Avi Loeb
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אברהם לייב | |
Loeb in April 2020
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Born |
Abraham Loeb
February 26, 1962
Beit Hanan, Israel
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Nationality | Israeli American |
Alma mater | Hebrew University (PhD) |
Scientific career | |
Fields | Cosmology, astrophysics |
Institutions | Institute for Advanced Study at Princeton Harvard University |
Doctoral advisor | Shalom Eliezer Lazar Friedland |
Other academic advisors | John N. Bahcall |
Doctoral students | Daniel Eisenstein |
Abraham "Avi" Loeb (Hebrew: אברהם (אבי) לייב; 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. He had been the longest serving chair of Harvard's Department of Astronomy (2011–2020), founding director of Harvard's Black Hole Initiative (since 2016) and director of the Institute for Theory and Computation (since 2007) within the Harvard-Smithsonian Center for Astrophysics.[1][2][3][4][5][6]
Loeb is a fellow of the American Academy of Arts and Sciences, the American Physical Society, and the International Academy of Astronautics. In July 2018, he was appointed as chair of the Board on Physics and Astronomy (BPA)[7] of the National Academies, which is the Academies' forum for issues connected with the fields of physics and astronomy, including oversight of their decadal surveys.
In June 2020, Loeb was sworn in as a member of the President's Council of Advisors on Science and Technology (PCAST) at the White House.[8][9] In December 2012, Time magazine selected Loeb as one of the 25 most influential people in space.[10] In 2015, Loeb was appointed as the science theory director for the Breakthrough Initiatives of the Breakthrough Prize Foundation.
In 2018, he suggested that alien space craft may be in the Solar System, using the anomalous behavior of ʻOumuamua as an example.[11] In 2023, he claimed to have recovered material from an interstellar meteor that could be evidence of an alien starship,[12] claims which were criticized by some experts as hasty and sensational.[13]
Loeb was born in Beit Hanan,[14] Israel in 1962. He took part in the national Talpiot program before receiving a PhD in plasma physics, at age 24, from the Hebrew University in Jerusalem, in 1986. From 1983 to 1988, he led the first international project supported by the U.S. Strategic Defense Initiative. Between 1988 and 1993, Loeb was a long-term member at the Institute for Advanced Study at Princeton, where he started to work in theoretical astrophysics. In 1993, he moved to Harvard University as an assistant professor in the department of astronomy, and was tenured three years later.[4][6][2]
Loeb has written eight books and authored or co-authored about 800 papers on a broad range of research areas in astrophysics and cosmology,[2][5] including the first stars, the epoch of reionization, the formation and evolution of massive black holes, the search for extraterrestrial life, gravitational lensing by planets, gamma-ray bursts at high redshifts, 21-cm cosmology, the use of the Lyman-alpha forest to measure the acceleration/deceleration of the universe in real time (the so-called "Sandage–Loeb test"[15]), the future collision between the Milky Way and Andromeda galaxies,[16] the future state of extragalactic astronomy,[17] astrophysical implications of black hole recoil in galaxy mergers,[18] tidal disruption of stars,[19] and imaging black hole silhouettes.[20][3] In 2010, he wrote a textbook entitled How Did the First Stars and Galaxies Form?[21][22]
In 1992, Loeb and Andy Gould suggested that exoplanets could be detected through gravitational microlensing. In 1993, he proposed the use of the C+ fine-structure line to discover galaxies at high redshifts. In 2005, he predicted, in a series of papers with his postdoc at the time, Avery Broderick, how a hot spot in orbit around a black hole would appear; their predictions were confirmed in 2018 by the GRAVITY instrument on the Very Large Telescope which observed a circular motion of the centroid of light of the black hole at the center of the Milky Way, Sagittarius A*. In 2009, Broderick and Loeb predicted the shadow of the black hole in the giant elliptical galaxy Messier 87, which was imaged in 2019 by the Event Horizon Telescope.
