THE COPERNICUS COMPLEX
At a rather pleasant spot in the Aegean Sea in the third century B.C., on the vine-rich island of Samos off the western coast of what is now Turkey, the Greek philosopher Aristarchus had just had a brilliant idea. He proposed that the Earth spun and moved around the Sun, placing this scorching solar orb at the center of the heavens. It was, to say the least, a bold notion—Aristarchus’s idea of “heliocentrism” was as outrageous in his time as Copernicus’s revival would be in the distant future.
Records of Aristarchus’s works are fragmentary, and most concern the clever geometrical analyses that he used to argue that the Sun is significantly larger than the Earth. But it’s clear that from that insight he arrived at the idea that the Sun was central to the known cosmos, and that the stars were extraordinarily distant. This was a huge conceptual leap to ask of people. It also required understanding a phenomenon called parallax.
Parallax is earthbound as well as celestial, and is an easy concept to grasp. Close an eye and hold one hand up, fingers spread and viewed on edge. If you move your head side to side you will see different fingers appear and disappear from behind each other as your vantage point, or your angle of view, changes. This is all that parallax is: the apparent change in where distant objects appear relative to each other, depending on a line of sight. The farther away those objects are, the smaller that apparent change—the smaller the perceived angular displacement between them.
Part of Aristarchus’s bold argument involved the fact that the stars in the night sky didn’t appear to have any parallax; they never moved among themselves. So if the Earth were not stationary at the center of all existence, he reasoned, the stars must be so distant, so enormously far away from us, that we couldn’t measure their parallax as the Earth moved its position.
Not long before Aristarchus made his ideas known, the great philosopher Aristotle had already dismissed the possibility that the stars were any more distant than planets by appealing to this same lack of parallax, among other things. Aristotle’s argument was founded in reason and common sense. It built on even earlier ideas that the Earth was central to existence. The way he put it was simple: if no parallax could be seen in the stars—they did not shift around relative to one another at all—they must be all affixed to some layer of the sky that surrounded us at the unmoving origin.
All of which sounds logical, except that Aristotle’s own preferred cosmology (elaborating on ideas from his mentor, Plato) consisted of approximately fifty-five thick, crystalline, transparent spheres concentrically nested about the stationary Earth and carrying the planets and stars about their business. In this geocentric universe we were at the focus of all natural motions, with the stars and planets simply following perpetual circular paths around us as the crystalline spheres slid and rotated.
You might well ask why it took fifty-five spherical crystalline layers for Aristotle to build his cosmology. Part of the reason is that he had to justify a system of cosmic mechanics, a transfer of forces whereby one shell would rub on another, pushing it around—a great scheme of motions and machinery to keep everything tracking through the sky. This structure was intended to deal with the other most critical issue facing would-be cosmologists of the time; unlike the stars, the planets do move around the skies in a complicated fashion.
These tricky motions were a major piece of the puzzle that Aristarchus, and later Copernicus, tried solving by displacing the Earth. The word “planet” is derived from the Greek phrase for “wandering star,” and our brightly reflective planets most certainly do wander. Not only do they appear to move relative to the stars, noticeably shifting in position as the nights go by; sometimes they reverse course, performing a celestial loop-the-loop over a few months before carrying on. Planets like Venus and Mercury are even more subversive; often they’re nowhere to be seen. And even the speed of planetary paths across the heavens seems to be slower and faster at different times, with the brightness of these miscreants changing as well.
So you might think that when Aristarchus proposed his heliocentric system there would have been a huge sigh of relief, because placing the Earth on its own circular path around the Sun quickly provided a solution for much of the curious backward motion of the planets—what would later be known as “retrograde” movements. In this configuration the simple reason for such odd behavior was that our own vantage point was shifting as the Earth itself moved in a circle. There would naturally be times when our motion relative to a planet was either forward or backward, and our distance from a planet would change—lowering or raising its apparent brightness.
It was a lovely, elegant, and fact-based idea—and many people hated it. If the Earth moved, there should be a noticeable parallax among the stars, which surely couldn’t be that far away. And apart from this lack of observable parallax, displacing the Earth from its vaunted central position was anathema; it was ludicrous to consider that the very hub of our existence was not at the core of everything, and so poor Aristarchus got it in the neck.
The other part of this antipathy toward heliocentricity likely came from distaste for ideas that hinted of pluralism. In opposition to the likes of Plato and Aristotle, who argued for a divine and unique creation of the Earth, Greek thinkers such as Democritus and Epicurus instead advocated a picture of reality rooted in the notion of indivisible pieces and empty void—atoms and space. These atoms weren’t atoms as we now know them, but a philosophical concept of units of matter—too small to be seen, solid and uniform within, varied in size, shape, and weight—that could be used to describe an infinite number of structures. The idea of atoms led these thinkers to consider that the Earth was unlikely to be unique. Far from it—there should be an infinite number of inhabited worlds located within an abstract form of space and time and what, in retrospect, amounted to parallel universes. Not surprisingly, the plurality of worlds did not sit well with anyone following the Platonic or Aristotelian schools of thought.
What happened instead was that a number of natural philosophers in the decades following Aristarchus came up with a geocentric “fix” to account for the annoyingly unconventional motion of the planets across the skies, and to keep Earth rooted as the unique center of existence. Their solution to the dilemma of celestial movements probably first originated almost a century after Aristarchus and Aristotle butted heads, with the astronomer and geometer Apollonius of Perga around the turn of the second century B.C.
Later on, this explanation was subsumed into the works of Claudius Ptolemy. Living some three hundred years after Aristarchus, the Greek-Roman citizen Ptolemy resided in Egypt under the rule of the Roman Empire. He was a prolific thinker, producing significant works on many topics, including astronomy, geography, astrology, and optics. And most important, he produced an astronomical treatise known as the Almagest that laid out a cosmological vision that would stick for the next 1,400 years.
