Physicist Avi Loeb thinks there's a 'serious possibility' that 'Oumuamua was an alien spacecraft

Are we alone in the universe?

It's a question humans have been asking for thousands of years—but when a bizarrely fast, cigar-shaped interstellar object jetted past Earth on its trip through our solar system, Harvard professor Avi Loeb believes scientists weren't ready to seriously consider that it was of artificial origin. But Loeb is beyond consideration — he says it's very possible that 'Oumuamua (pronounced "oh moo ah moo ah") was an interstellar spacecraft.

Back in October 2017, a postdoctoral researcher named Robert Weryk at the University of Hawaii was sifting through the usual data stream from the Pan-STARRS astronomical survey of the sky when he noticed an unexpected object. It appeared to be highly elongated, like a stick, with a long axis 10 times longer than its short axis — unprecedented for an asteroid. Some hypothesized that 'Oumuamua swung towards our solar system as a result of a gravitational slingshot of a binary star system; others, that it might be an odd comet, though no tail was evident. Thus the search began to collect and analyze as much data as possible before it left our solar system.

Immediately upon discovering its physical properties, researchers realized its shape — which would minimize abrasions from interstellar gas and dust — would be ideal for an interstellar spacecraft. The idea understandably sent shockwaves through the scientific community and stoked controversy. Ultimately, scientists coalesced behind the idea that it was of natural origin, rather than artificial. But Loeb, who is the former chair of astronomy at Harvard University, remains certain that it was something akin to a light sail — a form of interstellar propulsion — spacecraft created by an extraterrestrial civilization. So much so that he wrote a whole book about it.

That book would be "Extraterrestrial: The First Sign of Intelligent Life Beyond Earth," in which Loeb argues that the scientific community's resistance to discussing the possibility of extraterrestrial life has hindered taking seriously his hypothesis that 'Oumuamua was an alien light sail. Loeb reflects on how what happened with 'Oumuamua was a bit of a missed opportunity, and that academia must invest more in the search for life in our universe to better prepare us for another interstellar visitor. But perhaps, most importantly, in a time when Earth faces an urgent global warming crisis, Loeb says that it could be finding extraterrestrial life that saves us from ourselves.

As always, this interview has been condensed and edited for clarity.

What makes you think that 'Omuamua was a light sail spacecraft created by an extraterrestrial civilization?

At first, astronomers assumed it must be a comet, because these are the objects that are most loosely bound to stars. We have mostly comets in the outer parts of the solar system. These are rocks covered with ice, and when they get close to a star they warm up, and the ice evaporates into a cometary tail.

It was natural to assume that about 'Oumuamua, because it came from outside the solar system, so the assumption was it must be a comet. The problem with that was there was no cometary tail. Some people say, "okay it's not a comet, maybe it's just a rock." But the problem is, about half a year later, it was reported that there was an excess push in addition to the force of gravity acting on it by the sun. It exhibited some additional force. Usually that force comes from the rocket effect of the cometary tail, but there was no cometary tail. So the question was, what produces this excess push?

Moreover, during the time that it was observed, the reflected sunlight [off of 'Oumuamua] varied by a factor of 10. So, that implied that it has an extreme geometry. Even if you consider a razor-thin piece of paper tumbling in the wind, the amount of area that is projected in your direction is not varying by more than a factor of 10, because the chance of seeing it edge on is really small. It is tumbling in the wind. So it looked like this object has an extreme geometry. The most likely model that explains the reflective sunlight as a function of time — as it was doubling every eight hours — was that it has a flat, pancake-like geometry, not cigar-shaped the way it was depicted in some cartoons.

On top of that, it was on the shinier end of all the objects we have seen from the solar system. It also came from a special frame of reference that is called the Local Standard of Rest. That is sort of the galactic parking lot where, if you find a car, you don't know what house it came from, because this is the frame of reference where you operate with the motion of all the stars in the vicinity of the sun. Only one in 500 stars is so much addressed relative to that frame as 'Oumuamua was. So it was just like a buoy sitting on the surface of the ocean and then the solar system is like a giant ship bumping into it.

