Extraterrestrial

by Avi Loeb

  I can imagine their engineers doubting the project’s feasibility. What of damage to the craft due to the impact of interstellar dust grains or atoms? Their board members likely would have nodded, as I did, and noted that a coating of just a few millimeters would prove sufficient to protect the craft and its cameras. The more optimistic of their engineers might well have bemoaned the absence of any deceleration mechanism, and it likely would have been politely pointed out that this was a built-in constraint. Given the distances, the necessary minimal weight of the craft, the speeds at which it had to travel, taking photographs during fly-bys was a sufficiently grand ambition. And grand ambition sums it up well. Perhaps these photographs would let us know if there was vegetation there, or an ocean, or even some signature of civilization, all things we would want to see from up close rather than at the distance of our most powerful telescopes.

  I would be willing to bet that as these scientists made the case for the project, they would have confronted fiscal conservatives who doubted if such an undertaking was worth the price tag. And I imagine in turn the board behind the effort would have pointed out, just as the Starshot board did, that the economies of scale were actually stunning. In our case, I said that, yes, the construction of the laser would be expensive. And, yes, getting the lightsail craft above the planet’s atmosphere would be costly, but the craft themselves would be cheap; the StarChips would cost only in the range of hundreds of dollars each. Which meant that once the costly investments had been made, it would be perfectly reasonable to launch one every several days, aiming them at many hundreds, if not thousands, of targets.

  And then, I hope, the optimists among my distant counterparts, armed with scientific knowledge and accompanying humility, would have pointed out that for all the limitations and risks, launching these lightsail craft represented the next giant leap forward. And enough of these alien scientists would have stared out at their stars, just as we stare out at ours, that—awed by the scale of the universe when placed against the scale of their planet, even their solar system—they would have blessed the effort. They would have concluded that these lightsails were the next, best feasible step toward reaching the stars. And, perhaps, they would have allowed themselves to imagine, just as we are doing, that their fast-moving, peculiar-shaped lightsail craft would someday be seen and understood as an announcement and an invitation: “Welcome to the interstellar club.”

  …

  It requires imagination as well as humility to acknowledge the utter ordinariness of humanity. Both qualities, I believe, are integral to our ability to outrun the great filter. But so is another: our willingness to entertain the simplest explanation for ‘Oumuamua’s properties—that they reflect designed intent, not complex accident.

  Earlier in this book I invoked William of Occam and his famed razor—that is, the injunction that the simplest solution is likely the right one. Whether confronting ‘Oumuamua or any phenomenon, we would be well advised to pick it up. It is a razor that, I have found, struggles to shave an arrogant chin.

  Alas, simplicity is not always in vogue.

  “Should we make our theoretical model more complex so that our explanation of the data will not appear too trivial?” The question came up in a meeting with my postdocs as they described their projects, a few of which were nearing completion. I was initially surprised and then, as they explained their reasoning, sobered.

  The virtue of simplicity should be obvious, especially to astronomers. After all, the power of Copernicus’s heliocentric explanation of the solar system was its simplicity; the prevailing theory he helped overturn, Greek astronomer Ptolemy’s Earth-centered planetary system, demanded ever more torturous contortions the more evidence accumulated. The failure of Ptolemy and the success of Copernicus remains among the most cited to budding astronomers. Their task, centuries of instructors have explained to students, is to seek the simplest explanation to the data and avoid the hubris of the Greek polymath Aristotle, who, for all his genius, was driven by his need for perfection in the universe to declare, despite the evidence, that planets and stars could move only in perfect circles. His error became unquestioned fact for centuries.

  Similarly, for the last decades of the twentieth century, astrophysicists were skeptical of a model of the early universe that was characterized by a small number of parameters—in a word, simplicity. The data was scarce, and the majority of astrophysicists concluded the model was surely naive. But by the beginning of the twenty-first century, enough data had been collected to prove that the universe did indeed start from the simplest possible initial state. The early universe, the data showed, was nearly homogeneous (the same everywhere) and isotropic (the same in all directions), and the complex structures we find in it today can be explained by an unstable gravitational growth of small, primordial deviations from these ideal conditions. This simple model is now the foundation of modern cosmology.

  Given all these cautionary tales, it might seem incomprehensible that a group of Harvard postdocs in the early twenty-first century were wondering aloud if they ought to add complexity to their work. But in fairness, they had good reasons.

  In today’s fierce job market, the single greatest imperative appears to be impressing one’s senior colleagues. The junior scholar can feel it necessary to produce lengthy derivations marked by challenging mathematical complexity. As one postdoc said to me, “I am facing the strategic dilemma of choosing between two options for my future career: long complicated projects or short insightful papers.”

  In many cases, senior scholars wish to make their work nuanced and less accessible to scrutiny. They have learned that sophistication is valued as a trademark of the elite, and many are rewarded accordingly.

