Related:

What counts as "another" universe? Space from the same big bang that would be unreachable without the wormhole? Space accessible through a spinning black hole?

@extent_of_foxes another observable universe (probably within the same entire universe). That is, it is outside our cosmological horizon. (Since the term technically has multiple meanings, I guess I will specifically pick the cosmic event horizon for concreteness.)

Also useful background: https://en.wikipedia.org/wiki/Roman_ring

https://arxiv.org/abs/1907.03623

https://www.aleph.se/Trans/Tech/Space-Time/wormholes.html

Casimir Wormholes

Casimir energy is always indicated as a potential source to generate a Traversable Wormhole. It is also used to proof the existence of negative energy which can be built in the laboratory. However, in the scientific literature there is no trace of the consequences on the traversable wormhole itself.…