The Hawaiian word “‘Oumuamua” loosely translates to “scout.” It was applied half-jokingly in 2017 to the first known interstellar object ever observed in our solar system, a rocky, asteroid-like visitor that originated outside the sun’s gravitational pull and flew past Earth on its journey from ... well, nobody knows.
Unfortunately, we didn’t get a great look at it. At the time of its detection, ‘Oumuamua already was speeding away from the sun, from which point it could provide only limited data.
But what astronomers did see was strange: ‘Oumuamua, which was roughly the size of a football field and shaped like either a cigar or pancake, was accelerating as it left the solar system. This does happen with comets, which release gases as they’re heated by the sun, producing visible tails and bursts of speed, a phenomenon called “outgassing.”
‘Oumuamua, however, produced neither a tail nor any indication of outgassing, which means it accelerated for some other reason. But, four years later, there still is no scientific consensus about why.
The Harvard astrophysicist Avi Loeb attracted international attention when he proposed a sensational explanation: What if ‘Oumuamua was created by intelligent extraterrestrials and sent in our direction intentionally? What if it was a probe or a buoy or, to interpret its nickname literally, a scout from another world?
Loeb’s proposition generated a media frenzy.
Here was a highly credentialed researcher making a compelling argument that we’d witnessed evidence of extraterrestrial intelligence, suggesting ‘Oumuamua’s acceleration could be explained by artificial technology such as a lightsail, and that several other features appeared too bizarre to have occurred naturally.
In his new book, “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth,” Loeb expands his ‘Oumuamua hypothesis and reluctantly emerges as the new public face of the search for extraterrestrial intelligence (SETI), a position that has attracted widespread criticism and ridicule from others in the scientific community.
What begins as an act of intellectual self-defense widens into an elegant argument for scientific open-mindedness. “Extraterrestrial” denounces what he describes as scientific groupthink that stifles extraordinary discoveries, and indeed, nothing would be more extraordinary than confirmation of alien life.
But many scientists involved with SETI, he explains, participate in secret for fear of damage to their careers or reputations, while more esoteric concepts such as parallel universes and string theory are widely accepted despite being essentially unprovable.
As Loeb explains, SETI enjoyed broad public interest in the 1960s and ‘70s as radio telescopes around the world began scanning the heavens for signals from other worlds. Since being drastically defunding in the 1990s, SETI has moved to the fringes, inspiring as much science fiction and conspiracy-theorizing as credible science.
But while that’s happened, our understanding of the universe has deepened in ways that only justify renewed public interest and investment. In the last three decades, astronomers have found thousands of planets outside our solar system, and now suggest potentially habitable worlds in our galaxy alone could number in the billions.
Such discoveries continue to recalibrate the relationship between the two concepts underlying SETI: There is the Drake equation, which estimates the probability of intelligent life based on the number of sun-like stars and Earth-like planets known to exist.
Then there is the Fermi Paradox, which attempts to reconcile the likely abundance of extraterrestrial life with the lack of observable evidence for it.
Loeb suggests adding a third concept to this list: ‘Oumuamua’s Wager, a variation on the famous Pascal’s Wager, which suggests the upsides of believing in God outweigh the downsides, even if he doesn’t really exist.
Assuming ‘Oumuamua came from an alien civilization, Loeb argues, will enrich humanity and leave us better prepared for true extraterrestrial contact, even if we’re wrong this time.
The “if” or “when” of that scenario is unknowable, of course, because we have no way of calculating how common life is in the universe until we find it somewhere else.
The reason to keep searching the cosmos, in wonder and humility, is that we already know it has happened at least once.