Imagine that technology and knowledge become so advanced on Earth that it is commonly accepted as fact that there are multiple realities simultaneously occurring and interlinking between the observer aspect in each of us.
Imagine that switching between these realities becomes as easy and common place as dreaming or going on an adventure in your home town as a child.
People could live an ancient existence in one reality, and through some methodology or another (we already experience other existences here, it happens all the time, the advanced aspect would simply be the control of that) people can return to a future aspect of the same civilization or a multi-dimensional aspect that goes beyond time and influences all others.
Only movies have come close to offering what is truly out there (guided by what’s “in here”). There could be multiple civilizations worth of experiences right here and now, all linked together through a faster-than-light communication capacity of DNA.