Our Neighbor’s Grass May Not Be Green ______By Avi Loeb on December 14, 2020
It is presumptuous to assume that we are special and worthy special attention from advanced species in the Milky Way. We may be a phenomenon as ordinary as ants are on a sidewalk. When crossing a sidewalk, we never pay tribute to every ant along our path.
Our Sun formed at the tail end of the star formation history of the Universe. Most stars are billions of years older than the Sun. So much older, that many Sun-like stars have already consumed their nuclear fuel and cooled off to a compact Earth-size remnant, a white dwarf. We also learned recently that of order half of all Sun-like stars host an Earth-size planet in their habitable zone, allowing for the chemistry of life in liquid water on the planet’s surface. Since the dice of life was rolled in billions of other locations within the Milky-Way under similar conditions to those on Earth, life-as-we-know-it is likely common. If that is indeed the case, some intelligent species could be billions of years ahead of us in their technological development. When weighing the risks involved in interactions with less developed cultures, these advanced civilizations may choose to refrain from contact. The silence implied by Fermi's paradox: “where is everybody?”, may mean that we are not he the most attention-worthy cookies in the jar.
As a first approximation to how people look like, it is reasonable to glance at the mirror. This approach relies on the assumption that the viewer shares a common genetic ancestry with all people. But this might not be the case for life that developed independently on disconnected planets. For example, animals and vegetation on the nearest habitable exo- planet, Proxima Centauri b, could be shockingly different from those on Earth. In particular, the animals might possess strange-looking eyes, optimized to detect the infrared radiation emitted by Proxima Centauri, which is a dwarf star with half the surface temperature of the Sun. Since Proxima b is 20 times closer to its star than the Earth is from the Sun, it is expected to be tidally locked – showing the same face to its star at all times. The species residing on its permanent dayside may be completely different from those on its colder nightside, exhibiting distinct patterns of mandatory sleep. Any vegetation on the planet’s surface would adapt to harvesting infrared light, showing a “red edge” at a longer wavelength than plants on Earth. As a result, the grass in our neighbor’s yard may be dark red and not green like ours.
It is even more difficult to forecast how technologies which are billions of years old would look like. In searching for them, we must flag anomalies seen through our telescopes and not sweep unexpected signals under the rug of conservatism. If our instruments are not sensitive enough or our search techniques are inadequate, we will not discover techno- signatures. Processing data without suitable machine-learning algorithms may resemble an ineffective fishing net which never catches fish because its holes are too big.
We design our searches based on what we see in the mirror. After radio communication and lasers were invented, we started searching for radio and laser signals from outer space, and similarly with the technology of light sails. As we imagine new technologies, we may ultimately find the one that would allow us to detect many other species who use it.
However, caution should be taken with anecdotal evidence that is not up to the standards of quantitative scientific evidence. This includes new conspiracy theories without supporting evidence or reports about Unidentified Flying Objects (UFOs) which do not stand up to the scrutiny of reproducibility, the prerequisite for being counted as credible scientific data. UFO reports provide clues that are always on the borderline of detectability. Since our recording devices improved considerably over time, one would have expected that a fuzzy image taken by an old camera from fifty years ago would turn into a crisp image in today’s advanced cameras, thus providing conclusive evidence beyond any reasonable doubt. But the clues stay marginal at all times, implying that UFOs are most likely artifacts in our instruments or in their interaction with natural external phenomena. To gain scientific credibility, any finding of an unusual object must be followed by studying it or other objects of its type quantitatively through well-documented scientific procedures. Scientific evidence restricts our imagination and brings salvation from far-fetched ideas.
Fermi’s paradox is pretentious in assuming that that we carry cosmic significance. The reality may be that we are ordinary and doomed to perish, just like the dinosaurs, due to some catastrophe. Why would our galactic neighbors care about how green our grass is? Given that stars like Proxima Centauri are much more abundant than the Sun, most habitable planets may be covered with dark-red grass, which appears pretty to the infrared eyes of most exo-vacationers. As a result, interstellar tourist agencies may find Proxima b as a more attractive destination than Earth. We could lament, as Enrico Fermi did, why no exo-tourists sign our track-and-trace visitor forms. But better yet, we could travel to Proxima b and entice the locals to visit us, while sharing a water-based drink with them.
ABOUT THE AUTHOR
Avi Loeb Avi Loeb is the former chair of the astronomy department at Harvard University (2011-2020), founding director of Harvard's Black Hole Initiative and director of the Institute for Theory and Computation at the Harvard- Smithsonian Center for Astrophysics. He also chairs the Board on Physics and Astronomy of the National Academies and the advisory board for the Breakthrough Starshot project, and is a member of the President’s Council of Advisors on Science and Technology. He is the author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth”, forthcoming from Houghton Mifflin Harcourt in January 2021. (Credit: Nick Higgins)