Multiverse only started becoming mainstream just a few years
   ago. It was always a fringe idea from the 1950s when it first
   came out. It inspired a LOT of Science Fiction stories from the
   50s, 60s, 70s, 80s, 90s in the meantime. I'd say it's only been
   in the past 7-8 years that it has become seriously discussed,
   mostly due to the efforts of a few very public cosmologists, the
   Science Channel and a huge nod from the BBC. Even still, among
   friends of mine who are quantum physicists, both theoretical and
   practical (atom smashers), they just kinda shake their heads at
   the whole thing.   Multiverse within qm just like other concepts
   such as anti-time, are primarily utilized as a convenient
   mathematical device. They're not stating "This is how the
   universe really is". What they're doing is borrowing a little
   from impossible things, which are acting as substitutes for
   other unknowns, in order to make the math work and help provide
   new insight. That's not to say it might not be true. It could
   be.