A Dying Universe (1997): The Five Ages of the Universe Explained

The five ages of the universe come from “A dying universe”, a 1997 review by astrophysicists Fred Adams and Gregory Laughlin. Using known physics, they traced what happens to stars, galaxies and matter far beyond today, and divided cosmic history into eras: Primordial, Stelliferous (the age of stars, ours), Degenerate, Black Hole and Dark.

The question before the paper

Most of astrophysics looks back in time. A few physicists, notably Freeman Dyson in Time without end, had asked what happens in the very distant future. But there was no systematic account of how every kind of astrophysical object, from planets and brown dwarfs to galaxies and black holes, would evolve over times vastly longer than the current age of the universe. What does the whole future look like, and what physics sets each stage?

What the paper found

• A new clock: cosmological decades. To handle immense spans, the authors measure time in cosmological decades, η, the power of ten of the age of the universe in years. Today is about η = 10. Each step of one is a factor of ten.
• The Stelliferous Era (6 < η < 14). Energy comes mainly from stars. On a logarithmic scale we live near its middle, but on a linear scale we are very near its beginning: normal star formation in galaxies ends around η = 14, or 100 trillion (10¹⁴) years.
• Running out of gas. After about 1 to 10 trillion years the supply of interstellar gas runs out, though collisions between brown dwarfs keep forming a few stars at a very low rate.
• The Degenerate Era (from η = 15). Most ordinary mass is locked in white dwarfs, brown dwarfs and neutron stars. Adopting a representative proton lifetime of 10³⁷ years, these dead stars slowly evaporate through proton decay.
• The Black Hole Era (to η = 100). Black holes become the main concentrations of mass. One with the mass of a whole galaxy evaporates by Hawking radiation after about 10⁹⁸ years.
• The Dark Era (η > 100). What remains is a thin, cold sea of particles and radiation.

How they did it

The paper is a long review in Reviews of Modern Physics. Adams and Laughlin combined stellar evolution, galactic dynamics, particle physics and black hole physics, including Hawking’s evaporation and Don Page’s emission rates, and followed each class of object forward until the next process takes over. Where physics is uncertain, such as whether and how fast protons decay, they adopted representative values, such as a proton lifetime of 10³⁷ years.

Why it mattered

The paper turned speculation about the end of everything into a framework built from known physics. It gave the future of the universe a timeline and named the age we live in: the Stelliferous Era, the age of stars. It is the scientific backbone of this site’s name and of our Deep Time explorer, where each era has its own page: the Primordial Era, the Stelliferous Era, the Degenerate Era, the Black Hole Era and the Dark Era.

What we know now

The 1998 discovery of accelerating expansion added a new player: dark energy, which empties the sky of distant galaxies long before the stars die, as Krauss and Scherrer showed in the end of cosmology. If dark energy grew stronger it could end everything early in a Big Rip; DESI’s 2025 results from the Dark Energy Spectroscopic Instrument lean the other way. A 2025 proposal by Falcke and colleagues would shorten the Degenerate Era dramatically. The broad sequence of eras still stands. See is the universe young? and the heat death of the universe.

Who wrote it

Fred Adams and Gregory Laughlin wrote the review together. Adams has kept working on the far future: in 2026 he co-authored a study of how the dying Sun could break up the outer Solar System. The paper has about 250 citations in Semantic Scholar as of October 2026.

Read the original

Adams, F. C., and Laughlin, G. (1997). “A dying universe: the long-term fate and evolution of astrophysical objects.” Reviews of Modern Physics 69, 337. doi:10.1103/RevModPhys.69.337. Free on arXiv: astro-ph/9701131.

Questions people ask

What are the five ages of the universe?

In Adams and Laughlin’s 1997 scheme they are the Primordial Era before stars, the Stelliferous Era of shining stars, the Degenerate Era of dead stars, the Black Hole Era, and the Dark Era after black holes evaporate, beyond 10¹⁰⁰ years. We live in the Stelliferous Era.

What era of the universe are we in now?

We are in the Stelliferous Era, the age of stars, which runs from about a million (10⁶) to 100 trillion (10¹⁴) years after the Big Bang. At 13.8 billion years old, the universe is near the middle of that era on a logarithmic scale, but very near its start on a linear one.

When will the last stars die?

Normal star formation in galaxies ends around 100 trillion years from now, and the longest-lived small stars fade around then, closing the Stelliferous Era. A trickle of new stars may still form afterward when brown dwarfs collide, but at an extremely low rate.