M6 Cosmic Expansion and Cosmic Microwave Background

Topic

The central element of this model is the universe's scale factor, alongside the relic radiation that preserves a record of its earliest history.

Hubble's law establishes that galaxies recede from us at a speed directly proportional to their distance from us, with a constant of proportionality close to seventy kilometers per second per megaparsec. This consistent proportionality implies that the universe's scale factor itself has expanded by a factor of roughly one thousand from the Big Bang to the present day.

In turn, the Friedmann equation governs the evolution of this scale factor based on the universe's total density, its curvature, and the cosmological constant.

The cosmic microwave background is the relic radiation released when protons and electrons first recombined, allowing photons to travel freely for the first time in the universe's history. The fact that this radiation retains minute temperature fluctuations means these fluctuations served as the seeds for all subsequent large-scale structure, while also encoding information about matter density, baryon density, the expansion rate, and the global geometry of the universe.

Primordial nucleosynthesis, which occurred during the first three minutes of the universe's history, produced the abundances of hydrogen, helium, and trace amounts of lithium observed today—abundances determined by the baryon density present at that time. The independent observational confirmation of these abundances corroborates the very same model that independently describes the cosmic microwave background. Thus, from the universe's scale factor—with which this document begins—to the independent corroboration with which it concludes, and encompassing Hubble's law, the Friedmann equation, and the cosmic microwave background, cosmic expansion ensures that the entire history of the universe, from its first minutes to its current size, is written twice—independently—in both the relic radiation and the primordial abundances.

ID:3943