Tim Mulgan in Aeon:
Suppose we woke up tomorrow to learn that extraterrestrial life had been discovered. What difference would that make? Set aside the extreme scenarios of popular fiction. The truth will probably be more mundane – not massive spaceships suddenly filling the sky but, instead, microorganisms found deep inside an ice-covered Moon, a non-random radio signal from a distant star system, or the ruins of a long-dead alien civilisation. What difference might those discoveries make? Would they strengthen or weaken our faith in God, or science, or humanity? Would they force us to re-evaluate the importance of our own lives, values and projects?
In academic philosophy today, an interest in extraterrestrial life is regarded with some suspicion. This is a historical anomaly. In Ancient Greece, Epicureans argued that every possible form of life must recur infinitely many times in an infinite universe. In the 17th, 18th and 19th centuries, as modern astronomy demonstrated that our Earth is just another planet and our Sun just another star, the default hypothesis among informed observers was that the Universe is filled with habitable planets and intelligent life. One principal argument for this ‘pluralism’ was philosophical or theological: God (or Nature) does nothing in vain, and therefore such a vast cosmos could not be home to only one small race of rational beings.
My goal here is to explore some unexpected implications of the discovery of extraterrestrial life, and my conclusions are very speculative: extraterrestrial life would lend non-decisive support to several interesting and controversial philosophical positions.