Dennis Danielson. American Scientist. Volume 97, Issue 1. Jan/Feb 2009.
In 2005 they dug up the remains of Nicolaus Copernicus. At least, they thought it was him, and they wanted to be sure. So the Polish archaeologists at work in the red brick cathedral in Frombork—where Copernicus had served as administrator and in his spare time hatched a new cosmology—turned to the police for help. Without divulging the name of the “victim,” they sent the skuU to the central forensic lab in Warsaw. And the resulting computerenhanced reconstruction of a craggy 70-year-old man so closely matched Copernicus’s own younger self-portrait that the researchers declared themselves 97 percent certain this was truly the face of the iconic astronomer. Even more recent evidence, based on DNA samples, suggests they were right.
But people have been probing Copernicus’s remains for much longer than a few years. He is widely acclaimed as the founder of modern science—the first to get the ball rolling, almost literally. He proposed in the early 1500s that the sphere on which we live is not at the center of the universe but instead belongs to a class of round, rotating bodies known as planets, which circle about the Sun. Such are his prestige and fascination that for 400 years scientists have claimed him as a patron. Today, however, there appear to be fresh opportunities for discerning Copernicus’s scientfic legacy—along with his facial features—with enhanced clarity.
In the middle of the 20th century, astronpmer Hermann Bondi evoked the image of Copernicus to support his and two Cambridge colleagues’ steady-state cosmology. Bondi coined the term “Copernican principle” (CP) to sum up the idea that Earth “is not in a central, specially favoured position” in the universe. Since that time, the CP has continued to be endorsed by scientists even though steady-state cosmology has not.
In 1973, the year of Copernicus’s quincentenary, Stephen Hawking and George Ellis pubUshed The Large Scale Structure of Space-Time and enlisted the Copernican principle to serve Big-Bang cosmology. The geometry of this expanding universe (on a large scale) is such that it would appear the same in aU directions no matter where the observer is located. Thus was the Copernican denial of centrality appropriated by what has now become the Standard Model.
But Hawking and Ellis, rather than restricting themselves to an expUcation of cosmic geometry, openly admitted into their account of the CP what they called “an admixture of ideology”:
Since the time of Copernicus we have been steadily demoted to a medium sized planet going round a medium sized star on the outer edge of a fairly average galaxy, which is itself simply one of a local group of galaxies. Indeed we are now so democratic that we would not claim that our position in space is speciaUy distinguished in any way. [emphasis added]
Yet today, emerging historical weaknesses in such sweeping interpretations of the CP, together with accumulating scientific objections to it, are causing some cosmologists to suspect that the CP may be about due for burial.
The “Privilege of Being the Center”?
The pervasive “pessimistic” interpretation of the Copernican principle, and of Copernicus generally, is growing fraUer as scholars increasingly recognize that the astronomer and his foUowers did not themselves view Earth’s “removal” from the center of the universe as a demotion. According to Aristotle, whose physical theory was the dominant one right into the 17th century, our sphere sat motionless at the center of the universe because earth (among the other elements: water, air and fire) was the heaviest of all substances—and the center of the universe was where heavy things settled. So it was simply Earth’s heaviness, not its nobility or privilege, that accounted for the cosmic centrality of us Earth-dwellers.
Furthermore, writers of the Middle Ages and Renaissance interpreted that location as anything but an enthronement. The poet Dante in his Inferno famously depicted the lowest pit of hell as coinciding with the center of the Earth, which thus constituted the dead center of the whole universe. In 1486, in a work often considered a humanist manifesto, Italian philosopher Giovanni Pico referred to Earth as occupying “the, excrementary and filthy parts of the lower world.” In this prevalent view, therefore, the center was, in more ways than one, the pits. In 1568, a quarter century after the death of Copernicus, French philosopher Michel de Montaigne wrote that we are
lodged here in the dirt and filth of the world, naUed and rivetted to the worst and deadest part of the universe, in the lowest story of the house, and most remote from the heavenly arch …
Earth’s centraUty was thus seen much more as exile than enthronement. But Copernicus broke those bonds. The first account of any astronomical use of the telescope—Galileo’s 1610 Starry Messenger—conveyed its author’s excited realization that Earth (being a planet) is no longer
excluded from the dance of the stars. For … the earth does have motion, … it surpasses the moon in brightness, and … it is not the sump where the universe’s filth and ephemera collect.
Whereas Aristotelian-Ptolemaic cosmology had implied that the place of Earth was both low and lowly, Galileo could see that humanity’s new Copernican perspective was, in more senses than one, uplifting, even uppity.
