The Era of Atoms (380,000 years – 1 billion years or so) began as the universe finally cooled and expanded enough for the nuclei to capture free electrons, forming fully-fledged, neutral atoms. The first galaxies formed when the universe was roughly 1 billion years old and heralded the current Era of Galaxies.

How do we determine the conditions that existed in the very early universe? We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size.

Why can’t current theories describe what happened during the Planck era? We do not yet have a theory that links quantum mechanics and general relativity. unify the strong force and the electromagnetic and weak forces. An enormous amount of energy was released when the strong force froze out from the GUT force.

The Planck era is defined as the time when the universe was the size of the Planck length, 10−33 cms, and less, and the universe’s age was 10−43 sec, the Planck time, and less. It is the earliest epoch we identify after the Big Bang. The Planck temperature at the end of the epoch was about 1032 degrees Kelvin.

In the Big Bang theory, the era that started when the gravitational effect of matter began to dominate the effect of radiation pressure. Matter is thought to have become predominant at a temperature of around 104K, roughly 30 000 years after the Big Bang. This marked the start of the matter era. See also Radiation era.

[‚rād·ē′ā·shən ‚ir·ə] (astronomy) The period in the early universe, lasting from roughly 20 seconds to 105 years after the big bang, when photons dominated the universe.

three epochs