The real story of how the scientific and religious establishments
greeted the Copernican revolution is quite different from the folklore. And it's a lot more interesting.
Perhaps the most famous of all scientific revolutions
is the one associated with Nicolaus Copernicus (1473–1543). The popular version of the
story goes as follows:
The ancient Greeks, although they were
great philosophers and good at mapping the motions of stars and planets, tended to create models
of the universe that were more influenced by philosophical, aesthetic, and religious considerations
than by observation and experiment. The idea that Earth was the stationary center of the universe,
and that the stars and planets were embedded in spheres that rotated around Earth, appealed to them
because the circle and the sphere were the most perfect geometric shapes.
In the Christian era, the
model also pleased religious people because it gave pride of place to human beings—God's
special creation. The prestige of Greek philosophers like Aristotle was so great, and commitment
to religious doctrine so strong, that many scholars stubbornly tried to retain Ptolemaic astronomy
even though increasingly complicated epicycles had to be added to make the system work even moderately
well.
So when Copernicus came
along with the correct heliocentric system, his ideas were fiercely opposed by the Roman Catholic
Church because they displaced Earth from the center, and that was seen as both a demotion for human
beings and contrary to the teachings of Aristotle. Therefore the Inquisition persecuted, tortured,
and even killed those who advocated Copernican ideas.
Because of the church's
adherence to philosophical and religious dogma, scientific progress was held back for a millennium.
It was the later work of Tycho Brahe (1546–1601), Johannes Kepler (1571–1630), Galileo
Galilei (1564–1642), and Isaac Newton (1642–1727) that finally led to the acceptance
of heliocentrism.
Variations on this breezy
version of the Copernicus story are common in science textbooks.1 How much of the story
is true? Apart from the final sentence, not much. But it's a good illustration of how scientific
folklore can replace actual history.
Let us start with the myth
that the Copernican model was opposed because it was a blow to human pride, dethroning Earth from
its privileged position as the center of the universe. Dennis Danielson, in his fine article on
the subject,2 shows how widespread that view is by quoting the eminent geneticist
Theodosius Dobzhansky. With Copernicus, Dobzhansky contends, "Earth was dethroned from its
presumed centrality and preeminence." Carl Sagan described Copernicanism as the first of a series
of "Great Demotions . . . delivered to human pride." Astronomer Martin Rees has written,
"It is over 400 years since Copernicus dethroned the Earth from the privileged position that Ptolemy's
cosmology accorded it." And Sigmund Freud remarked that Copernicus provoked outrage by his slight
against humankind's "naive self-love."
The squalid basement
Danielson, however, points out that
in the early 16th century, the center of the universe was not considered a desirable place to be.
"In most medieval interpretations of Aristotelian and Ptolemaic cosmology, Earth's position
at the center of the universe was taken as evidence not of its importance but . . . its
grossness."
In fact, ancient and medieval
Arabic, Jewish, and Christian scholars believed that the center was the worst part of the universe,
a kind of squalid basement where all the muck collected. One medieval writer described Earth's
location as "the excrementary and filthy parts of the lower world." We humans, another asserted,
are "lodged here in the dirt and filth of the world, nailed 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." In 1615
Cardinal Robert Bellarmine, a prominent persecutor of Galileo, said that "the Earth is very far
from heaven and sits motionless at the center of the world."2
In Dante Alighieri's The
Divine Comedy, hell itself is placed in Earth's innermost core. Dante also speaks of hell in
ways consistent with Aristotelian dynamics—not full of flames, which would be displaced
skyward by the heavier Earth, but as frozen and immobile.
By contrast, heaven was
up, and the further up you went, away from the center, the better it was. So Copernicus, by putting
the Sun at the center and Earth in orbit around it, was really giving its inhabitants a promotion
by taking them closer to the heavens.
When and why did the history
become distorted? Danielson doesn't pinpoint when the erroneous view gained supremacy, But he
says that from 1650 onward one can find some writers making this revisionist claim. By the late 18th
century it had taken hold completely. Johann Wolfgang von Goethe (1749–1832), for example,
wrote: "Perhaps no discovery or opinion ever produced a greater effect on the human spirit than
did the teaching of Copernicus. No sooner was the Earth recognized as being round and self-contained,
than it was obliged to relinquish the colossal privilege of being the center of the world." Here
Goethe managed to propagate another major distortion: the notion that before Copernicus (and
Columbus) it was not known that Earth was a sphere.3,4
Aristotle's cosmology
Even Aristotle did not believe Earth
to be the center of the universe. He thought it rather to be at the center. This fine distinction
was not driven by religious dogma or human self-importance but by physics arguments: In Aristotle's
cosmology the universe was finite and the heavens existed beyond its outermost sphere. The universe
had a center—defined as the center of the large outer sphere in which the stars were embedded—and
matter was drawn to that center. In that cosmology, "up" and "down" were well defined. "Down" was
toward the center of the universe and "up" was away from it, toward the sphere containing the stars.
