Extraterrestrial

by Avi Loeb

  Yet another scientist, an astrophysicist at McMaster University, went back to the evidence to see if he could provide an answer. He evaluated all the brightness models the data allowed and concluded the likelihood of ‘Oumuamua being cigar-shaped was small and the likelihood of ‘Oumuamua being disk-shaped was about 91 percent. You should keep this percentage in mind when you see the umpteenth artist’s rendering of ‘Oumuamua as a cigar-shaped rock. You should also keep it in mind when reading any explanation for a naturally occurring oblong object, such as the low probability process of melting and tidal stretching along a rare trajectory that passes very close to a star, the value of which is mooted when it comes to ‘Oumuamua, given this analysis.

  Is there a simpler way to achieve the required surface-to-volume ratio for a pancake-shaped object? Yes, there is. You could build a thin, sturdy piece of equipment capable of deviating due to the effects of solar-radiation pressure to exactly such specifications.

  4

  StarChips

  Years before ‘Oumuamua’s discovery, I became interested in the search for extraterrestrial civilizations and the possibility that Earth was not the only planet supporting life. It is an interest that stems from science and evidence rather than from science fiction. I love storytelling and I love science, but as I have confessed, I worry that narratives that violate the laws of physics and encourage a fascination with “improbables” get in the way of not only science but our own progress.

  Anyway, who needs improbables when we have such a strong probable? The existence of intelligent life on Earth is more than sufficient justification to approach seriously the scientific, as opposed to fictional, search for life elsewhere in the universe.

  I have felt this way since the start of my career in astrophysics. But this peculiar interest of mine became public only in 2007, when the cosmologist Matias Zaldarriaga and I proposed to eavesdrop on extraterrestrial radio signals.

  It was a debut, of sorts—and it would prove to be transformative.

  …

  My unusual surveillance project with Matias grew out of my work on the early universe, the cosmic dawn that had attracted my attention back in 1993 when I moved from Princeton’s Institute for Advanced Study to Harvard. A question that preoccupied me then was: When had the stars first “turned on”—that is, when was the moment the laws of nature declared, “Let there be light”? Contemplating the birth of stars would lead me, years later, to ponder how civilizations might eavesdrop on one another. But at the time, it was simply a question that I did not have the means to answer.

  In brief, the effort to look far back in time to the earliest eons of the universe requires listening to the feeble radio emissions from primordial hydrogen, the most abundant element in the universe. This is best done with telescopes capable of searching for that early hydrogen’s signature, an intrinsic wavelength of twenty-one centimeters that is stretched (shifted toward redder—longer—wavelengths, what is called “redshifted”) to the scale of meters by the universe’s expansion since the cosmic dawn.

  By the mid-2000s, this theoretically possible field of experimental research was becoming a reality. Long-wavelength radio telescopes were at last under construction; one of them, the Murchison Widefield Array (MWA) in the desert of western Australia, was an international project involving scientists and institutions from Australia, New Zealand, Japan, China, India, Canada, and the United States.

  As is true for so many of the world’s observatories, the remote location of this kilometers-wide network of antennas was chosen for its lack of pollution—in this instance, not the absence of light pollution but the absence of radio waves broadcast by humans. Our televisions, cell phones, computers, and radios all emit radiation at the very frequencies to which the MWA telescope was tuned in its effort to pick up radio emissions from primordial hydrogen in the early universe—just another example of how technological advances can hinder rather than help astronomers.

  All of this radio-wave pollution led me to a thought one day while I was eating my lunch alongside Matias and others. If our civilization emitted so much noise at that frequency, then perhaps other civilizations did too—extraterrestrial, alien civilizations that might exist out there among the very stars that Matias and I were studying.

  It was an intuitive, spontaneous idea, one that initially elicited a laugh from Matias. But it became something more serious to both of us when I learned of the Foundational Questions Institute (FQXi) inaugural request for outside-the-box projects. With no baggage of past activity on related topics and resting on our reputations as mainstream scientists, I suggested to Matias that we turn this intriguing anecdote into an original research project. The fact that we were cosmologists not associated with the Search for Extraterrestrial Intelligence (SETI) Institute, which has always stood outside of the circle of more fashionable scientific organizations and has less advanced radio detectors and analysis, gave the project more credibility, and funding.

  …

  I have long been aware that within the discipline of astronomy, SETI faces hostility. And I have long found that hostility bizarre. Mainstream theoretical physicists now widely accept the study of extra-spatial dimensions beyond the three we are all familiar with—plainly put, height, width, and depth—and the fourth dimension, time. This is despite the fact that there is no evidence for any such extra dimensions. Similarly, a hypothetical multiverse—an infinite number of universes all existing simultaneously in which everything that could conceivably happen is happening—occupies many of our planet’s most admired minds, again despite the fact that there is no evidence that such a thing is possible.