  In my research and my mentorship, I try to offer my junior colleagues a counterexample. I tell my own postdocs that accessible short insights tend to stimulate the field, encouraging follow-up work by the scientific community; I urge them to believe, as I do, that brief, intellectually rich work will improve their job prospects; and I tell them that the ability to explain research clearly depends on their describing only those things that they understand and admitting those things they do not. But they inevitably respond: That’s easy for you, chair of the Harvard astronomy department, to say.

  This is a dilemma indeed, and I fear the effect it will have on science in the twenty-first century—and not just within the scientific community. In academia, rewarding complexity for complexity’s sake directs talent and resources in some directions and not others. It can also encourage the isolation of scholarship among a self-identified elite, leading them to disregard the interests of the public that substantially fund their efforts.

  This is a serious problem with consequences that reach far beyond the academy. To understand why this is the case, consider one of the greatest mysteries confronting astrophysicists today: the science of black holes.

  …

  Within weeks of our announcing the Starshot Initiative, in April of 2016, I inaugurated Harvard’s Black Hole Initiative, or BHI—the world’s first center for the interdisciplinary study of black holes. The timing of the two events were close enough that after Stephen Hawking appeared alongside me, Yuri Milner, and Freeman Dyson in New York City, he was able to join me and my colleagues in Cambridge, Massachusetts, to announce the goals of BHI.

  It was fortuitous that Stephen could be involved, and BHI’s launch was auspicious for another reason: a hundred years earlier, Karl Schwarzschild, the German astronomer and physicist, solved Albert Einstein’s equations for general relativity, a solution that described black holes decades before there was any astronomical evidence that they existed. And a hundred years on, astronomers still hadn’t managed to photograph one.

  BHI’s inaugural event was memorable for many reasons. For one thing, the launch of this historic project was a sought-after professional objective for me—one more matchbox in which to collect promising matches. For another, BHI represented an interdisciplinary approach to scie
nce that I have long advocated, bringing together under one roof astronomers, mathematicians, physicists, and philosophers.

  But there were simpler satisfactions as well. At the launch event, a photographer was on hand, and in one picture my younger daughter, Lotem, joined Stephen Hawking and my colleagues on stage. It wasn’t planned, but in hindsight I think her presence was essential. Scientific advances are cross-generational efforts, and the benefits of human progress accumulate over centuries. Think of the many thousands of telescopes that now dot the planet and the few that orbit it, all of which stand in lineal descent from the one Galileo used on the same sky.

  Later, my wife, daughters, and I hosted Stephen and a small number of colleagues at our house for Passover dinner. Of all the speeches that were given over the course of days BHI was announced to the world, the most meaningful to me was the short, several-minute one Stephen gave at my home. Speaking to a small group assembled in our living room, he drew our attention back to the Starshot Initiative and out into the cosmos. “It’s been a busy trip,” he said.

  Last week in New York, Avi and I announced a new initiative that is about our future in interstellar space. Breakthrough Starshot will attempt to build a spacecraft that can reach twenty percent of the speed of light. At that speed, my trip from London would have taken less than a quarter of a second (though longer, if you count customs at JFK). The technology that Breakthrough Starshot will develop—light beams, lightsails, and the lightest spacecraft ever built—could get to Alpha Centauri just twenty years after launch. Up to now, we have only been able to observe the stars from a distance. Now, for the first time, we can reach them.

  Stephen’s words stayed with me, especially because this would prove to be his final visit to the United States. He had told our little gathering, “I hope to return soon in support of the new Black Hole Institute,” but he passed away less than two years later, never to witness the project’s success or the interstellar exploration of which he had dreamed.

  Another set of remarks from around this time has also stayed with me—but for less happy reasons. At that first BHI conference, a philosopher concluded his talk by stating that “conversations with some prominent theoretical physicists led me to conclude that if the physics community agrees on a research program for over a decade, then it must be correct.” My prompt skepticism brought to mind a single word—or, actually, a name: Galileo.

  Galileo is supposed to have declared after looking through his telescope, “In the sciences, the authority of a thousand is not worth as much as the humble reasoning of a single individual.” Einstein, centuries later, got at the same idea when twenty-eight scholars contributed essays to a 1931 book titled A Hundred Authors Against Einstein that declared his theory of general relativity wrong. He is supposed to have replied that if he were wrong, then one author with conclusive evidence to disprove the theory would have been sufficient.

  A guiding premise of the Black Hole Initiative is valuing the conflicting insights arising from the reasoning of many individuals approaching problems from differing vantage points. That participants were all interested in slightly different things was a strength. The astronomers were hoping to get the first image of a black hole; the physicists were focused on solving an apparent paradox about how the laws of physics are affected by black holes; and the mathematicians and philosophers were working to figure out the nature and stability of the singularity at the center of a black hole. (The philosophers, in particular, were an essential part of this team, for an honest philosopher constitutes the canary in the coal mine, warning the gathering if intellectual honesty is violated.)

