Our universe is not alone.  We have a sister universe.  13.7 billion years ago the Big Bang spawned two identical universes.  Both universes occupied the same 'space' but they were held apart by a tiny time differential, making them entirely invisible and unknown to each other - until our universe reached the beginning of the 22nd century.  The two universes exactly mirrored each other in every detail, atom for atom, blade of grass for blade of grass, person for person, thought for thought - every detail except that tiny time differential.    Tiny though that time differential was, over the course of 13.7 billion years it had gradually accumulated until it had exceeded 2,000 years, with our sister Earth being our Earth's younger sibling.  It still precisely mirrored every detail of our Earth, but as our Earth was over 2,000 years ago.  Meanwhile, that gradually accumulated time differential also meant that our universe had expanded for 2,000 years longer that the younger universe, which meant that the two Earths had drifted three light years apart in their separate spheres of space-time.    This is the story of what happened when scientists on our planet Earth discovered the existence of our sister universe and the means to 'hop' between the two universes .... and the carnage that ensued when a small group of mostly well-meaning scientists decided to pay our sister Earth a visit.