In the last few decades, it has become clear that almost every single star has at least one planet orbiting it.
There are 100 billion stars in our galaxy alone. Perhaps it will never happen. Perhaps the unfathomable distances between worlds means that we will always think that we’re alone, at least in our corner of the cosmos. But it’s possible that, one day, a radio observatory pointed toward a constellation of diamantine specks glinting in that deep, dark ocean above will pick up something that will change everything.
Maybe it’s a radio signal, one not coming from the death of a star, or a distant planet’s aurora. It sounds technological. It’s not an accidental interception of one of Earth’s myriad broadcasts. And it has a purposeful structure to it. Astrophysicists cannot identify the meaning of the signal. But at that stage, the cryptic content doesn’t matter as much as the source: it came from a planet 40 light-years away, which meant that, 40 years ago, someone on a technologically advanced world decided to send Earth a message.
The search for extraterrestrial intelligence, or SETI, has succeeded. We are not alone; someone, whoever they are, is reaching out. What happens next? And how might we decide to respond to our enigmatic galactic neighbors?