In Ptolemy’s system, the Earth is firmly stationed at the center of the universe. Moving outward are the Moon, Mercury, Venus, then the Sun, and then Mars, Jupiter, Saturn, and the fixed tapestry of stars—all following circular paths. To translate this arrangement into the messy movements seen in our skies, he added a clever set of extra motions along special circular paths called deferents and epicycles. And these were, rather ironically, centered on a location offset from the Earth (a peculiarity that seems to have escaped the scrutiny of zealous geocentrists across the centuries).
In this ingenious arrangement, the planets and the Sun move around the smaller perfect circles of the epicycles, which in turn move along the larger circles of the deferents, which rotate around a point separated from the Earth. The end result matches up with the major features of the looping, back-and-forth pathways of the planets. To do this, Ptolemy’s system had to be very fine-tuned to actual observations of the planets. Each and every deferent and epicycle was meticulously sized and located in order to give the best fit possible to the real meanderings of the known worlds.
Even with such fine engineering, the system couldn’t quite get everything right—there were little deviations here and there from astronomers’ measurements over the years. Planets would arrive a bit early or late to certain positions on the sky—not enough, though, to discourage everyone. Here was a plausible model for the nature and motion of the Sun, Moon, and planets that was geocentric, grounded in the precision and truth of geometry, and in agreement with the thinking of the Great Philosophers. The model comforted mathematicians and theologians alike.
Later, as Ptolemy’s ideas were subsumed and integrated into the religious and philosophical doctrines of the Western world in the Middle Ages, they became intricately attached to a unified conceptual framework. Like arterial conduits helping to keep the blood flowing, the geocentric spheres and their epicycles were a key part of the machinery of the perceived universe. If you challenged geocentric cosmology you effectively challenged the whole body of scientific, philosophical, and religious thought—including its powerful institutions of rule and administration.
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Despite geocentrism’s importance, in the fourteen centuries between Ptolemy and Copernicus there was in fact no single generally accepted picture of the detailed specifics of the arrangement of the universe. This disconnect is one of the most interesting aspects of the development of “cosmology”—or at the very least the development of a model of our solar system. During this entire time span, bits and pieces of ideas and worldviews were typically cobbled together for convenience, as and when needed—a cosmic mix-and-match. It depended on whether you wanted a mathematically driven universe, or a more abstract philosophical one. And all of these ideas in turn reached back to the varied hypotheses and proposals of a multitude of long-departed Greek thinkers.
Equally important for this cosmological history was that so much of its character hinged on the available precision of measurement. Aristotle and Aristarchus were no slouches when it came to making careful astronomical observations, but they were severely limited with only human eyes and basic tools for assessing angles and distances. This limitation meant that they actually had no idea what something like the true parallax motion of the stars really was; they just assumed it was zero.
The data on the motion of the planets themselves was also of limited precision, and it left gaps in knowledge that would let Aristotle and Ptolemy squeeze geocentric models, with their increasingly elaborate geometric arrangements, into the picture. The models may not have been perfect, but humanity’s observations of the heavens weren’t good enough to disprove them.
So by the late 1400s there had been little real progress in formulating a better model for the motions of the Earth, the planets, and the stars—especially given the accepted need to be consistent with the religious and philosophical doctrines of the Western world. In fact, I think it’s fair to say that to our modern scientific eyes, medieval cosmological models were in a thoroughly messy and inconsistent state. The time was certainly ripe for some drastic improvements to be made. All that was needed was the right person.
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Nicolaus Copernicus was born on February 19, 1473. Growing up in a part of Prussia that had recently been ceded to Poland, Copernicus had the good fortune to be part of a sophisticated and well-off family. He got an excellent education that included a thorough grounding in philosophy (which by default was the intensive study of the works of the ancient Greeks), mathematics, and the natural sciences—including astronomy. He was also genuinely voracious in his appetite for knowledge, and doesn’t seem to have shied away from hard work during his entire lifetime, even producing manuscripts on poetry and politics in addition to his scientific investigations.
His early schooling led him on to further studies in Italy, where he began to get more and more interested in astronomical observations, especially those that related to the measurable deviations of lunar and planetary behavior from the Ptolemaic system. Other investigators of the time were also well aware of these deviations, but the industrious Copernicus was particularly moved to step outside the usual bounds in looking for answers, and was eager to find a more accurate solution than the one that Ptolemy had devised so long before.
In the early 1500s Copernicus drafted what would later become the basis for his full heliocentric model of the solar system—a forty-page work known as his Commentariolus, or “little commentary.” It was never officially published during his lifetime, but instead a few copies circulated in a limited fashion, garnering interest and respect from his contemporaries and no doubt some stern glares from the prevailing establishment. While it may have been little, the commentary contains seven critical and visionary axioms.
Paraphrasing these in more modern terms, this is what Copernicus had to say about the cosmos:
• There is no single center to the universe.
• The Earth’s center is not the center of the universe.
• The center of the universe is near the Sun.*
• The distance from the Earth to the Sun is imperceptible compared with the distance to the stars, and so no parallax is seen in the stars.
• The rotation of the Earth accounts for the apparent daily rotation across the sky of the Sun and of the stars, which are immovable.
• The annual variations of the Sun’s movements across the sky are actually caused by the Earth revolving around the Sun.
• The looping (retrograde) motion that we see for the planets is actually caused by the movement of the Earth.
After this last idea Copernicus was sufficiently excited to add in his brief commentary: “The motion of the earth alone, therefore, suffices to explain so many irregularities in the heavens.”
