The true history of science and religion, part 1: Galileo

The true history of science and religion, part 1: Galileo

There is a popular myth that science and religion are at odds and have been throughout history. Maybe you were even taught this myth at school.

I’m sure you’ve heard of Galileo Galilei. He’s that famous 17th century scientist who tried to convince everyone that the Earth revolves around the sun. Then the Catholic Church demonized and imprisoned him for his troubles. Or so the story goes.

It’s not true. At least, not entirely.

Welcome to the first in what will be a series of blog posts about the true history of science and religion. I say true because this series will shoot down some pervasive myths that you may not have been aware are actually myths.

It’s long been thought by many that the story of science and religion is full of conflict. But, as I hope to make clear in these articles, the real story is much more benign. Sure, there have been conflicts between science and religion, but fewer and less serious than you might think.

The Conflict Thesis

Two men popularized the idea of constant conflict between science and religion (now known as the conflict thesis) in the late 1800’s. The first, John William Draper, was a scientist. He wrote a book called History of the Conflict between Religion and Science (1874). The second, a writer named Andrew Dickson White, wrote a book called A History of the Warfare of Science with Theology in Christendom (1896). Both books remained influential for a while, but historians eventually realized that they made their cases by distorting the facts.

Historians of science have rejected the conflict thesis since the 1970’s. But it hasn’t gone away.

Portrait of Galileo

Galileo Galilei

That brings us back to Galileo. His trial by the Catholic Church is often used as an example of conflict between science and religion. On the surface, this sounds reasonable. After all, the Church tried him for heresy. But the details matter.

In Galileo’s time, educated people believed that the earth was a motionless sphere located at the center of a spherical universe. The sun, moon and five known planets orbited the earth. This was a well-defined worldview, accepted since the time of Aristotle and Ptolemy, and we can use the words geocentric (earth-centered) and geostatic (stationary earth) to describe it.

Copernicanism is Born

Portrait of Copernicus

Nicolaus Copernicus

In 1543, Nicolaus Copernicus introduced a new worldview in his book On the Revolutions of the Heavenly Spheres. In this new worldview the universe was still spherical and the moon still orbited the earth, but the earth rotated around its own axis and orbited the sun, along with the 5 other known planets. We can use the words heliocentric (sun-centered) and geokinetic (moving earth) to describe this worldview.

The Copernican worldview was not actually new. A Greek philosopher named Philolaus came up with it nearly 2000 years earlier, but it never caught on (this was before the days of internet marketing!). Copernicus simply described it better and with more evidence. Nonetheless, his book still faced a lot of criticism, as it contradicted so much of what was known about the universe at the time.

The biggest objection to the geokinetic view was simple and quite obvious. If the earth is really in motion, we should see and feel it. But we don’t!

In those days most scientists (called natural philosophers) believed their senses to be reliable scientific tools. It was quite a stretch to tell them that their senses were lying to them.

Yet that is exactly what Copernicanism implied. Even though all of our senses tell us the earth is at rest, it’s actually rotating and zooming around the sun at incredible speeds!

Even today, you need pretty solid evidence to convince people of a theory that defies their own senses.

In fact, the foreword in Copernicus’ own book suggested that his theory should be viewed more as a useful tool for calculations than an actual description of reality (much like many view quantum mechanics today).

Enter Galileo.

Galileo Converts to Copernicanism

At first he was skeptical of the Copernican theory. But while he was working on a new theory of the physics of moving bodies, he came to realize that the physics actually worked better with the Copernican geokinetic theory than with the prevailing geostatic one.

Nonetheless he remained a skeptic. However, the invention of the telescope allowed him to make some new observations which added evidence to the Copernican theory and finally tipped him in favor of it.

Trial Part 1: The Letter

Support for the geostatic view was falling. Its supporters (including scientists), faced with a weakened scientific position, appealed to the Bible as an authority. Galileo argued strongly against this appeal in a letter to his friend Benedetto Castelli in 1613, which he later expanded on in his Letter to the Grand Duchess Christina (1615). He claimed that it was a matter of interpretation, and that the Bible was not an authority on matters of science anyway.

Ostensibly the expanded letter was addressed to the Grand Duchess, who had an interest in the topic, but Galileo was aiming at a much larger audience of critics and skeptics. He struck a tone that was a bit off for the task, coming across as arrogant, abrasive and high on his own genius. This didn’t win him a lot of converts.

Before the publication of the expanded letter, the original letter to Castelli was copied and spread around. Supporters of the geostatic view made sure that it ended up in the hands of the Inquisition and accused Galileo of heresy.

But Galileo was not standing alone. He had the support of several clergymen. One of them, Paolo Foscarini, had written a book explaining that the geokinetic view was compatible with the Bible.

