Göttingen 2025 – scientific programme

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GR: Fachverband Gravitation und Relativitätstheorie

GR 15: Cosmo III

GR 15.4: Talk

Friday, April 4, 2025, 12:00–12:20, ZHG008

FLRW Constants of the Motion and the Issue of Their Fine-tuning — •Marc Holman — Utrecht University, Utrecht, Netherlands

It seems to be contended at times that quantum gravity considerations could in principle provide justification for a “blindfolded creator” view on the initial value of the curvature parameter, Ω, in FLRW models. That is, even though there are no sound classical motivations for adopting a uniform probability distribution on initial values of Ω, according to such a line of thought, there could in principle exist quantum gravity motivations to that extent. Here it is shown explicitly - in agreement with previous assertions made by the author - that for the radiation- and dust-filled FLRW models of nonzero curvature, a uniform measure on Ω for Planck-scale initial conditions necessarily entails large amounts of fine-tuning in FLRW constants of the motion. This means that, unless there exist specific reasons for fine-tuning these physical constants, a flatness problem in the fine-tuning sense does not exist, whether quantum gravity motivated or not. Time permitting, comments will also be made on more recent arguments, which purport to establish the existence of a flatness problem in the above sense using Bayesian analysis.