The Cosmological Principle (CP) was a major achievement of modern cosmology to turn qualitative statements into quantitative ones. It makes the strong assumption that space is globally homogeneous and isotropic. By doing so, it reduces Einstein’s Field Equations to provide highly symmetric cosmological models. The latter then enable us to interpret a very sparse amount of data and put them into a common cosmological context. Consequently, cosmologists could probe large-scale properties of the known universe starting in the 1920s. Observational techniques greatly advanced over the last century and provided myriads of data with increasing quality. So, what started as “all places in the universe are alike” – a vague but well-working formulation back then – now faces a semantic debate how to define “isotropy” and “homogeneity” in the era of statistical, data-driven inferences. Given the increased amount of observations, we may ask whether the model-driven approach of using the CP as an a priori assumption is still adequate or can be abandoned in favour of a data-based approach.
Within this setting, I will give a review on the current status of the usage and the validity of the CP in recent cosmic data evaluations based on our community white paper Aluri et al. Class.Quant.Grav. 40 (2023) 9, 094001, which jointly discusses several tensions that challenge not only our cosmological concordance model but the entire class of homogeneous and isotropic cosmologies.
BIO
Dr. Jenny Wagner holds a master degree in particle physics working at the ALICE experiment at CERN and a PhD in machine learning for bio physics in collaboration with the German Cancer Research Centre. Since 2014, she has held two grants from the German Science Foundation to separate model-dependencies from observation-based evidence in strong gravitational lensing -- an endeavour for which she was awarded the Prize for Courageous Science 2020. Currently, she is transferring this methodology to other cosmological probes as a researcher at the Bahamas Advanced Study Institute and Conferences, an interdisciplinary institute founded by E. Guendelman and T.L. Curtright. More details on her homepage: https://thegravitygrinch.blogspot.com