In 2013, a report was published on the discovery of the "Einstein Planet" Kepler-76b,[23] the first Jupiter size exoplanet identified through the detection of relativistic beaming of its parent star, based on a technique proposed by Loeb and Gaudi in 2003.[24] In addition, a pulsar was discovered around the supermassive black hole, Sagittarius A*,[25] following a prediction by Pfahl and Loeb in 2004.[26] Also, a hypervelocity star candidate from the Andromeda galaxy was discovered,[27] as predicted by Sherwin, Loeb, and O'Leary in 2008.[28] 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.[29] 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 Milky Way's central supermassive black hole Sagittarius A*.[30]
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 the dark matter.[31] Loeb led a team that reported tentative evidence for the birth of a black hole in the young nearby supernova SN 1979C.[32] In collaboration with Dan Maoz, Loeb demonstrated in 2013 that biomarkers, such as molecular oxygen (O
2), can be detected by the James Webb Space Telescope (JWST) in the atmosphere of Earth-mass planets in the habitable zone of white dwarfs.[33]
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. Together with his former student Steve Furlanetto, Loeb published a textbook, The First Galaxies in the Universe.[34] In 2013, Loeb introduced the new concept of "The Habitable Epoch of the Early Universe",[35][36] and mentored Harvard undergraduate, Henry Lin, in the study of industrial pollution on exoplanets as a new method to search for extraterrestrial civilizations.[37] In April 2021, Loeb presented an updated summary of his ideas of life in the early universe.[38]
In 2020, Loeb published a research paper about the possibility that life can propagate from one planet to another,[39] followed by the opinion piece "Noah's Spaceship" about directed panspermia.[40]
In December 2017, Loeb cited ʻOumuamua's unusually elongated shape as one of the reasons why 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,[41] although earlier limited observations by other radio telescopes such as the SETI Institute's Allen Telescope Array had produced no such results.[42] On December 13, 2017, the Green Bank Telescope observed the asteroid for six hours. No radio signals from ʻOumuamua have been detected.[43][44]
On October 26, 2018, Loeb and his postdoctoral student Shmuel Bialy submitted a paper exploring the possibility of the interstellar object ʻOumuamua being an artificial thin solar sail accelerated by solar radiation pressure in an effort to help explain the object's non-gravitational acceleration.[45][46][47] Other scientists have stated that the available evidence is insufficient to consider such a premise,[48][49][50] and that a tumbling solar sail would not be able to accelerate.[51][52] In response, Loeb wrote an article detailing six anomalous properties of ʻOumuamua that make it unusual, unlike any comets or asteroids seen before.[53][54]
On November 27, 2018, Loeb and Amir Siraj, an undergraduate student at Harvard College, proposed a search for ʻOumuamua-like objects which might be trapped in the Solar System as a result of losing orbital energy through a close encounter with Jupiter.[55] They identified four candidates (2011 SP25, 2017 RR2, 2017 SV13, and 2018 TL6) for trapped interstellar objects which could be visited by dedicated missions. The authors pointed out that future sky surveys, such as with Large Synoptic Survey Telescope, could find many more.[56]
In public interviews and private communications with reporters and academic colleagues, Loeb has become more vocal regarding the prospects of proving the existence of alien life.[57] On April 16, 2019, Loeb and Siraj reported the discovery of the first meteor of interstellar origin.[58] Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, a popular science account concerning ʻOumuamua, written by Loeb,[59] was published in 2021.[60][61][62]
In July 2021, Loeb founded The Galileo Project for the Systematic Scientific Search for Evidence of Extraterrestrial Technological Artifacts.[64][65] The project was inspired by the detection of ʻOumuamua and by release of the Office of the Director of National Intelligence report on Unidentified Aerial Phenomena (UAP). As stated on the project's web-site, the aim is:
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 (ETCs), and that science should not dogmatically reject potential extraterrestrial explanations because of social stigma or cultural preferences, factors which are not conducive to the scientific method of unbiased, empirical inquiry. We now must 'dare to look through new telescopes', both literally and figuratively.[64]
The three main avenues of research are:[66]
A picture is worth a thousand words. For example, a megapixel image of the surface of a human-scale UAP object at a distance of a mile will allow to distinguish the label: "Made in Country X" from the potential alternative "Made by ETC Y" on a nearby exoplanet in our galaxy. This goal will be accomplished by searching for UAP with a network of mid-sized, high-resolution telescopes and detector arrays with suitable cameras and computer systems, distributed in select locations. The data will be open to the public and the scientific analysis will be transparent.
