The Tyranny of Extraterrestrial Messaging - Scientific American Blog Network https://blogs.scientificamerican.com/life-unbounded/the-tyranny-of-extraterrestrial-messaging/
Some of the basic assumptions we make about extraterrestrial communication can be woefully naïve. Consider the situation in its gory detail.
You decide (perhaps as a species, or perhaps as some resource-rich subset) that you want to ping the cosmos to find out if something else is
listening, thinking, and as technological as you are. So you fire up your radio transmitter, or your big laser and start shooting off ‘Hello’
If our circumstances represent a useful template it means that the earliest possible response might come within about 8 years (Earth years of
course). That's assuming that there is a responder in the nearest exoplanetary system, listening and receiving your first message at the right
time, ready to fire back a response right away, willing to fire back a response, and capable of firing back something recognizable as a response.
So, you start listening carefully 8 years later. But nothing comes in. So, you keep listening, telling yourself that it may take time for anyone
to put a response together. And you keep listening.
Meanwhile, you’ve been busy. In the last 8 years you’ve been pinging the next furthest stellar systems. But for these the roundtrip light travel
times go up to 10 years, 20 years, 40 years. Within the sphere of space for a 40-year messaging roundtrip are roughly 150 stars.