Typical Scales — From Observation and Theory

Abstract

The aim of most modern theories of the structure of the universe is to explain the extreme inhomogeneities observed at present — the sizes and shapes of galaxies, and the clustering hierarchy of galaxies into groups, clusters, and superclusters — as a result of the growth by gravitational interaction of initially small perturbations in a smooth background density. Clearly, there must be some scale, where local physics — radiation hydrodynamics, — is the dominant effect in shaping the obiects. But it is not clear what this scale is.

“Since as the Creation is, so is the Creator also magnified, we may conclude in consequence of an infinity, and an infinite all-active power, that as the visible creation is supposed to be full of siderial systems and planetary worlds, so on, in like similar manner, the endless immensity is an unlimited plenum of creations not unlike the known.... That this in all probability may be the real case, is in some degree made evident by the many cloudy spots, just perceivable by us, as far without our starry Regions, in which tho’ visibly luminous spaces, no one star or particular constituent body can possibly be distinguished; those in all likelihood may be external creation, bordering upon the known one, too remote for even our telescopes to reach.”

Thomas Wright (1750)