  My complaint isn’t with such endeavors; by all means, let theories multiply (and, perhaps, produce replicable experiments that provide supporting evidence). In fact, I take issue with the suspicion often visited on SETI. Compared to some flights of theoretical physics, the search elsewhere in the universe for something that is known to exist on Earth, the phenomenon of life, is a conservative line of inquiry. The Milky Way hosts tens of billions of Earth-size planets with surface temperatures similar to our own. Overall, about a quarter of our galaxy’s two hundred billion stars are orbited by planets that are habitable in the way Earth is, with surface conditions that allow liquid water and the chemistry of life as we know it. Given so many worlds—fifty billion in our own galaxy!—with similar life-friendly conditions, it’s very likely that intelligent organisms have evolved elsewhere.

  And that’s counting only habitable planets within the Milky Way. Adding all other galaxies in the observable volume of the universe increases the number of habitable planets to a zetta, or 1021—a figure greater than the number of grains of sand on all of the beaches on Earth.

  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.

  By limiting interpretations or placing blinders on our telescopes, we risk missing discoveries. Recall the clerics who refused to look through Galileo’s telescope. The scientific community’s prejudice or closed-mindedness—however you want to describe it—is particularly pervasive and powerful when it comes to the search for alien life, especially intelligent life. Many researchers refuse to even consider the possibility that a bizarre object or phenomenon might be evidence of an advanced civilization.

  Some of these scientists claim that they simply will not dignify such speculation with their attent
ion. But as I’ve noted, other forms of speculation are enshrined in the scientific mainstream—the existence of multiple universes, for example, and the extra dimensions predicted by string theory, and this despite the fact that there is no observational evidence for either of these ideas and perhaps never will be.

  I will return to the subject of SETI and the academic community’s resistance to it later in this book, since it is a topic that grows even more consequential once you understand the full scope of its implications. For now, suffice to say that in comparison to lots of mainstream scientific ideas, the search for alien life—even the intelligent variety—is not such a speculative endeavor. After all, a technological civilization emerged here on Earth, and we know that there are a lot of other planets like ours out there.

  …

  When Matias and I pursued our questions about eavesdropping on alien civilizations, it was less because we thought we would promptly hear the communications of such civilizations and more because we believed it would help direct attention and effort toward another question: Are we alone?

  In the years that followed my endeavor with Matias, I was drawn to more and more SETI-related issues. What would be an evidence-backed approach to answering its guiding question? And because it joined a list of topics that aroused my curiosity—the nature of black holes, the beginnings of the universe, the possibility of near-light-speed travel—I found myself keeping company with any scholar whose interests overlapped my own, including some scientists who were exclusively identified with the search for alien intelligence.

  Subsequently, Ed Turner, an astrophysicist at Princeton University, and I were the first to consider how one might go about seeking evidence of artificially produced light. We had the idea that we might try to find the glimmer of, say, a spacecraft or a city at great distances with our modern telescopes. Encouraged by Freeman Dyson, we then turned the question on its head and started to wonder whether you could see a city of the size and brightness of Tokyo on Pluto, which at that time was the most distant planet in our solar system. (It has since been reclassified as a dwarf planet.) Our proposition was more theoretical than practical; we never seriously considered focusing our telescopes on the icy ball that is Pluto in search of a city. Rather, our thought exercise was designed to figure out what we (or any civilization, for that matter) might do to seek out a city’s telltale light signature among the twinkling stars.

  It turns out that if you used an instrument of the technological sophistication of the Hubble Space Telescope and sought the signature of artificial light for long enough, you could indeed see Tokyo from the edge of the solar system. And you could tell that the light was intrinsic and not reflected sunlight based on how the source dimmed with increasing distance from the Sun.

  By 2014, my reputation for taking seriously the question of whether or not we are alone in the universe had grown to the point that a writer from Sports Illustrated contacted me to address a fanciful notion raised by the president of FIFA: the possibility of an interplanetary World Cup. However tongue-in-cheek the original comment was, the magazine wanted someone to weigh in on the viability of such an idea. I gamely walked the writer through the various barriers, from the technology necessary to transport teams to the playing fields to the need to agree on atmospheric conditions of play, after pointing out the obvious: first, we needed to find intelligent life to compete with.

  We were closer to that goal than I realized, for it was also around this time, and with far more serious purpose, that Yuri Milner sought me out.

  …

  A billionaire entrepreneur from Silicon Valley, Yuri Milner radiates an intensity of purpose. He was born in the Soviet Union, studied theoretical physics at Moscow State University, received his MBA from the Wharton School of the University of Pennsylvania, and became a stunningly successful investor. Companies he has helped to support include Facebook, Twitter, WhatsApp, Airbnb, and Alibaba.

  In May of 2015, Yuri and Pete Worden, the former director of NASA’s Ames Research Center, came by my office at the Harvard-Smithsonian Center for Astrophysics to encourage me to participate in a new program they were launching, a project they would come to call the Starshot Initiative. They wanted to support a team that would engineer and launch spacecraft capable of reaching the star system closest to ours: Alpha Centauri, a group of three stars orbiting one another some 4.27 light-years from Earth.

