Observable does not mean total
Our observable universe is limited by causal history. We see only regions whose signals have had time to reach us. The whole spatial slice may extend much farther, perhaps even infinitely, depending on the global geometry. Regions beyond today's horizon are not automatically separate universes.
Particle and event horizons
The particle horizon describes the maximum comoving distance from which information could have reached us since an initial time. An event horizon asks which events will ever be able to communicate with us in the future. Accelerated expansion changes both intuition and accessibility.
What “outside” can mean in a bubble model
In false-vacuum eternal inflation, a pocket region can be represented as part of a larger spacetime. In that technical sense the pocket has an exterior inflating region in the model. That does not imply an external room, a preferred observer, or a location reachable by ordinary travel.
Higher dimensions and branes
Some theories place a lower-dimensional universe on a brane embedded in a higher-dimensional bulk. Then an embedding space is mathematically part of the model. Evidence for such constructions would require specific measurable effects; the existence of an embedding in an equation is not itself evidence for a literal external viewpoint.
The safest scientific wording
Ask whether a model contains a larger spacetime, extra dimensions or multiple causally separated regions. Avoid turning that mathematical structure into claims about beings, observers or places outside reality unless the theory actually predicts an observable consequence.