Abraham Loeb, chair of Harvard’s department of astronomy, recently gave a freewheeling interview to the Israeli newspaper Haaretz in which he defended his hypothesis that a piece of alien technology recently passed through our solar system. “If it turns out to be correct, it’s one of the greatest discoveries in human history,” he said in the interview, which was published on Monday. Loeb made largely the same argument in an interview with the New Yorker on Wednesday, in which he said, “My motivation, in part, is to motivate the scientific community to collect more data on the next object rather than argue a priori that they know the answer.”
What is Loeb talking about? Did we discover alien life and fail to notice? Not exactly—in October 2017, astronomers at the University of Hawaii detected an object moving rapidly across the night sky using a telescope mounted on top of a volcano. Upon further investigation, the astronomers discovered that they were the first people ever to observe an object known to have originated outside our solar system. The university’s researchers dubbed the object ‘Oumuamua, which translates to scout in Hawaiian, and published their findings in a paper in Nature.
A year later, Loeb and postdoctoral student Shmuel Bialy published a follow-up paper in the Astrophysical Journal Letters analyzing the movements of the object. In their conclusion, the authors suggest that ‘Oumuamua may be “debris from an advanced technological equipment” or “a fully operational probe sent intentionally to Earth vicinity by an alien civilization.”
Given its implications of intelligent extraterrestrial life, the article generated an immense amount of conversation and coverage in the press (including Slate). However, the overwhelming response from other academics and science outlets is that Loeb’s hypothesis, while possible, is extremely unlikely to be true. The ensuing debate, which reignited when Loeb let loose to Haaretz earlier this week, serves as a reminder of the challenges inherent in assessing whether something behaving oddly in the sky is a sign that we’re not alone in the universe, or, to put it more simply, the challenges inherent to debating aliens.
Critics wield Occam’s razor to argue that it is very, very improbable that Loeb’s hypothesis is accurate. Michele Bannister, an astrophysicist at Queen’s University–Belfast in Northern Ireland, was recently quoted in Popular Science arguing that there are plausible explanations for ‘Oumuamua’s movements that don’t involve aliens. “Do the data need extreme hypotheses when you have reasonable hypotheses that perfectly fit the data?” she asked. Bannister pointed to a study published in Nature last year that found data supporting the hypothesis that heat from the sun is causing ‘Oumuamua to emit a stream of gas powerful enough to cause acceleration.
Even in the face of these dissents, Loeb has maintained his faith in the alien explanation. He told the Verge in November, “I cannot think of another explanation for the peculiar acceleration of ‘Oumuamua.” In the Haaretz interview, he argued that no one has observed a trail of dust behind ‘Oumuamua, which we would expect if gas were propelling the object.
We’ve never been able to produce any hard evidence that extraterrestrials exist, which places some hard limits on determining whether an object like ‘Oumuamua is artificial. How do you even start to conceptualize the likelihood of something that has never been observed?
“When you have no information at all, it’s not a formal thing anymore,” says Don Lincoln, a senior scientist at Fermi National Accelerator Laboratory. “It’s very satisfying to know the answer, but sometimes that’s not possible. Sometimes the best you can do is to start checking off the boxes of what it isn’t.” Researchers at the Search for Extraterrestrial Intelligence Institute trained a radio telescope at ‘Oumuamua in 2018, but they were unable to detect any signals being emitted from the object that would indicate an artificial origin. Other astronomers have observed that the object lacks the smooth motion and thinness needed for a light sail and that an alien civilization would not be able to retrieve any data from ‘Oumuamua for millions of years if it were in fact a probe.
The infinitesimally small chance that any of the bizarre things we’ve observed in space are proof of intelligent alien life makes having these debates difficult to portray in proper context. Combine this dynamic with the general hunger among space enthusiasts for signs of extraterrestrial intelligence and it’s easy for a nuanced scientific debate like the one around ‘Oumuamua to get warped in the public imagination. In 2015, astronomers considered the possibility that the star KIC 8462852 may be an alien megastructure because it was exhibiting bizarre fluctuations in light. Most astronomers treated it as a remote possibility that was worth discussing and perhaps looking into further, though some press outlets treated it as an actual discovery of an alien megastructure.
There appears to be less of this sort of misconstruing in the press with ‘Oumuamua. Indeed, apart from Loeb, most scientists quoted in media outlets seem to be treating this more as a thought experiment than an actual development in the search for aliens. The general consensus is that it’s worth thinking about the type and scale of evidence it would require to confirm that ‘Oumuamua is artificial, but that such evidence has not yet been presented.
“This is how that kind of science is done: You take a crazy hypothesis and say, ‘OK, maybe it’s true. If it’s true, then it’ll be X, Y, and Z,’ ” Lincoln said. “[Loeb’s hypothesis] has been evaluated in strong qualitative and slightly quantitative ways, and the hypothesis has been found wanting.”
It’s also difficult to balance the fathomless significance of confirming extraterrestrial life with the minuscule probability that any one hint is legitimate. An apt corollary is the discussion around asteroids potentially causing destruction on earth. There has never been a documented case of an asteroid killing a person, but the thought of an apocalyptic scenario still seems to loom large whenever there’s a remote chance that a sizable one may cross paths with our planet. As Mark Boslough, a physicist at Los Alamos National Laboratory, told the Washington Post when discussing the fact that the Earth will pass through a dense patch in the Taurid meteor stream this year, “It’s one of those very low-probability but potentially high-consequence-type risks, which is hard to quantify and hard to talk about. The probability of a lot of people dying from an asteroid impact is super, super low, but it’s not zero.”
Talking about the ‘Oumuamua, then, is like talking about a large asteroid that’s coming slightly closer to Earth than others. The fact that ‘Oumuamua is an object visiting from outside our solar system, and that someone with Loeb’s stature has thrown his formidable knowledge and academic bona fides behind an alien-origin hypothesis, makes it seem like this time we might just have stumbled across some solid proof. But it’s hard to adequately convey just how ridiculously unlikely this scenario is, even if this alien claim has slightly more heft to it than others.
Lincoln, however, believes that speculative conversations about possible extraterrestrial artifacts are productive. While it’s easy to overplay the “ ‘Oumuamua is an alien probe” narrative, these musings stoke the curiosity that motivates our exploration of the cosmos. “I’m perfect happy with this sort of thing,” he says. “It feeds the fascination of humanity and space and the stars.”