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Review: Interstellar

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Interstellar: The Search for Extraterrestrial Life and Our Future in the Stars
by Avi Loeb
Mariner Books, 2023
hardcover, 256 pp.
ISBN 978-0-06-325087-1

Some authors mark the release of a new book with a book tour or magazine profile to gain publicity. Avi Loeb published a scientific paper. The Harvard astrophysicist led a team that published a preprint August 29 summarizing efforts to find pieces of a potential interstellar meteor that fell into the Pacific Ocean in 2014. That work, which involved dredging a portion of the ocean floor off the coast from Papua New Guinea, yielded five spherules whose composition, they concluded, was so different from terrestrial materials that it could be best explained if they were from an object, designated IM1, that came from outside the solar system based on its high atmospheric entry speed.

“I hope before 2023 is over to find and hold evidence of an extraterrestrial artifact. And maybe, just maybe, when I do find it, it will have a button or two that I can push.”

The preprint, submitted to the journal Ocean Science for peer review, has met with a sharp reaction from many of his peers, who have expressed doubts. They take issue with the findings in the paper, such as data based on Space Command sensors that the object hit the atmosphere at velocities that could only be explained by an interstellar origin: those sensors tend to overestimate reentry speeds, other scientists have found. Others noted the spherules would have drifted in ocean currents before reaching the seabed and thus the team was not looking in the right location, and that there can be other, terrestrial explanations for the composition of the spherules seen.

The preprint was posted the same day as the official publication of Loeb’s newest book, Interstellar. In it, he describes plans for that meteorite search based on the analysis that IM1 has interstellar origins among other efforts that he says will demonstrate the existence of objects from beyond the solar system, including potentially of intelligent origins.

IM1 is not the only object that Loeb believes has been found from beyond the solar system with unusual characteristics. Astronomers discovered in 2017 an object called ‘Oumuamua whose trajectory clearly showed came from outside the solar system and headed back out as well. Loeb argued that unusual accelerations seen by the object as it passed through the solar system could be explained if it was an artificial object: a version of a lightsail, perhaps, he concluded. Other scientists have concluded that the object’s motions can be explained by other means, such as outgassing of hydrogen ice as ‘Oumuamua warmed during its passage by the Sun. No alien technology required.

Loeb, a theoretical physicist, seems undaunted by critiques by people with expertise in planetary science, cosmochemistry, and related fields. In his book he describes how there is strong evidence, in his view, that ‘Oumuamua, IM1, and potentially other objects are not only of interstellar origin, but also are not natural. Discussing the planned search for IM1 fragments, he writes, “I hope before 2023 is over to find and hold evidence of an extraterrestrial artifact. And maybe, just maybe, when I do find it, it will have a button or two that I can push.” (Later in the book he adds, “This is admittedly unlikely.” Loeb’s preprint reported finding no objects with buttons to push.)

Loeb writes his efforts are driven by the scientific method: collecting data and presenting its analysis in the open, such as in the IM1 preprint. The same is true for another effort discussed in the book to gather data on unidentified anomalous phenomena (UAP), more popularly known as UFOs. His Galileo Project is developing instruments to gather more data on UAPs, although the book does not discuss any findings from those instruments so far.

Interstellar, though, serves as a reminder that science remains a human process with human motivations and failings. He seems perplexed at times in the book that others do not see how the evidence shows that there is intelligence beyond our solar system whose technologies can be detected in our skies or on our seabeds. Those of a different mindset, though, may be unconvinced by his book, just as scientists are skeptical of the conclusions that Loeb and his team reached in the preprint. As one scientist told Science magazine, “They knew what they were looking for and that makes it prone to confirmation bias.” When you’re looking for anything, you’re likely to see evidence for it, even if others with different biases don’t see it.

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