Elizabeth Kolbert at The New Yorker:
In an equation-dense paper that appeared in The Astrophysical Journal Letters a year after Weryk’s discovery, Loeb and a Harvard postdoc named Shmuel Bialy proposed that ‘Oumuamua’s “non-gravitational acceleration” was most economically explained by assuming that the object was manufactured. It might be the alien equivalent of an abandoned car, “floating in interstellar space” as “debris.” Or it might be “a fully operational probe” that had been dispatched to our solar system to reconnoitre. The second possibility, Loeb and Bialy suggested, was the more likely, since if the object was just a piece of alien junk, drifting through the galaxy, the odds of our having come across it would be absurdly low. “In contemplating the possibility of an artificial origin, we should keep in mind what Sherlock Holmes said: ‘when you have excluded the impossible, whatever remains, however improbable, must be the truth,’ ” Loeb wrote in a blog post for Scientific American.