A measure of de Sitter entropy and eternal inflation

Nima Arkani-Hamed, Sergei Dubovsky, Alberto Nicolis, Enrico Trincherini, Giovanni Villadoro

    Research output: Contribution to journalArticlepeer-review


    We show that in any model of non-eternal inflation satisfying the null energy condition, the area of the de Sitter horizon increases by at least one Planck unit in each inflationary e-folding. This observation gives an operational meaning to the finiteness of the entropy SdS of an inflationary de Sitter space eventually exiting into an asymptotically flat region: the asymptotic observer is never able to measure more than e SdS independent inflationary modes. This suggests a limitation on the amount of de Sitter space outside the horizon that can be consistently described at the semiclassical level, fitting well with other examples of the breakdown of locality in quantum gravity, such as in black hole evaporation. The bound does not hold in models of inflation that violate the null energy condition, such as ghost inflation. This strengthens the case for the thermodynamical interpretation of the bound as conventional black hole thermodynamics also fails in these models, strongly suggesting that these theories are incompatible with basic gravitational principles.

    Original languageEnglish (US)
    Article number055
    JournalJournal of High Energy Physics
    Issue number5
    StatePublished - May 1 2007


    • Black holes
    • Cosmology of theories beyond the SM
    • dS vacua in string theory

    ASJC Scopus subject areas

    • Nuclear and High Energy Physics


    Dive into the research topics of 'A measure of de Sitter entropy and eternal inflation'. Together they form a unique fingerprint.

    Cite this