Brett: Many scientists and philosophers have talked about the concept of a multiverse. But we’re talking about a very strict, very sober understanding of what a multiverse is.
All of these universes in this multiverse obey the same laws of physics. We’re not talking about universes where there are other laws of physics.
We used to think that everything in our universe—other planets, stars, the sun, the moon—orbited around us. We existed on this tiny planet.
Then our vision of reality got expanded a little bit. We realized that, in fact, we were not the center of the universe—the sun was the center. We also realized the sun and some of the other planets—Jupiter, Saturn and the other gas giants—were bigger than our planet. So our universe became larger.
Then we realized that we were just one star system among many in a huge galaxy of hundreds of billions of stars. Later we realized that this galaxy is one of hundreds of billions of galaxies.
The history of ideas and science is a history of us broadening our vision of exactly how large physical reality is.
The multiverse is another step in that general trend, and we should expect it to continue. It shouldn’t be that hard for people to accept that this is the way to understand things.
Do we know everything about quantum theory and how this multiverse works? No. We haven’t united the multiverse with general relativity. We still need a space-time or a geometry of the multiverse.