Avi Loeb
Based on Wikipedia: Avi Loeb
The Harvard Astronomer Who Keeps Finding Aliens
Avi Loeb wants you to know that aliens might be here. Not in some distant galaxy, not in the realm of science fiction, but right here in our solar system. Maybe that strange object that tumbled past the sun in 2017. Maybe those metallic spheres he pulled from the bottom of the Pacific Ocean. Maybe that comet hurtling toward us right now from the constellation Sagittarius.
Most of his colleagues think he's wrong. Some think he's worse than wrong—that he's actively damaging science itself.
But Loeb keeps looking anyway.
From Israeli Prodigy to Harvard Professor
Abraham Loeb was born in 1962 in Beit Hanan, a small village in central Israel. At eighteen, he entered Talpiot, an elite Israeli Defense Forces program that identifies the country's most gifted young scientists and gives them intensive training in exchange for military service. The program has produced an outsized number of Israel's tech entrepreneurs and scientific leaders.
Loeb moved through academia at a pace that makes most careers look glacial. By age twenty-one, he had his bachelor's degree in physics and mathematics. Two years later, his master's. One year after that, his doctorate in plasma physics—all from Hebrew University of Jerusalem. His doctoral research took place at the Soreq Nuclear Research Center, where he modeled how plasma could accelerate charged particles to extreme velocities.
This wasn't purely theoretical work. From 1983 to 1988, Loeb led an international project funded by the Strategic Defense Initiative—Ronald Reagan's ambitious "Star Wars" missile defense program—investigating new ways to propel projectiles at high speeds. The Cold War was still on, and the United States was willing to fund creative ideas about shooting things very fast through space.
In 1988, Loeb made the leap that would define his career. He joined the Institute for Advanced Study in Princeton, the same institution where Einstein spent his final decades. There, under the mentorship of the legendary astrophysicist John Bahcall, Loeb transformed himself from a plasma physicist into a theoretical astrophysicist. It was like a jazz musician deciding to become a classical composer—same underlying skills, entirely different application.
Harvard came calling in 1993. Within three years, he had tenure. By 2011, he was chairing the astronomy department, a position he held for nearly a decade. In 2016, he founded the Black Hole Initiative, one of the world's first interdisciplinary centers dedicated to studying these cosmic objects where space and time collapse in on themselves.
A Serious Career in Cosmic Questions
Before the alien hunting began, Loeb built a formidable reputation studying questions that most people never think to ask but that keep astrophysicists up at night.
What were the first stars like? These weren't the stars we see today. The universe's original stars formed from nothing but hydrogen and helium, the only elements that existed after the Big Bang. Without heavier elements to help gas clouds cool and collapse efficiently, these primordial stars were monsters—perhaps hundreds of times more massive than our sun, burning so hot and so fast that they lived only a few million years before exploding. Loeb wrote textbooks on this subject that graduate students still study today.
What about the cosmic dark ages? After the Big Bang's initial flash faded, the universe went dark. For hundreds of millions of years, no stars shone. Then, gradually, the first galaxies flickered to life. Loeb has spent decades modeling this transition, trying to understand how we got from a universe of uniform hydrogen gas to one filled with the intricate structures we see today.
He's made predictions that other scientists could test. Working with a postdoctoral researcher named James Guillochon, Loeb predicted that somewhere out there, stars are hurtling through the universe at nearly the speed of light—ejected from galactic centers by encounters with supermassive black holes. With collaborators John Forbes and Howard Chen, he proposed that the intense radiation from Sagittarius A*, the black hole at the center of our galaxy, might have stripped the atmospheres from planets that ventured too close, transforming puffy Neptune-like worlds into rocky super-Earths.
In 2013, Loeb and physicist Paolo Pani ruled out one possible explanation for dark matter—that mysterious substance that makes up most of the universe's mass but refuses to interact with light. They showed mathematically that dark matter couldn't be made of primordial black holes in a certain mass range. (Though in 2025, Loeb proposed a new theory: perhaps dark matter consists of remnants from something called Planck Stars, exotic objects that might form when tiny black holes evaporate.)
