Jim Greenfield wrote:

Sooner or later some Big Banger will go on about living on an
expanding 'membrane' similar to a balloon. That would represent the
sides I refer to here. I agree; there are no sides because the
dimensions are infinite.
George, the concepts of infinity and BB are oxymoronic and
incompatible.
Thanks for your reply
Jim G

There are many possible models to consider. Provide the
mathematical modeling for your preference, then we'll
talk.