Unlike other similar projects, the goal of the Galileo Project is to search for physical objects, and not electromagnetic signals, associated with extraterrestrial technological equipment.[67] The project was covered by many independent publishers, among them Nature, Science, New York Post, Scientific American, The Guardian, etc.[68] To the allegations that studies of UFOs is pseudo-science, Loeb answers that the aim of the project is not to study UFOs based on previous data, but to study Unidentified Aerial Phenomena "using the standard scientific method based on a transparent analysis of open scientific data to be collected using optimized instruments".[69]
In June 2023, Loeb announced the project had found interstellar material on the ocean floor[70] which could be remnants of an extraterrestrial starship.[71] The findings were the result of Loeb and the Galileo Project seeking the remnants of a fireball observed by the US Department of Defense in 2014.[71] These claims were criticized by other scientists as hasty, sensational, and part of a pattern of improper behavior. Peter Brown, a meteor physicist at the University of Western Ontario argued the material can be explained as non-interstellar, noting that measurements from Defense Department data are opaque and error-prone. Brown further said he was disturbed by Loeb's lack of engagement with relevant experts.[13] Loeb countered Brown's argument by saying the Defense Department data is reliable enough to justify the finding.[70] Astrophysicist Steve Desch, at Arizona State University, commented "[his claims are] polluting good science — conflating the good science we do with this ridiculous sensationalism and sucking all the oxygen out of the room" and said several of his colleagues are consequently refusing to engage with Loeb in the peer review process.[13] Monica Grady from the Open University argued that the evidence behind Loeb's claims was "rather shaky," and pointed more plausibly to terrestrial pollution.[71]
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[72] after proposing in 2011 (with E.L. Turner) a new technique for detecting artificially-illuminated objects in the Solar System and beyond,[73] 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.[74]
Science magazine published an article about Loeb's career in April 2013,[75] and Discover reviewed his research on the first stars in April 2014.[76] The New York Times published a science profile of Loeb in December 2014.[77] In May 2015, Astronomy posted a podcast of an hour-long interview with Loeb in its series entitled "Superstars of Astronomy".[78] In April 2016, Stephen Hawking visited Loeb's home and attended the inaugurations of the Starshot and Black Hole Initiatives that Loeb leads.[79]
Loeb's eBook on Kindle details his career path from childhood on a farm with interests in philosophy to chairing the Harvard astronomy department and directing the ITC, and includes opinion essays on the importance of taking risks in research and promoting diversity. Loeb writes opinion essays on science and policy.[80][81] On January 14, 2021, Loeb appeared on the Lex Fridman Podcast (#154),[82] on January 16, 2021, on the Joe Rogan Experience podcast (#1596),[83] on August 11, 2021, on the Mick West TFTRH (#55),[84] on November 4, 2022, on the H3 Podcast (#258).[85]
Loeb has received many honors, including:[5]
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ignored (help)Green Bank telescope in West Virginia will listen for radio signals from ʻOumuamua, an object from another solar system ... "Most likely it is of natural origin, but because it is so peculiar, we would like to check if it has any sign of artificial origin, such as radio emissions," said Avi Loeb, professor of astronomy at Harvard University and an adviser to the Breakthrough Listen project. "If we do detect a signal that appears artificial in origin, we'll know immediately." ... While many astronomers believe the object is an interstellar asteroid, its elongated shape is unlike anything seen in the asteroid belt in our own solar system. Early observations of ʻOumuamua show that it is about 400m long but only one tenth as wide. "It's curious that the first object we see from outside the solar system looks like that," said Loeb.
So far limited observations of 'Oumuamua, using facilities such as the SETI Institute's Allen Telescope Array, have turned up nothing.
No evidence of artificial signals emanating from the object so far detected by the Green Bank Telescope, but monitoring and analysis continue. Initial data are available for public inspection in the Breakthrough Listen archive
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