If aliens exist, here’s how we’ll find them

Two esteemed astrophysicists peer into the future of space exploration. In the context of space exploration, a new technological revolution has only just started. What will it bring? Martin Rees and Mario Livio consider an array of fascinating and mind-boggling potentials in the search for extraterrestrial life. 
 “Suppose that there are indeed many other planets where life emerged, and that on some of them Darwinian evolution followed a similar track to the one on Earth. Even then, it’s highly unlikely that the key stages would be synchronized. If the emergence of intelligence and technology on a planet lags significantly behind what has happened on Earth (because, for example, the planet is younger, or because some bottlenecks in evolution have taken longer to negotiate) then that planet would reveal no evidence of ET. Earth itself would probably not have been detected as a life-bearing planet during the first 2 billion years of its existence.”