So there were many peculiar facts. I tried to explain the excess push, especially. The only thing I could think of is it comes from the reflection of sunlight. Then it needed to be very thin, sort of like a sail on a boat that is pushed by wind. I couldn't imagine a natural process that would make a lightsail, a sail that's pushed by light. In fact, our civilization is currently pursuing this technology in space exploration.

If this object came from an artificial origin, the question is who sent it? I should say that in September of this year, 2020, there was another object discovered that exhibited an excess push. It was called 2020-SO by the Minor Planets Center that gives names to celestial objects. It turned out that this one ended up being a rocket booster from a failed mission of lunar lander, Surveyor II, that was launched in 1966. So astronomers figured out that it intercepted the Earth if you go back in time to 1966.

But this object actually also showed an excessive push, because it's a hollow rocket booster that is very thin and pushed by sunlight. We know that it's artificially made. It had no cometary tail. We know that we made it. So that provides evidence that we can tell the difference between a rock and an object that is pushed by sunlight. To me, it demonstrated the case that perhaps 'Oumuamua was artificial, definitely not made by us. because it's been only a few months close to us. We couldn't even chase it with our best rockets.

That's fascinating. Can you explain to our readers what is a light sail?

So a light sail is just like a sail on a boat that reflects the wind, the wind is pushing it. In the case of a light sail, it's the light reflected off its surface that gives it the kick, the push. Light is made of particles called photons. Just like billiard balls bouncing off a wall, they exert some push on it. So the particles of light — photons — reflect off the surface and push and give it a kick.

The advantage of this technology is that you don't need to carry the fuel with the spacecraft [as you do with rockets]. Rockets carry the fuel and they expel gas from the exhaust, and that's how they get pushed forward, just like a jet plane. In the case of a light sail, it is light that is being reflected. That's why you don't carry your fuel. You can have a lightweight spacecraft. In principle, you can even reach the speed of light with this technology.

So, as you know, after your paper was published, another one was published in 2019 in Nature Astronomy. That paper proposed a natural origin, that 'Oumuamua could have been a small asteroid that came from a solar system with a gas giant orbiting a star, and that it could have been fragmented and ejected into our solar system. Is there any part of you that thinks that's still a possibility— why or why not?

No. And that is one out of three suggestions that were made by astronomers about the astral origin, and I'll mention all three.

Great.

The [theory] that you mentioned has to do with a disruption of an object that passes close to a star. There are problems with that scenario. First of all, the chance of coming close enough to a star to be disrupted like that is small. Most of [these] kinds of objects do not pass close to the star. So you need a huge population of objects to account for those that pass close to the star and fragment. The more important problem is that if you make shrapnel or fragments as the result of the destruction near a star, they would be elongated — like cigar shaped. The best model for 'Oumuamua was that it was pancake-shaped. You can't get that from the destruction of a bigger object. It's not natural to get that.

So that's my caveat about this scenario — that first, it's unlikely that you would get so many — I mean, you need a lot of objects to explain that we detected 'Oumuamua. More than one, you would expect naturally, given all the rocks that exist in planetary systems. Yet, this model even wants 'Oumuamua-like objects to be produced very close to the host star. So that makes it even less likely to happen.

More importantly, the shape is the issue. How do you get pancake shape?

Then there is another suggestion of a natural origin which is that it's a "dust bunny," of the type that you find in a household. But it needs to be like a football size. The dust bunny, the collection of particles, is sort of like a cloud that then is 100 times less dense than air, more rarefied than air, so that sunlight can push it around. To me, that sounds not so plausible. This object was the size of a football field and it was tumbling around every eight hours. So making that out of a dust bunny, a cloud of dust particles, and imagining that this dust bunny would survive for millions of years in interstellar space — I find that hard to believe.

Then the third possibility that was suggested is that it's frozen hydrogen; that it's a hydrogen iceberg. We've never seen anything like it before. We didn't see a dust bunny, we didn't see a hydrogen iceberg. The idea was that if it's made of hydrogen, then when the hydrogen evaporates, it's transparent so you can't see it. So there is a cometary tail you just can't see. But the problem with this scenario is that we showed in the paper that a hydrogen iceberg would evaporate very quickly in interstellar space because of starlight hitting it. Therefore, it would not survive the journey.

