In my post I said that I wouldn't include time, as it wasn't necessary to understand this model. However correctly our universe is 3+1-dimensional. This model says we might be a bubble in a 4+1 dimensional universe.
That clears things up. I appreciate the clarification.
I have no idea how another spatial dimension would manifest, but then again, I am not a four dimensional being!
It makes me wonder: if our universe (3+1) is essentially a 'bubble' within another, larger (4+1) universe, are there other (3+1) universe bubbles also in existence and if so, can they interact? i.e. collide?