The Galileo Myths

Galileo never dropped any balls from the Tower of Pisa and he never spent time in a dungeon. But myths, repeated often enough, are taken as truths. Especially when they are repeated by famous scientists such as Carl Sagan, Neil DeGrasse Tyson and Stephen Hawking.

22 of the more common Galileo Myths are listed below. To show or hide the explanation of a myth you can click/tap the Myth's title.

There is documented evidence of only two Tower of Pisa experiments during Galileo's time; neither conducted by Galileo. One of the experiments was done by Vicenzio Renieri, a Roman Catholic monk and professor at the University of Pisa. Renieri was a friend of Galileo's and reported it immediately to Galileo ( see Galileo's Contemporaries ). Another experiment was done by Giorgio Coresio, another University of Pisa professor.

Several free fall experiments from towers had been conducted before the suggested date of Galileo's mythical experiment (these include experiments by Simon Stevin, Giuseppe Moletti, Varchi, John Philoponus). John Philoponus had conducted his experiment about 1000 years before Galileo was born. The image below is taken from a book on the lives of great scientists (Story-Lives of Great Scientists,Rowbotham).

The first mention of the Eppur si muove myth in the English language was by Giuseppe Baretti in 1757, more than a century after Galileo's death. Early biographies of Galileo never mentioned the event. Records of Galileo's trial do not reference any similar statements being said by Galileo.

By the late nineteenth century, historians were skeptical of Baretti's account. The myth was revived in the early twentieth century, aided by an art hoax. The details of the hoax are only unravelling now (see The Eppur Si Muove Hoax). A portrait of Galileo was discovered with the words "E pur si muove" in the background. The painting was purported to have been painted in the seventeenth century near the time of Galileo's death for the brother of one of Galileo's best friends. The painting is more likely a Belgian painting from the nineteenth century.

Fortunately, we have the floor plan of the 5-room suite in the Palace of the Holy Office that had been assigned to Galileo(see image below) [_1_] . It was about the size of the average American home (approximately 230 sq. m. or 2500 sq. ft.). Two of the rooms overlooked the Vatican Gardens. The suite came with a personal valet. The ante room (similar to a waiting room) allowed Galileo's valet to greet visitors before ushering them to meet him. Galileo was given two choices for food, eat his meals with the Cardinals of the Inquisition or to have his favoured Tuscan food and wine provided to him by the Tuscan Embassy. He chose the food and wine from the Tuscan Embassy ( see Galileo's Battle for the Heavens ).

What if no one invented the scientific method ( see Nobody Invented the Scientific Method ). There is no agreement on exactly what the scientific method is. But even if you use the definitions typically taught in grade school there is a problem. The scientific method is a specific approach to inductive reasoning. There was continuous discussion of inductive methods similar to the scientific method from the time of the Greeks, and through the early and late middle ages by Greek, Islamic and Christian scholars. Galileo's first important position was at the University of Padua. The University was already an important center for the development of inductive reasoning techniques (the double regress) which was very similar to the scientific method (see Medieval Methodologists).

Modern refracting telescopes owe more to Johannes Kepler than to Galileo, and modern reflecting telescopes owe more to Laurent Cassegrain than to Isaac Newton. For the last 350 years astronomical refracting telescopes have been based on Johannes Kepler's suggested design (see Timeline of the Telescope) not Galileo's. The first champions of the Keplerian design were Jesuit contemporaries of Galileo (see Jesuits and the Early Telescope). When reflecting telescopes became the preferred approach for building research telescopes, it was Cassegrain's design, not Newton's, that was adopted. Laurent Cassegrain was a Catholic priest contemporary with Newton. .

The reason why the Galilean telescope design was dropped so quickly was problems with the field of view. The image below shows a view of the moon from a 20X Keplerian telescope and a 20X Galilean telescope. The bubble in the middle of the moon is the field of view of a Galilean telescope. As you increase the power of a Galilean telescope the field of view decreases to the point where the telescope becomes useless.

Tim O'Neil outlines some problems with crediting Galileo as the first modern scientist in "Why is Galileo considered the "Father of Modern Science"?. Galileo's use of observation and carefully designed experiments was not unique in his time. The various free fall experiments conducted by Galileo's contemporaries all exhibit good design. For instance, when Galileo was only 12 years old, Giuseppe Moletti (a professor at the University of Padua) conducted a free fall experiment by dropping balls from a tower. Moletti, like others of his time, knew about controls. He controlled for shape, material and volume (see Galileo's Predecessors). Galileo's use of mathematics to describe natural events also wasn't unique. The use of mathematics in the study of motion was already widespread throughout Europe and had been for more than two centuries ( see The Oxford Calculators). We know that Galileo had been exposed to this previous work from his own notes as a student [_2_] . Galileo did champion the use of physical experiments in his writings. Although he talked the talk, Galileo didn't always walk the walk. He often fell back on "Mind Experiments" instead of actual physical experiments. The use of mind experiments to support arguments was common amongst renaissance scientists. Galileo didn't always describe the experiments such that they could be easily replicated. In fact, there is still some controversy over whether some of the experiments he described were real physical experiments or just mind experiments.