Here in these sentences was the genesis of a colossal revolution in human thought. Through the power of little more than deductive reasoning, Copernicus had set the cherished Earth spinning and traveling through the universe. But although the circulation of the Commentariolus helped him gain a considerable reputation, it wasn’t until decades later that he finally took these writings and more thoroughly worked out the mathematical pieces of his theory in order to have them published—effectively posthumously—in the great De revolutionibus orbium coelestium, “On the Revolutions of the Celestial Spheres,” in 1543.†
As much as this model shook the heavens into shape, it was also still very far from perfect. Despite, as we now know, correctly arranging the Earth, the Sun, planets, and stars in their respective places, Copernicus still assumed certain properties that made fitting his model to astronomical observations awkward. In fact, rather than doing away with all of Ptolemy’s complicated geometrical devices, Copernicus merely did away with some parts. He continued to use epicycles to get a better match to the real behavior of the planets and the Sun as they passed through their annual tracks.
The underlying physical arrangement was better, but the application of the model was still a bit of a nightmare, and the reason was that Copernicus was clinging to a set of ideas that went all the way back to Aristotle. He assumed that all motions, whether on great shells or in epicycles, followed perfect circles and took place at constant velocity. This was consistent with classical ideas, wonderfully geometric, and—unknown to him—completely wrong. But Copernicus had certainly seeded the revolution of scientific thought, and what a revolution it would turn out to be.
* * *
The decades that came after Copernicus’s De revolutionibus brought a host of new dissenters from the Ptolemaic universe, as well as many equally vociferous defenders. Some of the dissenters, such as Giordano Bruno, paid dearly for their views. The Dominican friar was born in 1548, five years after Copernicus’s death. His scientific and philosophical studies led him to advocate not only the heliocentric worldview, but also the idea that the universe was truly infinite, that the Sun was merely another star, and that there must be an endless number of other inhabited worlds across the immensity of existence. By building on the works of the ancient Greek atomists, Bruno advocated a prescient vision of nature. But together with his extremely provocative stance on other religious matters, it caught the full attention of the establishment, and in 1600 the Roman Inquisition burned poor Bruno at the stake for heresy.
During this same period the wealthy Danish nobleman and astronomer Tycho Brahe was making enormous strides in the observation and record keeping of the heavens. Without telescopes he used his keen eyes and clever measuring devices to track the cosmos—inventing new versions of quadrants, sextants, and armillary spheres to measure angles, positions, and coordinate systems with impressive accuracy. One night in 1572 the twenty-six-year old Brahe witnessed a new star in the November skies of Western Europe. It showed no discernible parallax but had clearly not been there in previous nights, and Brahe came to the conclusion that the universe was therefore not immutable—it could change and it could change dramatically.
We realize now that he had observed a supernova, in this case the powerful implosion of a critically overweight white dwarf stellar remnant, some 8,000 light-years from the solar system. The experience of seeing this primal event helped encourage Western astronomers to devise even better ways of measuring the positions and brightness of objects and to explain their arrangements. Brahe himself worked hard to try to combine, or at least reconcile, the Ptolemaic cosmology with that of Copernicus. He produced his own “Tychonic” geo-heliocentric system, in which the Sun and Moon orbited the Earth, but all the other planets orbited the Sun.
As contrived as it was, he found this arrangement satisfying because he had still not detected a parallax for the stars, and keeping the “sluggish” Earth stationary meant he could easily account for that fact. Better yet, his system allowed a convenient compromise position for advocates of the Copernican vision who were still feeling very nervous about their scientific beliefs. But it was Brahe’s meticulous care with astronomical observations that really set the stage for one of the most critical next steps—steps that came from his onetime assistant, the German-born Johannes Kepler.
Four years before meeting Brahe in 1600, Kepler had published a rousing defense of the Copernican system of the heavens in his Mysterium Cosmographicum—“The Cosmographic Mystery.” Interestingly, Kepler was not only an obsessive mathematician, but also deeply religious, and he felt that everything that determined the positioning and motion of celestial bodies was of divine influence. (This might help explain why his first stab at modeling a heliocentric cosmos relied on a series of three-dimensional polyhedra nestling inside each other—a geometric and appealingly designed, but deeply flawed, concept.)
The full story of Kepler’s life and studies is convoluted; he was an exhaustingly busy and productive person, particularly in matters of science. His investigations of optics led him to deduce the fundamental inverse-square law of brightness: the intensity of a light source is proportional to the inverse of the square of its distance. With the observation of another supernova in 1604, Kepler also reasoned, just as Brahe had, that in the absence of a measurable parallax, Aristotle’s unchanging and immutable universe was probably not a correct model. But most important, when it came to the problems of the Ptolemaic and Copernican explanations of planetary motions, Kepler found himself in a unique position.
The high-living Tycho Brahe suffered an unfortunate and untimely death from an infection in late 1601, and Kepler wound up inheriting that master astronomer’s most complete and precise tabulations of celestial positions and variations. Some sources suggest that Kepler was instrumental in making very sure that he got his hands on these records before Brahe’s estate was disbursed. Having already started working with Brahe, he knew exactly what he needed.
Brahe’s unprecedented measurements gave Kepler an opportunity to keep tackling the endlessly nagging issue of finding a perfect fit to the motions of planets, where solutions in the existing schemes were still full of holes, including so-called residuals, gaps between the predicted positions of planets and their actual places at various times. Planets would simply not be quite where models said they should be on particular nights, which was quite a glaring problem.
When Kepler settled down to study these extensive data, he chose to focus his attention on the observations of the planet Mars. That choice was, I think, one of the biggest strokes of educated luck in the entire history of Western science, even if it was likely encouraged by Brahe’s earlier suggestions.