Cardinal Robert Bellarmine

Cardinal Bellarmine

Foscarini sent a copy of his book to a Cardinal named Robert Bellarmine, a respected and reasonable theologian involved in the debate. Cardinal Bellarmine replied that the Aristotelian (geostatic) view not only fit with experiential evidence (that the Earth was not moving and rotating at high speed) but confirmed a literal interpretation of the Bible. He added, however, that were sufficient and convincing evidence to be presented in support of Copernicanism, a reinterpretation of the Bible would be warranted. The evidence so far presented was simply not compelling enough.

Bellarmine did not see a need to do away with the heliocentric view. He advocated treating it as a useful mathematical tool without any physical reality. But Galileo believed the theory to be literally and physically true, not just a calculation device, and was quite adamant that others should see it his way.

After examination of the evidence, the Inquisition did not find Galileo guilty of heresy. Instead, they appointed a committee of consultants to look into the matter of Copernicanism. The committee adopted a harsher stance than Bellarmine. They determined the heliocentric view to be not only heretical, but philosophically and scientifically unsound. They banned Foscarni’s book and asked Bellarmine to warn Galileo that he was not to hold Copernicanism to be literally true.

Galileo agreed.

Interlude: Galileo’s Big Mistake

The ironic thing about the whole Galileo affair is that, although Galileo was ultimately shown to be correct in his pursuit of Copernicanism, he was not correct at the time. In fact, he likely would have rejected the heliocentric view if he had followed the evidence to its logical conclusion.

The stars Galileo was seeing through his telescope were not stars at all, but diffraction patterns called Airy disks. In essence, they were artefacts of stars created by the telescope. Galileo couldn’t have known this because no one had discovered diffraction yet.

Galileo based his support of Copernicanism on two main pieces of evidence which he observed with his telescope. First, Jupiter had moons. Supporters of the geocentric view claimed that if Earth was moving, the moon would be left behind. But Jupiter was moving and clearly Jupiter’s moons were not left behind. Second, Venus had phases. This was significant because it meant that sometimes Venus was on the other side of the sun. In the geocentric model, Venus couldn’t be on the other side of the sun because both it and the sun were orbiting the Earth.

A contemporary of Galileo’s named Simon Marius saw the same Airy disks through his own telescope and came to the correct conclusion (correct based on the evidence and knowledge available at the time). These ‘stars’ were far too close to the Earth to fit with Copernicanism. Instead they fit with the Tychonic model (or geoheliocentric model) invented by a man named Tycho Brahe, who believed the sun orbited the Earth, the planets orbited the sun, and the stars were located in an unmoving sphere behind the planets. In the Tychonic model, the phases of Venus were explained because the planets orbited the sun. Furthermore, the stars would be rather close and thus appear as large as the Airy disks.

Tycho Brahe

Tycho Brahe

Copernicanism, on the other hand, required that the stars be very far away. Thus they should have appeared as tiny points of light (as they do on modern telescopes). In fact, it was Tycho Brahe who realized the necessity for the stars to be so far away under a heliocentric model. In order for the stars to appear as large as they did, they would have to be absolutely enormous, dwarfing the sun (Brahe sadly died before the invention of the telescope and did not get to see the Airy disks which seemed to support his model).

Brahe pointed out the absurdity of such enormous stars. Supporters of Copernicanism replied that it was not unreasonable because the Creator could make stars as large as He wanted (Tycho, for his part, used Biblical authority to bolster his claim of a stationary Earth).

Anyway, due to these Airy disks, Galileo calculated the stars to be far closer to the Earth than they actually were. This fit much better with the Tychonic model than the Copernican model, as Simon Marius realized. Nonetheless Galileo stuck with Copernicanism, doggedly pursuing the right theory with the wrong evidence.

Trial Part 2: The Book

Portrait of Pope Urban VIII

Pope Urban VIII

Pope Urban VIII, who took over in 1623, did not see Copernicanism as heresy, although he did believe it unprovable. After several conversations with the Pope, during which they got along quite well, Galileo started to write his book Dialogue on the Two Chief World Systems, Ptolemaic and Copernican(1632). He pitted the two systems against each other with the clear intention of supporting the Copernican view.

The book raised a lot of complaints. Galileo went about making his points in his usual abrasive way, which didn’t help his cause. Worse, one of his main arguments in support of Copernicanism was an incorrect idea that tides were caused by the rotation of the Earth. Galileo even made a mistake in claiming a tidal cycle of 12 hours, which was observably false. Notably, Johannes Kepler and René Descartes, two other scientists of the time who you might have heard of, were also followers of Copernicanism, but did not agree with Galileo’s theory of the tides.

