In June 2012, I was a speaker at SETICon, a convention about the search for extra-terrestrial intelligence and related space topics. A slew of presentations detailed just how far we have come in finding and characterizing planets around other stars. Given that telescopes like Kepler are now able to detect Earth-size planets, and telescopes like Hubble have been able to detect specific gases in some planet atmospheres, the prospects for discovering signs of life are more enticing than ever.
However, there is still one great unknown, and it was emphasized in a discussion by the original SETI pioneer, Frank Drake. About five decades ago, he identified seven factors that, taken together, can help estimate how many technological civilizations should exist in our galaxy. He noted that significant progress had been made on six of the factors, while scientists are powerless to do anything about the seventh.
The great unknown is time. Once a technological civilization is established, how long does it last?
Stars have been continually forming in our galaxy for billions of years. Life on Earth took another four and a half billion years to develop into a technological civilization. Yet we have had that technology for only about 100 years.
If another civilization developed around a nearby star millions or billions of years ago, would they still be there for us to discover? We have no evidence that civilizations can survive for the billion-year timescales that are typical of stars and the development of life.
In fact, the best chance we have for improving our estimate of this factor would be to actually discover an extra-terrestrial civilization. Then, we could finally have a second data point on how long such civilizations can last. It is one of those things where patience is not just a virtue, it is the only possibly response.
Only time will tell.