The best model being argued during Galileo's day was Kepler's model, the one that is taught in grade schools today. Galileo's preferred model was the Copernican. Galileo felt that Kepler was so erratic that it was best to ignore his work completely (see Galileo's Contemporaries). The Keplerian model already had one major success before Galileo's Dialogue of Two Chief World Systems when it successfully predicted the Transit of Mercury (see Gassendi and the Transit of Mercury). The image below is Gassendi's drawing of the transit. In this experiment, the Copernican model faired badly, performing even worse than the Ptolemaic model. The Copernican Model did not fit with observations any better than any of the competing models, including the ancient Ptolemaic Model. This has been confirmed by modern computer-based statistical analysis [_3_] .. The Copernican Model may have been more simply calculated, but this wasn't as important as it may seem. Users of the models would be working from pre-calculated tables not the models themselves.

Galileo's "proof" that the earth revolved around the sun was more a strawman that a scientific proof (see Galileo's Strawman). During Galileo's time there were six competing cosmological models. Galileo chose one model, the Ptolemaic, and demonstrated that some of his observations (retrograde motion, phases of Venus) made it impossible, From this he assumed the Copernican model was correct. But all the cosmological models except the Ptolemaic model accommodated Galileo's observations. At the time the heliocentric models had their issues. If the earth really did revolve around the sun, there should be evidence of stellar parallax but none was observed (see Copernicus and Stellar Parallax ). Another problem for scientists of the time is that if Galileo was correct you should expect the Copernican Model to predict planet positions better than earth centered models; it didn't. Galileo also presented a disastrous support for heliocentrism based on tides, but in his world there was only one tide per day. Having a good idea and some supporting evidence doesn't make a scientific proof. This was true of Alfred Wegener in the 20th century, Charles Darwin in the 19th century and yes, Galileo Galilei in the 17th century (see Wegener, Darwin and Galileo).

There were many free fall experiments before Galileo's experiment. These started about 1000 years before Galileo (John Philoponnus) but there were many in the sixteenth and early seventeenth century (Varchi, Borro, Buonamici,Moletti, Mazzoni, Harriot, Stevin, Coresio, Renieri).

When science commentators discuss the blind faith put in Aristotle, they ignore what happened in the century before Galileo's birth; European mariners crossed the equator and rounded the Cape of Good Hope, and Europeans colonized the Western Hemisphere. Aristotle and Ptolemy had written extensively on Geography, Meteorology and Biology. The observations by the mariners and Spanish Jesuit naturalists based in South America showed how disastrously wrong both Aristotle and Ptolemy could be on all of these subjects (see Galileo's Contemporaries). The maps below show a Ptolemaic map from before Columbus' voyage and a Spanish map from about 3 decades after his voyage.

A few years before Galileo was born, Domingo de Soto, a Roman Catholic priest, published a physics text that stated the objects in free fall undergo constant acceleration obeying the "times square law". This was Galileo's Law of Free Fall. The book was tremendously successful and had gone through 8 printings before Galileo had graduated from university (see Galileo's Predecessors). The behaviour of objects undergoing constant acceleration had been discussed for centuries before Galileo (see The Oxford Calculators). The "times square rule" and "Galileo's Odd Number Rule' had been proposed by the Parisian doctors (e.g. Nicole Oresme ) centuries before as well. Galileo never experimentally discovered the law of free fall; he experimentally proved it.

Thermometers must have a scale in order to measure differences in temperature. Galileo invented a thermoscope that gave an indication of the temperature but didn't have a scale. It was Santorio Santorio who invented the thermometer in 1612.

As with some other Galileo Myths, the truth is the exact opposite of the Myth. The Cardinals from Galileo's time were early adopters of telescope technology. Galileo's first public demonstration of his telescope was to the Doge of Venice in August of 1609. By that time, Cardinal Borghese of Rome had already acquired a telescope from artisans in Northern Europe [_4_] . After the demonstration in Venice, Galileo started building telescopes for others. Many of his clients were Cardinals.

