The Importance of One Other Example

We have evidence for one intelligent civilization in the galaxy. The discovery of just one other would be decisive. The chance of finding another communicative civilization is almost zero unless the galaxy is teeming with life. Thus, such a discovery would imply that the number of intelligent civilizations in the galaxy is large.

As the late Carl Sagan often emphasized, it would tell us something else important: it would imply that it is possible for technical civilizations to survive the introduction of technology. Since technical civilizations such as our own have the ability to destroy themselves, this would be an important discovery.