The elements were earth,
air, water, and fire, and each element had its natural affinity for a location in the universe. As
could be seen from the fact that rocks fell to the ground, earth, being heavy, was drawn to the center.
Flames leaping upwards showed that fire, being light, was drawn towards the heavens. The model
explained many things, such as why objects fell to the ground when released from any point and why
Earth's surface was spherical. It also explained why Earth was motionless at the center. For it
to move, there would have to be something that took it away from the center. And no such agent was in
evidence.
In his book The Copernican
Revolution, historian Thomas Kuhn pointed out that Aristotle was clearly saying that Earth
was at the center of the universe not because it was especially important but simply because it was
massive: "It so happens that the Earth and the Universe have the same center, for the heavenly bodies
do move towards the center of the Earth, yet only incidentally, because it has its center at the center
of the universe."5
Problems with heliocentricity
Copernicus's heliocentric model,
on the other hand, created all manner of difficulties. It required Earth to be in motion, but it did
not say what caused it to move away from the center. If Earth was not stationary at the center but was
midway in the sequence of planetary orbits around the Sun, how could you define "up" and "down"?
Why would objects fall "down" if Earth were not at the center of the universe? How could objects thrown
upward fall back to the same point if Earth was not at rest? Earth was still believed to be the most
massive object in the universe. So if it was not drawn to a fixed point at the center, did that mean
that the universe had no center? Could that mean that the universe was infinite?
Kuhn argues that there
were thus excellent reasons for rejecting the upstart Copernicus and retaining Aristotelian
cosmology and its elaboration in Ptolemaic astronomy. Accepting Copernicus would not simply
replace one astronomical model with another. It also meant that a whole class of physics problems
that had been considered solved were now suddenly unsolved. Therefore much of the initial resistance
came from within the physics and astronomy communities rather than from the church.
In fact, awareness of Copernicus's
work was at first largely restricted to the community of astronomers. Only they were interested
in improving the calculation of planetary motions. Copernicus was widely respected as one of Europe's
leading astronomers, and reports about his work, including his heliocentric hypothesis, had
been circulating since 1515. So when his De Revolutionibus Orbium Coelestium (On the Revolutions
of the Celestial Spheres) was published 28 years later, it was hardly a surprise to other astronomers.
They accepted it as the most comprehensive account of celestial motions since Ptolemy.
But most astronomers also
felt that the Ptolemaic system, although complicated, could ultimately be made to work. So while
they hailed Copernicus's work and used his tables and methods, they were skeptical of his central
idea of a moving Earth. They dismissed it as an ad hoc trick (much as Max Planck's quantum hypothesis
was initially viewed centuries later) that turned out to be a useful tool for calculations. The
idea that the motion described by some artificial model was a convenient fiction was not unprecedented.
Ptolemy himself had said that not all of his epicycles had to be considered physically real. Some
were to be thought of as merely mathematical devices that gave sound results.
Initially, however, the
Copernican system did not give better numerical results than the Ptolemaic. Part of the problem
was that some of the existing astronomical observations were simply erroneous, a problem that
plagued Ptolemaic and Copernican astronomy alike. Although better observations soon eliminated
some of those problems, other problems remained obdurate for a long time. Furthermore, at the level
of accuracy available to Copernicus, the introduction of ellipses in place of circular orbits
would not have helped. What Copernicus needed to do, as historian Owen Gingerich puts it, was to
"treat Earth and Mercury the same way as the other planets."
Kuhn says of Copernicus:
"His full system was little if any less cumbersome than Ptolemy's had been. Both employed over thirty
circles; there was little to choose between them in economy. Nor could the two systems be distinguished
by their accuracy. When Copernicus had finished adding circles, his cumbersome sun-centered
system gave results as accurate as Ptolemy's, but did not give more accurate results. Copernicus
had failed to solve the problem of the planets."5
Advantages
The Copernican model did have some aesthetic
and qualitative advantages. It provided a more natural qualitative explanation for the zigzag
motion of planets like Mars as observed from Earth, and it answered some important questions about
the ordering of the planets. That's why heliocentrism was eventually accepted. As Kuhn puts it,
"De Revolutionibus did convince a few of Copernicus' successors that sun-centered astronomy
held the key to the problem of the planets, and these men finally provided the simple and accurate
solution that Copernicus had sought."5
That's an important point
about scientific revolutions. At the start, the new theory rarely gives convincingly better results
than its predecessor. What usually happens is that it has some appeal, often aesthetic, that attracts
others to work within the new model. And if, over time, the new model proves fruitful in resolving
many puzzles, it gains adherents.6
The success of the Copernican
model was aided by the work of the Danish astronomer Tycho Brahe, who died a few years before the invention
of the telescope. Tycho is considered the greatest of the naked-eye observers. His wide-ranging
and accurate observations had an enormous impact.
