Copernicus Revolution

Movement of the Sun (yellow), Earth (blue) and Mars (red). On the left, according to the heliocentric theory of Copernicus. On the right, according to geocentric theory.

The Copernicus Revolution is the title by which the scientific revolution that takes place in Western Europe is usually known, represented in astronomy by the passage of the traditional Ptolemaic system geocentric to the innovative heliocentric Copernican system, initiated in the 16th century by Nicolás Copernicus (whose work De revolutionibus, does not allude to the traditional concept of revolution, but to that of a cycle or trajectory circle of celestial bodies) and culminated in the 17th century by Isaac Newton. Largely as a consequence of this revolution, the intellectual landscape of the late 17th century and early XVIII is considered the crisis of European consciousness and will open the eighteenth century as the Age of Enlightenment or of the Enlightenment.

The expression Copernican revolution or Copernican turn has become popularly synonymous with "radical change" in any field.

History

The transition of Western society from the Middle Ages to the Modern Age, in its aspect of change of mentality towards modernity, meant a new consideration of nature from a new scientific thought, allowed by the use of human reason without subjection to the principle of authority. Since the Renaissance, humanistic anthropocentrism has replaced the theocentrism of scholasticism. The Baroque will revalue the senses and experience as a source of knowledge. Rationalism and empiricism will be two opposite but complementary philosophical orientations.

Copernicus' theory

Nicolas Copernicus.

Galileo Galilei.

In the 16th century, Nicholas Copernicus' De revolutionibus orbium coelestium presents a comprehensive discussion of a heliocentric model of the universe. Copernicus discusses the philosophical implications of the system he proposes, elaborates it geometrically in detail with selected astronomical observations to derive the model parameters from it, and writes numerous astronomical tables that allowed the past and future positions of stars and planets to be calculated.

Copernicus argues that the universe comprises eight spheres. The last, most distant and outer, consists of fixed stars without movement, with the Sun still in the center. The known planets revolve around the Sun, each in its own sphere, in this order, from the center out: Mercury, Venus, Earth, Mars, Jupiter, Saturn. The Moon, however, revolves in its sphere around the Earth. What seemed to be a daily revolution of the Sun and the stars around the Earth was actually the rotation of the Earth on itself.

Copernicus adhered to one of the general beliefs of his time, that the movements of the celestial bodies should be composed of uniform circular movements. For this reason, he could not account for the observed motion of the planets, for example Mars and Mercury, without retaining a complex system of epicycles similar to those of the Ptolemaic system. Despite Copernicus's adherence to this aspect of ancient astronomy, his radical proposal for a heliocentric, not a geocentric cosmology, was a serious blow to Aristotle's science – it laid the foundations for what we now call the Scientific Revolution.

Galileo's method and Kepler's elliptical motion

Johannes Kepler.

In Galileo's time, physics acquired the status of a model of science, a model that should be followed by all knowledge that wanted to reach the category of scientific knowledge. The task of 17th century science was to find precise techniques for rational control of experience and to show how mathematical concepts can be used to explain natural phenomena.

Essentially, Galileo's success was due to his ability to combine the roles of scholar and craftsman. For this he accepted the techniques of the artisans —lenses, the astrolabe, the bombs— and the logical-mathematical reasoning developed by the Greeks and medieval scholasticism. From repeatable data, ordered under mathematical principles, Galileo formulated the law of falling bodies, the laws of movement of projectiles and the law of the pendulum. That is, he reduced the various observed facts to laws using inductive reasoning.

Galileo glimpsed that, to a large extent, the difficulties in understanding planetary motion were caused by the geocentric model, and that such difficulties disappeared by accepting the heliocentric model proposed by Copernicus. In relation to the study of planetary trajectories, particularly that of Mars, it was known that in the XVI century there was no concordance between what could be predicted with Ptolemy's instruments and the true trajectories observed in the sky. The Ptolemaics assumed that each planet revolved around a circumference (epicycle), whose center, in turn, described another circumference (deferential) centered on the Earth. Danish astronomer Tycho Brahe in the mid-16th century, proved the theory flawed and made precise new planetary observations. Two options were then presented: admit, as Copernicus, and later Galileo and Kepler had done before, that the geocentric theory was failing, or else that the auxiliary hypotheses about the number and size of epicycles and other explanatory resources were insufficient. The Ptolemaics had taken the latter position for many centuries, until Kepler was able to explain what was happening by assigning each planet a unique elliptical path around the Sun. In this way Kepler formulated his laws of planetary motion.

Newton's Mechanics

Isaac Newton.

Galileo's ideas were decisive in the intellectual and scientific revolution of the 17th century. His works on mechanics and dynamics, added to the efforts of Copernicus and Kepler, were integrated and systematized by Isaac Newton.

Newton's mechanics showed that the Galilean and Keplerian laws could be deduced from the principles of the theory that bears his name. In this way, he was able to deductively unify what would otherwise have remained a dispersed set of empirical laws. It is often concluded that the project of modern science finds its culmination in Newton's physics. Newton's theory, as presented by the author in the Philosophiae Naturalis Principia Mathematica, of 1687, is often considered one of the most spectacular achievements in the history of science.

This theory was considered a revolution for the world of science because it was one of the bases of scientific research along with observation and experimentation and allowed us to have a more concrete idea of astronomy.

Use of the term in philosophy

The term «Copernican turn» is usually used in philosophy as a metaphor alluding to the radical change of perspective that the general approach of the philosophy of Immanuel Kant implies, with respect to traditional philosophy. Kant believes that philosophy, to enter the safe path of progress in knowledge, has to do the same thing that Copernicus did in astronomy: if Copernicus, in order to explain celestial movements, understood that it was better to start from the assumption that he was the spectator who turned, in a similar way Kant believes that we can only have a true knowledge of things – a universal and necessary knowledge – if the object depends on thought, to be known, and not vice versa. This is the assumption from which Kant's transcendental philosophy starts.