Big Bang. Simon Singh

Success 1. Common sense It still requires a leap of imagination and logic to see that the Earth might circle the Sun

2. Awareness of motion Galileo was en route to explaining why we do not sense the Earth’s motion around the Sun

3. Falling to the ground There is no obvious explanation in a model where the Earth is not centrally located; only later would Newton explain gravity in this context

4. Stellar parallax The Earth moves, so the apparent lack of parallax must be due to huge stellar distances; parallax should be detected with better telescopes

5. Predicting planetary orbits Perfect agreement, after Kepler’s contribution

6. Retrograde paths of planets A natural consequence of the Earth’s motion and our changing vantage point

7. Simplicity Very simple – everything follows ellipses

8. Phases of Venus Successfully predicts the observed phases

9. Blemishes on Sun and Moon No problem – this model makes no claims about the perfection or imperfection of heavenly bodies

10. Moons of Jupiter No problem – this model tolerates multiple centres

      However, the Copernicans continued to argue that the Sun-centred model was good at predicting reality for the very reason that the Sun really was at the centre of the universe. Not surprisingly, this provoked a stern reaction from the Church. In February 1616, a committee of advisors to the Inquisition formally declared that holding the Sun-centred view of the universe was heretical. As a result of this edict, Copernicus’s De revolutionibus was banned in March 1616, sixty-three years after it had been published.

      Galileo was unable to accept the Church’s condemnation of his scientific views. Although he was a devout Catholic he was also a fervent rationalist, and had been able to reconcile these two belief systems. He had come to the conclusion that scientists were best qualified to comment on the material world, whereas theologians were best qualified to comment on the spiritual ‘world and how one should live in the material world. Galileo argued: ‘Holy Writ was intended to teach men how to go to Heaven, not how the heavens go.’

      Had the Church criticised the Sun-centred model by identifying weaknesses in the argument or poor data, then Galileo and his colleagues would have been willing to listen, but their criticisms were purely ideological. Galileo chose to ignore the views of the cardinals, and year after year he continued to press for a new vision of the universe. At last, in 1623, he saw an opportunity to overthrow the establishment when his friend Cardinal Maffeo Barberini was elected to the papal throne as Urban VIII.

      Figure 18 Copernicus (top left),Tycho (top right), Kepler (bottom left) and Galileo were responsible for driving the shift from an Earth-centred to a Suncentred model of the universe. Together their achievements illustrate a key feature of scientific progress, namely how theories and models are developed and refined over time by several scientists building on each other’s work. Copernicus was prepared to make the theoretical leap that relegated the Earth to a mere satellite and promoted the Sun to the central role. Tycho Brahe, despite his brass nose, provided the observational evidence that would later help Johannes Kepler to identify the outstanding flaw in Copernicus’s model, namely that the planetary orbits are slightly elliptical, not perfectly circular. Finally, Galileo used a telescope to discover the key evidence that should have convinced doubters. He showed that the Earth is not at the centre of everything, because Jupiter has its own satellites. Also, he showed that the phases of Venus are only compatible with a Sun-centred universe.

      Galileo and the new pope had known each other ever since they had attended the same university in Pisa, and soon after his election Urban VIII granted Galileo six lengthy audiences. During one audience, Galileo mentioned the idea of writing a book that compared the two rival views of the universe, and when he departed the Vatican he was left with the firm impression that he had received the Pope’s blessing. He returned to his study and made a start on what would turn out to be one of the most controversial books ever published in the history of science.

      In his Dialogue Concerning the Two Chief World Systems, Galileo used three characters to explore the merits of the Sun-centred and Earth-centred world-views. Salviati presented Galileo’s preferred Sun-centred view and was clearly an intelligent, well-read and eloquent man. Simplicio, the buffoon, attempted to defend the Earth-centred position. And Sagredo acted as a mediator, guiding the conversation between the other two characters, although his bias sometimes emerged when he scolded and mocked Simplicio along the way. This was a scholarly text, but the device of using characters to explain the arguments and counter-arguments made it accessible to a wider readership. Also, it was written in Italian, not Latin, so clearly Galileo’s objective was to win widespread popular backing for a Sun-centred universe.

      The Dialogue was eventually published in 1632, almost a decade after Galileo had apparently won the Pope’s approval. That huge delay between inception and publication turned out to have severe consequences, because the ongoing Thirty Years’ War had changed the political and religious landscape, and Pope Urban VIII was now ready to quash Galileo and his argument. The Thirty Years’ War had begun in 1618, when a group of Protestants marched into the Royal Palace in Prague and threw two of the town’s officials out of an upper window, an event known as the Defenestration of Prague. The local people had been angered because of the continual persecution of Protestants, and by taking this action they sparked a violent uprising by Protestant communities in Hungary, Transylvania, Bohemia and other parts of Europe.

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