The Dark Era

The Dark Era is the final age of the universe. It begins after about 10¹⁰⁰ years, when the last black holes have evaporated, and in the standard picture it never ends. What remains is a cold, nearly empty space holding photons of enormous wavelength, neutrinos, electrons and positrons, drifting ever farther apart.

It is the fifth era in the scheme of Fred Adams and Gregory Laughlin: cosmological decades above 101 in their 1999 book The Five Ages of the Universe, and above 100 in their 1997 review, “A dying universe”. The era has no end date. In our Deep Time explorer the scale simply stops at 10¹⁰⁶ years, because a scroll has to stop somewhere.

What is left in the Dark Era?

Adams and Laughlin describe the Dark Era as the time when protons have decayed and black holes have evaporated, leaving only the waste products of those processes:

• Photons from Hawking radiation, proton decay and every earlier source, stretched by expansion to wavelengths far longer than anything we observe today.
• Neutrinos, the most elusive particles, produced throughout cosmic history.
• Electrons and positrons, left over from proton decay and black hole evaporation.
• Dark matter, unless it decays or annihilates, since we still do not know what it is.

There are no stars, planets, galaxies or black holes. Matter is spread so thin that a typical particle may never meet another.

How cold is the Dark Era?

Nearly, but never exactly, absolute zero. Today’s background, the cosmic microwave background, is 2.725 kelvin and cools as space expands. If dark energy is a cosmological constant, the expansion approaches a steady exponential rate and the universe has a cosmic horizon. In 1977 Gary Gibbons and Stephen Hawking showed that such a horizon has a temperature. With Planck’s measured expansion, that floor is about 2 × 10^-30 kelvin. We show the calculation in heat death of the universe.

Does anything happen in the Dark Era?

Very little, and only slowly. Adams and Laughlin list a few possibilities, all depending on untested physics:

Possible process	Approximate time (η)	Condition
Positronium “atoms”, wider than today’s observable universe, decay	About 141	Only in a flat, decelerating universe
Higher-order proton decay	About 100 to 200	If first-order proton decay does not happen
Black holes the size of today’s horizon evaporate	About 131	Only if such huge black holes could form, which accelerating expansion prevents

With accelerating expansion, most of these are suppressed: particles are diluted too fast to pair up, and no new structures larger than galaxies can collapse.

Adams and Laughlin themselves suggest the era may look empty partly because extrapolating so far is so hard, not necessarily because nothing happens. They proposed a “Copernican Time Principle”: our epoch has no special place in time, and interesting things might keep happening at ever lower energies.

Heat death arrives

The Dark Era is where the heat death of the universe is finally complete. Adams and Laughlin showed that cosmic processes keep producing energy and entropy until about 10¹⁰⁰ years, so heat death is postponed until this era. After that, the universe can become effectively inert: no temperature differences, no engines, no chemistry.

Could the Dark Era be cut short?

Possibly, by physics outside the standard picture:

• Vacuum decay. If the Higgs field is metastable, a bubble of lower-energy vacuum could eventually form and spread. Over the endless span of the Dark Era, even a very improbable process gets many chances. See vacuum decay.
• A change in dark energy. If dark energy is not constant, as recent DESI data hint, the far future could differ: see Big Rip vs Big Crunch vs Big Freeze.
• A new beginning. Roger Penrose’s conformal cyclic cosmology proposes that an infinitely expanded, empty future is equivalent to the Big Bang of a new universe. It is speculative and contested; PBS Space Time’s “What Happens After the Universe Ends?” explains it, in our video library.

Why the Dark Era matters now

The Dark Era is the reason the present is precious. Everything interesting in the universe, from stars to life, happens in the first few eras, and on the scale of the full timeline the Stelliferous Era we live in is a brief, bright beginning. For the whole story, read our guide to the future of the universe, or go back one step to the Black Hole Era.