Cardinals were Galileo's perfect client. He didn't want his telescopes getting into the hands of mathematicians or scientists since that could mean more competition for astronomical discoveries. The more powerful princes and dukes might have court mathematicians or astrologers. The Emperor of the Holy Roman Empire was not able to get a Galilean telescope. This is likely because his court mathematician was Johannes Kepler. The Emperor complained to the Tuscan ambassador as to why he shouldn't get priority over the Cardinals [_5_] . Eventually Kepler was able to borrow a telescope from the Catholic Archbishop of Cologne.

A related myth replaces 'Cardinals' with 'Aristotelian professors'. This is questionable too. There was a letter from Galileo to Kepler about learned people who do not wish to try out the telescope, but it doesn't mention names. Galileo's colleague and friend, Cremonini, told him that he would not look through the telescope, after looking through it. He complained that it gave him a headache. Given the questionable quality of the optics from that time, this is believable. The only professor known to refuse to try out Galileo's telescope was Giulio Libri.

After Galileo's trial there was no change in his ability to receive the sacraments of the church [_6_] . When he moved back to Florence due to illness, he made a special request that he be allowed to be carried to a local church to attend Mass on feast days. It was approved. Galileo's contemporary, Johannes Kepler, was excommunicated from the Lutheran church in 1619.

Galileo did not argue against a flat earth because he didn't have to. Medieval scholars, like the Greeks before them, believed in a spherical earth. And this knowledge went beyond the scholars, since there were many references to a spherical world in important popular literature from the middle ages. The myth probably originated as part of a propaganda war between Protestants and Catholics in the Early Modern Period to portray the Catholic Church as backward. The myth was taken up by several nineteenth century authors to support the thesis that the church and science conflict. The history of the Flat Earth myth is discussed in detail in Inventing the Flat Earth by Jeffrey Burton Russell.

Popular myths die hard. Although Jeffrey Burton Russell soundly thrashed the Flat Earth Myth, the news hasn't reached everyone. Generations living today grew up being taught the Flat Earth Myth as fact. They would have no reason to doubt that they were being taught the truth when they graduated, so they would have no reason to revisit what they were taught. That is why it is so easy to find famous figures in recent times who believed or believe the myth. These include Neil deGrasse Tyson (Flat Earth Tweets), George Bush Sr. [_7_] and Barack Obama ( Obama Speech 2012). This is another reminder that the best place to get your history of science is from a historian, not a scientist, TV personality or politician.

The photo above is an aerial view of Galileo's Villa Il Gioiello in Arcetri. It was a casa da signore, a landowner's villa. The villa was named The Jewel because of the beautiful view. Villas in the hills surrounding Florence had been used for centuries by the rich of Florence to escape the oppressive summer heat of the city. They were often larger than the owner's homes back in Florence. Arcetri was considered so beautiful that a few years before Galileo's arrival the Medicis had selected Arcetri as the site of their summer palace. Galileo's wine cellar at Villa Il Gioiello, stored the equivalent of 1200 bottles of wine. Detailed knowledge of the size, layout and contents of Villa Il Gioiello, during Galileo's lifetime are known through the letters from his daughter and an inventory taken by his son on his death [_8_] .

There was no reference to the myth during Galileo's lifetime. The chandelier that supposedly sparked Galileo's great discovery wasn't even installed in the cathedral until after his student days. Galileo didn't pay serious attention to the isochronicity of pendulums until much later in his career. In 1614, Santorio Santorio, developed a device called a pulsilogium which used a pendulum to time a patient's pulse. Galileo was not the type who would sit idly by if he felt someone was getting credit for something he rightly deserved [_9_] . Galileo never challenged Santorio's priority.

The picture above is Dante's medieval vision of the center of the universe (illustrated by Gustave Dore). It was the ninth circle of hell located at the center of the earth. Here, Satan is half-encased in a frozen lake, chewing on three men who betrayed their benefactors. In Copernicus's time you couldn't demote earth any further. The demotion myth is an example of presentism; assuming attitudes of times past were the same as the present. Being at the center of the universe wasn't a great place to be in medieval or early modern Europe. Thomas Aquinas described a medieval cosmology where the earth was at the centre, being the most material and coarse. Even Galileo thought Copernicus's model was promoting the earth.

“I will prove that the Earth does have motion . . . and that it is not the sump where the universe's filth and ephemera collect.

Galileo did not blind himself by "peering at the sun through his telescope". The medical term for sun blindness is solar retinopathy. If Galileo had solar retinopathy he would have been centrally blind but would have retained his peripheral vision. This is because the sun would have only burned the small spot on the retina where vision is very sharp (the macular). There is no indication that Galileo was centrally blind.

