De Sitter space was a concept that was first postulated by a Human physicist.
It was a meta-etheric medium which was a kind of "overspace" that contained the standard universe as well as countless other ones. (TTN novel: The Red King)
In the War of the Prophets alternate timeline, Miles O'Brien posited that there was a De Sitter space where the universe did not end in the year 2400. (DS9 - Millennium novel: Inferno)