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Science Forum Index » Philosophy Forum » History of Physics : On Aristotle and Aristarchus
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| Sir Frederick |
 Posted: Thu Jan 01, 2004 7:07 pm |
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HISTORY OF PHYSICS: ON ARISTOTLE AND ARISTARCHUS
ScienceWeek http://www.scienceweek.com
The following points are made by Edward Teller (citation below):
1) The Greeks considered the Earth the center of the Universe.
The Greeks before Aristotle (384-322 BC) described the motion of
the heavenly bodies, but it was Aristotle who codified all facts
known to his time. His ideas were based on a distinction between
heaven and Earth. There was one set of rules for Earth: On Earth,
everything had its proper place, the heavy objects below and the
lighter media above. On Earth, everything had its proper state,
the state of rest. Forces may and do disturb this rest, but this
is temporary and uninteresting.
2) With respect to the heavens, the set of laws were completely
different. In heaven, the law was motion and, in particular, the
most ideal motion: uniform motion on a circle. Almost all the
heavenly bodies, the beautiful array of thousands of stars, are
seen in this simple motion of perfect uniformity. That there are
exceptions to the uniform circular motion is a sign of
imperfection, but even these motions are approximated, and should
and must be approximated by some combination of uniform circular
motions. The Sun, the Moon, and the planets are the exceptions.
These deviates move on circles whose centers move on circles;
they move on "epicycles". But these approximations were not
enough, they actually move on circles whose centers move on
circles whose centers move on circles; at least as complicated as
that. The Greek astronomers worked on this and could, with
circles on circles on circles on circles, describe any motion of
the heavenly bodies. By the first century after Christ, the
system was complete and it was petrified by the astronomer
Ptolemy (c. 2nd century AD) in his famous book. A few hundred
years later, Arab scholars called it "Almajest", the Majestic
Work.
3) There were some who disagreed and, in particular, there was a
remarkable man Aristarchus of Samos (c.310-c.230 BC). He lived in
Alexandria around 200 BC, and he asserted that the Earth rotates
on its axis and revolves around the Sun, that the Sun is at rest
and that, if you make these assumptions, you greatly simplify the
circles on circles on circles. Learned men of his time happened
to disagree. He was ignored and his ingenious suggestion was
lost. The only reference to this part of his work is to be found
in Archimedes (c.287-212 BC), who was kind enough to criticize
him instead of ignoring him completely. (Nothing is as deadly as
silence.)
4) I want to tell you a story which is not essential to the
development of the Copernican system, but it is remarkable, a
little ironic, and a little sad. The Greeks knew the distance to
the Moon reasonably accurately. This was done by the same method
by which I can estimate your distance, by observing the
displacement of your head on the background if I look at you
first with one eye and then with the other. This method of
measuring the distance to nearby objects is the parallax, and it
won't work on distant objects unless your eyes are sufficiently
far apart. By taking observations sufficiently far apart on the
Earth, the Greeks were barely able to notice a parallax of the
Moon and to get a reasonable estimate of its distance from the
Earth. The parallax of the Sun was much too small to be noticed
(besides, it is difficult to see stars near the Sun).
5) Aristarchus made a suggestion which, in principle, is both
ingenious and correct. He wanted to find the distance between the
Earth and the Sun. If we see exactly one half of the Moon, then
the triangle defined by the Sun, Moon, and Earth has a right
angle at the Moon. Aristarchus measured as accurately as he could
the time at which the moon was in its first quarter (we see it as
1/2) and the time it was in its last quarter (again we see it as
1/2). Then, by noting the difference in time it took the moon to
travel from the first quarter to the last quarter, and the time
it took to travel from the last quarter to the first quarter, and
using trigonometry, Aristarchus calculated the distance from the
sun. Unfortunately, it was impossible for Aristarchus to
determine the exact position of the Moon when it was 1/2, so his
result was in error by more than a factor of ten. This erroneous
result the Greeks accepted. Even this inaccurate determination
showed that the Sun was much larger than the earth and he jumped
to the conclusion that the tail should not be wagging the dog.
But, as mentioned, the academy, the followers of Plato and
Aristotle, disagreed with this unphilosophical wisdom.
Adapted from: Edward Teller: Conversations on the Dark Secrets of
Physics. Perseus Publishing 1991, p.37. More information at:
http://www.amazon.com/exec/obidos/ASIN/0738207659/scienceweek
--------------------------------
ON NICOLAUS COPERNICUS (1473-1543)
The following points are made by Philip Morrison:(American
Scientist 2003 91:111):
1) Nicolaus Copernicus is the Latinate name of the renowned
astronomer and polymath, born in 1473 to a well-placed mercantile
family in the Polish town of Torun. (Note that in those parts,
national frontiers, place names and even shorelines shift over
the centuries.) The bright boy, who at age 10 lost his father,
found a generous guardian in his uncle Lucas, who soon became a
bishop, his see including the Frombork cathedral, set on the
shore of the delta of the river Vistula in northern Poland.
Mathematics and astronomy drew the young student in time to the
national university at Krakow. He continued study at three
celebrated Italian universities and returned to Baltic shores at
around age 30, as Doctor of Canon Law, Licentiate in Medicine and
astronomical revolutionary.
