Civilizations Beyond Earth

Extraterrestrial Life and Society

Douglas A. Vakoch, Albert A. Harrison, Douglas A. Vakoch, Albert A. Harrison

• Verlag: Berghahn Books
• Jahr: 2011
• ISBN:
  9780857452122
• Auflage: 1
• Thema: Sciences sociales
• Thema: Sociologie

Astronomers around the world are pointing their telescopes toward the heavens, searching for signs of intelligent life. If they make contact with an advanced alien civilization, how will humankind respond? In thinking about first contact, the contributors to this volume present new empirical and theoretical research on the societal dimensions of the Search for Extraterrestrial Intelligence (SETI). Archaeologists and astronomers explore the likelihood that extraterrestrial intelligence exists, using scientific insights to estimate such elusive factors as the longevity of technological societies. Sociologists present the latest findings of novel surveys, tapping into the public's attitudes about life beyond Earth to show how religion and education influence beliefs about extraterrestrials. Scholars from such diverse disciplines as mathematics, chemistry, journalism, and religious studies offer innovative solutions for bridging the cultural gap between human and extraterrestrial civilizations, while recognizing the tremendous challenges of communicating at interstellar distances. At a time when new planets are being discovered around other stars at an unprecedented rate, this collection provides a much needed guide to the human impact of discovering we are not alone in the universe.

Part I

DOES EXTRATERRESTRIAL
LIFE EXIST?

Chapter 1

ARE WE ALONE?

Estimating the Prevalence of Extraterrestrial Intelligence

Seth Shostak

The idea that other thinking beings inhabit the cosmos is surely more popular today than ever before. “Aliens” (the routine shorthand for extraterrestrial sentients) infest books, movies, and television dramas. Recent polls of the American public show that more than half the citizenry believes they infest deep space as well (Pettinico 2011).

The proposal that other beings exist on other worlds dates back at least 2,400 years. To the classical Greeks, the cosmos consisted of everything they could see: the Sun, planets, and naked-eye stars. But the Greeks had the temerity to suggest that there might be other cosmoses, other complete universes.

What Motivates the Hypothesis
That Intelligent Beings Might Be Widespread?

By definition, these other cosmoses could not be observed. However, this fact hardly inhibited speculation, as the Greeks were generally more disposed to theory than experiment. The postulated existence of other universes was a spin-off from the Greek atomic theory that Democritus and others were proposing around 400 BCE. According to these early savants, our world was created from whirling atoms that collided and coalesced after swarming in from infinity. But since the number of atoms itself was believed to be infinite (an assumption that modern scientists are unsure about adopting), and as only a finite number of atoms are necessary to construct our own cosmos, the Greeks concluded that an infinite number of parallel cosmoses also exist. Curiously, this virtually unprovable philosophical notion has its modern-day counterpart. Some theoreticians have speculated that our own universe is but one of an endless number of parallel, but non-interacting universes (Kaku 2005).

In an infinite number of cosmoses, anything that can happen, has happened—over and over. If physics does not preclude the creation of life, then we should expect it in abundance, at least if the universe is large, or “semi-infinite,” enough. This is simply the fecund and unavoidable consequence of “infinite.”

Aristotle offered an alternative to this expansive, multi-world scenario, insisting that our cosmos was unique. Earth—and its mantle of life—was deemed the nexus of creation, the focus of existence. Aristotle’s view dominated thought in the western world for almost two millennia. Only when the discoveries of the Renaissance dethroned our spinning, planetary perch from its central position in the solar system did the possibility of other beings come back into vogue. Copernicus’s De revolutionibus was published in 1543, barely half a century after Columbus’s voyage to the new world, and it is difficult to say which event more radically altered European minds. With the proof of a Sun-centered universe, the Earth had become merely another heavenly body, and a priori no more privileged than Venus, Mars, or Jupiter. The question naturally arose: if Earth is merely one planet among many, why couldn’t earthly life be only one biota among many?

