According to Quantum Physics, Elvis is alive and well, performing in a building somewhere ... I have to say the hope that we somehow progress is not shared by the originators of the true doctrine, who see the spiral heading in two directions.
... the enduring question with regard to reincarnation for me is to dispute the assumption that what we think of as the individual and particular 'self', that which says 'me', is that which reincarnates ... I don't think it does.
I rather tend to see reincarnation as 'life goes on', it's the universal and generic nature or essence that we call 'humanity' that brings forth instances of itself in time and space. Each one unique unto 'itself', but all participating, to a greater or lesser degree, in the dynamism of the essence.
Karma in that sense is what we make of this world for those who follow — our children — or as Scripture says, the sins of the fathers will be visited on their sons. They are born into the world we have shaped, with all its brilliance and all its burden. We go forward as best we can, equipped with the baggage that has been bequeathed to us. Another way of saying it is 'original sin'.
As for different worlds, well the original doctrines assure us there are many.
As for reincarnating backwards in time, I'm not sure any doctrine has touched upon that.
