On October 19, 2017, astronomers at the University of Hawaii spotted a strange object travelling through our solar system, which they later described as “a red and extremely elongated asteroid.” It was the first interstellar object to be detected within our solar system; the scientists named it ‘Oumuamua, the Hawaiian word for a scout or messenger. The following October, Avi Loeb, the chair of Harvard’s astronomy department, co-wrote a paper (with a Harvard postdoctoral fellow, Shmuel Bialy) that examined ‘Oumuamua’s “peculiar acceleration” and suggested that the object “may be a fully operational probe sent intentionally to Earth’s vicinity by an alien civilization.” Loeb has long been interested in the search for extraterrestrial life, and he recently made further headlines by suggesting that we might communicate with the civilization that sent the probe. “If these beings are peaceful, we could learn a lot from them,” he told Der Spiegel.
I recently spoke by phone with Loeb, who was frustrated that scientists saw ‘Oumuamua too late in its journey to photograph the object. “My motivation for writing the paper is to alert the community to pay a lot more attention to the next visitor,” he told me. During our conversation, which has been edited and condensed for clarity, we discussed why Loeb thinks we need to consider the possibility that ‘Oumuamua was sent by aliens, the dangers of unscientific speculation, and what belief in an advanced extraterrestrial civilization has in common with faith in God.
Your explanation of why ‘Oumuamua might be an interstellar probe may be hard for laypeople to understand. Why might this be the case, beyond the fact that lots of things are possible?
There is a Scientific American article I wrote where I summarized six strange facts about ‘Oumuamua. The first one is that we didn’t expect this object to exist in the first place. We see the solar system and we can calculate at what rate it ejected rocks during its history. And if we assume all planetary systems around other stars are doing the same thing, we can figure out what the population of interstellar objects should be. That calculation results in a lot of possibilities, but the range is much less than needed to explain the discovery of ‘Oumuamua.
There is another peculiar fact about this object. When you look at all the stars in the vicinity of the sun, they move relative to the sun, the sun moves relative to them, but only one in five hundred stars in that frame is moving as slow as ‘Oumuamua. You would expect that most rocks would move roughly at the speed of the star they came from. If this object came from another star, that star would have to be very special.
What are some of the other strange facts?
When it was discovered, we realized it spins every eight hours, and its brightness changed by at least a factor of ten. The fact that its brightness varies by a factor of ten as it spins means that it is at least ten times longer than it is wide. We don’t have a photo, but, in all the artists’ illustrations that you have seen on the Web, it looks like a cigar. That’s one possibility. But it’s also possible that it’s a pancake-like geometry, and, in fact, that is favored.
What would be the meaning of a pancake-like geometry—
Wait. The most unusual fact about it is that it deviates from an orbit that is shaped purely by the gravitational force of the sun. Usually, in the case of comets, such a deviation is caused by the evaporation of ice on the surface of the comet, creating gases that push the comet, like the rocket effect. That’s what comets show: a cometary tail of evaporated gas. We don’t see a cometary tail here, but, nevertheless, we see a deviation from the expected orbit. And that is the thing that triggered the paper. Once I realized that the object is moving differently than expected, then the question is what gives it the extra push. And, by the way, after our paper appeared, another paper came out with analysis that showed very tight limits on any carbon-based molecules in the vicinity of this object.
What is the significance of that?
It means that there is no evidence of gas that relates to the evaporation of ice. We don’t see the telltale signatures of cometary tail. Moreover, if it was cometary activity, then we would expect the spin period of this object to change, and we don’t see that. All of these things are indicative of the fact that it is nothing like a comet that we have seen before in the solar system. And it is also nothing like an asteroid. Its brightness varies by a factor of ten, and the maximum you typically observe is a factor of three. It has a much more extreme geometry, and there is some other force pushing it. The question is, what’s providing this force, and that was the trigger for our paper.
The only thing that came to my mind is that maybe the light from the sun, as it bounces off its surface, gives it an extra push. It’s just like a wind bouncing off a sail on a sailboat. So we checked that and found that you need the thickness of the object to be less than a millimetre in order for that to work. If it is indeed less than a millimetre thick, if it is pushed by the sunlight, then it is maybe a light sail, and I could not think of any natural process that would make a light sail. It is much more likely that it is being made by artificial means, by a technological civilization.
I should say, just as background, I do not view the possibility of a technological civilization as speculative, for two reasons. The first is that we exist. And the second is that at least a quarter of the stars in the Milky Way galaxy have a planet like Earth, with surface conditions that are very similar to Earth, and the chemistry of life as we know it could develop. If you roll the dice so many times, and there are tens of billions of stars in the Milky Way, it is quite likely we are not alone.
So this civilization would be out of the solar system and in the galaxy?
In the galaxy. It may be dead by now, because we don’t take good care of our planet. Imagine another history, in which the Nazis have a nuclear weapon and the Second World War ends differently. You can imagine a civilization that develops technology like that, which would lead to its own destruction.
It’s possible that the civilization is not alive anymore, but it did send out a spacecraft. We ourselves sent out Voyager I and Voyager II. There could be a lot of equipment out there. The point is that this is the very first object we found from outside the solar system. It is very similar to when I walk on the beach with my daughter and look at the seashells that are swept ashore. Every now and then we find an object of artificial origin. And this could be a message in a bottle, and we should be open-minded. So we put this sentence in the paper.
It’s different, of course, but the way you said that reminded me of an argument I have heard for creationism, which is that if you find a watch on the beach, you know it must be man-made, and, since our eyes are as complex as a watch, we must also be designed by a creator.
