I'm trying to write a bit of flash fiction about a guy who goes back to say Hi to himself as a youngster (give a bit of advice and buy a few shares). Problem I have is avoiding the many supposed paradoxes. He's only allowed to stay a short while and only meet one person (the boy). The other problem is that in the past the tech for getting him home must exist in some sort of future 'bubble'. Any other ideas or references welcome. Otherwise the story is a bit bland.