Of the six planets that Kepler knew of, Mars exhibited the worst residuals of all. In fact, Kepler demonstrated that Mars could not conceivably be following a fixed path if the Earth were at the center of everything. He went on to consider what had heretofore been absent from all models of the universe: the possibility that objects might not move with constant velocity all the time. By allowing this behavior into the mix he wrenched open a new window onto nature, because if objects moved with varying speed they might also move along paths that were not perfect circles. This wasn’t an easy task—it took Kepler eight years from the time he started his investigation to the time he had his answer.
Kepler tried out various shapes for his planetary motions; egg-like ovals didn’t work, nor did other forms. He then tackled the movements using only mathematics, obtaining a solution and rejecting it before coming back to the exact same idea by guesswork. The answer, he finally realized, was that all planetary motions belonged to a class of curves known as conic sections. These could be circles, parabolas, hyperbolas, and most critically—ellipses.
The reason why Mars has such awful residuals in the Copernican model is, as we now know, because it has the least circular, or the most elliptical, orbit compared with Venus, Earth, Jupiter, and Saturn. Of the planets familiar to Kepler, only Mercury had an orbit with greater ellipticity. But the observation of Mercury is complicated by its proximity to the Sun. Kepler deduced that in an elliptical orbit, a planet or any object slows down at its far point, and speeds up at its near point. This variation was exactly what was needed to eliminate the residuals afflicting Mars.
Gathering his ideas together, in 1609 Kepler published Astronomia Nova, “A New Astronomy,” to present the first two of his famous laws describing planetary motion: the path of every planet is an ellipse with one focus centered on the Sun; and a line joining a planet and the Sun sweeps out equal areas in equal time as the planet moves.
Kepler also realized that there might be some kind of unseen influence at play between the Sun and the planets (what we would today term a force). This concept was revolutionary, and although it was all couched in somewhat mystical terms, he went as far as suggesting that such an influence might be reduced with distance from the Sun. Hence the farther planets would move more slowly, which of course they do.
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Merely a year after Astronomia Nova, in 1610, Galileo Galilei made his telescopic observations of the periodic motion of the brightest moons around Jupiter and of the phases of Venus. Both of these observations brought the clash between celestial worldviews to a boiling point by providing even more convincing evidence for a Sun-centered system, putting Galileo into a head-on collision with the established doctrines of the time. But there is something else lurking in the picture of the universe that emerged out of Kepler’s work that is just as vital to our quest to understand our cosmic significance.
If planets follow elliptical paths as a general rule, and those paths need not be all within a single plane around a centrally massive star, the possibility exists for an extraordinary range of planetary motions and arrangements that nonetheless all obey Kepler’s rules (and what would soon be Newton’s physics). I doubt anyone suspected it at the time, but the door had been opened to a universe of far greater abundance and diversity than anything yet imagined, even by the atomists and pluralists of the past. Galileo’s observations produced other surprises as well. With a telescope he could find stars that were too faint to be noticed with normal human vision. When he looked at the seemingly smooth and cloudy expanse of the Milky Way, he was amazed to discover that it was in fact made of stars, so many and so tiny that the naked eye blurs them together. His observations of these other phenomena tend to get less attention than they deserve, but they were beginning to reveal the true enormity of nature.
Just like the shock of Tycho Brahe’s supernova, the notion that there were hidden objects in the sky ran counter to the cosmological perceptions of the time. These observations, together with Antony van Leeuwenhoek’s discovery a few decades later of the teeming microscopic universe in every speck of water and in human sputum, began to lift a previously opaque veil from the enormous intricacy and depth of reality. Yet these pivotal revelations of the sheer depth of nature—inward and outward—didn’t cause anything like the controversy sparked by the simple decentralization of our place in the universe.
The upset of that shift was mostly confined to the camps of the church and establishment. In fact, it doesn’t appear that either Galileo or Kepler saw heliocentrism as a demotion of the terrestrial status. Quite the contrary: it meant we were no longer at the “bottom” of the planetary pile; we were on a noble orb within the pathways of others. Ironically, Kepler even wrote that he considered this to mean that the Earth was at the center of the planetary globes (the orbits), with Mercury, Venus, and the Sun on the inside, and Mars, Jupiter, and Saturn outside. Yet again, such a robust certitude about our significance in the grand scheme of things actually lessened the impact of the growing evidence for the true immensity of nature, from the world within to the world without.
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Time passed, and the year 1642 saw the death of Galileo in January, and the birth of Isaac Newton in December. The full story of Newton’s life, much like those of Copernicus, Bruno, Brahe, Kepler, and Galileo, is immensely rich. But the most important piece for our quest comes with the publication in 1687 of his monumental Philosophiæ Naturalis Principia Mathematica—“Mathematical Principles of Natural Philosophy,” more often known simply as the Principia. In this text Newton lays out not only the mathematical laws of motion, including the concepts of inertia, momentum, force, and acceleration, but also a universal law of gravitation.
Newton saw that the attraction of bodies to each other could be described as a force that grew with mass but diminished as the inverse of the square of distance. From this hypothesis he derived the mathematical proof of Kepler’s empirical laws—showing for the first time that the rules governing the planets came from fundamental physics. He also presented analyses of the motion of the Moon, the paths of comets, and the gravitational interactions of more than two bodies. He noted that despite the clear heliocentric nature of the solar system, the Sun does in fact orbit around a variable point—the center-of-mass or balance point of all objects in the system. He even determined that this point was close to the observed surface of the Sun—well offset from its core, a result largely due to the gravitational bulk of Jupiter and Saturn. (This latter fact is familiar to modern astronomers, because the same type of offset in other star systems provides one of the key techniques for finding exoplanets, the planets beyond our solar system that we will encounter in a later chapter. We measure the orbital motion of a star around this pivot point, since it marks the presence of unseen but massive worlds.)
