initial fluctuations

The initial fluctuations (aka primordial fluctuations) are density variations in the energy/matter of the early universe that lead to the large scale structure of the universe today. According to modern Big Bang theories such as Lambda-CDM model, these were random quantum fluctuations that inflation expanded into the substantial density variations in the subsequent universe. Cosmology is interested in characteristics of the initial fluctuations, such as whether they appear to vary in the manner that theory predicts (initial fluctuation spectrum). The CMB is an observable phenomena offering clues to it (CMB anisotropies).