Era of Nuclei

The Dark Ages. After the first three minutes, the universe obeyed the Standard Model and settled down to a much longer period of expansion and cooling in which change was much less dramatic. High energy radiation (photons) dominated the cosmos. As the universe continued to cool, more and more matter was created. Expansion caused radiation to lose more energy than matter so that after a while, matter (nuclei) particles exceeded massless particles (photons). About 70,000 years after the Big Bang, radiation and matter were about equal in density, shortly thereafter matter began to dominate.

Recombination (380,000 Years)   For the next 310,000 years the universe continued to expand and cool, but was still fiery hot and dark. Any visible light was immediately scattered by collisions with the ubiquitous electrons and protons. It contained only the simplest elements, mostly hydrogen and helium ions. As the universe cooled further, the electrons (with a negative charge) begin to get captured by the ions (with a positive charge) forming atoms (electrically neutral). This process happened relatively fast and is known as "recombination". The first bits of structure began to form. These small clumps of matter grew in size as their gravity attracted other nearby matter. At about 380,000 years of cooling, light (photons) began to travel through the spaces between the atoms which now "bond" the electrons in their orbits. The universe had become transparent.

Cosmic Microwave Background (CMB).  The first early radiation that could freely travel was the CMB, the remnants of which we can detect in the current universe 13.75 billion years later. 380,000 years is the earliest point in time we can ever look back and "see" because everything before that was part of the dark ages.

Note the CMB picture to the left taken by the European Space Agency (ESA) Planck satellite. The Planck satellite launched in 2009 is the third satellite exclusively designed to map the early CMB. NASA has previously launched the COBE in 1989 and the WMAP in 2001. Check out the Cosmic Microwave Backgroundweb page.

Currently, the earliest galaxy we can "see" is MACS0647-JD which formed about 420 million years after the Big Bang.