Ptolemy (second century) was the first and boldest in a long succession of spin doctors for the primacy of human beings. The whole universe, he postulated, rotated around us, with the Earth sitting at the center of Heaven itself. Any marketing consultant will tell you that positioning is everything, and center–of–the–universe is hard to beat. A Polish astronomer named Copernicus (1473–1543) rudely pointed out: Sorry Earthlings, we spin around the Sun, not vice versa. . . . Giordano Bruno, a sort of sixteenth–century Carl Sagan, popularized these concepts, . . . saying, among other things, that “innumerable suns exist. Innumerable earths revolve around those suns. Living beings inhabit these worlds.” . . . Bruno’s crime, like Galileo’s, was to undermine the uniqueness of our planet, and by doing so, to threaten the intellectual security of the religious dictatorships of his time. . . . Over time, advances in astronomy have relentlessly reinforced the utter insignificance of Earth on a celestial scale.
So wrote Nathan Myhrvold in an article titled “Mars to Humanity: Get Over Yourself” in Slate (and excerpted in Time) one week after NASA’s announcement in August 1996 of possible evidence of life in a Martian meteorite. Myhrvold’s story of sixteenth–and seventeenth–century astronomy is part of the common positivist telling of history that, to its adherents, marks the victory of science over religious superstition. Positivists begin with Nicolaus Copernicus, Bruno, and Galileo, who removed man from the center of the universe, and follow with later scientific discoveries that have pushed us into ever more remote regions of the universe. This idea of our “mediocrity” has come to be known as the Copernican Principle (CP, for short). It enjoys wide public acceptance and has dominated higher education for several decades—many introductory astronomy texts still recount the CP within the positivist model.
Over the last four centuries the CP has evolved from a simple claim that the Earth is not located at the center of the solar system to an expansive philosophical doctrine that the Earth, and particularly its inhabitants, are not special in any significant way. This principle is sometimes seen in opposition to the Judeo–Christian belief that the fate of humans is central to God’s creation. Why being at the edge of the universe is supposed to be so devastating is never fully explained: after all, even among those in the medieval church who adopted the Aristotelian/Ptolemaic geocentric model, man was not “the very center of creation.” As Thomas Kuhn describes the fourteenth–century Christian cosmology in The Copernican Revolution, “Man’s location, too, is intermediate: the Earth’s surface is close to its debased and corporeal center but within sight of the celestial periphery which surrounds it symmetrically. Man lives in squalor and uncertainty, and he is very close to Hell.” Most of the Church’s attachment to the Aristotelian/Ptolemaic model was a result not of arrogance or narcissism, but of the incorporation into Christian theology of Aristotelian physics. If anyone should be blamed for placing the Earth at the center of the universe, it is Aristotle, not the Church.
It is useful to distinguish between two versions of the CP: the simple physical claim of the non–centrality of the Earth and the non–uniqueness of the substances of which it is composed, and the more general philosophical extrapolation to the claim that the Earth and its inhabitants are not special in any significant way. While CP advocates can rightly point to the astronomical discoveries in support of the physical thesis, they have been frequently disappointed in their quest to verify the more expansive philosophy. For example, CP advocates have often described the other bodies in the solar system as only slight variants of the Earth, believing that life and even advanced civilizations existed on other planets, the Moon, and even the Sun. Just a few decades ago some astronomers were still speculating about the possibility of advanced life on Venus and Mars, which the Venera and Viking missions respectively have revealed to be lifeless.
Two recent events show the contemporary influence of the CP philosophy. The first was the claim by NASA scientists that they had discovered the remains of ancient Martian life in the meteorite ALH84001. This event inspired Mr. Myhrvold to offer his grand pronouncements about the ubiquity of life in the universe (both simple and advanced) and the demise of Christianity. As of this writing, the case for ancient remains of life in ALH84001 is very weak. Even if life’s remains are found on Mars, as one day they probably will, this will not prove life is widespread in the universe. It would also have to be shown that life arose there independently rather than by contamination from Earth. The true lesson taught to us by ALH84001 and the multiple probes sent there since the 1960s is that Mars, possessing the most Earth–like climate of any other planet in our solar system, is apparently not presently capable of supporting life, even with the help of Earth’s microbes early on. What at first seemed like a major success for the broad version of CP has instead turned out to be a major blow against it.
The second event was the discovery of the first (giant) planet orbiting another solar–like star in October 1995. Since then, over two–dozen additional giant planet candidates have been announced. They have been accompanied by nearly half as many popular science books on the subject, almost all telling basically the same story—the newly discovered planets prove the solar system is not special, greatly improving the probability that extraterrestrial intelligence (ETI) exists. The great majority of these works cite the CP favorably in their introductory chapters.
