Transcript Slide 1
Progression of science: Greeks to geeks Solar system models Physics • Geocentric model; • Newton; • Heliocentric model. • Einstein; • The philosophy of science. The players • Tycho; • Kepler; • Galileo. The Geocentric Model: Ptolemy (~90-168 AD) His work builds upon Aristotle’s; Based upon a geocentric model; Involves circular orbits, uniform speeds; In initial conception, simple and beautiful; Codified in the Almagest. The Heliocentric Model: Copernicus (1473-1543) His work builds upon Aristarchus’; Based upon a heliocentric model; Involves circular orbits, uniform speeds; In initial conception, simple and beautiful; De Revolutionibus, published at his death Retrograde motion and stellar parallax Retrograde motion: Mars clearly travels BACKWARDS in the sky, for a few months, every year! Stellar parallax: if the Earth shifted its position, surely we would see the stars shifting in the sky! The geocentric mess In order to explain nonuniform speeds of objects in the sky, the following patches were introduced to the geocentric model. – Epicycles (green circles); – Deferents (post marking the radius of the epicycle); – Equants (displacement of Earth, and orbit, from the circle center); – Multiple circles. Model smack-down Geocentric + Aristotle said so; + Feels good; + Accurate; - Decreasing accuracy; - Complicated; - Retrograde motion Heliocentric + Retrograde motion; + Simple; - Not very accurate; - No parallax for stars. The odd couple Tycho Tycho 1546-1601 (Yin) Danish bon vivant; Fabulous parties (including jesters and elk); Metal nose; Extraordinary observer; Observed supernova (1572), no parallax; Observed comet (1577), further than the moon; Kepler German astrologer; Geek among geeks; Avoided distractions. Kepler 1571-1630 (Yang) Kepler’s three laws: Tycho 1546-1601 (Yin) Kepler 1571-1630 (Yang) K1: All objects orbit on elliptical paths, with the central object at one “focus” — i.e., does not require circles! Kepler’s three laws: Tycho 1546-1601 (Yin) Kepler 1571-1630 (Yang) K2: All objects orbit so that they sweep out equal areas in equal times — i.e., does not require constant speed! Kepler’s three laws: Kepler 1571-1630 (Yang) Tycho 1546-1601 (Yin) K3: The square of the orbital period is proportional to the cube of the semi-major axis (~radius) of the orbit: P2=a3 Galileo’s (1564-1642) observations Some of Galileo’s key discoveries – Jupiter has four satellites; (a case of something orbiting an object other than the Earth) – The Moon seems to be a world, with craters and mountains; (the planets were supposedly celestial orbs) – The Sun has spots; (how could it be imperfect?) – Venus has phases and a varying size. (it cannot be orbiting the Earth) Galileo’s troubles – He broke with Ptolemaic ideas of harmony of science, theology, poetry and music that all fit together in the Renaissance system. French theologian and mathematician Blaise Pascal, said, "The eternal silence of these infinite spaces fills me with dread.“ – It challenged the church's commitment to geocentricism. – Galileo began a crusade to change the Church’s policy toward geocentricism. He expected people to accept his authority. – Sarcastic attacks on those who refused to look through his telescopes. – He denied Kepler a scope. – He dismissed church authorities who asked for more definitive proof. – Galileo was forbidden (1616) from teaching Copernican theory as fact—“Dialogue on the Two Chief World Systems: Ptolemaic and Copernican” (1632). – Simplicio utters a text from a letter from Pope Urban VIII. – The Inquisition convicted Galileo of heresy (1633) using forged minutes. – Ultimately placed in house arrest for the last 9 years of his life. Newton (1643-1727) Some definitions Position – where something is; Speed – change in position; Velocity – change in position or direction; Acceleration – change in velocity; Mass – how much stuff is in something; Force – how hard something pushes/pulls. Newton (1643-1727) N1: An object at rest will stay at rest, while an object in motion will stay in motion with no change in its velocity (unless acted upon by an outside force). N2: If an object (with mass=m) is affected by a force (force=F), it will respond by accelerating (a): F=ma N3: For every force being applied, there is an equal and opposite counter force. Newton (1643-1727) NG: Two objects of mass (M, m), separated by a distance (R), will have a mutually attractive gravitational force, an action at a distance: Fg=GMm/R2 Grandmaster Geek: Einstein (1879-1955) Explored the affects of velocities near the speed of light (Special Relativity). Developed concepts of space-time, to redefine how we think of gravity (General Relativity). How science proceeds Observations hypothesis theory – Hypotheses must make testable predictions… – Science can only disprove, not prove… – Theories that survive, become more respected… – Simpler theories are preferred (Occam’s Razor). Bogus science Signposts of bogosity: 1) Being hopelessly complicated. - Complicated does not mean accurate. 2) It is a traditional belief. - Because your parents did it, does not make it right. 3) Explaining one observation by introducing another rule. - This is simply restating the observation as an assumption 4) Observations are not repeatable. - It may be correct, but it is unproven. 5) You must be a believer to understand it. - Ha ha ha.