[anonymouskimmer]

At that point aren't we getting into the idea of a multiverse, and not a universe anymore? We have no non-hypothetical knowledge of what exists beyond the limits of the universe as it descended from what we can still see of the radiation shortly after the Big Bang. However, from that radiation, can't we get a ballpark figure for the atomic limits of the Big-Bang-Universe?

[borissk]

No, the different multiverse hypotheses are something different. The size of "our" universe is unknown, we can can see a sphere with a diameter of 94 billion light years. How much is there beyond that sphere is a research topic. No light from beyond the sphere has reached us during the lifetime of the universe.

[anonymouskimmer]

This is about inflation, right? We don't know how much the universe inflated after the big bang, just that it did.