The Five Ages of the Universe : Inside the Physics of Eternity written by Fred Adams and Greg Laughlin posits that the Universe can be divided into five ages based on the predominant types of stars populating the Universe. To do this the authors introduce the concept of a cosmological decade. Cosmological decades are logarithmic in nature, so during cosmological decade δ=5, the Universe is 10^5 or 100,000 years old and during δ=30, the Universe is 10^30 or 1,000,000,000,000,000,000,000,000,000,000 years old.

The Primordial Era : δ = 0 to δ = 5

During this period from the Big Bang to 100,000 years, the basic forces of nature separate and the basic building blocks of matter appear, first baryons through baryosynthesis, then atomic nuclei through nucleosynthesis and finally the elements hydrogen, helium and lithium are formed by atomosynthesis.

The Stelliferous Era : δ = 6 to δ = 14

At the very beginning of this age galaxies are formed as quasars and a large proportion of the first stars are born as hot blue supergiants which quickly supernova and distribute matter which then becomes a second generation of the wide variety of main sequence stars we are used to seeing in the night sky today. We live in the middle of this age. Towards the end of this age, the majority of stars use up the nuclear material that makes them shine and go nova to produce stellar remnants such as white dwarfs, neutron stars, iron dwarfs or black holes. Red dwarfs last the longest of any main sequence stars and slowly fade away. At the end of this age, very few new stars are formed.

The Degenerate Era : δ = 15 to δ = 39

In this era, dark matter provides the energy that allows white dwarfs to continue shining for trillions of years while most of the rest of the Universe becomes darker and colder. Amongst the stellar remnants are Jovians and brown dwarfs. Towards the end of this era, proton and neutron decay destroy what is left of ordinary matter. By the end of this age, the only objects of note in the Universe are black holes.

The Black Hole Era : δ = 40 to δ = 100

The black holes left during this era slowly evaporate due to Hawking radiation. By the end of this era, the only particles left in the Universe are leptons and photons.

The Dark Era : δ > 101

During this age, photons' wavelengths shift deep into the infrared to unimaginably long wavelengths. The Universe is so large and so dark that any fundamental interaction between any of these particles becomes increasingly rare. The authors believe that in this age, the Universe could possibly undergo a phase transistion and start a new Universe with a different set of laws of physics related to this Universe in a kind of genetic code.

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