sea level is nearly always the same (except for local effects like crustal rock beneath you, which is denser or less dense than average). The scientific data for these gravity measurements have been gathered for more than a century and are widely published, although flat-earthers reject all scientists as part of the global conspiracy that includes NASA. (Of course, many flat-earthers don’t believe in gravity, either, but fall back on Aristotle’s antiquated notions that objects fall because they are heavier or lighter.)
12. Consider the solar system: Anyone with a decent telescope, good night visibility, and a chance to look at the moon or the other planets night after night can confirm what early astronomers (especially Galileo) could see: all the other bodies in the solar system are spherical. You can see the shape of the moon clearly, especially as the shape of the illuminated part of the moon changes with the cycle of the full and new moons every month. After several nights of closely observing Jupiter in a good telescope, you can confirm that it is round and spinning on its axis; even better, each night you can see its four largest moons moving around as they orbit around it. It’s a lot more difficult to do this with Mars or Saturn, but Galileo was able to see it when he first trained a telescope to the skies. So if all the other bodies in space are spherical, why would only the earth be flat?
If that’s not convincing enough to fair-minded flat-earthers or to people sitting on the fence on the issue or having doubts about the shape of the earth, then they are hopelessly lost in the mind-set of a cultist, and no amount of evidence will convince them. Sometimes they accidentally reveal the disconnect between their worldview and reality, as when a tweet from the Flat Earth Society read, “The Flat Earth Society has members around the globe.” Then there is the humorous internet meme “The only thing flat-earthers have to fear is sphere itself.” So we will consider this case closed and will move on to the next weird idea about earth: geocentrism.
Ptolemy Revisited
Religion versus Science
The scene is a dramatic one, depicted in many plays and novels. Galileo Galilei, now sixty-eight years old, gray haired, losing his sight, and bowed with age, stands before the Inquisition in early 1633 (fig. 3.1). He is on trial for heresy, since he has advocated the notion that the sun is the center of the solar system (heliocentrism), a view first published by Nicholas Copernicus in 1543. This contrasts with geocentrism, the plain, intuitive common-sense idea that the earth, not the sun, is the center of the universe, as Aristotle and people since earliest times long believed (fig. 3.2). In 1609, using one of the first telescopes ever built (invented almost simultaneously in Holland and in Venice) to study the night sky, Galileo concluded that the earth moved around the sun, and he published his celestial observations and ideas in a short book titled Sidereus Nuncius (“Heavenly Messenger”) in 1610.
By 1616, the Inquisition was scrutinizing his works for signs of heresy. They warned Galileo that he could talk about heliocentrism in a theoretical way but not actually claim that the earth really did move around the sun. Trying to steer clear of antagonizing the Church, Galileo argued that heliocentrism could be made consistent with religious dogma. But Church leaders disagreed, citing such passages as Psalms 93:1 and 96:10 and many other verses. In 1 Chronicles 16:30, the Bible says, “The world is firmly established, it cannot be moved.” Psalm 105:5 reads, “The Lord has set the earth on its foundations; it can never be moved.” Another example is Ecclesiastes 1:5, which says, “And the sun rises and sets and returns to its place.” And in Joshua 10:12, the Hebrew leader Joshua calls on the Lord to make the sun stand still so that they can continue their battle. Thus, Galileo was fighting not only thousands of years of established belief in geocentrism but also the Scriptures, since Europe was still ruled by either the Catholic Church or the Protestants.
Figure 3.1. Painting of Galileo defiantly facing the Inquisition. (Courtesy Wikimedia Commons.)
The last straw for the Church fathers was the 1632 publication of Galileo’s provocative book Dialogue Concerning the Two Chief World Systems. Encouraged by the election of his supporter Cardinal Maffeo Barbarini as Pope Urban VIII and the support of some Italian nobles, Galileo framed the argument as a dialogue, a miniature play between three characters. This allowed him to make his argument by letting the characters debate the ideas among themselves, as Plato had done with the philosophical debates of Socrates. Galileo could put his own ideas in the words of one character (Salviati, the scientist in the dialogue) but could plausibly claim that he himself wasn’t advocating heliocentrism; the heretical ideas were spoken by only one character in his “play.”
Salviati presents the Copernican arguments for heliocentrism in a debate with the other main character, Simplicio, who represents the traditional geocentric views of Ptolemy, Aristotle, and the Church. Although the name was drawn from Simplicius of Cilicia, a sixth-century commenter on Aristotle, it was a deliberate double entendre, since Simplicio also meant “simpleton” or “fool” in Italian. The third character in the play is Sagredo, an intelligent but uncommitted layman and merchant who acts as the target audience and jury for the arguments of the other two. He eventually agrees with Salviati’s heliocentric solar system—as would any reader, since Salviati demolishes Simplicio’s arguments.
Figure 3.2. Famous 1888 engraving by Flammarion showing the old geocentric view of the universe. The image depicts a man crawling under the edge of the sky, depicted as if it were a solid hemisphere, to look at the mysterious Empyrean beyond. The caption translates to “A medieval missionary tells that he has found the point where heaven and Earth meet.” (Courtesy Wikimedia Commons.)
Galileo thought that he had cleverly avoided being accused of directly advocating heliocentrism as a true description of the world, but the Inquisition was not amused. The pope did not like the public ridicule that was clear in the character of Simplicio. Galileo was called to Rome to face several days of trial, where they showed him instruments of torture and made him recant his views on pain of torture and death. As he bowed before them and confessed his rejection of the heretical heliocentric views, Galileo supposedly muttered under his breath, “Eppur si muove” (“And yet it moves!”). Rather than torture the old man, the pope sentenced him to house arrest, where he spent the last ten years of his life unable to leave his domain. There, Galileo wrote his last great work, Discourse and Mathematical Demonstrations Relating to Two New Sciences, where he laid down the foundations of modern physics, especially regarding the motions of objects (kinematics).
By 1638, Galileo was completely blind (partially due to staring directly at the sun with his crude telescope to see the sunspots) and was suffering from a painful hernia and insomnia, and his devoted daughter had to take care of him. He died on January 8, 1642, at the age of seventy-seven. His Dialogues, along with Copernicus’s work, was banned by the Church, so they could not be printed or read except in places where the Church’s power was limited. Galileo’s books and his ideas were still under official Church ban until 1835, even as the rest of the world had moved on to modern astronomy thanks to the work of Isaac Newton in the early 1700s. Finally, on Halloween 1992, Pope John Paul II officially acknowledged the errors of the Catholic tribunals and announced that a statue of Galileo would be placed in the Vatican. In December 2008, Pope Benedict XVI praised Galileo’s work on the four hundredth anniversary of Galileo’s earliest telescopic observations. However, the plan to put his statue in the Vatican has since been shelved.
The idea of a heliocentric solar system is most famously attributed
