Suppose astronomers discover a radio message from a civilization whose planet orbits a star 35 light-years away. their message encourages us to send a radio answer, which we decide to do. suppose our governing bodies take 2 years to decide whether and how to answer. when our answer arrives there, their governing bodies also take two of our years to frame an answer to us. how long after we get their first message can we hope to get their reply to ours? (a question for further thinking: once communication gets going, should we continue to wait for a reply before we send the next message? )