  That Yuri would advance such an undertaking was not surprising. In 2012, he and his wife, Julia, had established the Breakthrough Prize. Every year, it awarded prize money to international scholars working in three fields: fundamental physics, life sciences, and mathematics; each prize was worth three million dollars. Within a year, Yuri and Julia were joined by the likes of Mark Zuckerberg, cofounder of Facebook; Sergey Brin, cofounder of Google; and Anne Wojcicki, cofounder of 23andMe, in supporting these awards.

  By 2015, Yuri was thinking of other, more direct and ambitious ways of advancing scientific projects that excited him, so he launched the Breakthrough Initiatives. The focus was unambiguous. The project was to seek answers to two of the most fundamental questions confronting humanity: Are we alone? And can we, by thinking and acting together, make the great leap to the stars?

  Artist’s illustration of Proxima b, the nearest habitable planet outside of our solar system. This planet, discovered in August 2016, has a mass of roughly one to two Earth masses and revolves around Proxima Centauri, a dwarf star with 12 percent the mass of the Sun, at a distance of 4.24 light-years from Earth. Proxima b has a surface temperature comparable to that of the Earth, but because of its proximity to its faint host star, it is believed to be tidally locked, with permanent day and night sides.

  ESO

  Yuri had been fascinated by these questions ever since, at a young age, he read the book Universe, Life, Intelligence, published in 1962 by the Soviet astronomer Iosif Shklovskii. (Shklovskii later released in an English edition, Intelligent Life in the Universe, coauthored with the American astronomer Carl Sagan.) It may have helped that Yuri’s parents named him after the famed Soviet cosmonaut Yuri Gagarin, who in 1961—the year of the younger Yuri’s birth—became the first human to be launched into space.

  In truth, I was prepared to offer Yuri my help even before he had fully framed his request. His bold and sincere interest in exploring whether there was life beyond Earth resonated completely with my perspective. Still, his expectations were daunting. Yuri explained that he wanted me to lead a project to send a probe to the three-star system Alpha Centauri to determine if there was life there. The catch was that it had to be done within Yuri’s lifetime. I asked for six months to come up with the appropriate technological concept.

  Working with my students and postdocs, I critically examined the options for meeting the goal of the Starshot Initiative. An attractive target within the Alpha Centauri system was Proxima Centauri, the star nearest Earth. To our joy, and just a few months after the announcement of Starshot, it was discovered that this dwarf star hosted a planet, Proxima b, in its habitable zone.

  A chemical-propulsion rocket, which is what has sent all of our Earth-launched ships into space, would take approximately one hundred thousand years to reach Proxima b. Yuri was fifty-six, so given his stipulated timeframe—within his lifetime—a propulsion rocket was a nonstarter.

  To get to Proxima b within several decades, we needed a spacecraft capable of traveling at a fifth of the speed of light. Even if we used nuclear fuel, which has the highest energy density of all fuels (other than antimatter, which is unavailable), it would be impossible for a propulsion rocket to reach such speeds. And Newton’s second law of motion—which states that the acceleration of an object depends on its mass and the force acting upon it—dictated that our spacecraft would have to weigh as little as possible too.

  To get an object to accelerate to the desired speed would take a tremendous amount of energy; the lighter the object, the less energy would be required. Correspondingly, our spacecraft’s payload wou
ld have to be no more than a few grams. That led to another challenge. Not only would our spacecraft need to cover the vast distance in much less than one hundred thousand years, but once it reached Proxima Centauri, it had to be able to take pictures and send them back to Earth in a manner we could detect. It had to be light, small, and inexpensive to manufacture. This dictated that the camera and transmitter would be similar to what is in today’s mobile phones. By our calculations, that technology, with some modifications, would suffice.

  The journey to the nearest star system, Alpha Centauri, located about four light-years away, would take tens of thousands of years with a conventional chemical-propulsion rocket (if it had started when the first humans left Africa, it would be completing the trip now). The edge of the solar system is marked by the Oort cloud, stretching halfway to Alpha Centauri. Distances are labeled in units of the Earth-Sun separation (1 astronomical unit). In 2012, Voyager 1 crossed the heliopause, which is where the solar wind collides with interstellar gas.

  Image by Mapping Specialists, Ltd. adapted from NASA/JPL-Caltech

  We discarded ideas and refined the ones left, and eventually we converged on a plan to launch a lightweight spacecraft attached to a reflecting sail—a mirror, essentially. The idea of a solar sail—a manufactured object that would be propelled by the pressure sunlight exerted on it—was centuries old. As early as 1610, Johannes Kepler wrote to Galileo of “ships or sails adapted to the heavenly breezes.” The feasibility of building such an object, however, did not become even remotely possible until the 1970s. For one thing, light transforms into heat when absorbed, as any dog or cat who finds a sun patch to nap in knows. So our mirror could not be just any mirror; it had to absorb less than one one-hundred-thousandth of the light striking it so that it would not burn up. And then we would need to hit that lightsail with an extremely powerful, extremely accurate laser.