In the four centuries since the invention of the telescope, our concept of the universe has expanded greatly: from a clutch of planets separated from one another by a few light-hours, to a stupefyingly vast omneity that is tens of billions of light-years across. Admittedly, this is not the infinite cosmoses envisioned by the Greeks, but the latter’s hypothesis of inhabited worlds still seems reasonable in view of the universe’s immense size. The visible galaxies are home to approximately 10²² stars, and many scientists find it difficult to believe that in such a mammoth expanse of celestial real estate, only Earth has produced both life and its most recent incarnation, technically sophisticated life.

This “argument from large numbers” is perhaps the strongest motivation for those who search for beings beyond our planet. It may be that planets only occasionally spawn biology, and possibly only a small percentage of these worlds witness the emergence of intelligence. But even small probabilities produce many successes when the number of trials is large.

In addition to this probabilistic argument, a number of recent discoveries in astronomy and biology give credence to the suggestion that worlds with life could be common, and that the evolution of thinking beings might be a frequent occurrence. We will discuss some of these discoveries below. But here, in the bottom line of this section, it is well to state the bottom line of our search for extraterrestrial biology to date: not a single, confirmed bit of life (including the fossilized remains of life) from another world has yet been found.

Habitats That Might Spawn Intelligence

It is the general (and often unstated) assumption of those who search for extraterrestrial beings that such life will have evolved on a planet (or a moon). This seemingly obvious postulate derives from the nature of earthly life’s building blocks: the organic molecules that are the consequence of carbon’s affinity for other atoms. These molecules are assembled into yet more complex structures: proteins, for example, or the DNA molecules that are the blueprints for organisms. At temperatures even modestly above what we consider comfortable, these molecules break apart. At the surface temperature of stars (5,500 C in the case of the Sun), few molecules of any kind can remain intact. At the gelid, bitter temperatures of interstellar space, there is another problem: chemical reactions are slow, and the sort of rapid metabolism we associate with intelligent creatures is impossible. Only planets, which have the possibility for relatively moderate temperatures, seem suitable candidates for the evolution of advanced life.

One might argue that these assumptions reflect a lack of imagination and are unduly anthropocentric. This may be true. The possibilities for sophisticated life in less familiar environments, such as the cold expanses of an interstellar cloud (Hoyle 1957) or the surface of a neutron star (Forward 1980), have been explored by technically adept authors, albeit in works of fiction. Nonetheless, the usual modus operandi of astrobiologists (scientists who busy themselves with the matter of extraterrestrial life) is to be conservative, to be unabashedly terracentric. Many things might be possible, and Nature is undoubtedly ingenious beyond our imaginings. But by assuming that complex life needs the type of environments found on Earth, we can be sure that our postulates have not exceeded the possible. In addition, using the single example of intelligent life that we know (us) provides guidance in what to search for, and where.

Liquid water seems to be a necessity for biology of any type. A fluid environment dissolves organic molecules, so that they can interact in the chemical dance of life as compounds enter and leave cells. Metabolic reactions within cells are also facilitated by an aqueous environment. While other liquids might serve these functions, water remains fluid over a wider range of temperatures than the alternatives that would likely be found on other worlds (ammonia, methane, and ethane). Most astrobiologists opine that liquid water is the sine qua non of life.

There are, even within the provincial confines of our own solar system, at least six worlds other than Earth where liquid water might be found: Venus, Mars, Europa, Callisto, Ganymede, and Enceladus (the last four are moons of the outer solar system). However, these nearby bodies of water, if they exist, do not bestraddle the surface of their worlds; rather, they are sequestered underground (Mars), in the atmosphere (Venus), or beneath thick crusts of hard ice (the moons of Jupiter and Saturn). While life may arise and even thrive in hidden aquifers (for example, microbes exist in rock kilometers deep on Earth [Pedersen 1997]), it seems reasonable to assume that complex, intelligent life would only develop on the surface. The surface, after all, is exposed to stellar radiation, an abundant source of energy. In the case of the Earth, this amounts to about 1,370 watts/m² above the atmosphere. By comparison, the flux of energy from Jupiter’s interior is 250 times less (and this flux is still 1.7 times greater than the amount of energy the giant planet absorbs from sunlight [Hanel et al. 1981]). Without a source of radiant, stellar energy, which on our planet drives photosynthesis—which is the root of the food chain for nearly all terrestrial life—biological abundance and diversity would be less, and consequently the chance that intelligent beings would evolve would also be less.