Although Tycho's pivotal
role is recognized, what is less well known is that he, like most astronomers at the time, rejected
Copernicus's ideas of a moving Earth. It created more problems, he thought, than it solved. But
despite Tycho's opposition, his observations provided two major benefits for the heliocentric
model: They got rid of some erroneous old data that had plagued all the earlier models and thus helped
to remove some of the anomalies that the Copernican system couldn't explain. More important, the
precision of Tycho's data provided puzzles that enabled Kepler, a convert to Copernicanism, to
come up with the key idea that the motions of the planets were not circular—as Ptolemy, Copernicus,
and Tycho had all assumed— but elliptical.
In the folklore that surrounds
Copernicus, the introduction of elliptical orbits is rightly recognized as a crucial development
that led to ultimate acceptance of his model. The pre-Keplerian astronomers, however, are unfairly
characterized as insisting on circular motion because of aesthetic considerations, slavish
adherence to the authority of the Greeks, and so forth. But at the time, the reasons for assuming
circular motions were quite sensible. Because there were no good theories of force or gravity,
one needed to have an explanation of motion. Circular motion could be explained by a plausible hand-waving
argument. One could say that it was an initial condition—that once an object had been set in
circular motion it would, if undisturbed, continue circling forever.
More complicated motions
like elliptical orbits would mean that the planets' speeds and distances from the Sun were constantly
changing. But that required a dynamical theory that simply did not exist in those pre-Newtonian
times. Just introducing the idea of a moving Earth created all kinds of unsolved problems for the
physical theories of the day. Adding noncircular motion would have compounded those problems,
providing even stronger grounds for rejecting Copernicus.
Kepler's innovative idea
of elliptical orbits, coupled with his law of areas, did let the Copernican model dispense with
cumbersome epicycles. But his accurate Rudolphine Tables for planetary motion, published
in 1627, were difficult to use. It was Newton's theories of motion and gravity, not published until
60 years later, that sealed the scientific case in favor of Copernicus by putting his model on a firm
theoretical footing.
Religious objections
The actual religious reaction to the
heliocentric model also differs from the folklore. For one thing, Copernicus did not seem to fear
religious opposition to his ideas. After all, he was a reputable cleric himself. He even dedicated
his book to Pope Paul III with a letter in which he apologized for the seeming outlandishness of his
suggestion that the Earth moved. He explained that he was forced to that hypothesis by the inadequacy
of the Ptolemaic system for constructing calendars and predicting the positions of stars. A cardinal
and a bishop were among those who urged him to publish his book. In fact, for 60 years after Copernicus's
death just two months after its publication, De Revolutionibus was read and at least partially
taught at leading Catholic universities.
In 1600 the church did burn
at the stake the philosopher Giordano Bruno, an adherent of Copernicus, for heresy. But Bruno was
condemned for other heresies against Christian doctrine rather than explicitly for being a Copernican.
However, the fact that Bruno had been an advocate and popularizer of heliocentrism may have led
to the later perception that he was the first martyr of the new science.
For many years after the
publication of De Revolutionibus, while Copernicus's ideas remained within the mathematical
astronomy community, authors of more popular books on astronomy and cosmology were either unaware
of his work or chose to ignore it. A few nonastronomers did ridicule it—not for being heretical
but for promulgating the patently absurd idea of a moving Earth.
It was through popularizers,
some of them poets, that Copernicus's ideas eventually became more widely known and began to spark
religious opposition. But here too, the actual history is surprising. Opposition arose initially
among Protestant groups rather than from the Roman Catholic Church.
Kuhn suggests that this
was because Martin Luther (1483–1546) and other leaders of the Reformation were emphasizing
the Bible as the fundamental source of Christian knowledge and authority. And there were manifest
contradictions between the Bible and Copernicus. The Catholic Church, by focusing more on doctrinal
issues, actually had greater flexibility in dealing with science.