An advanced technological civilization is a good approximation to God. Suppose you took a cell phone and showed it to a caveperson. The caveperson would say it was a nice rock. The caveperson is used to rocks. So now imagine this object—‘Oumuamua—being the iPhone and us being the cave people. We look at it and say it’s a rock. It’s just an unusual rock. The point of this analogy is that, for a caveperson, the technologies we have today would have been magic. They would have been God-given.
Coryn Bailer-Jones, an astronomer quoted in one of the pieces on your paper, wrote, “In science we must ask ourselves, ‘Where is the evidence? Not’ ”—
Hold on. “ ‘Not where is the lack of evidence so that I can fit in any hypothesis that I like?’ ” [Bailer-Jones, of the Max Planck Institute for Astronomy, in Heidelberg, Germany, has identified four possible home stars for ‘Oumuamua, and was asked to respond to Loeb’s light-sail theory by NBC.]
Well, it’s exactly the approach that I took. I approached this with a scientific mind, like I approach any other problem in astronomy or science that I work on. The point is that we follow the evidence, and the evidence in this particular case is that there are six peculiar facts. And one of these facts is that it deviated from an orbit shaped by gravity while not showing any of the telltale signs of cometary outgassing activity. So we don’t see the gas around it, we don’t see the cometary tail. It has an extreme shape that we have never seen before in either asteroids or comets. We know that we couldn’t detect any heat from it and that it’s much more shiny, by a factor of ten, than a typical asteroid or comet. All of these are facts. I am following the facts.
Last year, I wrote a paper about cosmology where there was an unusual result, which showed that perhaps the gas in the universe was much colder than we expected. And so we postulated that maybe dark matter has some property that makes the gas cooler. And nobody cares, nobody is worried about it, no one says it is not science. Everyone says that is mainstream—to consider dark matter, a substance we have never seen. That’s completely fine. It doesn’t bother anyone.
But when you mention the possibility that there could be equipment out there that is coming from another civilization—which, to my mind, is much less speculative, because we have already sent things into space—then that is regarded as unscientific. But we didn’t just invent this thing out of thin air. The reason we were driven to put in that sentence was because of the evidence, because of the facts. If someone else has a better explanation, they should write a paper about it rather than just saying what you said.
One of your responses to these criticisms was, “I follow the maxim of Sherlock Holmes: ‘When you have excluded the impossible, whatever remains, however improbable, must be the truth.’ ” But when it comes to things we can’t explain or don’t understand, don’t we often turn to concepts that do exist in popular culture and society—
No. No! No. Let me give you a better example for the kind of argument you are making. The multiverse is a mainstream idea—that anything that can happen will happen an infinite number of times. And I think that is not scientific, because it cannot be tested. Whereas the next time we see an object like this one, we can contemplate taking a photograph. My motivation, in part, is to motivate the scientific community to collect more data on the next object rather than argue a priori that they know the answer. In the multiverse case, we have no way of testing it, and everyone is happy to say, “Ya!”
Another mainstream idea is the extra dimension. You see that in string theory, which gets a lot of good press, and awards are given to members of that community. Not only has it not been tested empirically for almost forty years now but there is no hope it will be tested in the next forty years. And yet your friend has no problem with that! Whoever you are quoting has no problem with the multiverse, with string theory. No problem!
We don’t know what the person, Coryn Bailer-Jones, thinks about these things, to be clear.
He never complains about it, he never mentions it.
I don’t even know it’s a “he,” and I don’t know his or her opinions.
The point I was trying to make is that we live in a culture where people talk about aliens.
No, but that’s different.
Hold on. Let me finish. The term U.F.O., in popular usage, has basically come to mean aliens of some sort. My question is whether we tend to see things that we can’t know or understand through the prism of things we have heard about since we were kids. Aren’t we more likely to see something like an alien society as an explanation than something we maybe can’t even comprehend or put into words?
I don’t enjoy science fiction because there are things in science fiction that violate the laws of physics. I like science and I like fiction separately. The main argument against any of the U.F.O. stories that you may have heard about is that the technology of detection have improved dramatically over the past few decades. We have cameras that are far better than we used to have, and nevertheless the evidence remains marginal. And so that is why there is no scientific credibility to U.F.O.s.
What we are talking about today is part of science. We have seen an object from outside the solar system, and we are trying to figure what it is made of and where it came from. We don’t have as much data as I would like. Given the data that we have, I am putting this on the table, and it bothers people to even think about that, just like it bothered the Church in the days of Galileo to even think about the possibility that the Earth moves around the sun. Prejudice is based on experience in the past. The problem is that it prevents you from making discoveries. If you put the probability at zero per cent of an object coming into the solar system, you would never find it!
Have your religious beliefs, or beliefs about God, changed in any way in the time you have been studying astronomy?
I am not religious. Why do you make that assumption?
I didn’t. I was wondering if your thoughts had changed one way or the other.
First of all, it depends on what you mean by God. But if you take something that is zero and multiple it by any number, it remains zero. I was secular to start with. I am not religious. I am struck by the order we find in the universe, by the regularity, by the existence of laws of nature. That is something I am always in awe of, how the laws of nature we find here on Earth seem to apply all the way out to the edge of the universe. That is quite remarkable. The universe could have been chaotic and very disorganized. But it obeys a set of laws much better than people obey a set of laws here. My work as a scientist is purely based on evidence and rational thinking. That’s all.
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