NASA has a big secret announcement coming up? Not aliens! Astronomers detected some weird radio noise coming from a nearby star? Not aliens! You wake up strapped to a table and a grey is probing you and you have no idea how you got there? Well, actually, yeah that might be aliens. But for the most part, anytime something weird happens in space you can rest easy knowing that it is 100 percent guaranteed not to be aliens.

Until it is, of course.

While many astronomers may concede that intelligent life exists somewhere in the universe, fewer are willing to speculate on whether we can—or should—make contact with it. Nevertheless, the scientific Search for Extraterrestrial Intelligence, or SETI, has counted legions of eminent scientists among its ranks since the very beginning and many have spent their entire career doing everything they could to hasten first contact. These people aren’t crazy, but they do share a conviction that one day it will be aliens. Maybe someday soon.

But even among these extraterrestrial evangelists you’d be hard-pressed to find anyone who thinks we've already had our first brush with ET. The notable exception is the Harvard astronomer Avi Loeb. The Israeli-born scientist has had a distinguished career and currently serves as the chair of Harvard’s astronomy department, the founding director of Harvard's Black Hole Initiative, and the director of the Institute for Theory and Computation (ITC) within the Harvard-Smithsonian Center for Astrophysics. But Loeb is arguably best known for his enthusiastic endorsement of theories that conclude that maybe, for once, it is aliens.

Back in 2017, when astronomers detected mysterious pulses of high-energy radio waves known as a fast radio burst coming from another galaxy, Loeb was the first to suggest that it might be an extraterrestrial message. Later that year, when astronomers detected ‘Oumuamua, the first known interstellar object to enter our solar system, Loeb suggested it could be the remnants of an alien solar sail and recommended scanning it for signs of radio emissions. (None were detected.)

Loeb’s willingness to indulge the possibility of extraterrestrial explanations has made him a darling of the media and the legions of astrophiles who want to believe. He hasn’t found ET yet, but he hasn’t given up either. His new book, Extraterrestrial: The First Sign of Intelligent Life Beyond Earth, doubles down on his theory that ‘Oumuamua was in fact a trashed piece of advanced alien technology—possibly a discarded light sail adrift in the cosmos. The book is not just an open-minded and fact-driven look at this extraordinary encounter with interstellar flotsam, but a poignant meditation on our place in the universe. It cuts to the core of the extraterrestrial question, which is less about whether aliens exist than whether we are ready to meet them.

Supercluster called Loeb at his home in Massachusetts to discuss the book and get his thoughts on whether we’ll ever know the truth about that mysterious encounter and the importance of taking SETI seriously.

It was a gradual process. But about 20 years ago I pioneered a new frontier which is trying to probe the conditions around very early cosmic times, the first stars and galaxies. The first galaxies produce ultraviolet light that breaks down the hydrogen atoms in the universe. This is called the process of reionization. One way to map that process, to see the scars that the galaxies left on the hydrogen around them, was to image the hydrogen, which emits radio waves at a wavelength of 21 centimeters. I worked on one of the very first papers suggesting to use this method for mapping hydrogen during reionization. It involved radiation that arrives to us, the observer at frequencies on the order of 100 to 200 megahertz. The biggest challenge is to get rid of interference from radio and TV stations on Earth. I went to lunch with Matias Zaldarriaga one day and I said these same observatories could also potentially eavesdrop on radio transmissions from another civilization or another planet. They’re so sensitive.

We wrote a paper about SETI, about the search for radio signals, and how far we can actually see what our civilization is producing over the past 50 years. We found that with current observatories, one can see what we produce out to tens of light-years. So if you had a copy of our civilization at the same technological stage, since the end of the Second World War until now, current observatories could see it out to tens of light-years. So that was my first encounter and I remember that Jill Tartar came to give a colloquium about SETI around the same time and she said, “even Avi Loeb is interested in SETI!”

I went to a conference in Abu Dhabi and a tour guide there was bragging that you can see some of their lights near the oil fields all the way to the moon. I asked one of my colleagues, Ed Turner, wouldn’t it be interesting to figure out how far away we can see artificial lights? We asked how far can the Hubble Space Telescope see a city like Tokyo? Turns out you can see it all the way out to Pluto. The edge of the solar system. So we wrote a paper saying now you can tell if an object — let’s say a spacecraft or some other source of light [similar to] a city like Tokyo — comes into the solar system, we can know that it produces artificial light, that it’s not reflecting sunlight. The reflection of sunlight as it changes its distance, the brightness drops inversely with the distance to the fourth power. Whereas if it produces its own light, it drops inversely with the square of distance. So as it changes distances you can tell if it is producing artificial light.

I remember that we had a visit by Mike Brown, from Caltech, who has discovered many of the objects in the Kuiper Belt. I asked him, ‘have you ever checked whether any of the objects you discovered changes its brightness inversely with the distance squared or with distance to the fourth? I explained why I was asking and he said, ‘what’s the point? It must be one over distance to the fourth.’

So first it seems to be most likely a flat object based on the variation of the light as it was tumbling. There is a paper on that from 2019 showing that with 91 percent confidence it was a disk-shaped object rather than cigar-shaped. The variation in the light implies that it has a very extreme geometry. The second is the fact that it didn’t have a cometary tail, but exhibited a push away from the sun that declines inversely with distance squared — just like you would expect from reflected light. Then, in September 2020, astronomers identified another object dubbed 2020 SO, which they identified as a rocket booster from a 1966 launch of the lunar lander surveyor 2. It also exhibited an extra push away from the sun as a result of reflected sunlight and didn’t have a cometary tail. And in that case, we know it’s artificial. So I would say the possible origin of ‘Oumuamua as a thin object pushed by the sun should be put on the table. I’m not saying that we know for sure that it is, but I’m saying it’s so weird. It’s unlike any comet or asteroid we’ve seen.

