So the paradox of going back in time is not such a mystery, we just go to another version of reality.

 

hes talking nonsense, the river analogy is wrong. yes you can get whirlpools (eddys) in rivers but they are small and local and they still travel downstream with the flow.

 

however, the idea of parellel universes using different frequencies is part of (my beloved) string theory. but its only a theory, not a fact.

This sort of stuff is far too complex for a human being to comprehend. Maybe some other civilisation has cracked it somewhere out there but we could be millions of years away.