Imagine an advanced civilization which can manipulate gravity like we manipulate electromagnetic radiation. Could they already be using gravitational waves for data transmission across different galaxies?
Unlike electromagnetic radiation which can be shielded, gravitational waves appear to travel through any medium at speed of light. Perhaps this explains why SETI is a wasted effort?
EDIT: didn't realize there was a similar question already raised: Would it be possible to transmit information through gravitational waves?