I would say mainstream astronomers divide into three groups. Those that are not really scientists that make statements, people like Neil deGrasse Tyson and Ethan Siegel, the guy that writes for Forbes. They call themselves scientists, but they haven’t published for a decade. Yet they pretend to guard the future of science by protecting it from what is being said in scientific papers that other people wrote. I wouldn’t be surprised if deep down they’re very intrigued by all this.

The second group of people or the bulk of the mainstream says business as usual, I don’t care about it, I don’t care about the details. One example of that is I went with a colleague of mine, he’s a traditional solar system astronomer, to a seminar about ‘Oumuamua and then when we left the room, he said, ‘this object ‘Oumuamua is so weird. I wish it never existed.’ Which to me implies that it simply moves him out of his comfort zone and he wants to forget about it. That’s the response of most people. Most people would say, let other people work out the details, it must be a rock, forget about anything else. Let’s move on. That’s a bad approach because sometimes nature is trying to tell you something. With quantum mechanics, I suppose that people would say, ‘no classic physics is right, forget about it.’

Practically it’s what Albert Einstein was trying to say about how there can’t be spooky action at a distance and he turned out to be wrong. Sometimes, nature tells you something and if you put on blinders and say, ‘extraordinary claims require extraordinary evidence, I don’t want to hear about it until the aliens touch my face,’ you would never be bothered. It’s just like the philosophers in Galileo’s day who didn’t want to look through a telescope, they actually avoided seeing the evidence. There is the lower level of saying ‘I don’t care about the details, I know the answer,’ but the higher level is when asked to look at the evidence — not even looking. That maintains our ignorance. It keeps you in your comfort zone. But the reality is whatever it is, and doesn’t care about whether you ignore it. People can choose to be ignorant, but it can’t be the professional scientist. Science is about finding knowledge.

That brings me to our third category of people that are the most serious scientists. There were four or five papers that were written trying to explain ‘Oumuamua’s properties by a natural scenario. One example is a hydrogen iceberg suggested by Seligman and Laughlin from Yale. It’s just frozen hydrogen the size of a football field and we’ve never seen that in space. Because it’s hydrogen, when it evaporates it does produce a cometary tail but we can’t see it because hydrogen is transparent. The only problem with that, I wrote a paper about it with a colleague of mine, Thiem Hoang, is that a hydrogen iceberg wouldn’t survive the journey. It would get evaporated along the way by starlight. There was another suggestion that it’s a dust bunny 100 times less dense than air floating in space and being pushed by reflected sunlight. Again, the problem I see with that is it doesn’t have the integrity to survive for millions of years through interstellar space. There was another suggestion that maybe it's the shrapnel from the disruption of an object near the nearest star. The thing is, tidal disruption of objects usually produces elongated cigar-shaped pieces, whereas this one looks flat. So it doesn’t work out.

People try to explain it using natural sources and I think that’s the right way to proceed. But I won’t say that any of these suggestions sounds more plausible than something thin that was produced artificially. Not necessarily a light sail, it could just be a surface layer or something that was torn apart, like this rocket booster. I don’t know what it looks like exactly, but my point is that it should be put on the table. Instead, what I see is people ridiculing this and not even allowing the discussion to go in that direction. That to me is a sign of a very bad scientific culture.

Right now we can discuss axions and WIMPS and all kinds of exotic dark matter particles we’ve never seen and that’s fine. We can spend hundreds of millions of dollars on that. We can, in the context of theoretical physics, discuss extra dimensions and string theory and the multiverse, things that have no connection to reality and no tests in the foreseeable future. People get elected to honor societies, give each other prizes, and are very proud of themselves discussing these speculations. All we’re saying is if the conditions on Earth are replicated on billions of other planets in the Milky Way galaxy, maybe you get similar outcomes. What could be more conservative than that? The scientific culture is in the exact opposite place of where it should be.

It’s a societal thing that can be changed. I make the analogy to a person stepping on the grass and asking why it doesn’t grow. If you discourage talent from entering the field, and you don’t get funding, we will not find anything. It’s a self-fulfilling prophecy. The way to change it is by what I’m doing right now. I’m trying to break it. I get ridiculed sometimes. But beyond academia, the public has much more common sense and a much healthier approach to the subject.

Two reasons come to mind. One is people are in the pursuit of ego-motivated agendas. They want to demonstrate that they are smart, and to demonstrate that you are smart you don’t want to make mistakes. You want to put the least amount of skin in the game. If you work on string theory that’s great, it will never be tested and you can just do mathematical gymnastics and work in anti-deSitter space and nobody would show you that you’re wrong. The second is that they try not to take risks and to maintain an image that is always respectable. They always shy away from directions that may deviate from what we already know. When you adopt this approach, you suppress innovation. This is really bad for the future of science. These people are boring because they always repeat the things that we already know. I hate that. We live for such a short time, why not figure out something new about nature. It’s not about us.

The scientific activity is a dialogue with nature. We listen to the evidence, try to see if it’s consistent with what we thought, and otherwise try to explain it. That’s the whole fun. You’re not supposed to put science on a pedestal as the occupation of the elite. That cannot be the case. If the public is interested in this question and the public funds science, then scientists should work on it. That’s not so complicated. Your ideas don’t necessarily need mathematical sophistication to be exciting. What many people in academia fail to understand is that sometimes nature is simple. You just need to figure out what this simple thing is without making it about showing how smart you are. It’s not about that.

I don’t care how many likes I have on Twitter because I don’t care so much about people. I care about nature.