Newton was a strange and complicated character with deeply held religious beliefs, and for him this beautiful physical explanation of planetary motion was evidence of a supreme divinity, maintaining the paths of objects in a perfect clockwork dance. For other thinkers in the following century, like the great French mathematician and scientist Pierre-Simon Laplace, it meant quite the opposite. There need be no guiding hand, no preordained paths or configurations in the Copernican universe, just the innate physical laws to determine where and when any object would find itself. But Laplace also felt that, armed with these laws, and with a complete knowledge of the locations and movements of all objects at any time, we could always know the past and future. There might be no guiding hand, but there was determinism in the universe.
* * *
Observations of the cosmos around us continued to improve as the next few hundred years went by, as did the toolbox of mathematics and physics available to work with. Mystical and philosophical reasons for the arrangements of nature gave way to the application of simpler, more general laws. At the same time, what we knew of the composition of the universe became richer and richer, and the notions of extreme scale and of the variety of phenomena that were hidden by time or by faintness grew and grew. The idea that stars were not only vastly distant, but perhaps scattered throughout an enormous volume, gained greater acceptance among philosophers and scientists. With this growing sense of scale, even the musings of the ancient Greek atomists on an infinite cosmos returned to people’s thoughts.
Our scientific sense of our own importance also evolved, in a variety of directions. Hot on the heels of Newton, the Dutch scientist Christiaan Huygens wrote about his thoughts on the possibility of extraterrestrial life just prior to his death in 1695. Huygens was convinced of the “plurality of worlds,” imagining a wealth of watery and hospitable locations in his telescopic observations of the planets, and even of the moons of Jupiter and Saturn. Life like ours seemed to him to be nearly inevitable elsewhere. This was certainly not a view shared by everyone, and debate on our place among the stars raged on.
Something else was also taking place during this period: a contentious and surprisingly underappreciated scientific debate that began in the early 1700s and arguably didn’t reach any kind of satisfactory closure until as recently as the 1970s. With the monumental advances in physics due to scientists like Kepler, Galileo, Newton, and Laplace, the solar system became a phenomenon whose origins now begged for a proper scientific explanation.
Where did the Sun and planets come from if they were less of a divine construction and more of a consequence of the laws of nature? The answer, as I’ll soon show you, is quite stunning, and neatly frames our more modern debate on origins and significance. Before that, though, we need to reach the present day in our brief history of cosmic perspective.
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By the end of the 1800s we were beginning to appreciate the true vastness of the universe. Stars were now accepted to be extremely distant analogues of our Sun, a fact supported by astronomers finally having success in measuring their barely noticeable parallax movements from Earth’s annual motion through space. New planets had also been discovered in our solar system—from the darkly distant Uranus and Neptune to minor but still massive objects like Ceres and Vesta, just beyond the orbit of Mars. And the elemental composition of extraterrestrial objects was beginning to reveal itself through the spectra of light, including the discovery of an atomic species in the Sun—the stuff we now call helium.
But other big questions remained: Was the universe infinite in space or perhaps even time? Was the spread of stars we call the Milky Way the full extent of the universe, or could some of these other strange little smudges of nebulosity, like the one called Andromeda, actually be other “island universes,” other galaxies?
In an unprecedented burst of discovery and invention, in the first three decades of the twentieth century there was another series of scientific revolutions. Their stories have been told innumerable times: Albert Einstein’s theory of relativity, the measurement of the true scale of the cosmos and the nature of galaxies, and the development of quantum mechanics. These all produced radical views of nature that dealt with the intertwined properties of the very large, the submicroscopic, the fast and the energetic, and the underpinnings of reality itself. These revolutions would also have to confront, and contend with, our perceived place in the cosmos.
The implication of a heliocentric Copernican model was that the universe would look more or less the same no matter which planet you stood on. The obvious extension was that the universe would look more or less the same wherever you stood within it—from our solar system to another, or from our galaxy to another that might be tens of millions of light-years away. For Einstein, working in the years following 1915, this was a philosophically comfortable proposition, and made the application of his theory of general relativity to the universe as a whole that much more straightforward, giving birth to the so-called Cosmological Principle.
In slightly more technical terms, the idea stated that the universe was homogeneous. While it might contain many small asymmetries, like patches of stars and galaxies, it would have the same amount of these lumps and bumps no matter where you were. It’s a bit like the Earth’s terrain: some places are mountainous and some places consist of flat oceans, but on average you can always find roughly the same mix of mountains and oceans wherever you are. This was very helpful if you were trying to apply a generalized theory of space and time, as Einstein was, to the workings of the cosmos.
It also meant assuming that the universe was isotropic, meaning that it would look the same in all directions from any place. This is a bit harder to swallow. After all, we can hardly claim that this is the way we experience the world or the solar system, and even the interstellar night sky is beset by big nonuniformities like the band of the Milky Way. But again, on scales that reach beyond our galaxy and out into the cosmos, the number and arrangement of objects seen in any direction should be more or less constant.
The first time that anyone seems to have publicly connected this cosmological principle to Copernican ideas was in the early 1950s, when the famous Austrian-born physicist Hermann Bondi used the phrase “Copernican Cosmological Principle” in his discussion of a now-disproven cosmological model known as the steady-state theory.
Much as its name implies, the steady-state theory proposed that the universe was eternal, with no beginning or end. To help make this theory palatable, Bondi asserted an even stronger principle: that not only would the universe appear the same in all directions to any observer anywhere, but for any observer at any time. Although we now know that our universe is most definitely not in a steady state, the Copernican Cosmological Principle reinforced the general notion that there was absolutely nothing special or privileged about our place in the cosmos, throughout space or time.