The other great Copernican of the early 17th century, Johannes Kepler, likewise saw Earth’s new planetary position as a cosmic promotion. We could now imagine ourselves as making “an annual journey on this boat, which is our earth, to perform [our] observations … There is no globe nobler or more suitable for man than the earth”—occupying, as it does, a place “exactly in the middle of the principal globes … Above it are Mars, Jupiter, and Saturn. Within the embrace of its orbit run Venus and Mercury, while at the center the sun rotates …” Only with the abolition of geocentrism, then, could we truly say that we occupied an optimal astronomical location.
The contrary, negative interpretation of Earth’s “decentering,” more familiar to us now, seems to have appeared for the first time in France more than a century after the death of Copernicus. Cyrano de Bergerac, though citing no actual evidence, associated pre-Copernican geocentrism with “the insupportable arrogance of Mankind, which fancies, that Nature was only created to serve it.” Most influentially, French science popularizer Bernard le Bouvier de Fontenelle’s Discourse of the Plurality of Worlds complimented Copernicus—who “takes the Earth and throws it out of the center of the World”—for knocking down “the Vanity of men who had thrust themselves into the chief place of the Universe.”
This was the likeness of Copernicus embraced and reproduced by the Enlightenment and framed magisterially in 1810 by the German poet Johann Wolfgang von Goethe: “No discovery or opinion ever created a greater effect on the human spirit than did the teaching of Copernicus,” for it obliged Earth “to relinquish the colossal privilege of being the center of the universe.”
And this pessimistic, ideological portrait of Copernicus is the one stiU endorsed by a majority of educators and scientists today. Even thoughtful cosmologists such as Paul Davies of Arizona State University continue to assert that the Ptolemaic, geocentric model represented humankind—by “a natural corollary”—as “the pinnacle of God’s creation,” and accordingly that Copernicus carried out our cosmic demotion.
Yet it is increasingly clear that reasonable people need not accept this picture—and that those who want to continue propagating it must offer more by way of support than mere “admixtures of ideology” and stale 200-year-old assumptions. The historical record amply suggests, as University of Alberta cosmologist Don Page puts it, that
the Copernican revolution itself did not necessarily demote humans from a privileged position at the center of the universe but often was interpreted as exalting humans from the dump heap at the bottom to a more heavenly position on a planet.
Perfect vs. Special
But what today is the status of the principle, rather than the portrait, that for more than half a century many scientists have associated with the name of Copernicus? To get some up-to-date answers, I asked a selection of active cosmologists and astronomers for their take on what is so often blithely passed off as textbook fact. The following discussion incorporates a range of their responses, which proved surprisingly diverse.
On at least one point there appears to be relative scientific agreement: Almost everyone now rejects a particular notion that earUer, steady-state theorists associated with the Copernican principle. Bondi not only asserted that the universe would look the same irrespective of an observer’s location in space; he also proposed a “perfect cosmological principle” whereby “the universe presents the same aspect from any place at any time” [emphasis added]. More and more features of the Standard Model have conspired to shatter that cosmologically uniformitarian, steady-state dream of temporal perfection.
Harvey Richer, stellar astronomer at the University of British Columbia and an expert on the age of the universe, cites evidence that certain kinds of galactic evolution were required before life forms could appear and be supported. “For example,” he says,
a certain level of heavier elements was necessary, and these are produced in stars over extended periods of time. So we could not have been “here” many billions of years ago.
The specialness of our own epoch is also indicated by a look into the future. Virginia Trimble of the University of California, Irvine, another stellar astronomer, points out that many galaxies, including our own, face a “last gasp” problem: “The current supply of gas won’t sustain the current star formation rate for very long.” She notes that “there used to be a sort of ‘that’s not Copernican’ tendency to say that infalling primordial gas would keep up the supply for another 10 or 15 billion years at least, so that ‘now’ is average.” But because “the star formation rate really has been dropping monotonically for the last half or so of the age of the universe,” concludes Trimble, we “do live in a somewhat special time.” For the processes we once counted on to ensure galactic sustainability are truly “past their prime.”
In case the perfect cosmological principle of Bondi and the steady-state theorists required any further nails in its coffin, physicists Lawrence Krauss of Arizona State University and Robert Scherrer of VanderbUt recently pubUshed, in the journal General Relativity and Gravitation, a sobering study probing conditions a hundred billion years in the future. If there are observers, the authors note, they will still be able to inspect our own galaxy, because it is gravitationally bound. But given the accelerating expansion of the cosmos overall, other galaxies wül have receded from view, and the cosmic background radiation will likewise be unobservable.
