Andrés Muedano (AM): Thank you for the opportunity to speak with you! Could you please tell me more about yourself and your research?

Avi Loeb (AL): I grew up on a farm in Israel, and I was mostly interested in philosophy at a young age—in the most fundamental questions about our existence. However, in Israel, it’s obligatory to serve in the military at age 18. There was an option for me to be in a program that allowed me to pursue physics and mathematics, and that was the closest I could get to philosophy.

I finished my Ph.D. at age 24 in Physics and Mathematics, and then I was offered a position at the Institute for Advanced Study at Princeton University. I was then offered a position at Harvard and was tenured three years later, so I’ve been here for 30 years—not that I’m counting!

Between 2011 and 2020, I was the chair of the Astronomy Department. I also was the founding director of the Harvard Black Hole Initiative. In recent years—over the past 5 five years or so—I have focused on the search for life in the cosmos. I wrote a textbook called Life in the Cosmos, published in 2021, and also established the Galileo Project, which aims to search for technological objects near Earth that were manufactured by another [non-terrestrial] civilization.

AM: Tell me more about the Galileo Project. How does it differ from past efforts seeking to find extraterrestrial life?

AL: In the past, the search for other [intelligent extraterrestrial civilizations] focused on looking for either radio or laser signals. However, that is like waiting for a phone call at home: [it’s possible that] nobody may call you while you’re waiting. However, there is a completely different method. You can be active and go out and check your mailbox to see if there are any packages. The sender may be dead, but he doesn’t need to do anything. If he sent any packages, the packages will still be waiting for you.

So far, we have sent five probes to interstellar space over the past 50 years: Voyager 1, Voyager 2, Pioneer 10, Pioneer 11, and New Horizons. Now, many stars are billions of years older than the Sun, and we know that it takes less than a billion years to move from one side of the Milky Way galaxy to the other with a Voyager-like spacecraft. So that means that they could have reached us by now!

Such probes would be bound by gravity to the Milky Way. They would not escape, so they would keep accumulating over time, just like plastics in the ocean. Nobody had searched for such objects, and only over the past decade have we found the first three of them; two of the three were unlike the rocks that we are familiar with in the solar system. That was intriguing to me.

I therefore established the Galileo Project to do a systematic search for interstellar objects. Just recently, we established that a meteor that landed near Papua New Guinea in 2014 is interstellar—that is, originating from outside our solar system. This meteor was moving faster than 95% of the stars in the vicinity of the Sun, relative to the mean motion of objects in the Milky Way.  It was moving very fast at 60 kilometers per second, and it also was able to maintain its integrity up to a very high stress in the atmosphere when it collided with Earth. That implied that it is tougher than all of the space rocks that NASA has cataloged over the past decade—272 of them. It intrigued me: it could have been a Voyager-like meteor. Imagine our own spacecraft colliding with a planet like the Earth; it would appear as a meteor of unusual material strength and high speed. Just this summer, I led an expedition to retrieve the materials from [this object], and we found molten droplets along the meteor path that were never seen before. These droplets are made of a composition that cannot be found on Earth, the Moon, Mars, or asteroids; we are still finishing the analysis, but it is all very exciting because it’s the first time that scientists put their hands on materials from a big object that came from outside the Solar System.

AM: Besides leading the Galileo Project, you are also a member of the Origins of Life Initiative, a community of Harvard scientists seeking to determine if life is abundant in the universe. How do you see the Galileo Project and the Origins of Life Initiative as complementary to each other?

AL: The search for life involves both primitive forms of life—microbial life and intelligent life. The fundamental question is which one is easier to detect. You might think that microbial life is much more prevalent and therefore easier to find, but that's not necessarily the case, since the imprint of primitive life is subtle. You need to look indirectly for molecules in the atmospheres of exoplanets that might be indicative of life, such as water, oxygen, and methane. The problem with that approach, however, is that even when you find these molecules, there is still the fundamental question of whether they were produced by some other natural process and not by life itself. On the other hand, looking for the technological imprints of a civilization might be relatively straightforward. For example, if there is a large amount of space trash due to other civilizations over the past few billion years, then you know that there was some technological process that produced it. That might be easier to find, especially if there is a large abundance of these things.

