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It’s the first Friday of the month, time for another post on the history of atom theory by physics professor (and my dad) Dean Zollman. Here, two 17th century French philosophers take very different approaches to atoms – as well as scientific hypotheses and religious beliefs.

By Dean Zollman

Dean ZollmanDuring the first half of the 17th century, mechanical philosophy emerged has a dominant way of thinking about the world. This approach to philosophical thought attempts to explain the world in terms of matter and motion. Certain attributes are assigned to matter. It moves in ways that cause different pieces of matter to collide and interact with other bits of matter. The philosophers’ job is to understand the attributes and the laws of motion.

This approach has its roots in the work of the ancient Greeks such as Democritus and Epicurus. After the rediscovery of Lucretius’s epic poem, these ideas were given further impetus by the heliocentric model of the solar system developed by Nicholaus Copernicus (1473-1543). Of course Copernicus was looking at very large objects. However, the philosophers thought, if the motion of planets and moons can be explained through mechanical means, should we not also be able to explain the actions very small matter in a similar way?

The Northumberland Circle, which was discussed last month, was one group that saw mechanical philosophy as an appropriate way to explain their observations. Two French philosophers, Pierre Gassendi (1592–1655) and René Descartes (1596–1650), were also foundational in developing ideas along these lines. However, when it came to atoms, Gassendi and Descartes had vastly different views.

Pierre Gassendi

1637 Portrait of Pierre Gassendi by Claude Mellan

Gassendi built on the perspectives of the early Greeks. In his view, and that of many mechanical philosophers, atoms were very small, unobservable objects which composed all matter. The fundamental atoms were indivisible but had very few properties themselves. Gassendi’s atoms had size, shape, and mass. Other properties that we observe – such as color, sound, and hardness – came about when atoms combined in different ways. In this view, atoms were in constant motion in a vacuum. Combinations and changes occurred when atoms collided with each other.

As a Catholic priest, Gassendi needed to deal with the claim that an atomistic approach did not leave room for the divine. Thus, he needed to distance his ideas from Epicurus’s view that the soul was made of atoms and decayed with the body. So, he concluded that material objects were made of atoms but that spiritual ones (souls, angels and demons) were not. Further, God created the atoms and gave them their initial motion.

René Descartes, circa 1649

Portrait of René Descartes, circa 1649, by Frans Hals

Descartes took a quite different approach. He saw matter as continuous and filling all of space. His philosophy was mechanical in the sense that he believed that matter was governed by some laws of motion that explained the objects that he saw and how those objects interact. However, he had no need for some smallest bits of matter and definitely did not believe in a vacuum. Using the ideas related to his laws of motion in which continuous matter is colliding with other continuous matter, he developed an explanation of essentially everything that he could observe.

Unfortunately, he also extended his model of the universe to some things that he could not see. In particular, he provided a mechanical explanation of Christ’s presence at the Eucharist. Some historians think that this description was a factor in Descartes’ Principia philosophiae being placed on the index of forbidden books in 1663. Thus, Descartes showed that the Eucharist was a problem for non-atomists as well as atomists and that trying to give scientific explanations to religious events was as bad an idea then as it is now.

Detail from René Descartes i samtal med Sveriges drottning, Kristina.

Queen Christina of Sweden (left) and René Descartes (right). Detail from René Descartes i samtal med Sveriges drottning, Kristina. Original by Pierre Louis Dumesnil (1698-1781); 1884 copy by Nils Forsberg

An aside for people who hate mornings. In 1649, Descartes was invited to Sweden to tutor Queen Christina. Typically Descartes stayed in bed until noon, but the queen was an early morning person. She insisted that the lessons begin about 5 a.m. Some historians think that this schedule led to a rapid decline in Descartes’ health. The 5 a.m. lessons began on December 18, 1649; on February 1, 1650 Descartes became ill with pneumonia and died on February 11. Not all historians agree that early mornings killed Descartes; some even think he was assassinated.

In England, Thomas Hobbes (1588–1679) developed ideas along the lines of mechanical philosophy. His model included a mechanistic description of the soul. Hobbs was also suspected of being an atheist. Thus, his embracing of the mechanical philosophy led to worries that such a philosophy would lead to atheism – a concern that we have seen before and will look at a little more the next time.

Images in the public domain, via Wikimedia Commons.


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Ancient Greeks Were the First to Hypothesize Atoms

The Poetry of Atoms

Atom Theory in Ancient India

Religion, Science Clashed over Atoms

Medieval Arabic Scholarship Might Have Preserved Scientific Knowledge

Rediscovering a Roman Poet – and Atom Theory – Centuries Later

Reconciling Atom Theory with Religion

Did Atom Theory Play a Role in Galileo’s Trouble with the Inquisition?

Dean Zollman is university distinguished professor of physics at Kansas State University where he has been a faculty member for more than 40 years. During his career he has received three major awards—the National Science Foundation Director’s Award for Distinguished Teacher Scholars (2004), the Carnegie Foundation for the Advancement of Teaching Doctoral University Professor of the Year (1996), and American Association of Physics Teachers’ Robert A. Millikan Medal (1995). His present research concentrates on the teaching and learning of physics and on science teacher preparation.