by Kenneth W. Krause.
Kenneth W. Krause is a contributing editor and “Science Watch” columnist for the Skeptical Inquirer. Formerly a contributing editor and books columnist for the Humanist, Kenneth contributes regularly to Skeptic as well. He may be contacted at email@example.com.
Wonderful things sometimes come in small packages. Such an observation—though certainly true—would normally seem inappropriate as a prelude to a new book about something as unimaginably huge as the cosmos. That is, unless the book consisted of the very brief and superbly crafted essays of Neil deGrasse Tyson, frequently commended as the planet’s most charismatic and telegenic astrophysicist. Tyson has packaged the universe into forty-two modest yet appreciable gifts, a veritable high-end display case of science history and cutting-edge cosmology accented with occasionally reluctant but often witty social commentary. In Death By Black Hole, Tyson explores everything from Goldilocks to God, highlighting the origin of stars and the life that, now and again, arises from their violent demise.
Hundreds of light-years deep, an interstellar gas cloud circles an ordinary galaxy’s heart, patiently awaiting its opportunity to collapse and conceive a star. Ironically, the cloud must first cool to less than 100 degrees above absolute zero in order to craft a star with the 10-million-degree core required for thermonuclear fusion. Only then can otherwise unruly atoms collide and adhere to fashion large, carbon-based molecules that, at some point, might seed the universe with the building blocks of planets, people, and perhaps much more.
That supernovas are primarily responsible for the universe’s varied collection and relative mix of heavy elements is the most under-appreciated discovery of the twentieth century, writes Tyson. Rare, high-mass stars, through traditional thermonuclear fusion and neutron capture, manufacture not only the elements common to life as we know it—hydrogen, nitrogen, oxygen, and carbon—but much weightier things as well. Fusion demands higher and higher temperatures as the elements grow heavier. Energy is released at nearly every stage, until the star is ready to make iron. Calamity ensues, at least for the star and everything near it. Energy is absorbed; the stellar mass collapses, and temperatures soar so rapidly that the star blows itself to bits, beaming a billion times brighter than ever.
The cosmos as a whole, however, reaps magnificent rewards—as Earth did when it materialized 4.6 billion years ago. After condensing out of a proto-solar gas cloud, a very young and unsightly planet continued to accrete particles until it grew big enough to absorb impacts from mineral-studded asteroids and water-laden comets. These early beatings may have been frequent enough to create the oceans as we currently know them. Volcanic out-gassing and the house-sized hunks of ice that continue to bombard Earth’s upper atmosphere help too. In any case, at 93 million miles from the Sun, our planet appears to have located a very special home for itself.
Or has it? The space between Venus and Mars is often referred to as the “Goldilocks habitable zone,” and many extrapolate from their solar-centric experience to conclude that only planets within similar distances from their stars can nurture life. But hold on. First, the Sun was a third less luminous back when Earthly life began to develop. Second, not all stars are created equal. A small, cool, low-luminosity star will tidally lock any planet within its comfort zone—which of course will be much nearer to a smaller star—much as Earth tidally locks the Moon. Thus, all planetary water would either evaporate or freeze, depending on its hemisphere. Conversely, although they provide relatively sprawling sweet spots for life, large, hot stars are rare and short-lived. The evolution of complex life, on the other hand, takes a very long time.
Recent and exciting discoveries, however, inform us that our old, stellar-distance based definitions of “habitable zone” are just plain worn-out. According to Tyson, in fact, Earth’s first life forms probably never experienced the light of day. “Extremophiles,” as they are now called, thrive on various sources of energy, including the geothermal belches that escape from ridges along the ocean floor. We now know as well that overwhelming gravitational forces heat icy Europa from within. Jupiter, its giant, gaseous host, creates the energy tidally—simply by tugging much harder on Europa’s proximate side than on its distal side. Indeed, substantial evidence suggests a sea of slushy water sloshing about only a kilometer beneath the satellite’s surface.
Which is not to imply that water is necessary for the creation of life. If only some sort of liquid is essential, as many believe it is, perhaps ammonia or ethanol—both plentiful in the universe, and both much more accommodating than water in ultra-frigid environments—will do. Although frozen water has been discovered on Titan, Saturn’s largest moon, temperature and air pressure have liquefied the satellite’s more considerable supply of methane. In 2005, Europe’s Huygens probe relayed images that seem to depict rivers and lakes full of the stuff. No wonder some astrobiologists now tout Titan as a ripe experimental window into Earth’s ancient past. Given such potential, then, one might readily infer that the cosmos is teaming with life. After all, ninety percent of the universe’s constituents are the hydrogen atoms from which all others are eventually created.
But intelligent life is another matter. Some estimate that, over the millennia, ten billion different species have evolved on Earth. In isolation, of course, that reality offers creatures like us a paltry one in ten billion chance of existence. Consider also that about half of all “stars” are actually binary or multiple systems driving chaotic or elongated planetary orbits and, thus, extreme terrestrial temperature swings. Faced with a thousand reasons to believe and a thousand reasons to disbelieve in deep space intelligence, maybe all we can do is to keep listening and transmitting.
Humans have been sending radio waves into space at the speed of light for nearly 100 years now. Although our goal has seldom been interstellar communication, radio is especially appropriate to that task because electromagnetic waves generally require no travel media and because radio waves specifically penetrate very efficiently through gas and dust clouds. To date, our “radio bubble,” as Tyson calls it, encompasses every star around which a planet has thus far been found, including Alpha Centauri, at 4.3 light years away, Sirius, our sky’s brightest star at ten light-years out, and about 1000 others. So if aliens are listening, they might have an opportunity to partake in any message sent at frequencies greater than 20 megahertz, including FM radio and television. Unfortunately for them, other signals are seized by our ionosphere and reflected back to the surface.
But there are more serious complications. Despite their relative efficiency, radio waves weaken even as they race through the vacuum of space. Cosmic rays, the microwave background, star formation, and radio-emitting galaxies are among the many forces that will ultimately obscure the most purposeful and well intended tiding. In order to gather a television station’s carrier signal only, an extraterrestrial would have to construct a receiver with a collecting area fifteen times larger than that of the 3000-foot Arecibo telescope in Puerto Rico, which is our planet’s largest. And if the yearning stargazer actually wanted to decode our message’s content, it would have to first adjust for Doppler shifts caused by the Earth’s rotation and revolution and, then, build a dish about twenty miles wide, or 400 times Arecibo. That’s a lot of work—and for what? A weekly dose of The Walking Dead and reruns of Dr. Phil.