monkeys in front of a million computers and letting them bang on the keyboards for an extremely long time. Eventually, through their random actions, one of them would type a Shakespearian sonnet.
The lower the probability for intelligent life to evolve, the farther we need to look to find it. Hence, before drawing conclusions about the current failure of the SETI mission to discern signals from within the Milky Way, we must expand our search to include other galaxies. Although the present-day program envisions civilizations with the capacity to broadcast messages over tens or hundreds of light-years, we can easily imagine extragalactic cultures with even greater capabilities. Moreover, because each galaxy potentially harbors hundreds of billions of worlds, there could very well be far more civilizations able to reach us with their signals outside the Milky Way than within it. Therefore, by aiming our radio dishes at intergalactic as well as intragalactic targets we might improve our search for extraterrestrial intelligence.
Suppose comprehensive scans of the heavens—including the broadest possible scope of galaxies—continue to fail to turn up signs of sentient life. Should the science community then conclude, like Tipler, that we are alone in the cosmos? Or could there be another reasonable explanation for the complete lack of communication?
To address this issue, let’s draw a valuable lesson from the way we resolved Olbers’ paradox. In that case we found that the finite age of galaxies and the finite speed of light conspire to shield us from the totality of radiation emitted in space, letting only a minute portion reach our skies. Similarly, perhaps the finite age of extraterrestrial civilizations and the finite speed of light preclude us from receiving alien broadcasts. In contrast to starlight and galactic light, maybe the effect is so severe that not even a single message would be able to reach us.
If that seems odd, think about the case of the Felix the Cat signals broadcast in the 1920s. Because of the limitations posed by the speed of light, only a small fraction of the stars in the galaxy are close enough (within 80 light-years) to have already come into contact