WC1 - Introduction Introduction The history of Astronomy...

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Unformatted text preview: Introduction Introduction The history of Astronomy Scientific theories Going to extremes Frontiers and edges of science Counting in powers of 10 Crazy ideas An expensive research Our Picture of the Universe Our Picture of the Universe Old and new questions about the Universe: How does the Universe behave ? Where did it come from and where is it going ? Does the Universe need a creator ? Originally the answers came from philosophy but more recently they came from astronomy, physics, cosmology. Early Answers Early Answers Archaeoastronomy has dealt with practical things such as: keeping time, marking the arrival of seasons, predicting eclipses of the Moon and the Sun. Stonehenge (2700 B.C.), Chichen Itza, Chaco Canyon Constellations were recorded by the Sumerians, Greeks, Chinese, Babylonian and Egyptians Earth at the Center ­ Aristotle (On the Heavens 340 B.C.), Ptolemy (140 A.D.) Round­shaped Earth ­ Pythagoras the size of Earth – Erathosthenes (size given in stadia; 1 stadium=160m) Ionian Theories Ionian Theories Ionian school: Thales, Phythagoras, Archimedes, Democritus (atoms), Aristarchus (Earth not at the center of the Universe; ca.230 BC) Unfortunately the Ionian idea that the Universe can be explained through general laws survived for only a short time. This idea was revived only in the 17th century. Cyclic Cosmologies Cyclic Cosmologies Almost all religions deal only with the creation of the Universe – similarities related to the study of constellations (google Zeitgeist on the Web) Hindu cosmology is unique in its presentation of a cyclic evolution of the Universe (cycles inside cycles). For instance one cycle would correspond to a day and a night in the life of Brahma, equal to 8.6 billions of years. A higher level cycle is a year in Brahma’s life, equal to 3.1 trillion years. Cyclical cosmology was also proposed by Heraclitus of Ephesus around 500 B.C. Modern Science Modern Science Sun at the Center: Copernicus(1514), Tycho Brahe, Giordano Bruno. Modern astronomy: Galileo (1609) Kepler’s laws(1609­1618) Newton’s laws (Philosophiae Naturalis Principia Mathematica 1687). Infinite static Universe ­ H.Olbers (1823) paradox Einstein’s General Relativity (1916) Expanding Universe (Big Bang) – E.Hubble(1929) 21 Century Science 21 st Superstrings and the M­Theory Quantum Cosmology Many dimensions Parallel Universes Where does the Universe come from ? Science more exciting than Science Fiction ! Stephen Hawking’s “The Grand Design”(2010) Non­scientific Answers Non­scientific Answers Answers provided by religions, astrology etc are easier to understand. Only 5% of the population of the Western world can read articles on science for laymen. For a long time science provided very few answers to the big questions about the Universe. Different roles for Science and Religion. “Human belief is not based on science and logic but on what makes us feel good to believe” W.James 1890. Scientific Theories Scientific Theories Definition: A scientific theory is a model of the Universe or of a part of the Universe which accurately describes a large class of observations makes predictions about the results of future observations. Any physical theory is provisional, in the sensethat it is only a hypothesis (K.Popper). Experiments prove it or disprove it. Frontiers and Edges of Science Frontiers and Edges of Science As you will see later in this course, some ideas about the origin of the Universe or about parallel universes qualify as theories “on the edge”. This situation might change in the future and these edges might become frontiers of science. The frontier in science is the boundary of current knowledge in the respective science. One can speak about frontiers in every area of research. The edge in science is different from a frontier in the sense that a theory “on the edge” is not a full scientific theory as it isn’t backed by experiment. Counting in Powers of 10 Counting in Powers of 10 Q: How many atoms in the Universe ? A: Easy to give an approximation: ­ Atoms in a gram 1024 ­ Grams in a star 1033 ­ Stars in a galaxy 1011 ­ Galaxies in the Universe 1010 Total atoms 1078 Note: the multiplication of the powers of 10 is done by adding the exponents Distances in the Universe (in 10N centimeters) N 28 24 20 16 12 8 4 0 -4 -8 -12 -16 Radius of the observable Universe (over 1028) Distance to the nearest galaxy(3x1024) Distance to the nearest star (4x1018) Distance to the Sun (1014) Diameter of Earth (1010) Diameter of neutron star (106) Height of a human being (2x102) Diameter of virus (10-4) Diameter of an atom (10-8) Diameter of an atomic nucleus (10-13) Other Distance Units Other Distance Units One light­year is the distance covered by light in a year. One atomic unit (a.u.) is the radius of the hydrogen atom in its ground state, which about 10­8 cm. As the speed of light is 300,000 km/sec, 1 light­year is equal to the speed of light times the number of seconds in a year, or about 1018cm. The nearest star to our Sun is Proxima Centauri at about 4.2 light­ years The distance Earth­Sun is 8.3 light­minutes Earth­Moon is 1.3 light­seconds. N 44 36 28 20 12 4 -4 -12 -20 -28 Weights in the Universe (in 10N grams) Mass of a galaxy (1044) Mass of Sun (1032) Mass of a mountain (1016) Mass of a human being (105) Mass of a heavy atom (10-21) Mass of electron (10-25) Crazy Ideas Crazy Ideas Arbitration by the experimental results liberate thought rather than constraining it. The more facts the more challenge to the imagination. Quantum theory was probably the most imaginative theory, which today explains in detail the workings of the micro­cosmos. N. Bohr’s famous comments in a 1958 seminar: “we all agree that your theory is crazy; what divides us is whether it is crazy enough” Newton’s “crazy” idea was that the same force that drove an apple towards the ground, also steers Earth in its rotation around the Sun. An Expensive Research An Expensive Research Modern telescopes and particle accelerators can cost hundreds of millions of dollars This is a research which cannot be justified by practical applications but by the need to understand the most fundamental questions about the Universe. (a few years ago R.Wilson, the director of the Fermi laboratory, asked by a senator about Fermi lab’s contribution to the defense program, said “this lab makes our country worth defending”). International cooperations: CERN, Fermi lab, Hubble Telescope, The International Space Station CERN Geneva CERN Geneva Hubble Telescope Hubble Telescope ...
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