ABSTRACT
Most World History courses start with early humans: either the first hominids 5 million years ago or the first homo sapiens 200,000 years ago. It is worth stressing that the scientific understandings the authors review in this chapter are recent. Indeed, it is likely that these will be revised in important respects in future. Nevertheless, scientists now have plausible explanations for the course of Big History. Scientists do provide a detailed description of the first fractions of a second of the history of the universe. Quarks, neutrons, and protons suddenly emerged and began to expand outward. Electrons were impossible at first but develop seconds later. Gravity plays a vital role in this next phase of our story. But for gravity to act, there must have been some unevenness in the distribution of particles in this expanding universe. Gravity strengthens as mass increases. Stars should then tend to collapse in size, for large stars pull mass powerfully toward their centres.
