But if you want one that goes back in time, you're screwed. Any mathematics which allows time travel (to date) requires that you have a receiver. There's no way to move that receiver back in time, not even to prove that mankind didn't start with one man and his invisible friend in a garden.
Irrelevant really though. No-one has found something in the mathematics which would allow information to travel faster than c, which pretty much means that the rest is just mathematical games.