Section 8: Inflation and the Origin of Structure Figure 27:
While the universe appears approximately uniform, we see varied
and beautiful structure on smaller scales. Source: © NASA, ESA,
and F. Paresce (INAPF-AIASF, Bologna, Italy). More info On the
largest cosmological scales, the universe appears to be
approximately homogeneous and isotropic. That is, it looks
approximately the same in all directions. On smaller scales,
however, we see planets, stars, galaxies, clusters of galaxies,
superclusters, and so forth. Where did all of this structure
come from, if the universe was once a smooth distribution of hot
gas with a fixed temperature? The temperature of the fireball
that emerged from the Big Bang must have fluctuated very
slightly at different points in space (although far from enough
to solve the horizon problem). These tiny fluctuations in the
temperature and density of the hot gas from the Big Bang
eventually turned into regions of a slight overdensity of mass
and energy. Since gravity is attractive, t