宇宙論には、宇宙が無限の周期で膨張と収縮を繰り返すというモデルがあるが、新しい研究により、この理論の最新版に決定的な欠陥があることが判明した Some cosmological models propose that the universe expands and contracts in infinite cycles, but new research finds a crucial flaw in the latest version of this theory
2022-08-04 バッファロー大学(UB)
この研究は、この理論の最新版である、エントロピーに関する長年の懸念を解決する周期的モデルが、新たな問題を引き起こす（というより、古い問題に戻る）ことを示しています。
＜関連情報＞
- https://www.buffalo.edu/news/releases/2022/08/005.html
- https://iopscience.iop.org/article/10.1088/1475-7516/2022/06/011
周期的宇宙論と測地線の完全性 Cyclic cosmology and geodesic completeness
William H. Kinney and Nina K. Stein
Journal of Cosmology and Astroparticle Physics Published 10 June 2022
DOI:10.1088/1475-7516/2022/06/011
Abstract
We consider recently proposed bouncing cosmological models for which the Hubble parameter is periodic in time, but the scale factor grows from one cycle to the next as a mechanism for shedding entropy. Since the scale factor for a flat universe is equivalent to an overall conformal factor, it has been argued that this growth corresponds to a physically irrelevant rescaling, and such bouncing universes can be made perfectly cyclic, extending infinitely into the past and future. We show that any bouncing universe which uses growth of the scale factor to dissipate entropy must necessarily be geodesically past-incomplete, and therefore cannot be truly cyclic in time.
