ABSTRACT
The modern hierarchical paradigm of structure formation arises from a theory in which most of the matter in the universe is composed of an as yet unidentified form of Cold Dark Matter (CDM), the seeds of structure are sowed by inflation, and these seeds grow into large-scale structures through gravitational instability. The details of inflation and the physics of the growth of perturbations in the early universe give rise to the characteristic shape of the power spectrum of matter density fluctuations in a CDM universe: more power on small scales than large means that small objects form first, and merge together to form larger and larger systems. The “bottom up” nature of this process gives rise to the term “hierarchical”.
