The impact of the cosmological constant on past and future star formation

Daniele Sorini; John A. Peacock; Lucas Lombriser

doi:10.1093/mnras/stae2236

paper

The impact of the cosmological constant on past and future star formation

arXiv:2411.07301 · doi:10.1093/mnras/stae2236

Abstract

We present an extended analytic model for cosmic star formation, with the aim of investigating the impact of cosmological parameters on the star formation history within the $Λ$ CDM paradigm. Constructing an ensemble of flat $Λ$ CDM models where the cosmological constant varies between $Λ = 0$ and $1 0^{5}$ times the observed value, $Λ_{obs}$ , we find that the fraction of cosmic baryons that are converted into stars over the entire history of the universe peaks at $\sim$ 27% for $0.01 ≲ Λ/ Λ_{obs} ≲ 1$ . We explain, from first principles, that the decline of this asymptotic star-formation efficiency for lower and higher values of $Λ$ is driven respectively by the astrophysics of star formation, and by the suppression of cosmic structure formation. However, the asymptotic efficiency declines slowly as $Λ$ increases, falling below 5% only for $Λ > 100 Λ_{obs}$ . Making the minimal assumption that the probability of generating observers is proportional to this efficiency, and following Weinberg in adopting a flat prior on $Λ$ , the median posterior value of $Λ$ is $539 Λ_{obs}$ . Furthermore, the probability of observing $Λ \leq Λ_{obs}$ is only $0.5%$ . Although this work has not considered recollapsing models with $Λ < 0$ , the indication is thus that $Λ_{obs}$ appears to be unreasonably small compared to the predictions of the simplest multiverse ensemble. This poses a challenge for anthropic reasoning as a viable explanation for cosmic coincidences and the apparent fine-tuning of the universe: either the approach is invalid, or more parameters than $Λ$ alone must vary within the ensemble.

arXiv commentPublished in the Monthly Notices of the Royal Astronomical Society (MNRAS). This is a pre-copyedited, author-produced version of the article accepted for publication in MNRAS following peer review. The version of record is available online at the DOI: 10.1093/mnras/stae2236

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