Translations of Encyclopedia about Physics

Following the research of Greek philosophers, further discussions concerning natural sciences were hindered by church dogmatism, a state which continued until late into the Middle Ages. At the start of the Renaissance period in the 16^th century, physics was still based on a geocentric image of the world, where the world was perceived as the centre of the universe.

In the year of his death, Mikuláš Koperník (473-1543) proposed a heliocentric image of the world. According to Koperník, the world, the moon and the other planets all revolve around the sun. However, this new theory did not bring with it true advancement if we compare it with the church recognised theory of epicycles at the time (epicycles are circular paths along which the heavenly bodies travel along other, main paths. For example, the moon moves along an epicyclical path surrounding the sun because it revolves around the earth, which itself revolves around the sun). Although Koperník’s model appeared elegant, it was not better in every respect what concerns predicting the movement of stars in the heavens. It was only until Johannes Kepler (1571-1630) that Koperník’s mathematics had been improved. Kepler replaced the circular paths with ellipses, the centre of which lies the sun. For his mathematical calculations, Kepler used data already submitted by Tycho de Brahe and Francis Bacon. In 1609, he then published his three "Kepler laws".

Galileo Galilei (1564–1642) used a telescope, which he himself built, to observe the stars and discovered other support for the accuracy of Kepler’s calculation in the movement of the moon and Venus. Galilei also found mountain ranges and valleys on the moon, as such overturning church propaganda of the clean face of all heavenly bodies. Besides that, he also discovered sun spots, once again against church doctrine, which says that all heavenly bodies must be perfect. By publishing his findings, Galilei got into conflict with the church inquisition. He also published his findings concerning hydrostatics and the free fall of objects, overturning Aristotle’s theory that the speed at which an object falls depends on its weight. In the end, the inquisition called him to Rome to defend himself against the inquisition courts, which eventually charged him of heresy. Based on his teachings, Galilei was doomed to a life sentence in prison. His defiant statement of "Eppur si muove" ("It rotates after all") when entering prison has been lost in history. The sentence was later reduced to domestic imprisonment, where Galilei spent the rest of his life studying the inertia and gravitation of objects.

Galilei’s notes concerning the mechanics of movement along a circular path were later further developed by René Descart (1596-1650), who also studied the subjects of mathematics and optics. Christian Huygens (1629–1695) then published his findings on the laws of vibrations and on the circular movement of objects.

Based on findings by Galilei, Descart and Huygense, Issac Newton then described the laws of mechanics. His most famous work includes Newton’s Laws, which describe the dynamics of objects within space. The wording of these laws is as follows:

Newton’s laws still apply until today. The basic idea behind Newton’s second law is so common to us that we do not even recognise the geniality of its gravitational law. This law was the first to describe universal gravitation. The force which causes an apple to fall is the same force which holds the moon in its place in a circulatory orbit around the earth. From this, it ensues that objects, whether they are located in space or on earth, mutually exert a gravitational force on one another which is directly proportional to their mass and indirectly proportional to the square of their distance from one another. This accomplished in casting doubt on Aristotle’s theory of division of movement between heavenly and earthly objects.

The most important proof of Newton’s gravitational laws was the correctly predicted calculation of the return of Halley’s comet in 1758. Furthermore, Newton’s calculation method was used to determine the existence of the yet unknown planet of Neptune, with its probable mass and position. Neptune was later discovered in 1846 at the location predicted by Newton.

Since Newton’s time, the study of mechanics has developed into a complex science which is only a part of overall physics. Other established fields of physics were acoustics, developed by Josef Saveur (1653-1716) and George Ohm (1789-1854). The basics of continual mechanics and the theory of convection were then laid by Daniel Bernoul (1707-1783).

James Clerk Maxwell (1831-1879) is another major figure in physics and whose work with electrodynamics have led to the theory that light and other forms of radiation must be perceived as waves in an electromagnetic field. Maxwell’s electrodynamics together with Newton’s law of mechanics create the cornerstone of classical physics.

Max Plancka’s quantum theory and the special and general theory of relativity by Albert Einstein marked the end of classical physics. Both these theories show that, with very small elements having very large masses and speed, the theories of classical physics fails.

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