We may be alone after all
By Owen Gingerich
September 8, 2014
The Copernicus Complex: Our Cosmic Significance in a Universe of Planets and Probabilities, by Caleb Scharf, Scientific American/Farrar, Straus and Giroux, 278 pp., $26
As a fan of Nicolaus Copernicus, the 16th-century astronomer who “stopped the sun and moved the Earth,” I am always suspicious of any popular book with Copernicus in its title. Mythmaking is rife in the secondary literature. In contemporary science, much is made of the
“Copernican principle,” which holds that Copernicus took away Earth’s centrality and made it merely one of many planets. Consequently, following in the path of Copernicus, we should not think of life on Earth as something unique, or ourselves as very special. But there is no evidence that
Copernicus ever thought he was demoting Earth. The insinuation that this was Copernicus’s principal achievement is a 20th-century invention.
Hence I picked up Caleb Scharf’s Copernicus Complex with considerable apprehension. Would this be another mythmaker? Would Scharf, director of the Columbia Astrobiology Center, lead us astray?
What I encountered was, in the first instance, a brilliantly written and engaging account of modern astronomy. Open the book almost at random and there will be a fresh phrase.
On page 82: “But lest you think that these planets are all smug giants sitting in their chairs close to the roaring fire, consider that some of them are doomed to die.”
On page 114: “The more young worlds are packed around a new star, the more likely it is that they’ll find themselves heading for chaos as their gravitational pull tugs at their siblings.”
On page 43: “The great Sol, our churning sphere of fearsome nuclear energy, is itself an imperious 865,000 miles across. But between the Sun and the outermost major planet, Neptune, is a staggering gulf of about 2.8 billion miles, on average. … Thus, what to us are entire worlds are barely more than specks to the cosmos—mere crumbs whizzing around a modest stellar candle in a cavern of space.”
Churning, fearsome, imperious, staggering—colorful, attention-grabbing descriptions that guide the reader through the history of our five-billion-year-old solar system and the intricate origins of life on Earth. There is some history as well, telling us about an idea that took root after Copernicus conjectured that we weren’t at the center of the universe after all, that we occupy an unimpor-tant, mediocre, and unprivileged position in the cosmos. But here, early in the book, Scharf hoists a red flag that is easily overlooked. This way of thinking, encapsulated in the Copernican principle and firmly embedded in our modern scientific method, he says, “creates some confusing situations.”
A leading corollary to the Copernican principle is that the universe is teeming with intelligent extraterrestrial life, a view championed by many astronomers including Kepler, Huygens, Percival Lowell, and Carl Sagan. In 1961, Frank Drake created a formula to estimate how many technologically advanced civilizations might exist in the Milky Way. The formula can start with the number of stars in our galaxy (roughly 200 billion) and include factors for the percentage of stars with a retinue of planets, how many of those planets would have moderate temperatures where water could exist in liquid form, what fraction would be congenial for evolution to lead to life, what fraction would go on to develop intelligent life with technological capabilities, and so on. By the end of the 20th century, astronomers assumed that roughly a third of the stars would have planetary systems very much like our own and a zone where water could remain in liquid form (essential for life). Since ours was the only planetary system known, it was the sole example from which to extrapolate.
When at the turn of the 21st century the first exoplanets (that is, planets around other stars) were discovered, the news media waxed ecstatic that the chances of finding life on other worlds had increased. In fact, the contrary was the case. Many of these exoplanets were found to be so close to their primary stars that they were much too hot for the presence of liquid water and were therefore uninhabitable. Their discovery, then, actually lowered the assumed probability of finding life elsewhere.
As Scharf moves toward the climactic finale of his book, he becomes more explicit about the drawbacks of the Copernican principle, including its use to raise expectations about finding extraterrestrial life. To the enthusiasts, he cautions, “[O]ne can easily argue that there has never been any data at all on the presence or absence of other life in the cosmos. I don’t want to make this sound too depressing, but it’s true—which is why we’re lucky we’ve discovered beer and chocolate to console ourselves.”
Moreover, Scharf challenges the idea that we and our habitat are not really special. In a chapter titled “There’s Something About Here,” he argues that we are far from occupying an unimportant, mediocre, and unprivileged position in the cosmos. To take but one example, our well-ordered planetary system with the planets nicely spaced and in the same plane seems to be the exception rather than the rule. Quite possibly the moon was formed in a collision between Earth and a Mars-sized planet, which after an era of chaotic confusion, ultimately had a powerful stabilizing effect on our terrestrial system.
Or take the final chapter, “(In)Significance.” Among terrestrial mammals we’re not the most massive, but we’re comparatively close when you consider that at the low end of the range is the pygmy shrew, weighing in at about two grams. I might add that the human brain is the most complex thing known to science, and that we are the only organism able to contemplate that something even more complicated might exist. Now that’s special!
Owen Gingerich is professor emeritus of astronomy and of the history of science at the Harvard-Smithsonian Center for Astrophysics.