Not long ago, someone asked me if I’d seen the documentary, The God Who Wasn’t There (2005), which explores the “Jesus myth” and Christianity in general. It’s been out for several years, and despite the fact that it’s viewable for free on YouTube, I haven’t bothered to watch it, because it looks like an uninspired retread of common challenges to the Christian faith that tend to be very weak. However, from what I can tell, it does perpetuate one historical distortion that is worth refuting. From a partial transcript on IMDb, TGWWT puts forth the idea that it was primarily Christians who were wrong about the Earth-centered universe:

Narrator: The Earth revolves around the Sun. But it wasn’t always that way. The Sun used to revolve around the Earth. It was like that for hundreds of years, until it was discovered to be otherwise, and even for a few hundred years after that. But, ultimately, after much kicking and screaming, the Earth did, in fact, begin to revolve around the Sun. Christianity was wrong about the solar system. What if it’s wrong about something else, too? This movie’s about what happened when I went looking for Jesus.

Or, more likely, what happened when he went looking for anything but Jesus, but never mind. The problem with this statement is that it implies only Christians were wrong about the solar system, when the truth is that just about everyone was wrong about the solar system at one time or another. So why single out Christians? Without having seen the movie, I am fairly confident of the answer (hint: look at who appears in the movie). Unfortunately, the notion that the medieval Church was scientifically ignorant and held back scientific progress is a fairly easy misconception to perpetuate, because people who believe it are usually already eager to believe misconceptions about Christianity and/or they do not know enough to evaluate its validity.

I made a point to cover geocentric theory in my astronomy 101 courses, so let’s explore what my college freshmen students knew about this subject that TGWWT‘s writer/director Brian Flemming apparently did not (or did not want you to know about).

The geocentric model of the solar system, which places the Earth at the center of the universe, is an idea that is found in nearly every ancient culture. In Western Civilization, the idea is usually attributed to the ancient Greek philosopher Aristotle (384 BC – 322 BC), and was later systematized by the Alexandrian astronomer Claudius Ptolemaeus (aka Ptolemy, ~64 AD – 165 AD). The geocentric model persisted for more than 1,700 years, and while medieval interpretation of biblical scripture seemed to loosely support the idea, its formulation had nothing to do with Christianity.

To understand why the geocentric model persisted for so long, I want you to place yourself, just for a moment, in the ancient world where there is no such thing as telescopes, astronauts, or satellites. Your only notion of the Earth’s place in the universe is based on what your human senses tell you about the apparent motions of the heavens. You notice that the Sun and Moon make daily journeys across the sky from east to west, and that the stars at night travel in the same daily east-west direction. The familiar constellations also seem to drift across the sky over the course of weeks and months. To your human senses, it appears that the Earth is stationary and that objects in the heavens move about it in very predictable cycles. Armed only with these observations, it is entirely reasonable to assume that the Earth is at the center of the universe.

We owe a tremendous debt of gratitude to the Greeks, who were the first to seek natural explanations for the phenomena they observed. This reliance on natural explanations heralded the birth of science. But what is science? It is actually a difficult concept to define. Most of us understand science to be the search for knowledge, but knowledge can be acquired by other means. The scientific method works by making observations and asking questions in a very systematic way. One observes a phenomenon in nature (say, the motions of the heavens) and posits an educated guess about the nature of the phenomenon (everything in the heavens orbits the Earth, which is stationary). This educated guess is referred to as an hypothesis. The hypothesis then makes a prediction (where objects in the sky will appear on a certain date), and one carries out tests or observations to determine how well the hypothesis performs. If the hypothesis fails the test or cannot account for new observations, then it must be revised or abandoned in favor of a new hypothesis.

One such test of the geocentric model came in the form of retrograde motions of the planets. The Greeks observed that a handful of objects in the heavens moved in a way that was different from the other objects. For one thing, their positions were not fixed like the stars, but appeared to wander over a period of months. (The word “planet” comes from the Greek word for wanderer.) This retrograde motion, or apparent looping back of the planet’s path in the sky, is now understood in the context of the Sun-centered (heliocentric) model, but in ancient times it represented a significant challenge to the geocentric model. This challenge was resolved by placing each of the planets in a smaller orbit, called an epicycle, upon its larger orbit about the Earth. This was a key feature of the model put forth by Ptolemy, which is referred to as the Ptolemaic model.

