The reaction to Avi Loeb’s new book Extraterrestrial (Houghton Mifflin Harcourt, 2021) has been quick in coming and dual in nature. I’m seeing a certain animus being directed at the author in social media venues frequented by scientists, not so much for suggesting the possibility that ‘Oumuamua is an extraterrestrial technological artifact, but for triggering a wave of misleading articles in the press. The latter, that second half of the dual reaction, has certainly been widespread and, I have to agree with the critics, often uninformed.

Image credit: Kris Snibbe/Harvard file photo.

But let’s try to untangle this. Because my various software Net-sweepers collect most everything that washes up on ‘Oumuamua, I’m seeing stark headlines such as “Why Are We So Afraid of Extraterrestrials,” or “When Will We Get Serious about ET?” I’m making those particular headlines up, but they catch the gist of many of the stories I’ve seen. I can see why some of the scientists who spend their working days digging into exoplanet research, investigate SETI in various ways or ponder how to build the spacecraft that are helping us understand the Solar System would be nonplussed.

We are, as a matter of fact, taking the hypothesis of extraterrestrial life, even intelligent extraterrestrial life, more seriously now than ever before, and this is true not just among the general public but also within the community of working scientists. But I don’t see Avi Loeb saying anything that discounts that work. What I do see him saying in Extraterrestrial is that in the case of ‘Oumuamua, scientists are reluctant to consider a hypothesis of extraterrestrial technology even though it stands up to scrutiny — as a hypothesis — and offers as good an explanation as others I’ve seen. Well actually, better, because as Loeb says, it checks off more of the needed boxes.

Invariably, critics quote Sagan: “Extraordinary claims require extraordinary evidence.” Loeb is not overly impressed with the formulation, saying “evidence is evidence, no?” And he goes on: “I do believe that extraordinary conservatism keeps us extraordinarily ignorant. Put differently, the field doesn’t need more cautious detectives.” Fighting words, those. A solid rhetorical strategy, perhaps, but then caution is also baked into the scientific method, as well it should be. So let’s talk about caution and ‘Oumuamua.

Loeb grew up on his family’s farm south of Tel Aviv, hoping at an early age to become a philosopher but delayed in the quest by his military service, where he likewise began to turn to physics. An early project was the use of electrical discharges to propel projectiles, a concept that wound up receiving funding from the US Strategic Defense Initiative during the latter era of the Cold War. He proceeded to do postgraduate work at the Institute for Advanced Study in Princeton, mixing with the likes of Freeman Dyson and John Bahcall, and moved on to become a tenured professor at Harvard. Long before ‘Oumuamua, his life had begun to revolve around the story told in data. He seems to have always believed that data would lead him to an audacious conclusion, and perhaps primed by his childhood even to expect such an outcome.

I also detect a trace of the mischief-maker, though a very deliberate one. To mix cultures outrageously, Loeb came out of Beit Hanan with a bit of Loki in him. And he’s shrewd: “You ask nature a series of questions and listen carefully to the answers from experiments,” he writes of that era, a credo which likewise informs his present work. Extraterrestrial is offered as a critique of the way we approach the unknown via our scientific institutions, and the reaction to the extraterrestrial hypothesis is displaying many of the points he’s trying to make.

Can we discuss this alien artifact hypothesis in a rational way? Loeb is not sure we can, at least in some venues, given the assumptions and accumulated inertia he sees plaguing the academic community. He describes pressure on young postdocs to choose career paths that will fit into accepted ideas. He asks whether what we might call the science ‘establishment’ is simply top-heavy, a victim of its own inertia, so that the safer course for new students is not to challenge older models.

These seem like rational questions to me, and Loeb uses ‘Oumuamua as the rhetorical church-key that pops open the bottle. So let’s look at what we know about ‘Oumuamua with that in mind. The things that trigger our interest and raised eyebrows arrive as a set of anomalies. They include the fact that the object’s brightness varied by a factor of ten every eight hours, from which astronomers could deduce an extreme shape, much longer than wide. And despite a trajectory that had taken it near the Sun, ‘Oumuamua did not produce an infrared signature detectable by the Spitzer Space Telescope, leading to the conclusion that it must be small, perhaps 100 yards long, if that.

‘Oumuamua seemed to be cigar-like in shape, or else flat, either of these being shapes that had not been observed at these extremes in naturally occurring objects in space. Loeb also notes that despite its small size and odd shape, the object was ten times more reflective than typical asteroids or comets in our system. Various theories spawned from all this try to explain its origins, but a slight deviation in trajectory as ‘Oumuamua moved away from the Sun stood out in our two weeks of data. That deviation also took it out of the local standard of rest, which in itself was an unusual place for it to have been until its encounter with our Sun caused its motion to deviate.

