Balloons or Extraterrestrial Devices?

Avi Loeb
6 min readFeb 15


Archimedes’ principle states that a body immersed in a fluid is subjected to an upwards force equal to the weight of the displaced fluid. For this reason, a balloon filled with gas of a low atomic-mass, such as hydrogen or helium, can rise up to an altitude where the ambient mass density of air equals its mean mass density. An application of this principle shows that a 3-meter balloon, the size of a small car, can rise up to an altitude of 12 kilometers, whereas a 12-meter balloon can rise up to 40 kilometers.

The US government shot down balloons of these sizes within these limiting altitudes. Physics works, even if it was derived by Archimedes about 2,270 years ago. As the physicist, Richard Feynman, noted: “Physics is like sex: sure, it may give some practical results, but that’s not why we do it.”

The first balloon was 60 meters tall, making it visible to the naked eye as it flew over the US. It was first spotted on January 28, 2023 in Alaska, then Montana and shot down off the east coast on February 4. It included multiple antennae, solar panels and surveillance equipment, substantiating the Pentagon’s classification of it as a Chinese spy balloon.

The second balloon was the size of a small car and had been flying at an altitude of 12 kilometers as it travelled in the direction of the North Pole. It was shot down over Alaska on Friday, February 10, because it posed a threat to commercial airplanes which go up to that altitude. The third object was first spotted over Canada’s Yukon territory on the same day and shot down the following day. The fourth object was first spotted on that day just north of the US border in Canada. The following day it was picked up again in Montana, tracked across Wisconsin and shot down above Lake Huron in Michigan. This one was a “small, metallic balloon with a tethered payload below it”, according to a Pentagon memo to US lawmakers. These four objects did not exhibit unusual flight characteristics and did not maneuver by a propulsion system. Therefore, they were most likely human-made.

At a press briefing on Monday, the White House press secretary, Karine Jean-Pierre, said: “I know there have been questions and concerns about this, but there is no — again, no — indication of aliens or extraterrestrial activity with these recent takedowns.”

In the 2022 report on Unidentified Aerial Phenomena (UAP), submitted by the Office of the Director of National Intelligence to the US Congress, there were 366 new sightings in 2022. Of these, 163 were balloons and 26 were drones. Clearly, UAP are a mixed bag.

After the first balloon was spotted, the radar operated by the North American Aerospace Defense Command (NORAD) was enhanced to pick up on smaller objects. The increased attention to UAP is a blessing because it removes the stigma from past discussions and fosters the acquisition of better data on all objects in the sky.

The government’s task is complementary to the scientific mission of the Galileo Project, which started to collect high-quality data on the entire sky from a single location, with the goal of identifying the nature of UAP using well-calibrated sensors and artificial intelligence algorithms. Human-made objects that are of greatest interest to the government, are of no interest to the Galileo Project. But even if only a single UAP originated from an extraterrestrial technological civilization based on its unusual image or motion, its discovery would forever change the future of humanity and its aspirations for space.

I do not believe in conspiracy theories. The US government does not share some information because it does not want adversaries to be aware of the quality of its sensors. But the sky is not classified and scientists could study it openly in geographical locations that are of no strategic importance. The Galileo Project plans to make copies of its first operational observatory in the coming months and place them in different locations. The number of copies will depend on the funding level available.

Governments are not scientific organizations. They focus on national security concerns and aim to protect the safety of their citizens. It is the civil duty of scientists to help governments in identifying the unidentified, and share results that do not overlap with the government’s focus, openly with the general public.

Scientific knowledge about our interstellar neighborhood does not adhere to national borders and should be shared with all humans because its implications are global. Most borders between nations are not visible from space; in reciprocity — they should not restrict the flow of information on what lies in interstellar space.

Since the diameter of the Milky-Way disk is nearly fifty thousand light years and humans were not distinguishable from nature tens of thousands of years ago, it is unlikely that any extraterrestrial probe sent to Earth had humans in mind — even if it traveled near the speed of light. The encounter is unlikely to represent a threat for us but rather an exciting opportunity to learn something new. The senders are probably far more technologically advanced than we are, given that our modern science and technology was only developed over the past century — which is a hundred-million times shorter than the age of most stars.

Our census of exoplanets suggests that most of the tens of billions of Sun-like stars in the Milky-Way galaxy formed billions of years before the Sun, and a substantial fraction of them have an Earth-sized planet at the Earth-Sun separation. It takes less than a billion years even for chemical rockets like ours, to traverse the Milky Way galaxy. The question of whether we are being visited by extraterrestrial devices must be answered by looking up and collecting data. It is not a philosophical question that will be settled on social media.

Altogether, the possibility of extraterrestrial gadgets near Earth is as ordinary as the possibility that dark matter is made of the lightest supersymmetric particle. The alternative perspective about humanity being unique and alone should be regarded as arrogant and extraordinary. The appropriate attitude is opposite to the current scientific mainstream view which classifies the possibility of extraterrestrial technological objects near Earth as extraordinary. This implies that common sense is not always common in academia. The switch between these opposite attitudes is required in order to fund a scientific search for extraterrestrial technological devices, just as it was in funding the Large Hadron Collider in its search for supersymmetric particles as dark matter.

At a conference that I attended while the balloons were shot down, I was asked what is the best path for fostering a paradigm shift in science. My answer had two parts: on content — it is best to work with young people who have no prejudice and are open-minded to exploring the unknown; and on funding — it is best to seek wealthy individuals or foundations who value innovation and risk taking. Federal funding committees, which are dominated by mainstream scientists, often argue that risk-taking should be limited so as not to waste taxpayers’ money. Ironically, if they had consulted actual taxpayers, these committee members would have found out that taxpayers prefer to explore the nature of UAP before we figure out the nature of dark matter.

Ignoring academic ego and professional prejudice will free us to collaborate on the infinite-sum endeavor through which we all benefit by knowing more about balloons or extraterrestrial devices in our neighborhood.


Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He chairs the advisory board for the Breakthrough Starshot project, and is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, is scheduled for publication in August 2023.



Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".


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