  If there was a common denominator at BHI, it was our shared excitement over seeking data to better explore the unexplained anomalies and questions about black holes. And what challenges they are. Here’s a short list.

  A major anomaly about black holes is what scientists call “the information paradox”: Quantum mechanics states that information is always preserved, and yet black holes can absorb information and then evaporate into purely thermal blackbody (information-free) radiation, a phenomenon demonstrated by Stephen Hawking. Do the laws of physics break down at the edge of black holes or is something else going on?

  Another major anomaly about black holes is the fact that they seem to “disappear” matter. Where does the matter pulled into a black hole go? Does it collect into a dense object at the center of the black hole, or does it exit our universe and emerge in another one, like water draining into a distant reservoir?

  But more generally, might black holes provide insights that would direct us toward unifying general relativity and quantum mechanics? On his deathbed, Einstein sketched his last thoughts on this theory but did not resolve the tremendous challenge. Stephen Hawking similarly spent his final years considering whether properties of black holes would resolve the challenge. While neither man’s considerable intellect was sufficient to crack the problem, many astrophysicists and cosmologists are working in their wake.

  Finally, one question bothering astronomers at the time of the BHI’s founding was less an anomaly than a glaring gap in our evidence. While we had decades of data confirming the existence and properties of black holes, we had never managed to photograph one.

  That changed in 2019. The story of how it happened—how the very first photo of a black hole was taken and how humanity was able to obtain such a crucial piece of evidence in our ongoing investigation of this cosmic mystery—is a wonderful illustrative example of how the deliberate, collaborative pursuit of evidence can accomplish the previously unaccomplished. For those of us who don’t consider ‘Oumuamua to be a closed case, who hope it proves sufficient provocation for humanity to bet on the more ambitious projects, the story of this incredible accomplishment is also a reminder that when humanity works together, we can achieve the unimaginable—feats of research, discovery, and technological innovation that under other circumstances would have been impossible. For instance, constructing a telescope the size of Earth.

  …

  In a 2009 article for Scientific American that I coauthored with my former postdoc Avery Broderick, we called the challenge “shooting the beast.” For starters, there is the distance. Sagittarius A* is the closest supermassive black hole to Earth, twenty-six thousand light-years away. Another target we were first to recommend, in a dedicated paper published in the Astrophysical Journal that year, was the black hole that was eventually photographed, M87, which is fifty-three million light-years away but is substantially bigger. Still, at that distance, photographing it was likened to trying to capture an image of an orange on the surface of the moon.

  Hence the need for a really big telescope. More accurately, what was needed was an Earth-size interferometer formed by linking radio dishes across the face of the planet. Accomplishing this required the collaboration of many sites around the world, an observational effort led by my BHI collaborator Shep Doeleman. It resulted in what was dubbed the Event Horizon Telescope (EHT).

  Astrophysical black holes, by definition, do not emit light on their own. In fact, they do the opposite—they consume light, along with everything else. But the matter, typically gas, that swirls around them does emit light as it heats up under the stress of the black hole’s gravity. Some of that light escapes the pull of gravity, and some is absorbed by the black hole, and the result is a silhouette surrounded by a ring of light that delineates the region around the black hole from which light cannot escape. This is the defining feature of a black hole, its event horizon, or the spherical boundary at which material flows only one way. It is the ultimate prison—you can get in but you can never get out. Astrophysical black holes are hidden behind event horizons, so, just as in Las Vegas, what happens inside the horizon, stays inside the horizon. No information leaks out.

  And that is what the EHT was seeking to do: directly observe a black hole and photograph its silhouette. The mission was years in the making. The Black Hole Initiative helped process the data that produced the images that
, for weeks in April of 2019, were ubiquitous, and not just within the halls of academia. This globe-spanning effort, requiring a globe-spanning telescope, produced a photograph that galvanized the imagination of humanity. A decade earlier, Broderick and I had sketched what we thought might be the result for the black hole in the giant galaxy M87, and it was particularly rewarding to see a real image of a black hole resembling those sketches appear on the front pages of major newspapers and magazines.

  There is a clear link between this success and my work on SETI. An explicit goal of the Black Hole Initiative is to spark interest not only across academic disciplines but also in the general public. We want—indeed, need—to capture the public’s imagination. We need our detective stories read, need our efforts to match theory with the rigorous contact with data sufficiently understood so that all of humanity can celebrate scientific successes. Only in this way will we cultivate as many bright, aspiring minds as we need to to meet the current challenges and those of the future.

  Then, too, scientists owe the public—literally. We are funded by the public. In large measure, most scientific advances can be traced back to government grants paid for by public taxes. Thus, every scientist who has directly or indirectly benefited (which means pretty much all of us) bears a burden to explain not only the work but also the methods used in that work. We have an obligation to report back about our most exciting discoveries and conjectures on topics that resonate with the public, such as humanity’s cosmic origins, black holes, and the search for extraterrestrial life.