Abstract :
The early Universe, at times prior to recombination 105.5 years after the Big Bang, can not be studied by looking at individual objects. However, there are several fossils from this epoch that can be studied. These include the abundances of light elements, and especially the Cosmic Microwave Background Radiation (CMBR). Several space missions (Copernicus, IUE), COBE, HST) have provided information about this era, and planned missions such as the Microwave Anisotropy Probe (MAP) and the PLANCK Surveyor will add to our knowledge. The last time when photon creation and destruction rates were fast enough to guarantee a blackbody spectrum was only a month after the Big Bang, so the lack of distortions in the spectrum of the CMBR puts limits on any processes that would add energy to the radiation field at times later than a month. The nearly perfect isotropy of the CMBR shows that the entire observable Universe had to be in causal contact prior to recombination — and this is evidence for inflation. The low amplitude anisotropies of the CMBR that do exist show “equal power on all scales” for large angular scales — more evidence for inflation — and also seem to show a preferred scale near 1°, which corresponds to acoustic oscillations in the baryon-photon fluid. Detailed studies of these acoustic oscillations by MAP and PLANCK will determine the initial conditions for the process of gravitational collapse that has produced the structures seen in the later Universe.
