Allowing for the Unexpected in an Interstellar Date

Avi Loeb
5 min readDec 16, 2022
Webb telescope image of a star forming galaxy, M74 (Credit: NASA/ESA/CSA)

When friends congratulated me today for the early admission of my daughter to Harvard College, I noted that I only take credit for half of her DNA, and added “The most consequential decision regarding your personal prosperity is who you marry.”

The same applies to interstellar dating. If we search for microbes on Mars or exo-planets, we will at best find microbes. If we search for interstellar gadgets that represent our technological future, we might find magic. What we find is often capped by what we allow ourselves to find

How can we find something unexpected? By searching agnostically for the unfamiliar and not pretending that we know what we will find in advance. This is an attitude common among children and rare among adults, especially after receiving tenured in academia.

Life-as-we-know-it results from organic chemistry in liquid water on the surface of rocky planets with an atmosphere. We only have one example for it on Earth but we use it to guide our searches. Similarly, the Search for Extraterrestrial Intelligence (SETI) was guided for seven decades by the fact that over the past century we developed radio and laser communication on Earth. But a century is only a part in a hundred million of the age of most stars, and we must allow for future technologies that were never imagined. So when the traditional SETI advocate, Seth Shostak, argued in a WSJ essay yesterday that we should not take unidentified objects in our sky seriously, he was arguing that to find others we should wait patiently for a phone call rather than search our mailbox for any packages that accumulated over time. The mistake in this argument is that the packages we sent so far to interstellar space move at the tenth of the escape speed from the Milky-Way and will be bound to it gravitationally. This is in stark contrast to electromagnetic signals that exit the Milky Way at the speed of light, leaving no trace from civilizations that perished by now because their host star formed billions of years before the Sun and died by now. Data on the cosmic star formation history implies that most stars formed several billion years before the Sun.

Life-as-we-do-not-know-it can take many possible forms, from chemistry in liquid methane and ethane in the rivers of the moon Titan to a bio-techno entity that combines biology with artificial intelligence and 3D printing to repair itself over the millions of years of its journey through interstellar space. It is often said that the sky’s the limit for our imagination, but it is often the case that our willingness to explore reality agnostically sets the limit on what we know.

So, what is the best path forward? The theme of the Galileo Project that I lead is to search for the unfamiliar. Our new suite of instruments is already collecting data and our software will identify the familiar in the form of natural objects — like insects, birds, space rocks, as well as human-made objects — like weather balloons, drones, airplanes, rockets and satellites. Sherlock Holmes, the fictional detective created by Arthur Conan Doyle, had the guiding principle: “When you have eliminated the impossible, whatever remains, however improbable, must be the truth.”

This was the theme I highlighted in my Q&A interview with Professor Matthew Halsted this morning. As a theologian, he asked for my opinion on personal experiences reported by individuals over the years. I explained that such experiences involve the interaction of a human with “the reality we all share.” As a physicist I care about “the reality we all share”; if I had been a psychologist, I would care about the human side of the interaction. As much as I am intrigued by reports from experiencers, advances in our scientific knowledge about “the reality we all share” will only originate from instruments recording quantitative data which is reproducible. He asked me why we chose Galileo for the Project’s name and I explained that our approach reflects Galileo Galilei’s legacy of finding answers to fundamental questions by looking through new telescopes. Individuals can put goggles on their head and live in the Metaverse where the Sun moves around the Earth but these experiences will not be consistent with recent images from the camera of NASA’s Orion spacecraft.

As much as I wish to validate the human experience by quantitative high-quality data from fully-controlled instruments, I am critical of scientists who are not allowing for the unexpected. After a colloquium about `Oumuamua, one of my colleagues who worked on Solar system rocks for decades commented: “`Oumuamua is so weird, I wish it never existed.” Another expert on space rocks told me recently that he believes `Oumuamua displayed a familiar cometary tail when we did not look at it. This is equivalent to insisting that an elephant is a zebra which shows its stripes when we do not look at it.

This approach is equivalent to going on a date while expecting only the familiar. We will never discover wonderful things without allowing for them. As Walt Disney said: “First, think. Second, believe. Third, dream. And finally, dare.”

There are many situations when physicists may face the unexpected. Entanglement in Quantum mechanics is still not understood at a fundamental level. The nature of dark matter is unknown. What happened before the Big Bang is unknown. What happens to matter inside a black hole is unknown.

Let us keep our childhood wonder in hoping for the unexpected, because it would allow us to find something new. This is true for dating on Earth but even more so in the search for extraterrestrial life.


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".