I've seen this tied up with one idea where space-time itself is ripped apart, leaving nothing that can expand and instead "everything" once against occupying th

I've seen this tied up with one idea where space-time itself is ripped apart, leaving nothing that can expand and instead "everything" once against occupying the same space less than an atom (if it can even be quantified), reduxing a Big Bang. Otherwise we increasingly approximate a transition to "nothing" into infinity.