I thought that in order for a holographic universe to exist, then the universe needs to have a non-flat e.g. slightly-curved spacetime; in order to "close the b

I thought that in order for a holographic universe to exist, then the universe needs to have a non-flat e.g. slightly-curved spacetime; in order to "close the boundary", so to speak. But my understanding is that so far all our evidence shows that spacetime is flat? i.e. we spacetime needs to be an Anti-de Sitter space. https://en.wikipedia.org/wiki/Anti-de_Sitter_space https://en.wikipedia.org/wiki/Anti-de_Sitter_space But I didn't think many actually think we live in an ADS universe? Also relevant to string theory, https://en.wikipedia.org/wiki/AdS/CFT_correspondence https://en.wikipedia.org/wiki/AdS/CFT_correspondence