Maintaining a surface liquid ocean requires the insulation of a reasonably thick atmosphere. Atmospheric gases are used for respiration by both planets and animals on our planet, and in the last two billion years, oxygen has become a plentiful component of Earth’s air. Oxygen is highly reactive and has fostered the high metabolic rates we associate with agile, complex animal life. It may be a requirement for intelligent life on other worlds as well.

Liquid, surface oceans and atmospheres containing oxygen are only some of the possible requirements for the development of intelligent beings, but even these few necessities suggest that sentient beings would most likely be found on worlds that are not only Earth-size (which allows them to retain an atmosphere) but also Earth-like.

As of late July 2013, 925 planets had been found orbiting other, main-sequence, hydrogen-burning stars (Extrasolar Planets Encyclopaedia n.d.) While the overwhelming majority of these are giant worlds, the preponderance of big planets is thought to be the inevitable consequence of the detection technique used for discovery. Most of these bodies are found by measuring the slight changes in the forward-and-back motions of their host stars, caused as both star and planet orbit their common center of mass.

Indeed, two lines of evidence suggest that small worlds, approximately the size of Earth, might be quite common. As the ability to find less weighty worlds has improved, the fraction of small planets found using the “wobble” technique has increased. Less massive worlds are now reliably inferred to outnumber the giant planets that have dominated the planet discoveries of the past. Furthermore, early results from NASA’s Kepler telescope (Kepler Mission n.d.) have already included more than fifty candidate planets that might not only be similar to Earth in mass, but also situated in the “habitable zone” of their solar systems: orbital distances from their suns that would allow them to support liquid water (Borucki et al. 2011). Extrapolation of these first Kepler results suggests that the number of planets in the Milky Way that might be suitable worlds for life numbers in the hundreds of millions, at least.

While most researchers continue to bet on small planets as the most likely locales for intelligent beings, such terrestrial analogs are no longer the only game in town. As mentioned, there is growing evidence that several moons of the outer solar system, most notably Europa, sport hidden oceans. This has opened our eyes to an entirely new class of water-washed habitats in which life might develop. Note that these satellites are far beyond that happy orbital zone where water will neither permanently freeze nor endlessly boil—the so-called “habitable zone.” These promising worlds are warmed not by starlight, but by the changing gravitational tug of their host planets during the course of their orbits, a process known as tidal heating.

Simply on the basis of energetics arguments, it is unlikely that very large, very complex life will evolve in the pitch-dark oceans of a moonlike Europa. But calculations suggest that far larger moons—the size of Earth—could be tidally heated at a hundred times the rate of the jovian moons (Sharf 2006). If moons this size exist around some of the large, extrasolar planets that astronomers continue to uncover, they might be sufficiently Earth-like at their surfaces to permit the emergence of a diverse biota, possibly including intelligent life.

Today, we know something that we could only guess at a decade ago: that planets around stars are commonplace. Indeed, it is reasonable to estimate that there are at least as many planets in the cosmos as there are stars. Within the next half-decade, we will learn if Earth-size planets are frequent or few, with most researchers guessing that the former will prove to be true. Additionally, the realization that moons can be habitable has increased the odds that there are numerous places—many billions in our galaxy alone—where life could have emerged and evolved.

The Evolution of Intelligence

Even if life is copiously abundant, it is not self-evident that intelligence frequently arises. For at least 3.5 billion years, Earth has been carpeted with life—but for all but the most recent sliver of time, that life was beastly and brainless. Intelligence is a very recent development, and some paleontologists would argue that it was also a very unlikely development.

Clearly, biology must reach a certain minimum level of complexity before sentient creatures can take the stage. Multicellular creatures (which only appeared on Earth after several billion years) are an obvious requirement. As we have noted, it is likely that an oxygen atmosphere—with its ability to supercharge metabolism—is also a necessity for intelligence. Competitive environments and social animals seem to be favored in the evolution of sentie...