Lesson 5 Intellectual Revolutions: The Copernican Revolution PDF

Intellectual Revolutions The Copernican Revolution GEC 17-STS COSMOLOGY Early cosmology, from Neolithic times of 20,000 to 100,000 years ago, was extremely local. The Universe was what was immediately interacted with. Cosmological things were weather, earthqu...

Intellectual Revolutions The Copernican Revolution GEC 17-STS COSMOLOGY Early cosmology, from Neolithic times of 20,000 to 100,000 years ago, was extremely local. The Universe was what was immediately interacted with. Cosmological things were weather, earthquakes, and cataclysms. Things outside daily experience were considered supernatural. This was the time of Magic Cosmology. About 20,000 years ago, humankind began to organize itself and develop cultures. This lead to the development of creation myths to explain the origin of the Universe. Many of the myths still maintained supernatural themes, but there was an internal logical consistency to many of the stories. In some sense, the creation myths are the first scientific theories. This is the time of Mythical Cosmology. The third stage, considered the core of modern cosmology, grew out of ancient Greece, later adopted by the Church. The underlying theme in Greek science is the use of observation and experimentation to search for simple, universal laws. We call this the time of Geometric Cosmology. COSMOLOGY FROM THE GREEKS’ POINT OF VIEW  Homer and Hesiod (the 8th century BC) postulated a flat or cylindrical earth located in a hemispherical cosmos Pythagoras (560-480BC) held the view that the earth was a sphere in a universe which was itself also fully spherical. The “round earth” claim was based on: (i) the belief that the circle or sphere was the most perfect of geometric shapes, and therefore appropriate for the earth and the cosmos (ii) the observations of a ship and its mast as the vessel receded beyond the horizon. COSMOLOGY FROM ARISTOTLE AND PLATO’S POINT OF VIEW  Plato believed that concepts had a universal form, an ideal form, which leads to Platonic Idealism. Aristotle believed that universal forms were not necessarily attached to each object or concept, and that each instance of an object or a concept had to be analysed on its own. This is Aristotelian Empiricism. For Plato, thought experiments and reasoning would be enough to "prove" a concept or establish the qualities of an object, but Aristotle dismissed this in favour of direct observation and experience.  COSMOLOGY: PLATO The world was the creation of a "Demiurge" (from the Greek "demos" or people and "ourgos" or work) out of materials provided by a pre-existing "chaos", or jumble of matter The Demiurge organized the world out of the elements -- Earth, Water, Air and Fire. These formed the "body" of the cosmos, which was also endowed with a "soul". The soul of the cosmos, which Plato considered as the more important part, was its principle of eternal and recurring circular motion, as done by the moon, planets, sun and stars. It is presumed, though not explicitly stated by Plato, that the Earth is the center of the cosmos, with the other heavenly bodies rotating about it.  COSMOLOGY: ARISTOTLE Aristotle based himself on various observations evident to the unaided eye (there were no telescopes in ancient Greece): – We see the sun "rise" and "set" each day – We don't feel that the earth moves under our feet – We see the stars describe a semi-circle about the horizon each night All of these seem to imply that the earth is fixed at the center and the sun moves around it. Moreover, it seemed appropriate that the earth -- the planet we inhabit -- be at the center, since after all, aren't humans (i.e. the Greeks) the most important part of the cosmos? COSMOLOGY: ARISTOTLE Acceptance of the four Platonic elements of Earth, Water, Air and Fire as the basis for phenomena on both the Earth (the planet) and in the atmosphere, The addition of a fifth element -- known as "aether" -- as the matter of the heavenly bodies (moon, planets, sun, and stars) The earth as the center of the cosmos – geocentrism The sun moves around the earth – heliodynamism All heavenly motions are circular (or spherical, in three dimensions) MODELS OF THE SOLAR SYSTEM  Most early models of the solar system were constrained by a belief in an ideal geometric universe in which the circle is the most perfect shape There are two main divisions among the models: – A geocentric model (earth as the center) – A heliocentric model (sun as the center) ARISTOTELIAN-PTOLEMAIC MODEL Aristotle proposed 55 concentric, crystalline spheres to which the celestial objects were attached and which rotated at different Velocities with the Earth at the center His model could not explain varying planetary brightness and the retrograde in their motions ARISTOTELIAN-PTOLEMAIC MODEL The solution to the deficiency in Aristotle’s model was to add epicycles (an orbit revolving around a point on the deferent. As a planet rotates around the earth, it also rotates around a point on that orbit). Ptolemy made the most sophisticated version of this model