This diagram reveals changes in the rate of expansion since the universe’s birth 15 billion years ago. The more shalow the curve, the faster the rate of expansion. The curve changes noticeably about 7.5 billion years ago, when objects in the universe began flying apart as a faster rate. Astronomers theorize that the faster expansion rate is due to a mysterious, dark force that is pulling galaxies apart.
I use this image for my post about the void theory published on Doc Madhattan (in the network Field of Science!). The post is a more detailed version of my answer to frankietwohats and I finally published the same post on my italian blog, DropSea.