De Sitter model

In 1917, Willem de Sitter proposed a cosmological model that differed from Einstein's by removing all matter. This model, known as the De Sitter model, remains static because there is no matter to move. If test particles are introduced, the cosmological term causes them to move away from each other, which astronomers considered a possible explanation for the recession of spiral galaxies.

Later, in 1932, Einstein and de Sitter proposed the Einstein–de Sitter universe. This model assumes zero spatial curvature, meaning the universe has a Euclidean geometry and an infinite volume. While space is Euclidean, spacetime is not flat. This model features a big bang, with galaxies receding forever, and the recession rate asymptotically approaches zero over time. Many found this model philosophically appealing due to its unique definition of spatial geometry and evolutionary properties.