https://imagine.gsfc.nasa.gov/observatories/satellite/wmap/shape.html
https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question35.html
https://www.astronomy.com/science/what-shape-is-the-universe/
https://bigthink.com/starts-with-a-bang/universe-flat/
https://www.space.com/34928-the-universe-is-flat-now-what.html