Years ago, one course in Geometry discussed the hypothetical. One of those hypotheticals is that the shape of the universe is a torus (donut shape) and the universe is inside. Is that possible?
I think Mobius strips and tori serve the purpose of trying to illustrate the concept of infinity in a finite frame of reference. Illuminating in some aspects but restricting in others.
If there was a blast or bang, it is possible indeed, as the shock wave (for lack of the proper term) continues to expand.
But... what if... outside of OUR observable universe there are multi-verses doing the same thing. In parallel or staggard in space time (unknown) but each expanding within its own “balloon”?
All hypothetical mind you but not outside the boundaries of astrophysical ruminations.
“One of those hypotheticals is that the shape of the universe is a torus (donut shape) and the universe is inside. Is that possible?”
Mmmm donuts.
Simply drop a bread crumb and if the Earth returns back to it, then the Universe is a donut.
But do not drop a donut crumb, that could get confusing.