From experiments to inquisition, discover the Renaissance scientist’s iconic clash with the pope and how he proved that the Earth goes around the Sun
Galileo Galilei was never destined for a life as an astronomer and physicist. Ironically, he attended school at the local monastery and after this had been well on his way for a future as a doctor. His father, Vincenzio, had high hopes for his son and arranged for him to study medicine at the University of Pisa from 1581. In spite of this, Galileo never cared for biology, developing a far greater interest in philosophy and mathematics. Against the protestations of his father, he promptly switched subjects and never looked back.
Studying hard for four years, Galileo left university without a degree and turned his hand to private tutoring. During this time he wrote his short treatise, Cosmography, which he used to teach his students about the mysterious celestial bodies. Cosmography adhered to the widely accepted, traditional geocentric philosophies of Aristotle and Ptolemy, which placed the Earth at the centre of the universe.
He soon moved on from his tutoring career and returned to the University of Pisa in 1589, where he spent the next three years as the professor of mathematics. It is likely that this is when he succeeded in disproving Aristotle’s theory that objects of different mass fall at different speeds, though whether Galileo actually tested this by dropping balls of the Leaning Tower of Pisa is disputed as the only record we have of it is a biography written by his pupil Vincenzo Viviani in 1717.
Unfortunately, his unconventional beliefs made Galileo unpopular so his contract at the university was not renewed. He moved once again in 1592 and travelled north to Padua, where he assumed a new, higher paid position as a professor of mathematics at the city’s university. Here, Galileo really began to hone his research. He conducted a number of experiments, many of which were in the field of mechanics.
Starting in 1602, he made some of the first scientific observations regarding pendulums. He also uncovered the principle of isochronism, where a pendulum would take the same time to complete a swing regardless of how big that swing was. Ultimately, this led to the invention of the accurate mechanical clock in 1656 – a device humanity came to rely on.
After a few years of dedicating his time to his experiments, everything changed. In 1609, Galileo heard rumours that a device that could make distant objects appear close had been invented in the Netherlands: the telescope. Once he learned that it had been simply made with just a tube and a lens on both ends, he immediately set out to re-create one for himself. His initial versions ranged in magnifying power, up to eight times, but by 1610, he had developed a telescope that could be magnified 20 times – far more powerful than the original, rudimentary invention.
Armed with his telescope, the possibilities open to Galileo were endless. Just between 1609 and 1610 alone, he discovered mountains on the Moon, the four satellites of Jupiter and numerous stars in the Milky Way. He observed the different phases of Venus and, mistakenly, believed that he had found two ‘ears’ that accompanied Saturn. Although he did not realise it, Galileo had actually observed Saturn’s iconic ring, which would first be confirmed in 1656.
Galileo’s celestial discoveries, coupled with his mathematical genius, placed him light years ahead of his contemporaries. His sudden fame came at a time when the Copernican Revolution was already well underway. Back in 1543, Nicolaus Copernicus published On the Revolution of Heavenly Spheres, which argued that the Sun, not the Earth, was at the centre of the universe. This theory became known as ‘heliocentrism’ (from the Greek ‘hēlios’ meaning ‘sun’), and contradicted the notion that the universe revolved around our planet, or geocentrism (from ‘gē’ meaning ‘Earth’). As Galileo was making his own celestial observations, German astronomer Johannes Kepler was also conducting significant research in the field.
Kepler’s Astronomia Nova was published in 1609 after his decade-long research into the motion of Mars. One of the most momentous works to ever grace the world of science, not only did Kepler conclude that orbital paths were elliptical and not circular, he also argued that his findings supported heliocentrism. With his telescope, Galileo’s revolutionary research was about to prove that Copernicanism was not just a hypothesis – it was reality.
