Abraham Loeb knows how improbable it is that he’s here. First, there had to be a Big Bang. Stars had to form, and planets. On one particular planet (and no one really knows how) single-celled organisms had to appear and evolve into complex creatures. One species of primate had to learn to speak and write and invent technology. And in 1936, Loeb’s grandfather had to have the foresight to leave Germany, making his branch of the family tree the only one to survive.
Now the Israeli-born astrophysicist, whom everyone calls Avi, is sitting on his porch in Lexington, Massachusetts, watching birds flutter around a feeder. He’s 59 years old, the Frank B. Baird Jr. Professor of Science at Harvard University, wearing a black blazer and black polo shirt. His eyes are blue behind rimless glasses, and his wide-awake face seems to emit its own light.
Loeb started out at Princeton in the late 1980s, studying the birth of the first stars. Harvard recruited him in 1993, and in 2011 he became the chair of the astronomy department, a position he held for nine years. Since 2007, he has directed Harvard’s Institute for Theory and Computation (which is part of the Center for Astrophysics, Harvard & Smithsonian). He has published more than 700 papers and essays, making major contributions to the study of black holes and to gravitational microlensing, a technique for detecting objects that are shrouded in darkness all throughout the observable universe.
But a few years ago, the trajectory of his well-established career took a dramatic turn. In October 2017, the University of Hawaii’s Pan-STARRS1 telescope caught the first-ever glimpse of an object from outside our own solar system whizzing past the Sun. They observed it for a few weeks until it disappeared from view, and named it ‘Oumuamua, a Hawaiian word that means “messenger from afar arriving first.” The sighting was especially dramatic because the object behaved in baffling ways. It accelerated suddenly without leaving any visible trail, and reflected sunlight indicated that it was flat like a pancake. It was unlike anything astronomy had ever seen.
Scientists proposed various theories in scientific journals. Maybe ‘Oumuamua was a piece of a Pluto-like planet ejected from another arm of the Milky Way galaxy. Maybe it was a dust cloud with an ultra-low density, held together by forces scientists couldn’t understand. Maybe it was a hydrogen iceberg. Loeb suggested something completely different: Maybe ‘Oumuamua was a light-powered sail manufactured by aliens.
It was an astonishing idea coming from the chair of Harvard’s astronomy department. This was a man who, just a year earlier, had launched Harvard’s prestigious Black Hole Initiative, the world’s first interdisciplinary program to focus on black holes. The legendary Stephen Hawking had flown across the Atlantic for the occasion, attending a Passover Seder at Loeb’s home during his visit. No one expected someone of Loeb’s stature to make such a suggestion, and some of his colleagues wished he hadn’t.
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