We don't know what we might find in either one of these pursuits, but I would argue that it may actually be easier to find intelligent life. So far we haven’t [found anything], but it may well be that the Galileo Project will find objects that imply a technological origin, and that would be the first time that we ever find such a thing.

AM: The search for extraterrestrial life has been met with controversy, thereby discouraging scientists from working on this topic. Ultimately, this constitutes a problem in the search for extraterrestrial intelligence: the controversy surrounding the idea hinders us from further exploring it. What do you make out of this?

AL: When you say extraordinary claims require extraordinary evidence, but you're not looking for the evidence, then you will never find that you're wrong. And I say, let's be agnostic. Many times in science, you don't know whether you will find something that you're looking for. 

Think of other areas of research in physics. There was $10 billion invested in the Large Hadron Collider at CERN to look for the lightest supersymmetric particles. Supersymmetry was believed by the majority of the particle physics community, and we haven't found any trace of supersymmetry. On the other hand, we do know that we exist. We know that, over the past 50 years, we sent five probes to interstellar space. We know that there are tens of billions of stars like the sun. We know that a substantial fraction of them, somewhere between a few percent to a few tens of percent, have a planet the size of the Earth, roughly at the same separation from these stars. So I say, it’s common sense to suggest that we search for something like us!

AM: Why do you think people are hesitant to accept such a suggestion?

AL: We like to think that we are extraordinary, and it’s arrogant for us to think that. People only think that because it boosts our ego, and we have been wrong about that in the past: we thought that we were the center of the universe. For a thousand years, after Aristotle, people preferred to believe this because it gave them a good feeling. Then came Galileo, who was willing to look through the telescope, and he saw the moons of Jupiter revolving around Jupiter, not around us. The clergy refused to look through his telescope, and he was put under house arrest. But the Earth kept moving around the Sun. So it’s not a popularity contest—it’s not a question of how many likes you get on social media for an idea. In the end, the definition of controversial has nothing to do with whether an idea is a good one. It has to do with how ignorant or motivated people are to argue one way or another.

The fact that it’s not common sense for scientists to engage in the search for intelligent civilizations, to me, is a shortcoming of academia. It should be part of the mainstream! There are lots of people who ridicule this effort and argue against it. Interestingly, the search for molecules in the atmosphere of planets—which might not be indicative of life—is part of the mainstream now, because it doesn’t threaten our ego: we can still think of ourselves as superior relative to microbes, and we can still believe that we are unique and special and important. But it is quite arrogant to do that, as we are probably not the pinnacle of creation.

We just need to search for 30 years and invest billions of dollars in the search for objects that might have a technological origin, and if we don’t find anything, we will be exactly at the same point as the search for dark matter particles. The public cares so much about this—about 55 percent of Americans believe in intelligent extraterrestrial life. That’s more than the fraction of Americans that believe in a biblical god. So given that the public pays taxes to fund science, it sounds completely natural for us to engage in [the search for extraterrestrial intelligence].

So, to summarize, the origin of life on Earth ultimately led to intelligent life. The question is whether that also happened in exoplanets. One way to look for intelligent life is to search for distant electromagnetic signals, but you need to intercept them at the right place and time, and they may be very far away right now. The advantage of looking for objects that were launched into interstellar space is that they would be around because they are bound by gravity to the Milky Way, and that’s what the Galileo Project is doing. In the end, that is also part of the Origins of Life research: if we find intelligent life, we know that there is also non-intelligent life that led to it.

In the end, it’s sort of like a race. The question is what we will find first.

This interview was edited for clarity.