Luther spoke out against
heliocentrism in 1539, saying that the idea of a moving Earth going around a stationary Sun clearly
went against the account in the book of Joshua that says Joshua commanded the Sun to stand still.
Luther's deputy Philipp Melanchthon followed up by finding other biblical verses that described
Earth as stationary.
The conflict between scripture
and Copernicanism was not limited to verses that involved the motion of Sun or Earth. The realization
was growing that acceptance of Copernicanism raised other profound theological difficulties
as well. As Kuhn points out, the problems just kept multiplying:
When it was taken seriously,
Copernicus' proposal raised many gigantic problems for the believing Christian. If, for example,
the Earth were merely one of six planets, how were the stories of the Fall and of the Salvation, with
their immense bearing on Christian life, to be preserved? If there were other bodies essentially
like the Earth, God's goodness would surely necessitate that they, too, be inhabited. But if there
were men on other planets, how could they be descendants of Adam and Eve, and how could they have inherited
the original sin? . . . Again, how could men on other planets know of the Savior
who opened to them the possibility of eternal life? Or, if the Earth is a planet and therefore a celestial
body located away from the center of the universe, what becomes of man's intermediate but focal
position between the devils and the angels? If the Earth, as a planet, participates in the nature
of celestial bodies, it cannot be a sink of iniquity from which man will long to escape to the divine
purity of the heavens. Nor can the heavens be a suitable abode for God if they participate in the evils
and imperfections so clearly visible on a planetary Earth. Worst of all, if the universe is infinite,
as many of the later Copernicans thought, where can God's Throne be located? In an infinite universe,
how is man to find God or God man?5
As time went on, Copernicus's
ideas were seen as seriously disturbing to Christianity; they had to be countered. Soon the Bible
became the main weapon used against Copernicus. Protestant and Catholic clerics in the 17th century
started combing through it for ammunition. People started calling the Copernicans infidels and
atheists and urged their repression. But the new Protestant churches did not have the powers of
suppression and enforcement that the long-established Catholic Church had.
Kuhn argues that it was
probably the menace of burgeoning Protestantism that caused the Catholic hierarchy in 1616 to
switch abruptly from tolerance of Copernicanism to repression. "Copernican doctrines were,
in fact, condemned during the Counter Reformation, just when the Church was most convulsed by internal
reforms designed to meet Protestant criticism. Anti-Copernicanism seems, at least in part, one
of these reforms. Another cause of the Church's increased sensitivity to Copernicanism after
1610 [the year Galileo first turned a telescope to the heavens] may well have been a delayed awakening
to the fuller theological implications of the Earth's motions. In the 16th century those implications
had rarely been made explicit."5
The idea of the Copernican
model being a demotion for humanity probably first developed around 1650, after the scientific
community had already accepted heliocentrism. Religious bodies undertook what was essentially
a propaganda war against Copernicus. What probably happened was that after the heliocentric model
had been well established, the location of the Sun did come to be perceived as a privileged place.
So people read back into history the newly believed excellence of the center and attributed that
belief retrospectively to the pre-Copernicans. The demotion idea may have been introduced as
part of the effort to rally nonscientific religious people to turn against Copernicanism by appealing
to their pride as human beings.
The Protestant churches
abandoned their opposition to Copernicanism fairly quickly when it became clear that the evidence
in favor of a Sun-centered system was overwhelming. But the Catholic Church, being a much larger
and more tradition-bound and bureaucratic institution, was left clinging to its anti-Copernican
views for a long time. Its ban on Copernicus remained until 1822, and his book remained on the forbidden
list until 1835. In fact it was only in 1992 that Pope John Paul II lifted the edict of inquisition
against Galileo. Thus the Roman Catholic Church is now generally regarded as the principal villain
in perhaps the most notorious episode in the history of science.
What can we learn from all
this? The story of the Copernican revolution shows that the actual history of science often bears
little resemblance to the popular capsule versions that are learned in school or college or portrayed
in textbooks and the popular media. Steven Weinberg calls them "potted history." The true story
is much more complicated, but it's also a lot more interesting.
My thanks to Owen Gingerich
for an enlightening discussion and many helpful suggestions.
Mano
Singham is director of the University Center for Innovation in Teaching and Education and
adjunct associate professor of physics at Case Western Reserve University in Cleveland, Ohio.
References
1. See, for example, P. Fishbane, S. Gasiorowicz, S. Thornton, Physics for Scientists and Engineers, 2nd ed., Prentice Hall, Upper Saddle River, NJ (1996), pp. 1, 320, 321.
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