Disentangling the Cosmic/Comoving Duality: The Cognitive Stability and Typicality Tests

TL;DR

The paper tackles the Boltzmann Brain and Freak Observer paradoxes that arise in a future-eternal ΛCDM Universe by comparing the standard cosmic-frame description with a dual comoving-frame perspective. It is shown that, while the cosmic frame predicts an infinite, observer-type-dominant increase in BBs/FOs, the comoving frame couples the Boltzmann factors to growing masses and contracting volumes, effectively suppressing BB/FO formation. This yields a dominant Ordinary Observer population and restores cognitive stability and typicality in the comoving picture. The work suggests that the cognitively stable description of our Universe is best captured in the comoving frame and hints at possible connections to fundamental issues like the Cosmological Constant problem.

Abstract

Cosmological scenarios wherein the cumulative number of spontaneously formed, cognitively impaired, disembodied transient observers is vastly larger than the corresponding number of atypical `ordinary observers' (OOs) formed in the conventional way -- essentially via cosmic evolution and gravitational instability -- are disqualified in modern cosmology on the grounds of Cognitive Instability -- the untrustworsiness of one own's reasoning -- let alone the atypicality of OOs like us. According to the concordance $Λ$CDM cosmological model -- when described in the (expanding) `cosmic frame' -- the cosmological expansion is future-eternal. In this frame we are atypical OOs, which are vastly outnumbered by typical Boltzmann Brains (BBs) that spontaneously form via sheer thermal fluctuations in the future-eternal asymptotic de Sitter spacetime. In the case that dark energy (DE) ultimately decays, the cumulative number of transient `Freak Observers' (FOs) formed and destroyed spontaneously by virtue of the quantum uncertainty principle ultimately overwhelms that of OOs. Either possibility is unacceptable. We argue that these unsettling conclusions are artifacts of employing the (default) cosmic frame description in which space expands. When analyzed in the comoving frame, OOs overwhelmingly outnumber both BBs and FOs. This suggests that the dual comoving description is the cognitively stable preferred framework for describing our evolving Universe. In this frame, space is globally static, masses monotonically increase, and the space describing gravitationally bounded objects monotonically contracts.