Multiple versions of earth, I think, is covered in -- have you read Alan Guth's 2007 paper, "Eternal Inflation and its Implications"? The universe is ever-expanding, but the thrust of the paper is essentially arguing that conceptualizing the expanding universe as just getting bigger in one direction is wrong. It's expanding into the past, the future, it's expanding in layers upon layers which essentially crafted the multiverse. I think Stephen Hawking was the person who talked about the notion that physics might differ slightly between each layer of the multiverse, which is what keeps them from collapsing in on themselves - but it's been a while since I've read his work.
But I think the concept of magnetosphere portals might... hold? I just don't know why it's chosen this place to spit us all out. But I guess it's better than Ohio.
I lean towards sentience: too many people here are - well, they're special. We're getting superheroes, scientists and Starfleet captains, not convenience store owners and cab drivers. There are two few of us and too many average people to think this is an accident.