[Lightspeed]

The filter would be at the level of the universe's creation. Universes that self-contradict are excluded from existing. If you find yourself in a universe, it's one that's survived the existing/not-existing filter.

Time travel in our kind of universe would contradict the existence of this universe. If we're here, it's because there's no time travel. We're as close to achieving it as we'll ever be.