Galileo may have had a congenital disease of the sinus where mucus buildup would force one or both eyeballs downwards and outwards [_10_] . The portrait above shows just that. It was done by the realist portrait artist, Ottavio Leoni, in Galileo's lifetime. Another possible explanation was simple glaucoma...Galileo was over 70 when he went blind.

There were ways to project images from telescopes that were completely safe and even if you didn't use these devices you can view the sun at sunrise and sunset with relative safety. The Jesuits at the time were using camera obscura (a prototype of the camera that could take any view and project it onto a two-dimensional surface (see Jesuits and the Telescope). Galileo is known to have used projection devices as well.

Galileo was never charged with heresy, let alone convicted. Galileo's trial was about whether he had broken an agreement he had made in a previous meeting with the Holy Office (1616) to not present Copernicism as a proven truth. If the agreement was authentic, Galileo had clearly backed out on this promise. The evidence was in print; Galileo's Dialogo sopra i due massimi sistemi del mondo. A key question in the trial was whether the documents on the agreement were authentic.

It is never a good idea for the untrained to interpret legal documents, even if they understand the 'literal' meaning of every word in the text. The legal implications of the text are what counts. Sites such as History.com reference quotes (as below) without explaining what they mean.

We pronounce, judge, and declare, that you, the said Galileo… have rendered yourself vehemently suspected by this Holy Office of heresy..

Formal heresy was a very serious charge. "Vehemently suspected of heresy" was a completely different charge. The severity of 'vehement suspicion' was at the level of missing Mass and eating meat when you weren't supposed to [_11_] . The judgement by the Holy Office did mention Galileo's cosmological beliefs and that they were contrary to scripture. This doesn't necessarily imply heresy. Previous statements by the Holy Office had accepted the possibility of heliocentricity, that if proven true, would require revisiting current interpretations of the Bible (see here).

Discussions of Galileo's trial often miss an important backstory. The pope at the time, Urban VIII, had been an admirer of Galileo since his days as a cardinal. He even arranged church funding to support Galileo's work (see Galileo and the Church). Correspondence from the time suggests that he was privately sympathetic to Copernicism, even though he didn't want to publically admit it [_12_] . The pope's endorsement (imprimatur) of Galileo's Dialogo was included right after its title page. It was given with the understanding that it would be an objective presentation of the strengths and faults of the different cosmologies. Galileo's Dialogo clearly advocated the Copernican model. This greatly compromised the Pope since it could be interpreted that the church was publicly endorsing Copernicism. At the time Copernicism was still contentious from both a scientific and theological viewpoint.

The Roman Inquisition's application of 'house arrest' doesn't match our modern definition of 'house arrest'. It didn't necessitate being confined to a house. It was typically an injunction specifying where you can and can't go. This looser definition allows for an offender to continue working, even if it was outside his/her house [_13_] . Sending a "breadwinner" to prison was tremendously punitive to the offender's family, especially for the poor or middle class. The Inquisition's version of house arrest could punish the offender with less impact on the offender's family. House arrest and the use of penances also minimized the need for a prison system. There might even be lessons here for us today.

According to Galileo's correspondence, he frequently visited his daughters at a nearby convent during his "house arrest" [_14_] . When his friend, Elio Deodati, requested a portrait, Galileo made multiple sittings over a three month period at the studio of Justus Sustermans. The Sustermans studio was about 2 kilometres away. This was considered the limit of his quarantine area [_15_] .

Jesuit contemporaries of Galileo were first to derive a reasonably accurate estimate of g ( <7% error). They developed a pendulum timing mechanism by having teams of Jesuits count the oscillations of pendulums of various lengths over a 24 hour period. The goal was to get a pendulum length that would generate 86400 oscillations in a day (since there are 86400 seconds in a day). They used an easily recognizable night-time celestial event to start and stop the timing. When they found a pendulum that oscillated at close to 86400 times a day, they used it to time balls falling from one of the tallest towers in Europe, the Torre Asinelli in Bologna. Their work pointed to an acceleration due to gravity of 914 cm/sec/sec versus the actual value of about 981 cm/sec/sec [_16_] . Galileo's value was about 467 cm/sec/sec, about 50% off the mark. The image below is a view from the top of the Torre Asinelli; the smaller tower below is just a few meters shorter than the Tower of Pisa.

Galileo died in Italy and Newton was born in England. Different calendars were used by Italy (Gregorian) and England (Julian) in the seventeenth century. Using a modern (Gregorian) calendar for both events, Galileo died on January 8, 1642 and Newton was born on January 4, 1643. Using the discarded Julian calendar, Galileo died on December 29, 1641 and Newton was born on December 25, 1642.