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Nicolaus Copernicus - Historical Background

 

 

Uppdated 2009-08-25
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Looking at the stars many of us have asked, "Where does everything come from and how long has it been here? Does the Universe have boundaries and how long will it last?" There are no obvious answers to these questions, but it has not discouraged us to search for clues. Even if the over-all picture of the Universe has improved since ancient time, it is still too early to classify Cosmology as a true science, because despite all information obtained so far there are no exact numbers or exact mathematical solutions at hand which can describe the precise nature of our Universe. It is interesting to note that some of the basic ideas of today are in fact rediscoveries from the past. For example, we learn from early records that Thales, 580 BC, believed the Moon to be illuminated by the Sun. About the same time Anaximander, 611?-547? BC, thought the Earth was round instead of flat. His contemporary, Anaximines, who at first agreed that the Earth is round and later changed his mind, was first to distinguish between planets and stars. In the fourth century BC Heraclides of Pontus amazingly suggests that the planets Venus and Mercury circle the Sun (Helios) rather than the Earth and that the motion of the stars could be explained by the rotation of the Earth around its axis once in every twenty-four hours. However, a colleague of his, the great philosopher Aristotle, rejected Heraclides' rotational idea arguing that if the Earth was spinning around its axis then all heavenly bodies, including the planets, would appear to move around us at the same speed. But since the planets move with different velocities it would prove that the Earth is standing still and the planets, including all other heavenly bodies, are moving around us at their own chosen velocities. In fact Aristotle felt that all heavenly bodies were falling in towards the Earth's center which he also believed to be the center of the Universe (this is the first notion of a collapsing universe). In Aristotle's own words: "As evidence that all heavenly bodies move towards the center of the Earth, we see that weights falling towards the Earth do not fall in parallel lines but always at the same angles to it. Therefore, they are moving towards the same center, namely that of the Earth. It is therefore clear that the Earth must be the center and immobile. From these considerations it is obvious that the Earth does not move, neither does it lie anywhere but at the center of the Universe." The belief that we are at the center of the Universe is shared by many theoreticians even today who have adopted the theory of relativity and its cosmological principle. Shortly after Aristotle's and Heraclides' deaths, Aristarchus of Samos extended Heraclides heliocentric idea so that all planets, including the Earth, were moving around the Sun just as we know it today. Heraclides and Aristarchus heliocentric theories were short-lived, mainly due to religious opposition, but were rediscovered nearly two thousand years later by Copernicus. That the Earth is round was deduced in early time from the fact that new stars and constellations will rise above the horizon as one travels north or south. Also, while traveling north or south stars straight above move off at certain angles making it possible to calculate the radius and circumference of the Earth by triangulation. Land disappearing beyond the horizon at sea also gave a clue to the spherical shape of Earth. In one of his essays, Aristotle wrote, "Mathematicians who tried to calculate the circumference of Earth put it at four hundred thousand stades" which is about 74,000 kilometers. It is believed that this written passage stimulated Columbus to undertake his famous new world voyage. Later, in the third and second century BC, the circumference of Earth was calculated more accurately by Archimedes who arrived at a value of 55,500 km; Eratosthenes and Hipparchus obtained 46,600 km; Posidonius 44,380 km (today's value is 40,000 km, Munitz (1962)). Eratosthenes is best known for his method of measuring the length and angles of shadows cast by vertical poles at different positions along the Earth's surface. By triangulation he then found the radius and circumference of the Earth. All the above discoveries might not seem very impressive today. We take for granted that the Earth is round and that we belong to one of the planets that encircles the Sun. But two thousand years ago such discoveries were giant leaps in science. To find the first puzzle pieces of our physical world could be compared to the difficulty one would have to imagine a new color never seen before. It is true that many difficult problems have simple answers, but once there is an answer there is no longer a problem and often, once solved, little credit goes to the problem solver. An example of this is the early American township which had posted a $20,000 award to whomever could devise the means or method for removing a large boulder which had rolled down and blocked main street (dynamite could not be used because of nearby buildings). There were many unsuccessful attempts until a bright person appeared who claimed he had a workable solution. When he revealed his idea, "bury it", the towns people felt that such a simple answer was not worth the $20,000 previously offered. Even today solutions and answers to scientific problems do not come easy, but the right answers usually turn out to be simple ones. It is easy to speculate, however, and often numerous and different theories appear about the same subject. This is especially true in the field of cosmology were exact measurements and exact mathematical solutions are not yet available thus making it difficult to rule out even the most exotic ideas. In the 14th century Cardinal Nicholas of Cusa tried to break away from Aristotle's theory that for nearly 2,000 years held our Earth as the center of the Universe, a belief which was cherished by the church. Cardinal Nicholas of Cusa thought that the Earth was a moving star like all other stars and that the Universe was infinite in size, because God would not have created anything smaller. The Cardinal's ideas were criticized as being mystical and unscientific because in his infinite Universe, he claimed, each and all bodies would be at the center at the same time. Each body would also be at the periphery and in the interior at the same time. The reason for this is that in an infinite Universe everything can be said to be at the center since there is no limit to its radius. It is interesting to note that modern cosmology follows the same line of thought, namely that any observer on any galaxy in the Universe can consider himself to be at the center of the Universe. This is called the cosmological principle, see page 17. Awkward situations arise when infinity and zero are incorporated into physical phenomena. For example, a point source of energy with zero radius will contain an infinite amount of energy just as a boundless Universe with an infinite number of centers would have. Absurd questions can be asked such as; "What happens if an infinite force strikes an immobile object? What is the probability that another world like ours exists in an infinite Universe?" The answer is that the probability is 1:1 and the probability that an infinite number of other worlds exist just like ours with a person like oneself reading the same book etc., is also 1:1. It is the author's opinion that infinity has no real meaning in physics. Nevertheless, many cosmological theories still incorporate infinity. Giordano Bruno was burned at the stake in the year 1600 for supporting the cardinal of Cusa's idea that the Sun and Earth are in motion like stars. Giordano Bruno wrote his first publication on an infinite Universe while residing in England from 1583 to 1585. It is possible that he was influenced by Thomas Digges' treatise Perfit Description of the Caelestiall Orbes, which was first published in London 1576. Thomas Digges treatise is a translation of Copernicus' work into the English language with some of his own additions. His most important addition was that he believed the Copernican Universe must be infiniti. Nicolaus Copernicus himself saw his scientific work De revolutionibus orbium coelestium published as he was dying in 1543.


 

Nicolaus Copernicus

Nicolaus Copernicus