Poor Abe, a brilliant mind with crippling Agoraphobia. Keeping himself at home he works studiously hoping to figure out portal technology for moving across space. And succeeds, sort of....
Instead of a plant or some rock, the Main six force their way through thinking the portal is a threat to Equestria, and end up getting stuck on the other side.
So now they have to live hidden on earth until Abe can fix the portal.