The observed late-time acceleration of the universe is standardly modeled with a small positive cosmological constant, and current data place the dark-energy equation of state near w = −1.

The observed late-time acceleration of the universe is standardly modeled with a small positive cosmological constant, and current data place the dark-energy equation of state near w = −1.

Why it is stated this way

This is the empirical anchor of the debate. Both camps accept it: the landscape side tries to reproduce a small positive vacuum energy from string constructions, and the swampland side has to explain the same observation without a stable de Sitter vacuum.

Scope and limitations

A successful model is not a proof of mechanism. Whether the vacuum energy is truly constant or slowly rolling is not settled by current bounds. Note also that the discovery-era supernova papers are outside the source map’s verified citation set, so they are not cited here; the sources listed are the in-set works that constrain the equation of state.

Sources

• Equation-of-state bounds on swampland quintessence ↗ · Heisenberg, Bartelmann, Brandenberger, Refregier · arXiv:1808.02877
• News from the Swampland — constraining string theory with astrophysics and cosmology ↗ · Schöneberg, Vacher, Dias, Carvalho, Martins · arXiv:2307.15060 · JCAP 2023(10), 039; doi:10.1088/1475-7516/2023/10/039

Related atlas concepts

Cosmological constantObservational cosmologyde Sitter spacetime