This middle period of the twentieth century saw the explosive development of a multitude of fields, from cosmology to microbiology and genetics, as well as the emergence of several generations of extremely influential scientists. But as it became clearer and clearer that the universe itself was an evolving and diverse place, several different people had begun to notice certain strange coincidences in the value of fundamental physical constants. These are numbers that describe things like the strength of gravity or the masses of subatomic particles, and in particular the estimated lifetime of the cosmos. Certain combinations of these numbers could yield surprising relationships. For example, the ratio of gravitational and electric forces, involving constant quantities describing the strength of gravity, and the masses and charges of electrons and protons is about 1039. This number is remarkably similar to the current age of the universe when described in atomic units of time (a unit being about 2×10-17 seconds), a fact first pointed out by the physicist Paul Dirac.
But why should these immutable constants be related to the age of the universe now? Too far back or forward in cosmic time, this obviously wouldn’t be the case. Furthermore, at some other cosmic time, conditions might not allow for any intelligent life to be around to observe these coincidences in the first place! This was a rather pesky issue for a Copernican Principle, since it suggested there was something special about when and where we found ourselves, and about the present physical properties of the cosmos.
The final, definitive proof that the universe was finite in age came in 1965, with the discovery of an all-pervasive flood of microwave photons originating from the young cosmos—effectively part of the remains of a hot big bang. This trace of a very different universe, one that was once upon a time ferociously dense and energetic, was more than one fly in the ointment. It was a whole bucket of flies, dumped into the vat of Copernican mediocrity. And things came to a head in a famous presentation by an Australian-born physicist named Brandon Carter in 1973.
Carter, who has played a central role in the modern development of black hole physics, was encouraged by the interest of a number of colleagues, including the physicist John Wheeler and a young Stephen Hawking. So he chose to stir things up at no less than a special conference in Krakow, Poland, held to commemorate the five hundredth anniversary of Copernicus’s birth. In his talk, Carter articulated the ideas that had been brewing among a number of scientists puzzling over all these apparent coincidences between cosmic properties and our circumstances. He plunged into the thick of it by discussing just how different the universe might be if just a few characteristics were changed—like the relative strength of the fundamental forces that glue matter together.
Considering these changes raised an intriguing idea that Carter elaborated on for his audience. A tweaked version of nature might, for example, make no stars, but since we come from the elements produced by stars, and since we are here observing the cosmos, this very fact can be used to tell us something about the universe we live in. In other words, our existence itself tells us something about the nature of physics in the universe—we might be more important than we thought. Carter labeled this approach to examining the cosmos as the “anthropic principle,” since “anthropic” means that something pertains to human existence. This wasn’t exactly what he was driving at, since it could be any observer of the universe, not just humans. But although he later proposed a more semantically accurate term, the word “anthropic” stuck.
The underlying sense of this approach to understanding the world is well summarized in Carter’s own words at the time: “Copernicus taught us the very sound lesson that we must not assume gratuitously that we occupy a privileged central position in the Universe. Unfortunately there has been a strong (not always subconscious) tendency to extend this to a most questionable dogma to the effect that our situation cannot be privileged in any sense.” The point being that one cannot, and should not, ignore the multitude of phenomena that apparently need to line up just right for life, and us, to exist.
Now, a great deal has been written about the anthropic principle. It’s been a veritable gold mine for some physicists and many philosophers, and an often confusing and confounding topic for snake-eats-own-tail conversations over cocktails. Extreme versions of the principle have even been constructed to argue that a viable universe must produce intelligent life capable of observing it—a notion that I’m going to steer very clear of.
However, the anthropic principle is an important idea, one that prompts us to face some of our preconceptions about the cosmos around us and to examine our innate biases of observation. And since it directly challenges the Copernican Principle (or rather, what has come to be the orthodoxy of our mediocrity), we ought to look at a couple of the details.
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These days, anthropic ideas tend to crop up mostly in discussions of a phenomenon called “fine-tuning,” which involves a more detailed examination of the cosmic coincidences that originally led to scientists’ puzzlement over these questions. The notion of fine-tuning goes as follows: if we look carefully at a variety of properties of the universe, embodied in constants of nature such as the strength of gravity relative to other forces, or the proportions of matter and energy in the universe, we can see that were these properties to be changed by a small amount, life might not have arisen.
Except this tweaking is a little more complicated, because what we really mean is that objects like stars and galaxies wouldn’t exist, or that they’d never forge the heavy elements, like carbon, that are so critical for the chemistry of life. So, in other words, a variety of primary cosmic functions would fail to set the stage for the secondary ones that we rely on. This, of course, also presumes that life has to be like us—but it does seem hard to imagine how a universe of just hydrogen and helium could give rise to structures with the complexity seen in carbon-based life.
Exactly which characteristics are most important to life’s existence is not immediately obvious. The best way of narrowing down the possibilities comes from making clever mathematical combinations of quantities that in turn relate to tangible phenomena. The scientists Bernard Carr and Martin Rees did just this in 1979, and later on, in 1999, Rees revisited the ideas and came up with six numbers that have to lie within a comparatively narrow range for our universe to be the way it is, and to be amenable to life as we know it. These numbers are:
• the ratio of the strength of gravity to electromagnetic forces
• the percentage of matter that’s converted to energy by the nuclear fusion of hydrogen into helium
• the total density of normal matter in the universe
• the energy density of quantum vacuum fluctuations (which may be the same dark energy that is accelerating the expansion of our universe)
• the sizes of the minute variations in the early universe that eventually grew into such structures as galaxies and their groupings
• the actual number of spatial dimensions in our universe
It’s quite an array, and the odds appear extraordinarily low for any universe popping into existence to—by chance—have all the necessary properties for life to arise. Of course, as you read this you may be thinking to yourself, “But if it weren’t like this we wouldn’t be around to think about it; we simply have to exist in this type of universe.” And that’s absolutely correct. However, if this is the one and only universe, with no universe before or after it, that raises the uncomfortable question of why it turned out this way: suitable for life.