I don’t want to go over ground we’ve already covered in some detail here in the past — a search for ‘Oumuamua in the archives will turn up numerous articles, of which the most germane to this review is probably ‘Oumuamua, Thin Films and Lightsails. This deals with Loeb’s work with Shmuel Bialy on the non-gravitational acceleration, which occurred despite a lack of evidence for either a cometary tail or gas emission and absorption lines. All this despite an approach to the Sun of a tight 0.25 AU.

The fact that we do not see outgassing that could cause this acceleration is not the problem. According to Loeb’s calculations, such a process would have caused ‘Oumuamua to lose about a tenth of its mass, and he points out that this could have been missed by our telescopes. What is problematic is the fact that the space around the object showed no trace of water, dust or carbon-based gases, which makes the comet hypothesis harder to defend. Moreover, whatever the cause of the acceleration, it did not change the spin rate, as we would expect from asymmetrical, naturally occurring jets of material pushing a comet nucleus in various directions.

Extraterrestrial should be on your shelf for a number of reasons, one of which is that it encapsulates the subsequent explanations scientists have given for ‘Oumuamua’s trajectory, including the possibility that it was made entirely of hydrogen, or the possibility that it began to break up at perihelion, causing its outward path to deviate (again, no evidence for this was evident to our instruments). And, of course, he makes the case for his hypothesis that sunlight bouncing off a thin sail would explain what we see, citing recent work on the likelihood that the object was disk-shaped.

So what do we do with such an object, beyond saying that none of our hypotheses can be validated by future observation since ‘Oumuamua is long gone (although do see the i4IS work on Project Lyra). Now we’re at the heart of the book, for as we’ve seen, Extraterrestrial is less about ‘Oumuamua itself and more about how we do science, and what the author sees as a too conservative approach that is fed by the demands of making a career. He’s compelled to ask: Shouldn’t the possibility of ‘Oumuamua being an extraterrestrial artifact, a technological object, be a bit less controversial than it appears to be, given the growth in our knowledge in recent decades? Let me quote the book:

Some of the resistance to the search for extraterrestrial intelligence boils down to conservatism, which many scientists adopt in order to minimize the number of mistakes they make during their careers. This is the path of least resistance, and it works; scientists who preserve their images in this way receive more honors, more awards, and more funding. Sadly, this also increases the force of their echo effect, for the funding establishes ever bigger research groups that parrot the same ideas. This can snowball; echo chambers amplify conservatism of thought, wringing the native curiosity out of young researchers, most of whom feel they must fall in line to secure a job. Unchecked, this trend could turn scientific consensus into a self-fulfilling prophecy.

Here I’m at sea. I’ve been writing about interstellar studies for the past twenty years and have made the acquaintance of many scientists both through digital interactions and conversations at conferences. I can’t say I’ve found many who are so conservative in their outlook as to resist the idea of other civilizations in the universe. I see ongoing SETI efforts like the privately funded Breakthrough Listen, which Loeb is connected to peripherally through his work with the Breakthrough Starshot initiative to send a probe to Proxima Centauri or other nearby stars. The book contains the background of Starshot by way of showing the public how sails might make sense as the best way to cross interstellar distances, perhaps like Starshot propelled by beamed energy.

I also see active research on astrobiology, while the entire field of exoplanetary science is frothing with activity. To my eye as a writer who covers these matters rather than a scientist, I see a field that is more willing to accept the possibility of extraterrestrial intelligence than ever before. But I’m not working within the field as Loeb is, so his chastening of tribal-like patterns of behavior reflects, I’m sure, his own experience.

When I wrote the piece mentioned above, ‘Oumuamua, Thin Films and Lightsails, it was by way of presenting Loeb’s work on the deviation of the object’s trajectory as caused by sunlight, which he produced following what he describes in the book as “the same scientific tenet I had always followed — a hypothesis that satisfied all the data ought to be considered.” If nature wasn’t producing objects shaped like that of a lightsail that could apparently accelerate through the pressure of photons from a star, then an extraterrestrial intelligence was the exotic hypothesis that could explain it.

The key statement: “If radiation pressure is the accelerating force, then ‘Oumuamua represents a new class of thin interstellar material, either produced naturally…or is of an artificial origin.”

After this, Loeb goes on to say, “everything blew up.” Which is why on my neighborhood walks various friends popped up in short order asking: “So is it true? Is it ET?” I could only reply that I had no idea, and refer them to the discussion of Loeb’s paper on my site. Various headlines announcing that a Harvard astronomer had decided ‘Oumuamua was an alien craft have been all over the Internet. I can see why many in the field find this a nuisance, as they’re being besieged by people asking the same questions, and they have other work they’d presumably like to get on with.

