Archive for flatness of space

Evidence for a Spatially Flat Universe?

Posted in The Universe and Stuff with tags , , , , , , on February 19, 2020 by telescoper

Yesterday I saw a paper by George Efstathiou and Steve Gratton on the arXiv with the title The Evidence for a Spatially Flat Universe. The abstract reads:

We revisit the observational constraints on spatial curvature following recent claims that the Planck data favour a closed Universe. We use a new and statistically powerful Planck likelihood to show that the Planck temperature and polarization spectra are consistent with a spatially flat Universe, though because of a geometrical degeneracy cosmic microwave background spectra on their own do not lead to tight constraints on the curvature density parameter ΩK. When combined with other astrophysical data, particularly geometrical measurements of baryon acoustic oscillations, the Universe is constrained to be spatially flat to extremely high precision, with ΩK = 0.0004 ±0.0018 in agreement with the 2018 results of the Planck team. In the context of inflationary cosmology, the observations offer strong support for models of inflation with a large number of e-foldings and disfavour models of incomplete inflation.

You can download a PDF of the paper here. Here is the crucial figure:

This paper is in part a response to a paper I blogged about here and some other related work with the same general thrust. I thought I’d mention the paper here, however, because it contains some interesting comments about the appropriate choice of priors in the problem of inference in reference to cosmological parameters. I feel quite strongly that insufficient thought is given generally about how this should be done, often with nonsensical consequences. It’s quite frustrating to see researchers embracing the conceptual framework of Bayesian inference but then choosing an inappropriate prior. The prior is not an optional extra – it’s one of the key ingredients. This isn’t a problem limited to the inflationary scenarios discussed in the above paper, by the way, it arises in a much wider set of cosmological models. The real cosmological flatness problem is that too many cosmologists use  flat priors everywhere!

 

My Even Newer Theory of the Universe

Posted in The Universe and Stuff with tags , , on June 13, 2012 by telescoper

I have decided this evening to unveil my new cosmological theory.

My previous work  was based on the idea that the Universe was obtained from the Swedish furniture and home accessory emporium IKEA. This “Easy Self Assembly” hypothesis dispenses with the need for creation from nothing, and also accounts naturally for the observed geometry of space (it came in a flat pack).

My subsequent study of this scenario has focussed on properties of the Universe that can’t be explained in the earlier version of the theory, specifically  the cosmic microwave background. However, making my supper just now I suddenly hit upon the answer to that particular puzzle. Clearly, wanting to achieve the best results possible, on his/her way back from IKEA the Divine Creator stopped off at Marks and Spencer …