Does Intergalactic SETI Make Any Sense?
The Breakthrough Listen project is proposing to extend its search for artificial radio and optical signals to include the 100 nearest galaxies.
But should we expect to find a beacon from a technological civilisation that is bright enough for us to detect over intergalactic distances?
The Andromeda Galaxy, number 31 in Messier’s catalogue, will be a good test case. It is the brightest of those shown within the 100 nearest galaxies, hence is presumably the largest, has a good line of sight from the Solar System, and is only one quarter of the distance of the most distant of the 100 to be observed in the Breakthrough Listen programme. It is closely similar to our own galaxy. If we can’t find extragalactic aliens in M31, we’re not likely to find them anywhere else.
Let’s ask what sort of transmitter power levels are expected of our alien pen-friends…