child-of-thecosmos:

Radio and television broadcasting may be only a brief passing phase in our technological development. When we imagine alien civilizations broadcasting signals with radio telescopes, are we any different from earlier generations who imagined riding cannon shells to the moon? Civilizations even slightly more advanced than ours may have already moved on to some other mode of communication, one that we have yet to discover or even imagine. Their messages could be swirling all around us at this very moment, but we lack the means to perceive them just as all of our ancestors, up to a little more than a century ago, would have been oblivious to the most urgent radio signal from another world. 

But there’s another more troubling possibility: Civilizations, like other living things, may only live so long before perishing due to natural causes, or violence, or self-inflicted wounds. Whether or not we ever make contact with intelligent alien life may depend on a critical question: What is the life expectancy of a civilization?

- Episode 11: The Immortals, Cosmos: A SpaceTime Odyssey