One of the most appealing answers is that ours is only one of a near-uncountable array of viable universes. It is a single example of a type of reality that is separated by time and space, or dimension, from gazillions of others. The word “appealing” may seem almost comical here—I’ve just invoked what you might think is an unsubstantiated hypothesis for the nature of reality. But this idea of a “multiverse” is a leading contender for the deeper truth of the physical world. Indeed, when Brandon Carter came up with the anthropic principle he was already thinking along these lines.
Although I don’t think anyone could yet claim that we have direct evidence for there being a multiverse, there are several compelling theoretical ideas that readily accommodate it, and that also seem to provide solutions to other aspects of fundamental subatomic physics and cosmology. If correct, it would mean that there is no fine-tuning problem per se. We simply exist in one of the universes that happen to be “right” for the formation of galaxies, stars, heavy elements, and complex carbon chemistry. It sounds as if this would neatly resolve the issue, and in many respects it would—if we actually knew that we lived inside a multiverse.
Another tricky thing about the multiverse solution is that it is still partially motivated by the notion that our particular universe is genuinely fine-tuned for life. It’s still thinking in pure anthropic terms—and in those terms it is assumed that life is entirely represented by us. One doesn’t need to invoke any other life, or type of life, anywhere else in the cosmos to make this argument, and that seems a bit parochial. It would be like arbitrarily basing your entire philosophy of science on the existence of a particular type of unusual parrot. The last thing we want is to be misled up a dead-end alley. So it’s worth pursuing this further, because we don’t yet know if we live in a part of a multiverse, and because none of the above gets us much closer to evaluating our immediate cosmic significance, or lack thereof.
With only some very simple changes to our perspective on the universe, one can appreciate how some aspects of fine-tuning and anthropic reasoning begin to look like a bit of a distraction in our quest for significance. I’ll visit some other ideas along these lines, but let’s kick off with the following—a playful question to make a serious point.
Let’s suppose for a moment that Galileo Galilei’s interpretations of his observations of the universe had been immediately embraced as a crowning achievement of reason and technology. Instead of being raked over the proverbial coals, he becomes the darling of the seventeenth-century church and state. And in this alternative timeline the enlightened establishment seizes this moment to initiate a grand technological push, seeing the potential economic benefit of engineering and science.
Flush with the warmth of acceptance and patronage, Galileo quickly sets to work building sophisticated telescopes that will let him become the first human to find planets around other stars, and to confirm the presence of biological systems across many of these worlds. It’s a lovely fantasy, a horse- and water-powered science-fiction reworking of history, but most critically it also lets us ask how things would be different today if this had really happened.
For the intervening centuries we would have known that life was not confined to Earth alone, and we might even have figured out if any of it was more than just microbes or uncommunicative creatures. In either case, the point is that we would have at our fingertips a real answer to the question of how likely, or how unusual, our type of life is in this universe.
Let’s suppose that in this parallel reality we find that life resembling Earth’s is moderately common. It occurs often, but it’s neither spilling across every suitable world, nor so unusual that it exists only in certain galaxies sparsely distributed across the universe. What then of the fine-tuning arguments embedded in the anthropic ideas about cosmology? It might not even occur to us to ask these questions in the first place. It would be like suddenly deciding to question why the world produces a certain number of snails. But even if we did ask, the notion of “tuning” doesn’t exactly hold up so well in this hypothetical reality.
The universe would appear to be suitable for producing only some life, hardly the stuff of great cosmic significance; a modestly fertile pond of occasionally making something functional. Now of course we could also discover that the answer lies at one of two possible extremes: from life as an utterly freakish rarity across 14 billion years’ worth of cosmic time, to life run amok, clogging every planetary system with some new variant.
In the former case we’d hardly think the universe was well suited to life, and the coincidence of physical parameters with the requirements of life would just be seen as a cruel joke. By contrast, in the latter case we might deduce that life itself, not so much the cosmic underpinnings, is a remarkably robust phenomenon. We might even be asking whether there were any (almost unimaginable!) circumstances in which life could not spring from the underpinnings of the physical laws.
There are two points to make here. The first is trivial, and it is that the questions we end up asking are themselves a direct function of what we’ve already observed about our surroundings. The second is much more important, because unlike the inhabitants of my fantasy Earth with its alternate astronomical history, we do not know at present which of the above scenarios applies in this universe.
Furthermore, fine-tuning may not be a make-or-break situation. Instead it could be a “coarse-tuning” problem with the real fine-tuning hidden inside. As in my fictional example, the issue of the universe being suitable for life is not an all-or-nothing question. It could rest within a spectrum of fertility and likelihood. In fact, I think that there is an implicit assumption in anthropic arguments that life is a bit wimpy, that it must have everything perfectly aligned or else it won’t happen.
Yet we know from the abundant and remarkable wealth of paleontological evidence on Earth that brutal natural selection has allowed life to fine-tune itself to the environment around it. In the face of varying chemical mixes and abundances of vital elements, as well as a multitude of different sources of energy, life has found a way. Admittedly this is within a set of circumstances determined by the basic laws of the universe. But life on Earth has become diverse enough to exploit a variety of secondary biochemical strategies—not just a single one.
It’s not obvious that life needs anything more than a rough-and-ready environment to originate and survive in. So true cosmological fine-tuning should be more about the particular ease with which life can occur—and for now, at least, I make no distinction between intelligent life and “simple” life, since there’s nothing simple about life in any form.
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This way of looking at things is consistent with studies of the coincidences of physical constants and other quantities such as the proportions of mass and energy in the universe. In most of these cases there is a little bit of wiggle room—an issue well illustrated by the way in which elements are produced by nuclear fusion inside large stars.
