Avi Loeb

Israeli American theoretical physicist

Abraham "Avi" Loeb (; born February 26, 1962) is an Israeli American theoretical physicist who works on astrophysics and cosmology. Loeb is the Frank B. Baird Jr. Professor of Science at Harvard University, where since 2007 he has been Director of the Institute for Theory and Computation at the Center for Astrophysics. He chaired the Department of Astronomy from 2011–2020, and founded the Black Hole Initiative in 2016. Loeb is a fellow of the American Academy of Arts and Sciences, the American Physical Society, and the International Academy of Astronautics. In 2015, he was appointed as the science theory director for the Breakthrough Initiatives of the Breakthrough Prize Foundation. Loeb has published popular science books including Extraterrestrial: The First Sign of Intelligent Life Beyond Earth (2021) and Interstellar: The Search for Extraterrestrial Life and Our Future in the Stars (2023). In 2018, he suggested that alien space craft may be in the Solar System, using ʻOumuamua as an example. In 2023, he claimed to have recovered material from an interstellar meteor that could be evidence of an alien starship, which some experts criticized as hasty and sensational, and for which other experts found more Earth related explanations instead, demonstrating that the seismic signal attributed by Loeb to the alleged interstellar space craft was actually caused by ordinary truck traffic.

Loeb was born in Beit Hanan, Israel, in 1962. He took part in the national Talpiot program of the Israeli Defense Forces at age 18. While in Talpiot, he obtained a BSc degree in physics and mathematics in 1983, an MSc degree in physics in 1985, and a PhD in physics in 1986, all from the Hebrew University of Jerusalem (HUJI). and The First Galaxies in the Universe. He has co authored many papers on topics in astrophysics and cosmology, the future collision between the Milky Way and Andromeda galaxies, the future state of extragalactic astronomy, astrophysical implications of black hole recoil in galaxy mergers, tidal disruption of stars, and imaging black hole silhouettes. the first Jupiter size exoplanet identified by detecting the relativistic beaming of its parent star, based on a technique Loeb and Gaudi proposed in 2003. In addition, a pulsar was discovered around the supermassive black hole Sagittarius A*, following a prediction by Pfahl and Loeb in 2004. Also, a hypervelocity star candidate from the Andromeda galaxy was discovered, as predicted by Sherwin, Loeb, and O'Leary in 2008. Together with his postdoc James Guillochon, Loeb predicted the existence of a new population of stars moving near the speed of light throughout the universe. Together with his postdoc John Forbes and Howard Chen of Northwestern University, Loeb made another prediction that sub Neptune sized exoplanets have been transformed into rocky super Earths by the activity of Sagittarius A*. Together with Paolo Pani, Loeb showed in 2013 that primordial black holes in the range between the masses of the Moon and the Sun cannot make up dark matter. Loeb led a team that reported tentative evidence for the birth of a black hole in the young nearby supernova SN 1979C. In collaboration with Dan Maoz, Loeb demonstrated in 2013 that biomarkers, such as molecular oxygen , can be detected by the James Webb Space Telescope (JWST) in the atmosphere of Earth mass planets in the habitable zone of white dwarfs. In 2018, he served a term as chair of the Board on Physics and Astronomy (BPA) of the National Academies.

In a series of papers with his students and postdocs, Loeb addressed how and when the first stars and black holes formed and what effects they had on the young universe. In 2013, Loeb wrote about the "Habitable Epoch of the Early Universe". In April 2021, he presented an updated summary of his ideas of life in the early universe. In 2020, Loeb published a paper about the possibility that life can propagate from one planet to another, followed by the opinion piece "Noah's Spaceship" about directed panspermia. In 2024, Loeb delivered a speech in which he declared his view that the Messiah will be an alien who arrives from outer space.

In December 2017, Loeb cited ʻOumuamua's unusually elongated shape as one of the reasons the Green Bank Telescope in West Virginia should listen for radio emissions from it to see if there were any unexpected signs that it might be of artificial origin, although earlier limited observations by other radio telescopes such as the SETI Institute's Allen Telescope Array had produced no such results. The Green Bank Telescope observed the asteroid for six hours, detecting no radio signals. On October 26, 2018, Loeb and his postdoctoral student Shmuel Bialy submitted a paper exploring the possibility that ʻOumuamua is an artificial thin solar sail accelerated by solar radiation pressure in an effort to help explain the object's non gravitational acceleration. The consensus among other astrophysicists was that the available evidence is insufficient to consider such a premise, and that a tumbling solar sail would not be able to accelerate. In response, Loeb wrote an article detailing six anomalous properties of ʻOumuamua that make it unusual, unlike any comets or asteroids seen before. On November 27, 2018, Loeb and Amir Siraj, a Harvard undergraduate, proposed a search for ʻOumuamua like objects that might be trapped in the Solar System as a result of losing orbital energy through a close encounter with Jupiter. They identified four candidates (2011 SP25, 2017 RR2, 2017 SV13, and 2018 TL6) for trapped interstellar objects that dedicated missions could visit. The authors pointed out that future sky surveys, such as with Large Synoptic Survey Telescope, could find many more. In public interviews and private communications with reporters and academic colleagues, Loeb has become more vocal about the prospects of proving the existence of alien life. On April 16, 2019, Loeb and Siraj reported the discovery of a meteor of interstellar origin. Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, a popular science account of ʻOumuamua by Loeb, was published in 2021. A followup book, Interstellar: The Search for Extraterrestrial Life and Our Future in the Stars, was published on August 29, 2023.

In 2006, Loeb was featured in a Time magazine cover story on the first stars, and in a Scientific American article on the Dark Ages of the universe. In 2008, he was featured in a Smithsonian magazine cover story on black holes, and in two Astronomy magazine cover stories, one on the collision between the Milky Way and the Andromeda Galaxy and the second on the future state of our universe. In 2009, Loeb reviewed in a Scientific American article a new technique for imaging black hole silhouettes. Loeb received considerable media attention after proposing in 2011 (with E. L. Turner) a new technique for detecting artificially illuminated objects in the Solar System and beyond, and showing in 2012 (with I. Ginsburg) that planets may transit hypervelocity stars or get kicked to a fraction of the speed of light near the black hole at the center of the Milky Way. He has been profiled a number of times, including in Science magazine, Discover, and The New York Times. He has been interviewed by Astronomy magazine, by Lex Fridman, Joe Rogan, and Mick West, and by the H3 Podcast. On August 24, 2023, The New York Times published an article about Loeb and his search for signs of extraterrestrial life.