So all together, I find these possibilities less appealing. All of them talk about it being something we have never seen before. So I'm saying, if we discuss it as a natural origin, and it involves something that we have never seen before—then why not also consider an artificial origin? That's also something we've never seen before? That's all I'm saying. I'm not saying it's definitely of artificial origin, but that it's one of the serious possibilities that we should contemplate.

How certain are you that 'Oumuamua was an object with artificial origin?

I would say, given everything we know, I would give a high likelihood that it could have been artificially made. The only way to know for sure, for certain, of course, is to take an image of something like that or get more data on something like that. We can't do it with 'Oumuamua because it's already too far away. It's now a million times fainter than it was when it was close to us. So we missed the opportunity. It's like having a guest for dinner, by the time you realize it's weird, it's already out of the front door into the dark street. That was the first guest, and we should look for more.

I definitely get the sense from your book how this was a missed opportunity to collect data. I thought about how, in your book, you described if cave dwellers were to find a modern cell phone, they would dismiss it as, like you said, as a shiny rock.

Exactly.

Is that what we did with 'Oumuamua?

Exactly. We tend to explain anything new that we see in terms of what we already saw. That's very natural but it also suppresses innovation, it doesn't allow us to see new things. As scientists, we should be open-minded.

Your book is about 'Oumuamua, but it's also about encouraging people to think differently about the possibility of extraterrestrial life, to be more open to it. I think it's interesting how you compare the hefty investments made by the scientific community to exploring dark matter to those invested in finding extraterrestrial life. Why do you think the idea of finding dark matter is more publicly acceptable and more interesting to scientists than searching for extraterrestrial life?

I think the reason is because it's less relevant to our lives. When something is close to home and affects you emotionally, that causes some distress. People prefer not to have that. They prefer to live in peace and be happy.

The point about reality is that it doesn't care about how uneasy you are with the notion. Reality is whatever it is. By ignoring it, you maintain your ignorance.

When the philosophers didn't look through Galileo's telescope, they were happy, because they thought the sun surrounded the Earth and they maintained their philosophical and religious beliefs that we are at the center of the universe. But that was temporary. It only maintained their ignorance for a little while. Eventually we realized that the Earth moves around the sun. The fact that they put Galileo in house arrest didn't change anything. The number of likes on Twitter or whatever we give each other, awards, or put someone in house arrest or anything, that only affects our relation with each other. Reality is whatever it is. By ignoring it, we don't gain anything, we just lose because we are more ignorant.

So my point is, the way to make progress is not to stick to your notions and maintain a prejudice. Of course that's a self-fulfilling prophecy. If you say I don't need to search, I know the answer, I don't need to look through Galileo's telescope, of course it's a self-fulfilling prophecy. You will never find that you're wrong because you bully people that will do this kind of search, and you don't fund the research in that direction. It's like stepping on the grass and saying look it doesn't grow. Science is not about that, science is about finding the truth.

In the book you emphasize how great the reward would be if we were to discover extraterrestrial life. I'm wondering if you could share more about that with our readers. I think people think that there would be a negative impact on our life, but you argue that it could have a positive impact on human life and on Earth.

First of all, it gives us a better perspective about ourselves. I think astronomy as a whole teaches us modesty. We are occupying one planet out of 10 to the power of 20 planets in the observable universe. We are really responsible for a tiny real estate piece out of the big landscape. Also, we live for a short time relative to the age of the universe. So this immediately tells us that we are not very significant.

Previously, people thought that an Earth-like planet around a sun-like star was something rare. Now, with the Kepler data, half of the sun-like stars have a planet the size of the Earth, roughly at the same separation. Therefore, if you arrange for similar circumstances, I think that you would get similar outcomes.

It would be arrogant to assume that we are unique and special. You know, I think we are as common as ants are on a sidewalk. They are out there and we need to look for clues. Of course if we maintain the idea that we are special and we are unique we will never find the evidence.

On the other hand, if we have the instruments to examine this — we have the telescopes — and the public is so interested in us finding the answer, I think it would be a crime for scientists not to address this interest from the public. Moreover, the public is funding science, so we should attend to the interests of the public. There are examples from history that on many occasions when we thought we knew the truth and we ended up being wrong.

