the Universe and on specific features of the theoretical models: general relativity, the
standard FLRW cosmology versus other cosmologies, all versions of inflation and
its alternatives, dark matter, dark energy and so on. In Section 8.4 we establish the
parameters, how they are related to each other, what observational values they have
and what information they give about possible cosmological models.
Introduction to Cosmology, Fourth Edition. Matts Roos
© 2015 John Wiley & Sons, Ltd. Published 2015 by John Wiley & Sons, Ltd.