All universes (great and mini) exist with in the supermembrane. It's not possible for the mini-universe (at the very least, the mini-universe they're residing in) to transmit to the great universe, but it is possible for the great universe to transmit messeges across the supermembrane to other universes. However, the energy for this is unfathomably vast, requiring a Milky' Ways worth of mass-energy. This all being said though, there are messeges and transmissions from other great universes on the supermembrane (some natural phenomena, others messeges from unknowable intelligent beings). The Returners send a messege to all the mini-universes from their own great universe, which contains over 1,570,000 languages, including the languages of Earth and Trisolaris, calling everyone to come back to save the future of the next universe. The messege sent out by the Returners. (From Death's End)