Supporters of the geostatic view found a way to attack Galileo on a technicality. They had evidence that Galileo had been warned by the Inquisition back in 1616 not to discuss Copernicanism anymore. Galileo’s signature was not on the document, but since the man who had supposedly issued the warning was dead by then, there was no easy way to substantiate or refute the evidence.

The Pope, forced to act, appointed a special commission to investigate. The commission found the complaints to be relevant, so the case went to the Inquisition in Rome. Galileo would have gotten off with little more than an admission of guilt and repentance (a slap on the wrist), but the Pope had the final say on the matter. He intervened and forced a trial.

Galileo before the Inquisition

Galileo before the Inquisition

The reasons for Pope Urban VIII’s intervention are not entirely clear, but he certainly had cause to be angry at Galileo.

For one thing, Galileo hadn’t bothered to mention that he’d been warned by Bellarmine not to defend the heliocentric theory. The Pope was unaware of Bellarmine’s warning when he gave permission for Galileo to write the book.

Second, Galileo had made the Pope look foolish. Before the publication of the book, while Galileo and the Pope were still on good terms, they had discussed heliocentrism. While the Pope did not believe the theory to be heresy, he was also not convinced by it. He gave permission for Galileo to write the book, but under one condition: Galileo had to include a particular argument.

The Pope’s argument had to do with Galileo’s (incorrect) claim that the tides are caused by the motion of the Earth. He said that because God is omnipotent, we can never know the true cause behind the effects we see. So although the tides may appear to be caused by the motion of the Earth, we cannot be sure that there isn’t a different cause.

Galileo placed the Pope’s argument on the very last page of the book, where it was uttered by a foolish character and received a sarcastic response.

Adding complication to insult, the incident took place during the thirty years’ war, which the Pope did not support. Things were going badly and he was feeling political pressure from all sides. It was not the best time to be betrayed by a man he had thought his friend, and he was likely not in the most forgiving of moods.

In the end, the Inquisition arrested Galileo for ‘vehement suspicion of heresy’, still a lesser charge than actual heresy.


As you can see, the main conflict in this story was not a conflict between science and religion, but between competing worldviews. There were scientists and men of the church on both sides. It just happened, as it often does, that those with the most power (the Inquisition and the Pope) came down on the side of conservatism. They defended the old, established worldview.

Today some people view religion as antithetic to progress and part of this old worldview. This can be true in specific situations, but as a general statement it’s far too simplistic.

Did you know that Islam led the world in scientific progress for a thousand years?

Did you know that the harmony of science and religion is a central tenet of the Bahá’i Faith?

In case you’ve never heard of the Bahá’i Faith, it’s a religion of Middle Eastern origin that started in 1863. It now has over 5 million followers throughout the world.

The relationship between science and religion is not about conflict, but complexity.

Things are often more complicated than they seem. If you want to live as a compassionate and open-minded person, then I encourage you not to settle for simplistic ideas. Embrace the complexity of life and consider other points of view.

An interesting thing to note about the story of Galileo is that theologians were actively engaged in scientific discussions and scientists were likewise engaged in matters of theology. Science and religion were intricately tied together. Philosophy too was part of the mix. You might have noticed that I listed Descartes as a scientist of Galileo’s day. Probably you are familiar with him as a philosopher. In fact he was both. That was not unusual in a time when scientists were still known as natural philosophers.

Separation of science and religion and philosophy into separate pursuits is largely a modern idea, but the seeds of it can be seen in Galileo’s attitude. He was adamant that theologians should keep away from science. On the other hand, he was happy to get involved in theological debates.

I’m going to revisit this series in the future, as there are other stories to tell on the fascinating topic of science and religion.

Main Sources:

Galileo on the World Systems: A New Abridged Translation and Guide (1997) – Galileo Galilei, Maurice A. Finocchiaro (editor & translator)

Science and Religion (The Teaching Company, 2006) – Professor Lawrence M. Principe

Galileo’s Religion Versus the Church’s Science? Rethinking the History of Science and Religion (Physics in Perspective, 1999) – D.B. Wilson

Seeds of a Tychonic Revolution: Telescopic Observations of the Stars by Galileo Galilei and Simon Marius (Physics in Perspective, 2010) – Christopher M. Graney

*Note: I am not endorsing or recommending these products. I provide links only in case you are interested in further reading on the topic. I will not get any affiliate money if you purchase them.

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1 thought on “The true history of science and religion, part 1: Galileo

  1. After meeting with the Inquisitors in Rome, Galileo never again wrote about the universal spirit that vivifies and moves all things. We don’t even know if the Inquisitors knew that, in private, secretly, quietly, Galileo too entertained such ideas.

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