The “multiverse” is a completely fictional construct which was created to provide an explanation for the mathematical impossibility of life spontaneously arising in our universe.
“Paging Dr. Strange, Paging Dr. Strange”…
The multiverse is a result of following Schroendingers wave equations to it’s end. It inventor was Everett. Sean Carroll is now it’s main champion. Look it up. It also requires faith for it seems impossible to test.