What is time in a scientific sense

"Galileo stands for a historical upheaval"

Interview with Max Planck Director Jürgen Renn on the importance of the Italian scholar who was born 450 years ago

On February 15, 1564 Galileo Galilei was born in Pisa. The philosopher, mathematician, physicist and astronomer still fascinates experts and laypeople alike. Science historians deal intensively with life and work, the media are celebrating his 450th birthday these days. Helmut Hornung spoke to Jürgen Renn, Director at the Max Planck Institute for the History of Science in Berlin, about the importance of Galileo.

What makes Galileo Galilei still interesting for research today?
Like no other scientist, Galileo stands for a historical upheaval, the birth of modern natural science. Since the time of Galileo, science has not only made rapid progress, but has also increasingly intervened in our lives. Since Galileo's time, knowledge and application have been closely and often problematic.

Science can stand for enlightenment and emancipation, but it can also be used for power interests. Both were already apparent in Galileo's time. Understanding Galileo's upheaval historically also means better understanding our own situation: How did modern natural science come about and how does it relate to our lives? That is still a key issue.

To what extent did Galileo shape the history of science?
Galileo became a legend during his lifetime through his public appearance for the Copernican doctrine, but above all also through the process that the Church made for him. His further development of the telescope and his astronomical discoveries - in particular the craters and mountains on the moon and the moons of Jupiter - made him world famous. The Jesuits carried his fame to China. His research on mechanics, the discovery of the pendulum law, the law of fall and the parabolic shape of the trajectory established classical mechanics.

For a long time in the history of science, his research stood for a paradigm shift that separated the scientific modern age from the Middle Ages. Today we know that this upheaval did not depend on a single scientist and was the result of a long-term development for which economic, political and cultural changes were also decisive.

In the Academy of Florence, the young Galileo gave lectures on "Measuring Dante's Hell". Was Galileo a mystic? Or just a child of his time?
Dante himself was a scientific pioneer in some ways. In any case, his Divine Comedy is a wonderful synthesis of medieval knowledge, which he made accessible to a wide audience through his literary processing in the vernacular Italian.

Through his lectures, Galileo placed himself in the tradition of this literary-scientific popular education. Here lies one of the secrets of his success: He was part of a broad, cosmopolitan culture, equally interested in science, art and literature, for which philosophical questions about the structure of the world were closely related to scientific and practical problems. The measurement of Dante's hell symbolizes this close connection.

Which of his works do you consider the most important?
It depends on what you put the emphasis on. Galileo was a gifted writer, astronomer, philosopher, mathematician, engineer, and physicist. Back then, these roles were not as clearly separated as they are today. His works are correspondingly multifaceted. His star messenger from 1610 heralds the new astronomical observations of importance to the history of mankind - arguably the first scientific bestseller.

The Dialogue on the Two Greatest World Systems, published in 1632, is Galileo's literary masterpiece par excellence, a cleverly composed conversation about the heliocentric system of Copernicus and the geocentric system of Ptolemy represented by the Church. There is only one catch: Galileo's supposed main proof of the superiority of the heliocentric system is a theory of ebb and flow - and overlooked the essential point, the role of the moon.

My personal favorite work is the Discorsi of 1638, the discussions about two new sciences. They are Galileo's scientific legacy and contain his most important contributions to mechanics, also packaged in a dialogue that allows important conclusions to be drawn about Galileo's own path of knowledge.

Where did Galileo's insights come from?
Galileo stood at the intersection of different traditions, which made it possible for him to combine previously separate elements of knowledge and thereby gain new insights. He studied medicine and, as a young man, dealt intensively with Aristotelian natural philosophy and the medieval scholastic tradition. At the same time he was familiar with the Renaissance tradition of artist-scientist-engineers.

He dealt with contemporary technology, was able to draw and do arithmetic like other contemporaries who made art or military architecture their main occupation. He admired the work of the ancient mathematician and physicist Archimedes, with whose help he wanted to reform the Aristotelian natural philosophy in his youth. It is in the nature of such transformation processes that these reform attempts would ultimately lead to an overcoming of the Aristotelian doctrine.

What is new about Galileo's approach? As is often claimed, is it really a combination of mathematical methodology and experiment?
Actually there is no new approach by Galileo, at least not as a starting point for his successes, but at most as their result. He experimented and used mathematical methods. But that was neither new nor critical. Galileo's work has remarkable similarities with those of other contemporaries. Thomas Harriot, for example, is considered to be an English Galileo who also pointed the telescope at the moon and discovered the laws of fall. This is a clear indication that this was not about individual revolutionary discoveries, but about the transformation of an entire system of knowledge.

The starting point was the common basis of all contemporaries of the ancient traditions that go back to Aristotle and Archimedes, among others. What they had in common was the challenge of contemporary technology, firearms and ballistics, shipbuilding and architecture, as well as the diverse use of machines.

Attempts to understand the new technology using the old terms gradually transformed the traditional system of knowledge. At its fringes, new terms emerged that finally moved to the center of a new system of knowledge, that of classical physics. It was a Copernicus process in which many traditional structures of knowledge were preserved, but similar to how the planets in the Copernican system were rearranged.

The "Galilei case", that is, the proceedings of the Inquisition against him in 1633, is regarded as the starting point for the division between church and science. How do you see this relationship today?
The "Galileo case" was the result of complicated political processes in the conflict between ecclesiastical hegemony and secular power. They were complicated because neither the church nor the secular powers nor science were uniform in themselves and formed closed fronts. It should not be forgotten that the Church was an important pillar of science during this period. Since Albertus Magnus and Thomas Aquinas, it had brought Christian doctrine together with Aristotelian philosophy and thus created the intellectual basis for a comprehensive worldview that was essentially based on science in the sense of the time.

At the same time, Christian religious orders such as the Jesuits in Galileo's time played a key role in the spread of scientific education. But for all the complexity of these historical processes: There was a basic conflict between the pursuit of knowledge and the interest of the ecclesiastical authorities in controlling and restricting the rapidly increasing knowledge - a conflict that came to a head in Galileo's condemnation.

In principle, this conflict still exists today. However, it cannot be resolved by absolutely separating power, moral values ​​and knowledge from one another and assigning them to different social authorities, which then have to search for a balance. Moral reflection should be as much a part of power as it is to science, just as knowledge is not only a prerequisite for power, but should also be that of morality. From the case of Galileo we learn that we cannot absolutely separate the spheres of knowledge, power and morality from one another.