The Drake Equation: Lifetime

Finally, the lifetime of a communicating civilization: L.

Its value is very conjectural, because there are several factors that can limit such a civilization’s lifetime.

1. Wars
2. Diseases
3. Environmental problems
4. Resource depletion
5. Loss of interest

(1) This was rather obvious from the Cold War. Both the United States and the Soviet Union built enough nuclear bombs to turn each other’s cities into radioactive wastelands, and other nations have tried to join in.

(2) That is a bit farfetched, but not impossible with suitable genetic engineering, like creating a time-bombed microorganism that spreads without causing symptoms, and then starts attacking its hosts.

(3) These include various ways of impairing the habitability of one’s homeworld, like ruining farmland and altering the climate.

(4) This includes running out of fossil fuels, metal ores, and the like, without developing good substitutes. I think that energy resources are especially critical, since without energy, you can’t do anything else. So it is important to learn how to use long-lived energy sources like the light of one’s homeworld’s star.

(5) There are several ways that this can happen.

1. Reversion to a lower level of technology
2. Turning inward
3. Feeling threatened by the possibility of intelligent entities elsewhere in the Universe
4. Deciding that such entities cannot exist
5. Quitting after failing to discover such entities
6. Considering self-advertisement too dangerous or too expensive
7. Considering searches likewise too dangerous or too expensive

But if a civilization can overcome these challenges, then it can last as long as the Universe has usable energy to run it.

This is arguably the most conjectural of all of Frank Drake’s parameters, and a good part of the reason is our very limited experience with it, much less than for the other parameters. So L is very up in the air.