The L Factor

The most influential and least known variable is L — the lifetime of a communicating civilization. If civilizations typically last 10,000 years, the galaxy might host a few thousand at any given time. If they self-destruct within a few centuries of developing radio, the galaxy could be full of ruins but empty of neighbors.

Humanity has been broadcasting radio signals for about 100 years. We do not know if we will last another 100 or another million. L is not just an astronomy question — it is a question about politics, war, climate, and whether intelligent species can survive their own technology.