What kind of evidence would the scientific community need to have incontrovertible proof that there is extraterrestrial life, or more 'Oumuamua-like light sails, in our universe?

That's an excellent question. One approach is, of course, to find objects like 'Oumuamua that we can take a photograph of. By the way, we don't necessarily need to chase them in space, because every now and then one of them may collide with the Earth. We see those as meteors. One of the meteors that comes from interstellar space may be space junk from another civilization. That offers us the possibility of putting our hands around it. If there is a meteor that lands on the ground, we can tell from its speed that it came from outside the solar system and it looks suspicious in terms of its composition, we can examine it. So there are ways to continue this search, even just on the ground rather than going to space.

Beyond that, we can look for industrial pollution in the atmospheres of other planets around other stars as a technological signature, rather than looking for oxygen from microbes. That would be one way of definitely finding evidence for life, industrial life, because the molecules like [CFCs] that contaminate the atmosphere of Earth cannot be produced naturally. These are complex molecules. If we find evidence for them on other planets, that would indicate that there is definitely life out there.

I think it's interesting that this book has been published in a time when there's a lot of anti-scientist sentiment. With the coronavirus pandemic, science has become politicized. Do you think that harms legitimizing the search for extraterrestrial life?

No, I would think the other way around. Because the way I see science is that it could be unifying, rather than divisive. As long as the scientific community attends to the interests of the public, and is honest about how much evidence it has for every statement. Right now what happens in the academic world is that the scientists say we should never approach the public until we are absolutely sure about something, because otherwise they might not believe us when we say there is global warming. I don't think that's the right approach.

I think the public should see how science is done in the sense that most of the time there is not enough evidence — and we collect more evidence, more data, and eventually we become convinced that one interpretation is correct. If the public sees that process in motion, then it won't suspect that there is a hidden agenda behind it because it's transparent. You look at the evidence and everyone that looks that has enough evidence and believes the evidence would agree on the conclusions.

It should be understandable by anyone, and it should be something that anyone can pursue. And by collecting evidence and therefore it's not an occupation of the elite. It should not be suspicious. It should not have any political agenda. It should also be independent of which nation conducts it. Indeed, we can bring different nations together.

I'm wondering what do you think really needs to happen for there to be a shift in the scientific community to take the search for extraterrestrial life more seriously?

Well, more people speaking like me. And I hope eventually it will shift also the funding agencies, the federal funding agencies, to go in that direction. I think that what astronomers need to realize is it's not speculative given what we know right now, it's one of the most conservative ideas to fall on. It's much more conservative than dark matter, where we are in the dark, so to speak, because there are so many possibilities. People speculate that we invested hundreds of millions of dollars in experiments without much success yet. We don't know what the "darkness" is made of.

Of course, science is a learning experience and nobody regrets trying those experiments, because we rule out possibilities. That is much more speculative because we've never seen any evidence for dark matter yet or direct evidence for the nature of dark matter. It's part of science to search for the unknown. I would regard the search for extraterrestrial civilization — it should be a mainstream activity especially given the interest of the public.

You've already received a lot of media attention regarding this book and it hasn't even been published yet. I'm wondering what you hope people will get from this book and what you hope comes out of it?

I have two messages and you already mentioned them. One is that 'Oumuamua was unusual. It showed a lot of anomalies that could indicate that it was some technological equipment and we should explore and look for other objects that appear anomalous like it and get more data on them. It's sort of like looking for plastic bottles on the beach.

The second message is that the scientific culture should change and be more open minded to change. I'm sorry to say, but the commercial sector — companies have had much more open-mindedness, much more blue sky research than the academic world these days.

There are companies like Google or SpaceX or Blue Origins — originally it was IBM — that had a lot of innovations in them. That is surprising to me. It should be the academic world that carries the torch of innovation because it has, in principle, the tenure system that allows people to explore without any risk for their jobs. Unfortunately, many practitioners in academia worry more about their image and their honors, and so forth, and engage much less in risk-taking and in thinking independently and looking for evidence than intellectual gymnastics that demonstrate how smart they are.

Avi Loeb's book, "Extraterrestrial: The First Sign of Intelligent Life Beyond Earth," is slated to be released on January 26, 2021 from Houghton Mifflin.