Lecture5_ch3 - The Birth of Modern Science A quick overview of ancient civilizations and their astronomy Ancient people of central Africa(6500 BC

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Unformatted text preview: The Birth of Modern Science A quick overview of ancient civilizations and their astronomy Ancient people of central Africa (6500 BC) could predict seasons from orientation of crescent Moon Days of week named for Sun, Moon, and visible planets North France: Cave paintings from 18,000 B.C. indicate knowledge of lunar phases (29 dots) England: Stonehenge (1550 B.C.) 1 Yucatan, Mexico: Mayan structure at Chichen Itza Mayans predicted eclipses, used “zero” (math) SW United States: “ Sun Dagger” marks summer solstice Accomplishments • • • • Time-keeping and standards Navigation Predicting seasons Predicting eclipses Why does modern science trace its roots to the Greeks? Greeks were the first people known to make models of nature They tried to explain the patterns in nature without resorting to myths and supernatural explanations Our mathematical and scientific heritage originated with the civilizations of the Middle East 2 Greek philosophers believed Earth to be at the center of the universe Gravity was thought to pull all matter to the center of the universe Plato Ideas are more important than observations Heavens were perfect: unchanging spheres, perfect circles. Happiness is a perfect circle … Some Greek achievements were very impressive -Eratosthenes accurately measured size of Earth Aristotle Aristotleʼs writings on this subject remained influential for nearly 2,000 years Recall: retrograde motion How did the Greeks explain planetary motion? Over a period of 10 weeks, Mars appears to stop, back up, then go forward again. In order to explain planetary motion in a Earthcentered (geocentric) system, Greeks made models with small circles rotation on bigger circles 3 The most sophisticated geocentric model was that of Ptolemy (A.D. 100-170) Ptolemyʼs Almagest was the most authoritative work on planetary motion for 1500 years: How did Islamic scientists preserve and extend Greek science? -star catalogue Ptolemy -motions and model for Sun, Moon, planets Muslim world preserved and enhanced the knowledge they received from the Greeks Al-Mamunʼs House of Wisdom in Baghdad was a great center of learning around A.D. 800 Artistʼs reconstruction of Library of Alexandria Much of Greek knowledge was lost to the Western world with the multiple burnings of the Library of Alexandria (last time A.D. 415) Copernicus proposed in 1543 that the Sun, not the Earth, was at the center of the solar system How did Copernicus, Kepler, & Tycho challenge the Earthcentered idea? Nicolaus Copernicus 4 Tycho Brahe was the greatest naked-eye observer of all time The system of Copernicus still had planets moving in perfect circles and did not predict planetary motion much better than Ptolemyʼs Measured motions of planets to better than one arcminute. He hired Kepler in 1600. Page from De Revolutionibus Tycho Brahe How did Tycho measure star positions? Kepler tried to explain Tychoʼs observations using circular orbits He was very rich. He had many workers. Because circular orbits could not explain all the observations, Kepler turned to elliptical orbits (1610, 1618). 3 meters He built BIG instruments (but not telescopes). Even though he had the observations, he did not believe the Earth went around the Sun… Johannes Kepler Keplerʼs system of elliptical orbits greatly simplified our picture of the solar system What’s an Ellipse? What are Kepler’s three laws of planetary motion? An ellipse is like an elongated circle 5 Eccentricity of an Ellipse Kepler’s First Law Eccentricity and semmjr The orbit of each planet around the Sun is an ellipse with the Sun at one focus. Kepler’s Laws Kepler’s Second Law 2. An imaginary line from each planet to the Sun sweeps out equal areas in equal intervals of time. Kepler_2 As a planet moves around its orbit, a line between it and the Sun sweeps out equal areas in equal times. Orbital Speeds of Planets Kepler’s Third Law More distant planets orbit the Sun at slower average speeds, obeying the relationship p2 = a3 p = orbital period in years a = avg. distance from Sun in AU Distant planets orbit slower (1 AU = Earth-Sun distance) 6 Kepler’s Third Law How did Galileo solidify the Copernican revolution? Using his telescope, Galileo saw mountains and valleys on the Moon, proving that it is not a perfect sphere Galileo Galilei Galileoʼs telescope Galileo also saw four moons orbiting Jupiter, proving that not all objects orbit the Earth. Galileo saw that Venus goes through a full cycle of phases, proving that it orbits the Sun and not Earth 7 The Catholic Church ordered Galileo to recant his claim that Earth orbits the Sun in 1633 His books on the subject were specifically removed from the Churchʼs index of banned books in the 18th century Galileo Galilei How can we distinguish science from non-science? Galileo was formally vindicated by the Church in 1992 Classic Scientific Method: Classic Scientific Method: 1) Make observations 1) Make observations 2) Form a question 3) Develop an educated guess (hypothesis) 4) Make a prediction 5) Do an experiment to test the prediction 6) Revise or change the hypothesis, if necessary 7) Keep making different tests Other approaches to doing science… Science doesnʼt always work this way 2) Form a question 3) Develop an educated guess (hypothesis) 4) Make a prediction 5) Do an experiment to test the prediction 6) Revise or change the hypothesis, if necessary 7) Keep making different tests Hallmarks of Science: #1 • Sometimes we start by “just looking”, discovering unexplained phenomena, then coming up with possible explanations (quasars). Modern science seeks explanations for observed phenomena that rely solely on natural causes • Sometimes we try sorting and classifying and looking for patterns (stars and their spectra). (A scientific model cannot include divine intervention) 8 Hallmarks of Science: #2 Science progresses through the creation and testing of models of nature that explain the observations as simply as possible Hallmarks of Science: #3 Modern science makes testable (or observable) predictions; scientific results can be repeated, reproduced, and verified. (Simple explanations are preferred over less likely complex ones; “Coincidences” are suspicious.) Scientific Theory What is a scientific theory? Anything that qualifies as a scientific theory must be supported by a large, compelling body of evidence. A scientific theory must be falsifiable. Are science and religion in conflict? • The Catholic Church no longer thinks so. • Faith: Romans 1:17 • Science can not make final statements about ethics or morality. – Science can tell you a heart is beating, not whether it is moral to stop it. • Science (and reason) cannot prove nor disprove the existence of God. • Conflict can arise if a religion makes a testable claim. Then science can test it. 9 ...
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This note was uploaded on 11/13/2011 for the course ISP 205 taught by Professor Donahue during the Fall '08 term at Michigan State University.

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