Imagine a warm summer night and a back yard out of which rise many fireflies, or lightning bugs, as we used to call them. One lights up for a moment over here, another over there, usually separated by some distance. Occasionally two close together will light up, but not too often. The back yard is our galaxy. Each firefly light— even if it’s from the same bug — represents a planetary civilization that is born, flourishes, and then dies. Only rarely do two civilizations very close together flourish at the same time. Usually, civilizations arise at different times, and usually they are not close to each other. But they all come to an end, and perhaps they end before their dream of finding other civilizations— if, indeed, they even have such dreams — is fully realized. This might have happened to many civilizations, and it might happen to us. In fact, it is almost certain to happen to us. The cycle of birth-life-death seems to be universal: plants, animals, humans, empires, stars, and apparently even the universe itself all go through that cycle. Why not planetary civilizations? What this means is that even if many technological civilizations have existed, exist now, or will exist in the future, the chances of us making contact with them are diminished not only because of distance but also because we and they simply don’t exist at the same point in time. And even if they are “close” to us, "close" in interstellar terms still means unimaginably vast distances. Intergalactic distances are vast way beyond that.