He's also worked on more practical matters, at least as practical as astrophysics gets. With Dan Maoz, he showed that the James Webb Space Telescope could potentially detect signs of life—specifically molecular oxygen—in the atmospheres of Earth-sized planets orbiting white dwarfs. White dwarfs are the dense, cooling remnants of stars like our sun, and planets in their habitable zones would be close enough that our telescopes might actually be able to analyze their air.
Life in the Early Universe
Here's a thought experiment Loeb proposed in 2013 that most people find delightfully strange.
We take for granted that liquid water requires a planet orbiting a star at just the right distance—not too hot, not too cold. But about fifteen million years after the Big Bang, the entire universe was at room temperature. The cosmic microwave background radiation—that faint glow left over from the Big Bang that now registers at a frigid negative 454 degrees Fahrenheit—was once warm enough to heat any planet to habitable temperatures, no star required.
Could life have emerged then, in that brief cosmic window when the whole universe was a comfortable temperature? Probably not—there weren't any planets yet, and the chemistry for life hadn't had time to develop. But it's the kind of question that reveals how Loeb thinks: What assumptions are we making? What possibilities are we ignoring?
Then Came 'Oumuamua
On October 19, 2017, astronomers in Hawaii detected something unprecedented. An object was tumbling through our solar system on a trajectory that could only mean one thing: it had come from interstellar space. This wasn't an asteroid or comet from our own cosmic neighborhood. This was a visitor from another star system entirely.
They named it 'Oumuamua, Hawaiian for "scout" or "messenger from afar."
The object was weird. Really weird.
First, its shape. Based on how its brightness varied as it tumbled, astronomers calculated that 'Oumuamua was extremely elongated—perhaps ten times longer than it was wide, shaped like a cigar or maybe a pancake. No asteroid or comet we'd ever seen looked anything like this.
Second, its acceleration. As 'Oumuamua swung past the sun and headed back out into interstellar space, it was speeding up slightly more than gravity and solar radiation could explain. Something was pushing it. Comets do this—gas jets from evaporating ice can act like tiny rockets—but 'Oumuamua showed no sign of the fuzzy coma or tail that comets produce.
Most astronomers proposed natural explanations. Maybe 'Oumuamua was made of nitrogen ice, which wouldn't produce visible outgassing. Maybe it was a fragment of a larger comet that had been stripped of most of its volatile materials. Strange, certainly, but nature produces strange things.
Loeb had another idea.
In October 2018, he and his postdoctoral student Shmuel Bialy submitted a paper exploring the possibility that 'Oumuamua was an artificial object—specifically, a light sail. Light sails are real technology that we humans have tested: thin, reflective sheets that catch photons from the sun like a sail catches wind, gradually accelerating without fuel. If an advanced civilization wanted to send a probe to another star system, a light sail would be an elegant solution.
The paper was careful to present this as a hypothesis to be considered, not a conclusion. But the reaction from the scientific community was immediate and largely negative. The evidence, colleagues argued, simply wasn't there. And a tumbling light sail wouldn't accelerate properly anyway—it would need to maintain a stable orientation toward the sun.
By 2021, a scientific consensus had emerged: 'Oumuamua's properties, while unusual, were consistent with a naturally occurring object. Case closed.
But not for Loeb.
Doubling Down
Rather than retreating, Loeb became more vocal. He published Extraterrestrial: The First Sign of Intelligent Life Beyond Earth in 2021, a popular science book arguing that 'Oumuamua deserved serious consideration as potential alien technology. A sequel, Interstellar: The Search for Extraterrestrial Life and Our Future in the Stars, followed in 2023.
He also expanded his scope. In 2021, he founded the Galileo Project, an initiative to systematically search for evidence of extraterrestrial technological artifacts. The project's name invokes the seventeenth-century astronomer who was persecuted for his views but ultimately vindicated—a comparison that critics find presumptuous.
The Galileo Project differs from traditional SETI (the Search for Extraterrestrial Intelligence) in a crucial way. SETI listens for radio signals from distant civilizations. Loeb wants to look for physical objects: alien spacecraft, probes, or debris that might be floating through our solar system or even entering Earth's atmosphere.
The project was inspired partly by 'Oumuamua and partly by a June 2021 report from the Office of the Director of National Intelligence on Unidentified Aerial Phenomena—the government's new term for UFOs. That report, requested by Congress, acknowledged that some aerial observations by military pilots remained unexplained. Loeb saw an opening.