2) For years thereafter he attended his bishop uncle as official
physician; in fact, most of his life was passed fulfilling a
dozen diverse appointments as a church official going wherever in
stormy times a learned and productive mind was of use. He made
maps, attended legislative bodies, held a variety of fiscal
posts, acted as diplomat and as civil and military inspector,
even wrote a treatise on the minting of money by the new Prussian
states. With age he rose to higher administrative positions,
although he probably never became a priest.
3) By his thirties Copernicus had developed a heliocentric theory
of the Solar System in a document of a few fruitful pages. He
improved and circulated it privately in Italy, and during quieter
years with his bishop. That phase passed when Lucas died in 1512,
and Copernicus embarked on long and varied service for and around
the Frombork cathedral.
4) His celebrated full volume, _On the Revolutions of the
Celestial Spheres_, was published three decades later, in
Nuremberg in 1543, the year he died. He may never have seen it in
print. His almanac tables, showing the moon and Earth with the
planets revolving about the sun, met the test of expert
observation as well as the old Earth-centered tables had. His
literary executors were seriously worried about the impact of his
new work; one of them added a preface to temper the author's
well-supported claims.
--------------------------------
ON THE COPERNICAN REVOLUTION
What is called the "Copernican Revolution" is considered to be
one of the most momentous events in the history of modern natural
science, an event that exemplifies the rise of the "world-view"
of modern civilization. But the "event" was more an era than a
single historical occurrence. The Copernican Revolution was
prolonged and complex, beginning shortly before 1514, when
Copernicus first described his theory that the Earth is a planet
in motion around the Sun, and extending to the year 1687, when
Isaac Newton published Principia Mathematica, which incorporated
Copernican principles in the construction of a dynamical
astronomy.
Copernicus developed his theory during a period of approximately
30 years, working out the system in full mathematical detail in
order to demonstrate how planetary positions could be calculated
with this new basis. Copernicus was apparently able with his
theory to determine the length of the Earth year to within 28
seconds. Although the work of Nicolaus Copernicus (1473-1543)
(born Mikolaj Kopernik) may have marked the beginning of the
important conceptual revolution that bears his name, very little
is actually known about Copernicus personally, and his burial
place in the town of Frombork in Poland is now unlocated.
The following points are made by Rosemary Sullivant (Astronomy
1999 October):
1) Copernicus lived a circumscribed life as a physician and civil
servant within the Catholic Church. Little is known about him,
and most of his papers have been lost. He studied painting before
medicine, but only copies of his self-portraits remain.
2) Copernicus was born 19 February 1473 in the Polish city of
Torun, then part of Prussia. He was born into a prosperous and
politically connected family, and his early professional life was
directed by his uncle, Lucas Watzenrode, a powerful Church
official. Copernicus eventually received an appointment as a
canon of the cathedral in Frombork, where he passed most of his
life. He never married.
3) It is believed that Copernicus began writing his magnum opus,
_De Revolutionibus_, around 1515. He had already outlined his
theory that the Earth revolves around the Sun before 1514. As
Copernicus continued work on _De Revolutionibus_ throughout the
1530s, interest in his work grew. In 1533, Pope Clement VII was
told about the theory of Copernicus, and several high Church
officials wrote to Copernicus to say they admired his work and to
offer to pay all his expenses. Copernicus was also urged to
publish his work without delay.
4) But in addition to approval of his work, significant criticism
existed. In 1539, Martin Luther wrote: "Mention has been made of
some new astrologer, who wanted to prove that Earth moves and
goes around, and not the firmament or heavens, the sun and
moon... This fool wants to turn the entire art of astronomy
upside down! But as the Holy Scriptures show, Joshua ordered the
sun, and not Earth, to halt!" Protestants were initially more
hostile to Copernicus; the Catholic resistance developed later.
5) In June of 1542, Copernicus dedicated the preface of _De
Revolutionibus_ to Pope Paul III: "I can easily conceive, most
Holy Father, that as soon as some people learn that in this book
which I have written concerning the revolutions of the heavenly
bodies, I ascribe certain motions to Earth, they will cry out at
once that I and my theory should be rejected." Copernicus added
that his work had been motivated by "the uncertainty of the
traditional mathematical methods of calculating the motions of
the celestial bodies," and he appealed to the Pope to "suppress
the bites of slanderers." Copernicus died 14 May 1543, the day
the finished book was placed in his hands [*Note #1]
Astronomy http://www.astronomy.com
--------------------------------
Notes:
Note #1: The book /De Revolutionibus/ was a collection of very
different materials. Its bulk was mathematical astronomy, in
which Copernicus first recast the reference frames for
observation and then produced his revised models for the moving
bodies. Before the mathematical section there appeared Book I, an
argument for the reality of the Earth's motions based on various
heuristic considerations. At the beginning of the book was a
preface by Copernicus, describing the problems he had solved and
warning that astronomy is a matter for experts. Before the
preface was an unsigned note addressed to the reader, the note
consisting of an apology for the strange theory and a disclaimer
that it represented reality. This note was apparently not written
by Copernicus, but by Andreas Osiander (1498-1552), who saw the
book through the press, and who apparently wrote the note to
avoid possible trouble from theologians. It is perhaps of some
significance that as an initiator of a cultural conceptual
revolution, Copernicus has a parallel in Darwin, who initiated
what is called the "Darwinian Revolution" in our cultural
conception of the human species as a biological entity, a
cultural conceptual revolution not yet complete and still under
attack by non-experts.
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