Time Travel

I have one major theoretical problem with time travel: the possibility that things can exist without any real origin. Say, for instance, that someone goes into the future and sees some new format for playing back recorded music. Then, he goes back to his current time and invents the thing. With time travel, that would work, but we are faced with the question of origin. The only reason he invented the item is because he saw it in the future--but it's only in the future because he invented it.