"Given the recently discovered abundance of Earth-Sun systems, the Galileo Project is dedicated to the proposition that humans can no longer ignore the possible existence of Extraterrestrial Technological Civilizations."
The Meteor From Beyond
In 2014, sensors operated by the United States Department of Defense detected a small meteor entering Earth's atmosphere over the Pacific Ocean near Papua New Guinea. This wasn't unusual—small meteors burn up in our atmosphere constantly. But years later, Loeb and Harvard undergraduate Amir Siraj analyzed the available data and made a striking claim: this meteor, designated CNEOS 2014-01-08, was traveling so fast that it must have come from outside our solar system.
If true, this would make it the first known interstellar meteor—a piece of another star system that had actually reached Earth.
In March 2022, the United States Space Force confirmed that their data supported an interstellar origin. But NASA was more cautious, stating that the evidence remained inconclusive. The defense sensors weren't designed for precise scientific measurement, and their margin of error was significant.
None of this stopped Loeb from taking the next step.
In 2023, he led an expedition to the Pacific Ocean, using a magnetic sled to dredge the seafloor where he believed the meteor had landed. His team recovered tiny metallic spheres—spherules that he claimed showed an unusual chemical composition potentially consistent with an origin outside our solar system. Perhaps, he speculated, these were fragments of an alien starship.
The scientific community's response was scathing.
Peter Brown, a meteor physicist at the University of Western Ontario, argued that the materials could easily have come from terrestrial sources. Monica Grady of the Open University called the evidence "rather shaky" and suggested the spherules might be industrial pollution. A paper in an American Astronomical Society journal concluded they were consistent with coal ash contamination.
But the most damaging criticism came from planetary seismologist Benjamin Fernando. In 2024, Fernando and his team analyzed the seismic signals that Loeb had used to pinpoint his search location on the ocean floor. Their conclusion was devastating: the signal hadn't come from a meteor impact at all. It had come from a truck driving on a road near the seismic sensor.
"Not only did they use the wrong signal," Fernando said, "they were looking in the wrong place."
A Third Visitor
In early 2025, astronomers using ATLAS—the Asteroid Terrestrial-impact Last Alert System, a NASA-funded telescope in Chile—spotted a new object approaching from the direction of the constellation Sagittarius. Its velocity confirmed what everyone suspected: this was another interstellar visitor, only the third ever detected. They named it 3I/ATLAS.
Loeb immediately began speculating publicly that it might be alien technology.
He noted that the object's orbital path around the sun lay within five degrees of Earth's orbital plane. The probability of that happening by chance, he calculated, was about 0.2 percent. Its trajectory would bring it close to Venus, Mars, and Jupiter—a path he estimated had only a 0.005 percent probability of occurring randomly. Its brightness suggested a diameter of about twenty kilometers, which he considered "too large for an interstellar asteroid."
"It might have targeted the inner Solar System as expected from alien technology," Loeb told Newsweek.
The scientific community pushed back hard. Richard Moissl, Head of Planetary Defence at the European Space Agency, stated flatly: "There have been no signs pointing to non-natural origins of 3I/ATLAS in the available observations." Subsequent observations found evidence that 3I/ATLAS contains water—a substance common in comets and consistent with a natural origin.
Nicola Fox, associate administrator of NASA's Science Mission Directorate, was direct: "We certainly haven't seen any technosignatures or anything from it that would lead us to believe it was anything other than a comet."
NASA Associate Administrator Amit Kshatriya put it even more bluntly: "All evidence points to it being a comet."
Loeb eventually conceded that 3I/ATLAS is "most likely" a comet. But he continued to publicly speculate about its potential technological nature anyway.
A Pattern of Controversy
What frustrates Loeb's critics isn't his willingness to consider unconventional hypotheses. Science has always progressed by questioning assumptions. The problem, they argue, is how he goes about it.
Steve Desch, an astrophysicist at Arizona State University, has been among the most vocal critics. He describes Loeb's claims as "ridiculous sensationalism" and argues they represent "a real breakdown of the peer review process and the scientific method." The issue isn't the ideas themselves but Loeb's tendency to announce findings to the press before subjecting them to proper peer review—the process by which other experts examine and critique scientific claims before publication.
