The default ending. Expansion never stops, everything slowly burns out, and the universe goes cold.
Standard ΛCDM Heat Death
The straight extrapolation of the standard model: a constant dark energy expands the universe forever, through a long sequence of darkening eras, to a cold equilibrium at maximum entropy.
Looping ambient scene for Heat Death and Eternal Expansion. The current best-fit cosmology, ΛCDM, has dark energy driving an accelerating expansion that never reverses. Extrapolated forward, this is the default future of the universe: galaxies outside the Local Group recede beyond reach, star formation ends, stellar remnants cool, and over almost unimaginable timescales matter and even black holes decay away. The end state is a cold, dilute, near-empty space at maximum entropy, the heat death. This family collects the eternal-expansion futures that follow from a positive, roughly constant dark energy. The variants differ in emphasis: the thermodynamic timeline of decay, the geometric end state of an asymptotic de Sitter horizon, and the open question of what a dynamical (quintessence) dark energy does to the long-term picture.
§1 · The claim, in one sentence
Standard ΛCDM Heat Death is the future you get by taking today's best-fit cosmology and running the clock forward. A fixed cosmological constant keeps the expansion accelerating, so galaxies beyond the Local Group eventually cross the cosmic event horizon and vanish from view. Star formation ends, stars burn out, and over vast timescales matter and even black holes decay, leaving a cold, dilute space at maximum entropy. Adams and Laughlin 1997 mapped the timeline; Krauss and Starkman 2000 traced what it means for the survival of life and information.
§2 · Why it might be true
The simplest reading of the data is that dark energy is a cosmological constant: a fixed energy of empty space, with an equation of state w equal to -1, that does not dilute as the universe grows. If that holds, the expansion accelerates forever. Distant galaxies recede faster and faster until their light can no longer reach us, and the observable universe empties out to just the gravitationally bound Local Group.
Adams and Laughlin 1997 laid out the long-term timeline as a sequence of eras. The Stelliferous Era of active star formation ends within roughly 100 trillion years as galaxies exhaust their gas. The Degenerate Era follows, a universe of white dwarfs, neutron stars, and black holes. If protons decay, ordinary matter dissolves over something like 10^34 to 10^40 years. In the Black Hole Era, Hawking radiation slowly evaporates even the largest black holes, the biggest taking on the order of 10^100 years.
Krauss and Starkman 2000 asked the next question: can anything survive this? Their answer was sobering. In an eternally accelerating universe, an event horizon limits the total energy and information any observer can ever gather, so no process, not even an idealised eternal civilisation, can compute forever. The heat death is not just the death of stars, it is a hard ceiling on what is possible at all.
The family stance
The universe ends by expanding forever and running down. There is no recollapse and no tearing apart, just an ever-thinner, ever-colder space approaching thermodynamic equilibrium. This is the fate implied by the standard cosmological model if dark energy is a cosmological constant or close to one.
§2.5 · Evidence
- Supernova, CMB, and baryon-acoustic-oscillation data are all consistent with w equal to -1 to within current uncertainties, which is exactly the constant dark energy this future assumes
- Measurements of spatial curvature are consistent with a flat universe, removing the main geometric route to a recollapse
- The heat-death timeline of Adams and Laughlin uses only standard stellar astrophysics and well-motivated particle physics, so the sequence of eras is robust given the constant-dark-energy premise
§3 · What you'd need to test it
- Dark energy's equation of state stays at w equal to -1 across cosmic time, with no measurable drift
- Spatial curvature stays flat, so the expansion has no geometric tendency to reverse
- The expansion rate asymptotes to a constant rather than slowing, locking in an eternal-acceleration future
- Star formation, stellar burnout, and (if it occurs) proton decay follow a fixed ordering of eras set by known and conjectured microphysics
§4 · Where it breaks
- The entire picture depends on dark energy being a true cosmological constant; a small drift in w toward more negative values would replace heat death with a rip
- The deep timeline assumes the proton decays, which has never been observed; if protons are stable, matter dissolves only through far slower channels, changing the late eras
- Every distinctive prediction lies far beyond any possible measurement, so the variant is tested only through present-day constraints on w and curvature, not through its actual endpoint
Go deeper
Adams and Laughlin 1997 (Rev. Mod. Phys. 69, 337) organise the far future into the Stelliferous, Degenerate, Black Hole, and Dark Eras, each set by a dominant physical process and spanning many orders of magnitude in time. Their framework predates the 1998 discovery of accelerating expansion, so the cosmological-constant version of the timeline tightens it: acceleration adds the event horizon cutoff that Krauss and Starkman then built on.
The event-horizon cutoff is the conceptually sharp part. In a de Sitter-like accelerating universe, each observer is surrounded by a cosmological horizon at a fixed comoving distance. Krauss and Starkman 2000 (Astrophys. J. 531, 22) showed this bounds the total energy harvestable by any observer, which in turn bounds total computation. This connects the heat-death future to the de Sitter equilibrium variant in this family, where the same horizon carries a temperature.
Cross-references: this future is the forward extrapolation of the Plain ΛCDM variant in the Chapter 5 Standard Cosmological Model family, and it is the w equal to -1 boundary case of the wCDM and w0waCDM variants there. The rip and recollapse families in this chapter are what you get if w departs from -1 in either direction, so the three families together map the dark-energy equation of state onto three distinct endings.
Variants in this family
Compare variants▸§5 · Who built it, and when(2 sources, 2 established)
- EstablishedAdams, F. C. & Laughlin, G. (1997). 'A dying universe: the long-term fate and evolution of astrophysical objects.' Rev. Mod. Phys. 69, 337
- EstablishedKrauss, L. M. & Starkman, G. D. (2000). 'Life, the Universe, and Nothing: Life and Death in an Ever-Expanding Universe.' Astrophys. J. 531, 22
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