# What is the theoretical geometry of bubble universes?

My research has led me to look into the idea of bubble universes which I don't know very much about. The first thing that I am looking for is understanding or visualising how could many bubbles co-exist geometrically, assuming each bubble universe is like ours (that is, a flat euclidean geometry). Are we talking about an n-manifold that has multiple bubbles embedded in it? Submanifolds? Or can we extend the idea of branes to the notion of bubbles? Is it perhaps a 3-sphere that houses multiple 2-spheres? Put simply, what is the theoretical geometry that engulfs all the bubbles and how would they be connected?

• You do understand that our universe does not have a flat, Euclidean geometry, right? – Danu Feb 3 '14 at 22:57
• I meant to say that the curvature of the universe appears to be flat (or near flat) from a number of observations, but yes, it is a 4 dimensional spacetime universe that can be represented as a simple manifold. – Luis Feb 3 '14 at 23:16
• Do you know the difference between a Euclidean and a Lorentzian manifold? – Danu Feb 3 '14 at 23:55
• Luis another way of putting @Danu's question is do you understand the nontrivial signature of the metric, i.e. we're dealing with a pseudo-Riemannian manifold. However, your question bespeaks a mathematics background, so I'm guessing you do, so are you asking about sections of spacetime? Otherwise, I think this is a perfectly good question, asking for a quick overview of global topology, and you want info on things like whether the bubbles are held to be topological embeddings / immersions and so on. Am I right? (not my field, so I won't answer - trying to improve the question) – Selene Routley Feb 4 '14 at 2:03
• Oh, I almost forgot :), +1 for the question BTW, I hope it gets an answer because I'd like to see one. – Selene Routley Feb 4 '14 at 5:30