Satellite images of Earth at night evoke ambiguous feelings: While on a ground level our cities appear as purely cultural artifacts, a traveler from outer space might just as well marvel at them as beautifully glowing organic fungi-like structures that sprouted on our planet. Less than a millennium ago, the Earth at night was all dark. Today it is all glowing and blossoming.
Scientists think the laws governing the structure of galaxies in outer space are the same laws underlying the growth of cities. Henry Lin and Abraham Loeb at the Harvard-Smithsonian Centre for Astrophysics have used models for showing how galaxies evolve based on matter density to propose a unifying theory for scaling laws of human populations.