WRT ELI5 (and bear in mind I'm a layman who's only briefly skimmed the article, but this may do till an expert chips in, corrections welcome): There are a coup

WRT ELI5 (and bear in mind I'm a layman who's only briefly skimmed the article, but this may do till an expert chips in, corrections welcome): There are a couple of main ways of calculating the speed of the expansion of the universe; they are very different and act at different scales, but should obviously tally. They don't, and the mismatch is often referred to as a crisis in cosmology in popular articles on the subject. It's a serious issue because each of the two different methods is foundational in our understanding of the structure of the universe in their domain; we can't just prefer one over the other. Our standard way of modelling the universe relies on Einstein's general relativity in a larger framework that caters for dark matter; a (controversial) "Newtonian" alternative is called MOND and this article proposes ways that elements of the two (but favouring the latter) might be combined to counter the discrepancies in the measurements, taking into account other difficulties in the process like the void in the title. Further reading; Crisis: https://www.quantamagazine.org/cosmologists-debate-how-fast-the-universe-is-expanding-20190808/ https://www.quantamagazine.org/cosmologists-debate-how-fast-... MOND https://www.wikipedia.org/wiki/Modified_Newtonian_dynamics https://www.wikipedia.org/wiki/Modified_Newtonian_dynamics Standard Cosmological Model https://www.wikipedia.org/wiki/Lambda-CDM_model https://www.wikipedia.org/wiki/Lambda-CDM_model