Some characterizations have been harsher. USA Today described Loeb's speculation about 3I/ATLAS as an "outlandish conspiracy theory." Other scientists have compared his theories to claiming "the moon is made of cheese."
Several of Desch's colleagues, he says, now refuse to engage with Loeb in the peer review process at all. They see him as polluting good science, "conflating the good science we do with this ridiculous sensationalism and sucking all the oxygen out of the room."
In 2024, Loeb delivered a speech declaring his belief that the Messiah will be an alien who arrives from outer space. Whether this was sincere theological speculation or a provocative thought experiment, it didn't help his standing among scientists who already questioned his judgment.
The Defense
Loeb has defenders, and his argument isn't entirely without merit.
He points out that the scientific establishment has historically been slow to accept paradigm-shifting ideas. Galileo really was persecuted for heliocentrism. Continental drift really was ridiculed for decades before being accepted. The history of science is littered with discoveries that were initially dismissed as impossible or absurd.
He also argues that SETI—the search for extraterrestrial intelligence through radio signals—has been ongoing for decades with no results, yet remains scientifically respectable. Why should looking for physical artifacts be any different? If advanced civilizations exist, they might well have sent probes to explore the galaxy, just as we've sent Voyager spacecraft beyond our solar system.
The Galileo Project, Loeb insists, uses rigorous scientific methods. The goal isn't to study UFOs based on blurry videos and eyewitness accounts. It's to deploy proper scientific instruments, collect data transparently, and analyze it according to standard practices. If nothing anomalous is found, that's a scientific result too.
And he has an impressive track record of legitimate scientific contributions. This isn't a fringe figure—this is a Harvard professor, former department chair, fellow of the American Academy of Arts and Sciences, and science theory director for the Breakthrough Prize Foundation's initiatives. His textbooks are respected. His papers on black holes and the early universe are widely cited.
What's Really at Stake
The Loeb controversy illuminates a genuine tension in how science operates.
On one hand, science requires openness to new ideas. The hypothesis that some interstellar objects might be artificial isn't inherently unscientific. It's a testable claim. We could, in principle, observe an object closely enough to determine whether it's a rock or a machine.
On the other hand, science also requires standards. Extraordinary claims really do require extraordinary evidence. Publishing to the press before peer review undermines the self-correcting mechanisms that make science reliable. And a prominent scientist repeatedly making claims that don't hold up to scrutiny can damage public trust in science itself.
There's also the question of opportunity cost. Loeb has enormous scientific credibility and resources. Every hour he spends on speculative alien hunting is an hour not spent on the kind of rigorous astrophysics where he has a proven track record of contribution.
But perhaps the deepest issue is about the culture of science. Loeb clearly believes the scientific establishment is too conservative, too quick to dismiss ideas that challenge the consensus. His critics believe he's too reckless, too eager to grab headlines, too willing to substitute intuition for evidence.
Who's right? The honest answer is that we don't know yet. If Loeb ever produces genuinely convincing evidence of alien technology, he'll be vindicated as a visionary who saw what others refused to see. If he never does—if every claimed discovery turns out to be coal ash or truck vibrations or comets—he'll be remembered as a cautionary tale about what happens when ambition outpaces evidence.
Looking Up
Loeb is still looking. The Galileo Project continues to operate. Every new interstellar object that appears in our sky will be scrutinized, analyzed, and probably followed by Loeb making statements that his colleagues find premature.
There's something almost admirable about this persistence, even if you think he's completely wrong. The universe is under no obligation to fit our expectations. The history of astronomy is the history of realizing how wrong our assumptions have been—that the Earth isn't the center of the universe, that our sun is just one of billions of stars, that our galaxy is just one of trillions. Each step has made us smaller and the cosmos stranger.
Is it really so absurd to wonder whether some of those strange things might be the products of other minds?
Loeb doesn't think so. Neither do many people who follow his work with fascination, even as the scientific establishment rolls its collective eyes.
Somewhere out there, 3I/ATLAS is hurtling through the inner solar system, following the path gravity dictates—or, if you're Avi Loeb, possibly following a path chosen by its makers. It will swing past Jupiter and head back out into the void, carrying with it either nothing more interesting than primordial ice or answers to the biggest question humans have ever asked.
We'll probably never know which. But Loeb will keep asking.