Cosmic history: This artist's conception illustrates the decline in our universe's "birth-rate" over time. When the universe was young, massive galaxies were forming regularly, like baby bees in a bustling hive. In time, the universe bore fewer and fewer offspring, and newborn galaxies have (white circles) matured into older ones more like the current Milky Way (spirals).

Credit: NASA/JPL-Caltech

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Early universe: Big Bang to 300 million years

• The universe begins with a cataclysm that creates space and time, as well as all the matter and energy it will ever hold.

• As the universe expands and cools, it becomes less dense, and the basic forces of nature become distinct: first gravity, then the strong force, which holds the nuclei of atoms together, followed by the weak and electromagnetic forces.

• Fundamental particles and energy arise: quarks, electrons, photons, neutrinos and so on. These smash together to form protons and neutrons. Eventually, neutral atoms are formed as electrons link up with hydrogen and helium nuclei.

Birth of stars and galaxies: 300 million years

• Gravity amplifies slight irregularities in the density of the primordial gas. As the universe continues to expand, pockets of gas become more and more dense, stars ignite and groups of stars form the earliest galaxies.

Birth of the Sun and Earth: 8.7 billion years to now

• Our Sun forms within a cloud of gas in a spiral arm of the Milky Way galaxy. A vast disc of gas and debris swirling around this new star gives birth to planets, moons and asteroids.

• Earth forms, cools and an atmosphere develops. Microscopic living cells evolve and flourish, eventually leading to microbes, fungi, plants and animals. Mammals arise, dinosaurs die out with an asteroid impact, and hominids appear 600,000 years ago.

Stellar Era ends: 100 trillion years into the future

• The universe gradually withers away as it continues expanding.

• This is the end of the Stelliferous Era (from 10,000 years to 100 trillion years after the Big Bang), during which most of the energy generated by the universe is in the form of stars burning hydrogen and other elements in their cores.

Degenerate Era begins: 100 trillion to 10³⁷ years in the future

• This era extends to 10 trillion trillion trillion years after the Big Bang. Most of the mass that we can currently see in the universe is locked up in degenerate stars, those that have blown up and collapsed into black holes and neutron stars, or have withered into white dwarfs.

• Energy in this era is generated through proton decay and particle annihilation.

Black Hole Era begins: 10³⁸ to 10¹⁰⁰ years into the future

• This era extends to 10,000 trillion trillion trillion trillion trillion trillion trillion trillion years after the Big Bang.

• After the epoch of proton decay, the only stellar-like objects remaining are black holes of widely disparate masses, which are actively evaporating during this era.

Dark Era begins: 10¹⁰⁰ years into the future

• The last dregs of the universe remain. Protons have decayed and black holes have evaporated and only the waste products from these processes still exist: mostly photons of colossal wavelength, neutrinos, electrons, and positrons.

• For all intents and purposes, the universe as we know it has dissipated and lies in ruins.

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