During the first half of the twentieth century, scientists realized that conditions inside stars could give rise to the fusion of atomic nuclei, powering their prodigious energy output and forging heavier and heavier elements. But the recipes were not straightforward, and in the early 1950s the English physicist Fred Hoyle realized that there was a problem with carbon. At the time, physicists’ emerging theories of stellar fusion were suggesting that stars should make relatively little carbon. But Hoyle observed that since we’re made with carbon, the universe must actually have a way to generate plenty of it. This puzzling discrepancy helped prompt him to find that carbon-producing process.
He discovered that carbon gets readily formed in the universe because of a specific phenomenon. The energy of one of the stages involved in combining three helium nuclei in a star’s interior almost exactly matches that of an agitated carbon nucleus—which is the natural product of combining those three helium nuclei. This correspondence results in what’s called a nuclear resonance, a harmonizing of energy states that boosts the efficiency of the nuclear reaction enormously, so that, instead of stars making almost no carbon, they can make lots of it.
For a long time, the carbon resonance was considered one of the strongest pieces of evidence for an anthropic principle to be in play—namely, the existence of carbon and carbon-based life itself suggested this special nuclear process in stars. This is true, but only up to a point, because there is a devil in the details. We now know that these nuclear energies need not match so precisely for carbon to be produced: there’s a certain amount of leeway, and so the fine-tuning is not quite so fine after all. And the same is true of many of the fine-tuning parameters. Things could be a teeny bit different and conditions would still be passably okay for life as we know it.
The concept of such wiggle room goes deeper still. If we are able to eventually measure the propensity of the universe for making life—the efficiency, or density, with which life occurs in any given patch of the cosmos—we will have a new tool for probing the basic properties of nature and for predicting the occurrence of life according to those fundamental circumstances.
This is not to say that there is necessarily something “special” about life but rather that life is an excellent example of a highly complex phenomenon, and one that is conceivably the most complicated in the cosmos, with an intricate web of connections to many key features of the physical laws in this universe. As such, life represents a natural litmus test of cosmic properties, a canary in a cage for examining the detailed interplay between characteristics where there are a vast array of potential permutations and combinations.
This is more than rephrasing the anthropic argument. At its core that argument states that a sole occurrence of life yields predictions about the universe. Instead I’m proposing a way to learn how to take the properties of the universe and predict the abundance of life, and therefore predict our significance. It’s a bit like taking an opinion poll and using that to predict the outcome of an election.
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The catch is that we have developed a bit of a complex thanks to Copernicus, whose ideas so clearly and accurately describe our solar system, and who helped break us out of a deep and awful rut of provinciality. The apparent confirmation of our unprivileged ordinariness is surprisingly compelling (flying as it does in the face of all our solipsistic and egotistic tendencies), and it has allowed us to make extraordinary progress in understanding the universe around us, as well as the universe within us. But it creates some confusing situations.
On the face of it, the Copernican Principle suggests that we cannot be alone in the universe; we are neither central nor special, and our circumstances should be representative of the circumstances in any number of physical locations at this point in the history of the universe.
So, by that logic, not only should there be plenty of other life out there, but a great deal of it should be very similar to that on Earth. But is the assumption of our own averageness really a sound basis for making such an argument? It smacks of an overly literal reading of the scientific gospel. Copernicus was simply trying to understand the motions of planets in our solar system in the least contrived and most mathematically logical way. Are we reading too much into what was primarily a mechanical solution to a mechanical problem?
Recognizing the limitations of the Copernican Principle is not a particularly controversial suggestion. Anthropic ideas are one good example of a counterpoint, and many astronomers and physicists find similar clues in some straightforward aspects of our circumstances. The fact that we are so manifestly located in a specific place in the universe—around a star, in an outer region of a galaxy, not isolated in the intergalactic void, and at just this time in cosmic history—is simply inconsistent with “perfect” mediocrity.
The situation is this: a Copernican worldview at best suggests that the universe should be teeming with life like that on Earth, and at worst doesn’t really tell us one way or the other. The alternative—anthropic arguments—require only a single instance of life in the universe, which would be us. At best, some fine-tuning studies suggest that the universe could be marginally suitable for heavy-element-based life-forms, rather than being especially fertile. Neither view reveals much about the actual abundance of life to be expected in our universe, or much about our own more parochial significance or insignificance.
And we want some answers! So to find the truth, we need to take a good, careful look at the nature of the multifaceted array of matter in the universe around us and within us. We need to navigate a path somewhere between the assumptions of mediocrity and the assumptions of fine-tuning and an anthropic worldview. We need to figure out a way to see around these extremes and to make actual measurements of what we find.
The story in The Copernicus Complex is about the great adventure and unfolding meaning of that effort to discover the universe within and without. It is also about our past and future—especially the future. But more than anything else, it is about that deep-rooted need, that frustrating yet recurrent itch that each and every one of us gets when we try to think about our place in the grand scheme of creation.
We need to know, to truly know, whether or not we are significant—not just emotionally or philosophically, but objectively, in cold, hard facts and figures. It’s one of the greatest scientific challenges facing us. Part of that challenge is to understand and see past our intricate models of the world, which serve us so well but time and time again need revision, updating, and sometimes discarding. So the next step to take is from the familiar Earth of today to the unfamiliar Earth of yesterday and tomorrow. If we want to place ourselves in context, we need to begin to reach up and out to cosmic time and space, as well as down into the microcosm. We’ll find that what the enterprising scientist Antony van Leeuwenhoek saw unfolding in his microscopes more than three hundred years ago was merely the beginning of a truly fantastic voyage.
Copyright © 2014 by Caleb Scharf