Galileo decided to share his new discoveries, starting with his book Sidereus Nuncius in 1610. Also known by its English name, Starry Messenger, it drew a lot of interest and raised his celebrity profile to new heights. That same year, he was appointed to the prestigious position of court mathematician to Cosimo II de’ Medici, Grand Duke of Tuscany, one of his former pupils. However, Starry Messenger also attracted a lot of criticism. Galileo’s conclusion that it was the Sun at the centre of the universe was not accepted by the Catholic Church, the most powerful institution in Italy – it steadfastly supported the traditional geocentric views of Aristotle and Ptolemy.
But all was not yet lost for Galileo. He was not confronted with total opposition to his astronomical findings – for instance, Jesuit astronomers managed to repeat his observations themselves. Galileo even had a few admirers from the Church, most notably Cardinal Maffeo Barberini. Despite being faced with all the evidence, the Church refused to reconcile with the Copernican model. Some astronomers within the Church, such as the Jesuits, advocated the Tychonic system, developed by astronomer Tycho Brahe, which mathematically supported Galileo’s research but also maintained the status quo. According to Brahe, the Sun and Moon revolved around the Earth but the other planets orbited the Sun – a mix of the two theories.
Infinitely frustrated that his evidence was being ignored, Galileo refused to back down. He campaigned incessantly in favour of Copernicus’ theories and clashed with theologians, who desperately clung to their geocentric views. Even though he provoked attention, his combative behaviour backfired and the Jesuits turned their back on him. Now the Catholic Church decided that they had let Galileo run wild long enough – it was time to put its foot down.
What followed was one of the most momentous events in history regarding the tentative relationship between religion and science: the ‘Galileo Affair’. In 1616, the Roman Catholic Inquisition investigated Galileo’s work, for which he was being accused of heresy. A group of theologians were asked to assess the theory of heliocentrism that Galileo had so defiantly defended and whether it held any merit.
Of course, the theologians’ primary task was the defence of the Catholic Church and the Bible and less than a week later, the judgement was passed. They announced that heliocentrism contradicted the Holy Scriptures and thus Copernicanism amounted to heresy. No sooner had the verdict been delivered than Galileo was ordered to stop his support for the theory and all works associated with it, including his, were banned pending suitable corrections. Instead of getting acceptance, Galileo had been left with disaster.
This was not a clear-cut case of science versus religion, of who was right and who was wrong. The possible ramifications of Galileo’s conclusions were terrifying to the Catholic Church. The Protestant Reformation had dominated Europe throughout the 16th century, shaking Western Christianity to its core. In order to maintain its authority during a time of great instability, the Catholic Church gripped onto tradition much tighter than they ever had before.
The last thing the papacy needed was Galileo advocating for Copernicanism, which not only threatened the traditional interpretation of the Holy Scriptures, but also the authority of the Church itself. This was a dangerous and sensitive time to go up against Catholicism, as Galileo had discovered. However, despite the ban, he was still allowed to discuss Copernicus’ theories on the condition that he treated them in a purely hypothetical sense.
Quietly waiting for the whole debacle to subside, Galileo continued his work. Despite the controversy, he had not wavered from his support for heliocentrism but by this point he was in his 50s and suffering from recurring periods of ill health, which made his research slow down significantly.
Then in 1623, seven years after his condemnation, it appeared that Galileo’s luck was finally about to change. His long-time friend and supporter Cardinal Barberini – who had valiantly defended him during the Inquisition – was elected to the head of the Catholic Church as Pope Urban VIII. Galileo was ecstatic. Although he was still banned from openly advocating heliocentrism, he believed that with his friend as the head of the Catholic Church, the opportunity to have his research accepted was now within his grasp.
With renewed vigour, Galileo started to work on a new book, which compared the Copernican and Ptolemaic systems. He received permission from the pope to do so during a visit to Rome in 1624, under the condition that Copernicanism would be treated purely as a theoretical hypothesis. After receiving approval from the watchful Vatican censors in 1630, Galileo finally published his Dialogue on the Two Chief World Systems two years later in 1632.