So there are reasons why Extraterrestrial is, to some scientists, a needling, even cajoling book. I can see why some dislike the fact that it was written. But having to talk about one’s work is part of the job description, isn’t it? It was Ernest Rutherford who said that a good scientist should be able to explain his ideas to a barmaid. In these parlous times, we might change Rutherford’s dismissive ‘barmaid’ to a gender-neutral ‘blog writer’ or some such. But the point seems the same.

Isn’t communicating ideas part of the job description of anyone employed to do scientific research? So much of that research is funded by the public through their tax dollars, after all. If Loeb’s prickly book is forcing some scientists to take the time to explain why they think his hypothesis is unlikely, I cannot see that as a bad thing. Good for Avi Loeb, I’d say.

And whatever ‘Oumuamua is, we may all benefit from the discussion it has created. I enjoyed Loeb’s section on exotic theories within the physics community — he calls these “fashionable thought bubbles that currently hold sway in the field of astrophysics,” and in many quarters they seem comfortably accepted:

Despite the absence of experimental evidence, the mathematical ideas of supersymmetry, extra-spatial dimensions, string theory, Hawking radiation, and the multiverse are considered irrefutable and self-evident by the mainstream of theoretical physics. In the words of a prominent physicist at a conference that I attended: ‘These ideas must be true even without experimental tests to support them, because thousands of physicists believe in them and it is difficult to imagine that such a large community of mathematically gifted scientists could be wrong.”

That almost seems like a straw man argument, except that I don’t doubt someone actually said this — I’ve heard more or less the same sentiment voiced at conferences myself. Even so, I doubt many of the scientists I’ve gotten to know would go that far. But the broader point is sound. Remember, Loeb is all about data, and isn’t it true that multiverse ideas take us well beyond the realm of testable hypotheses? And yet many support them, as witness Leonard Susskind in his book The Black Hole War (2008):

“There is a philosophy that says that if something is unobservable — unobservable in principle — it is not part of science. If there is no way to falsify or confirm a hypothesis, it belongs to the realm of metaphysical speculation, together with astrology and spiritualism. By that standard, most of the universe has no scientific reality — it’s just a figment of our imaginations.”

So Loeb is engaging on this very charged issue that goes to the heart of what we mean by a hypothesis, about the falsifiability of an idea. We know where he stands:

Getting data and comparing it to our theoretical ideas provides a reality check and tells us we are not hallucinating. What is more, it reconfirms what is central to the discipline. Physics is not a recreational activity to make us feel good about ourselves. Physics is a dialogue with nature, not a monologue.

You can see why Extraterrestrial is raising hackles in some quarters, and why Loeb is being attacked for declaring ‘Oumuamua a technology. But of course he hasn’t announced ‘Oumuamua was an alien artifact. He’s said this is a hypothesis, not a statement of fact, and that it fits what we currently know, and that it is a plausible hypothesis and perhaps the most plausible among those that have been offered.

He goes on to call for deepening our commitment to Dysonian SETI, looking for signs of extraterrestrial intelligence through its artifacts, a field becoming known as astro-archaeology. And he considers what openness to the hypothesis could mean in terms of orienting our research and our imagination under the assumption that extraterrestrial intelligence is a likely outcome that should produce observables.

As I said above, Extraterrestrial should be on your shelf because it is above all else germane, with ‘Oumuamua being the tool for unlocking a discussion of how we do research and how we discuss the results. My hope is that it will give new public support to ongoing work that aims to answer the great question of whether we are alone in the universe. A great deal of that work continues even among many who find the ‘Oumuamua as technology hypothesis far-fetched and believe it over-reaches.

Is science too conservative to deal with a potentially alien artifact? I don’t think so, but I admire Avi Loeb for his willingness to shake things up and yank a few chains along the way. The debate makes for compelling drama and widens the sphere of discourse. He may well be right that by taking what he calls ”Oumuamua’s Wager” (based on Pascal’s Wager, and advocating for taking the extraterrestrial technology hypothesis seriously) we would open up new research channels or revivify stagnant ones.

Some of those neighbors of mine that I’ve mentioned actually dug ‘Oumuamua material out of arXiv when I told them about that service and how to use it, an outcome Ernest Rutherford would have appreciated. I see Extraterrestrial as written primarily for people like them, but if it does rattle the cages of some in the physics community, I think the field will somehow muddle through. Add in the fact that Loeb is a compelling prose stylist and you’ll find your time reading him well spent.