Editing Physical cosmology (section)

===Timeline of the Big Bang===
{{main|Timeline of the Big Bang}}
Observations suggest that the universe began around 13.8 billion years ago.<ref>{{cite web
|title = Cosmic Detectives
|url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives
|publisher = The European Space Agency (ESA)
|date = 2 April 2013
|access-date = 2013-04-25}}
</ref> Since then, the evolution of the universe has passed through three phases. The very early universe, which is still poorly understood, was the split second in which the universe was so hot that [[subatomic particle|particles]] had energies higher than those currently accessible in [[particle accelerator]]s on Earth. Therefore, while the basic features of this epoch have been worked out in the Big Bang theory, the details are largely based on educated guesses.

Following this, in the early universe, the evolution of the universe proceeded according to known [[high energy physics]]. This is when the first protons, electrons and neutrons formed, then nuclei and finally atoms. With the formation of neutral hydrogen, the [[cosmic microwave background]] was emitted. Finally, the epoch of structure formation began, when matter started to aggregate into the first [[star]]s and [[quasar]]s, and ultimately galaxies, [[clusters of galaxies]] and [[supercluster]]s formed. The future of the universe is not yet firmly known, but according to the [[ΛCDM]] model it will continue expanding forever.