Dialogue consisted of a series of conversations between three characters, Salviati, Sagredo and Simplicio. Salviati, a Copernican scientist, argues in favour of Galileo’s theory, while Sagredo acts as an impartial scholar. Simplicio supports geocentrism and is depicted by Galileo as an idiot, emphasised by Simplicio’s derogatory name, which translates to ‘simpleton’ in Italian. After years of struggle, Galileo’s ambition had finally been achieved. His defence of Copernicus was printed in black and white for the world to see. He had deviously disregarded the stipulation that heliocentrism must be portrayed as mere theory – and he had even managed to do it all with the Church’s approval. Galileo basked in his success, unaware that his downfall was right around the corner.
Galileo had taken on the Catholic Church all those years ago but now the battlefield was completely different. Copernicanism had not actually been banned until the Inquisition in 1616 and the issue had not been about Galileo himself, rather the threat heliocentrism posed to the power of the papacy. Now Galileo had crossed a line by publicly promoting a theory that had been officially condemned by the Church.
To make matters worse, he had offended his powerful one-time ally, the pope – the one man who could have really helped him. When Pope Urban gave Galileo permission to write his Dialogue, he asked that the astronomer include his pro-geocentric arguments in favour of Ptolemy. Galileo’s creation of Simplicio insinuated that, along with those who supported the Ptolemaic system, the head of the Church was a fool. He had single-handedly ensured that any help he could have received from Pope Urban was now just a pipe dream.
To save face, the Church needed to make an example of the man who was causing so much trouble. After all, if Galileo could openly express his support for heliocentrism, what would stop others from starting to voice their own interpretations of the Bible and its scriptures? Denounced as a heretic, Galileo was summoned to Rome in 1632 to face trial, while his Dialogue was forbidden from sale.
By now, Galileo was almost 70 years old, frail and suffering from poor health. It took him an exhausting five months to reach Rome, so his trial did not begin until in February 1633. When he arrived, he was confined and interrogated as his accusers tried to coax a confession out of him. He had been charged with violating the 1616 injunction against him – something he vehemently denied.
The investigators hoped that by threatening Galileo with the prospect of torture, he would soon relent and admit to his wrongdoings. Instead, he stayed true to his ideas and insisted that he had followed the rules set before him by merely discussing Copernicanism. He even added that his Dialogue had been approved by the Church itself. However, after a couple of months, Galileo was struggling to maintain this tricky stance as his health continued to deteriorate. Finally, he gave in and told the investigators what they wanted to hear – that his Copernican argument had been too forceful.
The weak and elderly scientist clung to the hope that the Inquisition would take pity on him, considering his age and condition, but he had no such luck. In June, Galileo was convicted of heresy and forced to publicly renounce his support for Copernicus’ theory and heliocentrism. At the same time, he also had to announce that he wholeheartedly believed in the Ptolemaic system, with the Earth well and truly positioned at the centre of the universe. Meanwhile, his Dialogue was officially placed on the Church’s list of prohibited books.
Galileo’s punishment did not end there. Initially given life imprisonment, his sentence was commuted to house arrest and he spent the rest of his life cooped up in a Florentine villa. But this did not prevent him from continuing to work on his theories, even though he was slowly going blind. Choosing a less controversial topic, Galileo returned to his investigation into mechanics. During his last years, he wrote one of his most famous works, Dialogues Concerning Two New Sciences. This magnum opus summarised approximately three decades of Galileo’s research in the field of physics, including his ideas on the laws of motion.
As for the Catholic Church, it would take them over three centuries to admit that Galileo had been right all along. Despite the obstacles he faced, there is no doubt that Galileo helped to establish science in the intellectual world, even if this was not achieved during his lifetime. It is a testament to the man’s tenacity that 80 years after his death, his heliocentric theories were eventually vindicated by another great scientific mind, Isaac Newton. Galileo continues to be a scientific inspiration to this day. In 1989, an unmanned spacecraft sent to study Jupiter and its moons was named after the Italian scientist, so his legacy lives on – even in the stars.