Infinite Blueshift as a Challenge to Past Eternal Inflation

Gratus, Jonathan and Close, Sam (2026) Infinite Blueshift as a Challenge to Past Eternal Inflation. Classical and Quantum Gravity. ISSN 0264-9381 (In Press)

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Abstract

An observer in an eternally inflating universe, also known as a de Sitter universe, will see distant objects rushing towards them, in that both the distant objects' angular sizes will increase and light from these objects will be unboundedly blueshifted. They will produce a flash of infinite intensity when they first appear. The inflationary coordinate system contains a coordinate singularity and the light is emitted on the other side of this coordinate singularity. Our results are applicable to all universes which have eternal inflation in the past, whatever their current state. For a universe with a finite number of e-folds of inflation, we use this analysis to give an upper limit on the number of e-folds of the order of around 100.