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Nicolaus Copernicus - Historical Background
Uppdated
2009-08-25
webmaster bedr01@utb.lund.se
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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.
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