So in that distant future, cosmic expansion itself will have absconded with aU the fossils that today aUow us to trace the archaeology of our universe. Krauss and Scherrer thus predict “the end of cosmology.” Ironically, then, for inhabitants of the extrapolated far-future state of the cosmos, the very expansion that keeps us from beUeving in a static universe wül be invisible and so leave them no alternative to “the standard model of the universe c. 1900.” In such a model, the galaxy is the universe. With the chief signs of cosmic evolution thus obscured, the Ulusion of transtemporal stasis just might return with a vengeance.
For now, though, given the evidence arrayed before us, any large-scale temporal homogeneity is apparently a non-starter. From a chronological perspective, we do indeed dwell somewhere near the center—in what increasingly looks like a cosmological golden age. As Krauss and Scherrer conclude,
We live in a very special time in the evolution of the universe: the time at which we can observationally verify that we live in a very special time in the evolution of the universe!
Muddles about Mediocrity
Moving from time to space, we also find considerable unanimity regarding the geometry associated with the Copernican principle. Copernicus famously declared that “there is more than one center,” something Galileo confirmed observationally when he raised his telescope to the heavens and discovered four “Medicean stars” circling Jupiter. But today’s cosmologists go further, asserting both that there is no (unique) center and that everywhere is the center. How can this be?
As University of Texas Nobel laureate Steven Weinberg points out, the Copernican principle harmonizes with the space-time geometry implied by the Robertson-Walker metric, which describes a spherical universe in four dimensions. The simplest analogy is a three-dimensional sphere—like a perfectly round beach ball—on whose surface ladybugs are located at different points. The ball’s surface is their “space.”
Any one of these bugs might think she is located at the center of her space, because her spatial environment displays the same geometrical features in all directions; it is isotropic. And in one sense, she’d be right, because in whatever direction she measures, she finds herself equidistant from the farthest limit of her space. Yet if she claimed her particular spot as the center, we’d tell her she’s naive, because we know the measurements taken by other bugs elsewhere on the ball will produce exactly the same results.
In the Standard Model universe every point in space likewise behaves, geometrically, as if it were the center. Not only is this claim—often called the principle of mediocrity—consistent with the Copernican principle’s assertion that there is no unique center, but in fact one proposition is the flipside of the other. On the beach ball, each bug’s observations seem to be made from a central point of view; but from a larger perspective, each location is understood to be not so much central as mediocre, or merely typical—something that follows from the isotropy and homogeneity of the “universe” it inhabits.
The claim that spatially our universe is isotropic and homogeneous is known as the cosmological principle. According to Jim Peebles of Princeton, one of the modern pioneers of physical cosmology, it “was introduced as a philosophical/ad hoc/working assumption”—an assumption, Peebles suggests, “which maybe illustrates the influence of the Copernican principle.” But by now, he says, “the observations have spoken” and the cosmological principle “is a done deal.”
The cosmological principle is thus the least problematic among the trio of principles mentioned here. Its very name embodies truth in advertising: It is about cosmology, and its payload is unambiguously geometrical and scientific. The other two, by contrast, seem to invite divergent scientific interpretations. When asked what they see as the relationship between the Copernican principle and the principle of mediocrity, Paul Davies replies that he “uses them synonymously”; Wendy Freedman, director of the Carnegie Observatories in Pasadena, California, simply answers, “None.”
A still greater problem with the Copernican principle as well as the principle of mediocrity is the nonscientific inferences draw from them by both scientists and others. As already mentioned, since the mid-1600s the legacy of Copernicus frequently has been appropriated to serve a misanthropic agenda. Add to this tendency the potential ambiguity, even insult, of phrases like “mediocre,” “not special” and “not privileged,” and it’s little wonder that scientific rigor is often shrouded by amateur philosophizing. Even standard textbooks such as Edward Harrison’s Cosmology present humankind’s “renunciation of cosmic privilege” as being driven by the march of science.
Does Size Matter?
Yet suppose we restrict the Copernican principle and its geometrical, “mediocratic” twin to their scrupulously scientific roles. Isn’t it still true that Copernicus and the process he started rendered Earth and its inhabitants depressingly minuscule relative to the size of the universe?
Copernicus’s affirmation that the Earth’s orbit is immeasurably small in relation to the size of the sphere of the “fixed stars” entailed an enlargement of the volume of the universe by ho less than nine orders of magnitude. And that was before telescopic astronomy got going with its relentless unfolding of immensities. So it’s no surprise if an experienced astronomical all-rounder like Jay Pasachoff of Williams College concludes, “I don’t think that Earth or humankind has any special significance in the cosmos.” Peebles waxes poetic in the same dark vein: “We are exceedingly minor insignificant debris—a little dust—in the grand plan of nature.”
