Just before I came here, a planet was about to collide with earth. To stop the planets from meeting and destroying each other, a device was built to allow the planets to occupy the same space, just at different levels in a a multi-level universe. This created portals which some scientists tried to mine energy from. but instead of mining energy, they ended up pulling people from different dimensions, putting them where they didn't belong, and from universes that are not the same as each other.
I think their experiments are what have brought us here.