Superman is full of awesome sci-fi elements, but the most fascinating one might be Lex Luthor's pocket dimension. How does that even work?

What's the deal with Lex Luthor's pocket universe in James Gunn's 'Superman'?

Source: space
Source Link: https://www.space.com/entertainment/space-movies-shows/whats-the-deal-with-lex-luthors-pocket-universe-in-james-gunns-superman