But again, the philosophical CP is undermined rather than supported by these new findings. Although the discovery of these new planetary systems does show that the Sun is not the only star with orbiting planets, it turns out that those planets have very different characteristics than those in our solar system. Most of the new planets have highly eccentric orbits. Further, they have orbital periods as short as three days, while the shortest orbit in our system is Mercury’s eighty–eight days. And we have yet to find among the several stars considered to be “twins” of our own any with giant planets whose masses and orbits are at all close to that of Jupiter. All this implies that the solar system is not typical, a conclusion obvious to anyone who does not already assume the CP.
There are other examples from astronomy that demonstrate our special place in the universe. The solar system occupies a position in the disk of the Milky Way approximately halfway to its edge and in–between two spiral arms. We now know enough about the structure of our galaxy to understand why our location should be preferred over others. If our solar system were closer to the center of the Milky Way or closer to one of its spiral arms, we would encounter harmful radiation from supernovae and perturbations from stars that would send Oort cloud comets careening into the inner solar system. If the solar system had formed farther out in the disk of the Milky Way, there would not have been sufficient heavy elements to build a planet capable of supporting life. While most textbooks discuss the Sun as if it were a typical star, it is a more massive star than 90 percent of the stars in the Milky Way. The Sun is anomalous in other ways, including its composition, brightness variation, and Galactic orbit. It can be plausibly argued that each of these characteristics must be exactly as it is for advanced life to exist on Earth.
The general recognition that the universe appears to be finely tuned for humans is described by one of several forms of the Anthropic Principle (AP). The AP has been acknowledged for about a quarter of a century, but it was not until John Barrow and Frank Tipler published their massive technical work The Anthropic Cosmological Principle in 1986 that it was widely discussed. The Weak Anthropic Principle (WAP) is the most basic version—the simple recognition that the parameters we observe in our environment must not be incompatible with our existence. It is difficult to quarrel with the simple physical interpretation of the WAP: it is just a type of observer selection bias. We should not be surprised to observe, for example, that we are living on a planet with an oxygen–rich atmosphere, for the simple reason that we require oxygen to live. The WAP “explains” why we should not observe ourselves to be living on, say, Titan, but it fails to account for the origin of the oxygen in our atmosphere and hence for the rarity of planets with oxygen–rich atmospheres. However, Barrow and Tipler, no doubt motivated by the philosophical CP, have burdened the basic physical interpretation of the WAP with unwarranted philosophical extrapolations. In considering the WAP with regard to the observable universe, they claim that we ought not be surprised at measuring a universe so finely tuned for life, for if it were different, we would not observe it.
But as Richard Swinburne first explained and as William Lane Craig and John Leslie later argued, we should indeed be surprised at observing features of the universe that are highly improbable and are necessary for our existence. The strength of the argument against the CP—and in favor of design—is in the simultaneous fine–tuning of many aspects of the universe, from the atomic and cosmological constants to biochemistry.
Claiming that the universe is not special because it is one of an infinite set of universes, each with its own unique set of physical constants, is perhaps the grandest extrapolation of the philosophical CP. The so–called Many Worlds or World Ensemble hypotheses are invoked to try to explain away the “disturbing cosmic coincidence problems,” as cosmologists often phrase the issue in their technical papers. These proposals, apart from their scientific problems, can be criticized on philosophical grounds. An actual infinite set leads to logical inconsistencies, and there is no reason to think that an infinite set of universes should have a completely random distribution in their properties. World Ensemble advocates are obviously driven by the desire to avoid the “God–hypothesis,” and, in adopting such extravagant and unnecessary assumptions, they are effectively conceding that the WAP has been impotent in discrediting the teleological interpretation.
By insisting that the apparent fine–tuning of our solar system’s parameters is just due to chance, rather than pointing towards a greater truth, astronomers have missed out on many discoveries. Their reluctance to admit explanations other than chance has limited our understanding of the Earth’s habitability. There is, in sum, a great deal about Planet Earth and its inhabitants that is anything but “mediocre.” It is not scientific reason or evidence that stands in the way of exploring the finely tuned conditions that make possible our place in the cosmos but a dogmatic commitment to the philosophical CP—a commitment apparently motivated by fear of what we might discover.
Guillermo Gonzalez is Research Assistant Professor of Astronomy at the University of Washington in Seattle. Hugh Ross, who holds a Ph.D. in astronomy from the University of Toronto, is President of Reasons to Believe, an institute founded to research and proclaim the factual basis for faith in God and the Bible.