248 The cosmic microwave background
Figure 7.3. Two current measurements of the microwave background radiation
temperature power spectrum. Triangles are BOOMERanG measurements multiplied by
1.21; squares are MAXIMA measurements multiplied by 0.92. The normalization factors
are within the calibration uncertainties of the experiments, and were chosen by Hananyet
al(2000) to give the most consistent results between the two experiments.
shown in figure 7.3. The data from the two measurements appear consistent up to
calibration uncertainties, and for simplicity will be referred to here as ‘balloon
data’ and discussed as a single result. While a few experimenters and data
analysers were members of both experimental teams, the measurements and data
reductions were done essentially independently. Earlier data from the previous
year (Milleret al1999) had clearly demonstrated the existence and angular
scale of the first peak in the power spectrum and produced the first maps of the
microwave background at angular scales below a degree. But the new results from
balloon experiments utilizing extremely sensitive bolometric detecters represent
a qualitative step forward. These experiments begin to exploit the potential of the
microwave background for ‘precision cosmology’; their power spectra put strong
constraints on several cosmological parameters simultaneously and rule out many
variants of cosmological models. In fact, what is most interesting is that, at face
value, these measurements put significant pressure on all of the standard models
outlined earlier.
The balloon data show two major features: first, a large peak in the power
spectrum centred aroundl=200 with an amplitude of approximatelyl^2 Cl =