However, some scientists are voicing caveats against such humanly pessimistic readings of the history of cosmology. In words that might have cheered Copernicus himself, Freedman asserts that “there is a difference between being in a significant place and accomplishing something significant.” We may be nothing great “on the scale of the cosmos,” she says, “but the fact that a species developed the curiosity to look out into space and ask these questions is highly significant.”
Such rethinking of the cosmic role of Earth and its inhabitants is being fueled by three powerful trends in cosmology, all of them related directly to issues of the scale or mass of the universe. The most obvious trend, as already hinted at by Richer, is to recognize that we couldn’t be here unless the universe were as big, and therefore as old, as it is. So there’s no point bewailing our smallness relative to the immensity of the cosmos when our very existence is predicated on those staggering proportions.
Then there’s the growing recognition of how cosmically atypical is the stuff we’re made of. Recent estimates put baryonic matter—the atoms that make up galaxies, stars and humans at no more than 5 percent of the mass of the universe (after dark energy and dark matter). Exoplanet hunter Jaymie Matthews of the University of British Columbia reflects that
only three decades ago we believed we were composed of the basic primordial ingredients of the universe- the flour of the Cosmic Recipe. Now we are considered the condiments, or possibly (I would like to think) the spices.
He adds, “Does that make us insignificant? Only if you would prefer to dine in a world where spices don’t exist.”
Thus the “argument from size” can cut both ways. Superficially, the larger the universe is, the smaller and less significant we worry we are in relation to it. Yet the larger the universe is, and the more of it that’s too hot, too cold or otherwise hostile to life, the more exceptional, rare and special do our Earthly habitat and conscious existence appear to be.
A third trend is concerned less with the rarity of our place or our existence than with the specialness—the fine tuning—of the observable universe as a whole. So great appear the odds against a cosmos in which (for example) stars can form, and thus provide the prerequisites of carbon-based life, that many cosmologists are proposing an astonishing number, perhaps an infinitude, of other possible or even actual universes. At least part of their motivation for these “multiverse” scenarios is the desire to come up with a number large enough to even the odds against such a mindbogglingly special universe as ours is.
So even if we grant that life may exist elsewhere in our universe, reasons Don Page, it is still quite possible that life itself is cosmologically “special, since it might occur only in a tiny fraction of the universe or multiverse.” In any case, why should serious minds accept those slogans trying to tell us that bigger is better? Surely, as Page says, “most people would recognize that size alone, or fraction of the universe occupied by life, is not that important.”
One Resurrection and a Funeral
Where does all this leave Copernicus and the Copernican principle? The simple answer is: not necessarily in the same place.
Copernicus achieved the great things he did because he sought beauty in the structure of the world; he wasn’t satisfied with mere models that “saved the appearances” (he wanted to know how the universe really works); he expected nature and mathematics to agree; and he realized that the location, movement and participation of observers must be taken into account if we’re seeking a scientifically coherent picture of the cosmos.
Many of the items on today’s cosmological agenda-string theory, inflation, anisotropy probes, discussions of the multiverse, anthropic selection effects and more-are supported and guided by those robust Copernican impulses. To this extent, Copernicus is alive and with us still.
The cosmological principle remains healthy, though it might be even healthier if cut loose from its alter ego which bears the same “CP” insignia. The principle of mediocrity too might usefully survive, though only if restricted to the one thing it’s really good at: cosmological geometry. The Copernican principle itself, however, is in serious trouble. Page calls it “a working hypothesis that is being abandoned if taken in its original strict meaning.”
Others would like to pronounce it dead already. MIT’s Max Tegmark is among the most willing to offer an obituary. Asked for his assessment of the CP, he replies simply that it is “incorrect and belongs in the dustbin of history.” Citing various broad parameters of specialness and Ime-tuning already mentioned, he argues that
it is manifestly incorrect even in the part of space that we can observe (we live in a galaxy rather than an intergalactic void, on an unusually habitable planet, on its surface rather than in its more voluminous interior, etc.).
The Copernican principle’s sole remaining value, declares Tegmark, is, “as an example of how even very smart scientists can go wrong.”
So it is abundantly clear that at least some are ready to bury its bones. Adds Tegmark, as if this whole chapter of cosmology might be wrapped up in a single text message: “CP RIP”