I’m no expert either but I never got the idea of a new universe popping up everytime. Do other universes also cause popups of new universes or just ours? That’d escalate quickly :-)

I thought it goes that there’s already infinite universes existing from the big bang on. Otherwise universes would be created without big bang. (The new universe would just pop up and you’d still believe it was created by the big bang but there never was one)

Also I’m not sure if laws of thermodynamics had to span accross universes. Take two theoretical perfect vacuum/radiation sealed boxes you put an energy source into. There’s no way to communicate between boxes. Each box had it’s own entropy and state of energy. Both would obey the laws of physics while being separate “systems”.

That thought experiment wouldn’t work, if new boxes had to pop up if one of the boxes wanted to.