The Ptolemaic model persisted for almost two millenia, because, clunky as it was, it made accurate predictions about the motions of the planets. Moreover, several key objections to the heliocentric model were unresolved. Centuries before Ptolemy, the Greek astronomer Aristarchus (310 BC – ~230 BC) proposed a Sun-centered solar system, but was ridiculed by his peers for it. First, the idea that the Earth was moving was counterintuitive, because of the apparent motions of the heavens. But the most significant objection was that stellar parallax was not observed. This is the apparent shifting of position of closer stars relative to more distant background stars, which must occur if the Earth is moving around the Sun. As this was not observed, it was reasonable for Aristarchus’ fellow Greeks to reject his idea.

Fast-forward almost two millennia to Nicolaus Copernicus (1473 – 1543 AD), who was a true Renaissance man. In addition to being an astronomer, he was also a physician, scholar, cleric, and military leader. Like Aristarchus before him, Copernicus went against popular sentiment and proposed a heliocentric system. There is evidence that Copernicus knew he was recycling Aristarchus’ ancient model, but his genius was in recognizing its potential as a much more elegant and compelling model than the geocentric model. It is true that Copernicus’ book stirred some controversy within the Church, but contrary to popular belief, the Church was not monolithically opposed to, but rather divided on, the subject of heliocentrism. Secular scientists at the time likewise held to the Aristotelian school of thought, and mostly rejected Copernicus’ ideas. There was good reason for this, as the major objections to the heliocentric model had not yet been overcome. In particular, since Copernicus used circular orbits for the planets, instead of what we now know to be elliptical orbits, the predictions of the Copernican model were less accurate than those of the Ptolemaic model. Heliocentrists also had to contend with the lack of observed stellar parallax, and there were still more objections based on Aristotelian notions about nature. For instance, long before Newton developed his laws of motion, Aristotle held that all objects naturally come to rest, which meant that if the Earth was moving it would leave airborne objects (birds, clouds, etc.) behind. It was not until Galileo anticipated Newton’s first law (objects in motion tend to stay in motion) with simple experiments and made some key observations with his telescope—among them, that the stars are too far away to observe parallax¹—that these objections were overcome and the Copernican Revolution was solidified.

It is important to understand that there was as much objection to the Copernican model from secular scientists as from the Church. Perhaps more. (For instance, it was supposedly a secular rival who reported Galileo to the Inquisition, illustrating that scientific enterprise has always been a little cut-throat.) The objections of the Church were only partially founded on Christian doctrine, which was based at that time on interpretation of scripture that was consistent with the Aristotelian school of thought. There is, in fact, nothing in scripture that dictates an Earth-centered system. The politics of the time also complicated things, with the Catholic Church struggling to come to grips with the tremendous effects of the Reformation. The most influential figure of the Reformation, Martin Luther, strongly objected to the ideas of the “upstart astrologer” Copernicus, and the Catholic Church was anxious to stay abreast with Protestantism on such an important issue. It is also important to understand that Copernicus was eventually shown to be incorrect in his placement of the Sun at the center of the universe; we now understand that there is no ‘center’ to the universe, an idea that is difficult to accept for many people.

What can we conclude from all of this? We can conclude that the most important factor preventing wide-spread acceptance of the heliocentric model was simple human nature. As clever as we sometimes are, we are constrained by limited perspective and emotion. Limited perspective prevented scientists from perceiving the stellar parallax that was predicted by the heliocentric model. Human emotion means cherished ideas often have a powerful hold on people, especially when it comes to accepted ideas that have served mankind well for many centuries. Put these two constraints together and you have the very non-linear progression from old ideas to new ideas that is evident throughout human history.

Having not seen TGWWT, I can only surmise from the partial transcript that either Flemming knows very little about scientific history, classical thought, and theology, or he is being deliberately disingenuous to make Christians look bad. Which is unfortunate, because, with just a few changes to the quote from the transcript, I think we could have turned his movie into a much more interesting narrative on the fallibility of human reason:

Narrator: The Earth revolves around the Sun. But it wasn’t always that way. The Sun used to revolve around the Earth. It was like that for hundreds of years, until it was discovered to be otherwise, and even for a few hundred years after that. But, ultimately, after much kicking and screaming, the Earth did, in fact, begin to revolve around the Sun. Mankind was wrong about the solar system, but eventually figured it out. What is it today that we don’t yet understand that will be obvious to mankind hundreds of years from now? Let’s speculate…

[1] With the advent of larger and more sophisticated telescopes, stellar parallax was indeed observed.

Recommended reading:

• What’s So Great About Christianity by Dinesh D’Souza