by introducing epicycles In epicycles it also introduced the idea of the “equant”, an observation point slightly off from where the earth is  By the Middle Ages, Aristotle’s philosophy was merged with medieval theology in the great synthesis of Christianity and Reason undertaken by philosopher-theologians such as Thomas Aquinas. The Prime Mover of Aristotle's universe became the God of Christian theology, the outermost sphere of the Prime Mover became identified with the Christian Heaven, and the position of the Earth at the center of it all was understood in terms of the concern that the Christian God had for the affairs of mankind. Thus, the ideas largely originating with pagan Greek philosophers were baptized into the Catholic church and eventually assumed the power of religious dogma: to challenge this view of the Universe was not merely a scientific issue; it became a theological one as well, and subjected dissenters to the considerable and not always benevolent power of the Church.  COPERNICAN MODEL The Aristotelian – Ptolemaic model was sacrosanct for 1,300 years so that Copernicus waited until the year of his death (1543) to publish his famous essay titled, “On the Revolutions of the Heavenly Spheres.” Copernicus reasoned that: -While the Ptolemaic model was very good at predicting the positions of the planets, it wasn't precise, and over the centuries its predictions got worse and worse. -The Ptolemaic model had big epicycles to explain the retrograde motions of the planets. Copernicus knew this could be explained instead by having the Earth move around the Sun.  Copernican heliocentrism positioned the Sun near the center of the Universe, motionless, with Earth and the other planets rotating around it in circular paths modified by (fewer) epicycles and at uniform speeds. The shortcoming of this model is the use of circular instead of elliptical orbits.  It is believed by many that Copernicus’ book was only published at the end of his life because he feared ridicule and oppression by his peers and by the Church.  His ideas remained rather obscure for about 100 years after his death. In the 17th century, the work of Kepler, Galileo, and Newton would build on the heliocentric universe of Copernicus and produce the revolution that would sweep away completely the ideas of Aristotle and replace them with the modern view of astronomy and natural science. This sequence is commonly called the Copernican Revolution. His book was eventually included in the list of forbidden books by the Church. BRAHE MODEL King Fredrick II of Denmark built Tycho Brahe a naked-eye observatory to measure the position of planets with high accuracy. He developed the practice of measuring the error from his instruments in order to obtain accurate observations. He was unable to observe stellar parallax, which would have given strong proof for the heliocentric theory. His observations of a supernova and a comet showed inconsistencies with Aristotelian theory but he did not challenge it. BRAHE MODEL Brahe developed a model in order to explain Galileo’s observation that Venus had phases. His model had all the planets (except Earth) orbiting around the Sun, but then the Sun orbited around the Earth.  KEPLER MODEL Johannes Kepler was Tycho Brahe’s assistant. Brahe felt threatened and assigned Kepler to the difficult task of observing Mars. It was from the meticulous and extensive record of observation of Mars that Kepler formed his model of the solar system. Unable to fit Mars data into circular orbits, he was forced to come to the conclusion that the orbits must be elliptical.  THE SUM OF THE LENGTHS OF LINE SEGMENTS FROM THE FOCI TO ANY POINT IN THE ELLIPSE IS CONSTANT. The eccentricity of ellipses are anywhere between zero and one; the circle has an eccentricity of zero.  Kepler’s First Law: – The orbits of the planets are ellipses, with the Sun at one focus of the ellipse. Kepler’s Second Law: – The line joining the planet to the Sun sweeps out equal areas in equal times as the planet travels around the ellipse.  Kepler’s Third Law: – The ratio of the squares of the revolutionary periods for two planets is equal to the ratio of the cubes of their semimajor axes: – Let: P1 (period) be expressed in earth years or 1 year R1 (radius) be expressed in distance of earth from the sun, which is 1 astronomical unit or 1 AU Then, we can compute for the: – Radius of orbit of Mars if its period is 1.88 years – Orbital period of Pluto which has an average radius of 39.44 AU ISAAC NEWTON Contributions to different fields: – Mathematics, both pure and applied – Optics and the theory of light and color – Design of scientific instruments – Synthesis and codification of dynamics – Invention of the concept and law of universal gravity – Alchemy – Chronology, church history, and interpretation of the Scriptures ALBERT EINSTEIN Contributions: – Mass – Energy Equivalence – General and Special Theory of Relativity – Photoelectric Effect – Theory of Brownian Motion – Einstein Field Equations – Bose – Einstein Statistics – Bose – Einstein Condensate – Unified Field Theory