1 § 1.1 Physics as Natural Philosophy Physics is one of the liberal arts, combining elements of reason, philosophy, mathematics, language, and rhetoric. The term natural philosophy reflects the creative and dynamic interplay that exists in physics among experiment, theory, logic, insight, inspiration,symmetry, beauty, and language. 2 § 1.1 Physics as Natural Philosophy 1. Developing Theories The goal of the theory is to integrate as many observations of nature as possible under one conceptual umbrella—to discover how little must be known to explain as much as possible. (P 2 colum 2 paragraph 2) KIS principle: Keep It Simple. For instance: Newton’s theory → Einstein’s relativity § 1.1 Physics as Natural Philosophy Characteristics of a good physical theory 1. Include all known relevant observations and measurements 2.Account for observations and measurements with minimal complexity 3. Lead to new and different experiments with results that are consistent with the predictions of the theory 3 § 1.1 Physics as Natural Philosophy 2. Physics and equations If you feel that understanding physics amounts to memorizing myriad equations and formulas, and then searching for a “magic bullet” among them, you have missed the forest for the trees. “Doing physics” is the reasoning that leads from observations and experiments to a mathematical model or explanation of them. § 1.1 Physics as Natural Philosophy 3. Language and Physics When writing physics, one must be as precise as when crafting a legal document. When reading physics or the law , you likewise must be careful, deliberate. 4 § 1.2 Contemporary Physics: classical and modern Observation of nature and experimental results typically precede the general theories that account for them. 1. Kinematics and Dynamics Kinematics invented by Galileo Galilei is a theory that describes quantitatively motion. Dynamics invented by Issac Newton is a theory that explained the causes of motion. Principia is the first comprehensive physical theory. § 1.2 Contemporary Physics: classical and modern § 1.2 Contemporary Physics: classical and modern 2. Electricity and Magnetism The theory of electromagnetism integrated by James Clerk Maxwell is the second great physical theory of natural Philosophy. Benjamin Franklin, Charles Coulomb, Christian Oersted, Michael Faraday. This theory predicted : the existence of electromagnetic wave; Light is electromagnetic wave. 5 § 1.2 Contemporary Physics: classical and modern 3. Thermodynamics Engine efficiency(Sadi Carnot)—dissipation of mechanical energy and heat transfer(James Prescott Joule)—entropy(Rudolf Clausius)—the statistical meanings of entropy(Ludwig Boltzmann) The physical laws of thermodynamics (Willard Gibbs) § 1.2 Contemporary Physics: classical and modern 4. Modern Physics relativity developed by Albert Einstein in 1905 is a more general theory of space, time, and motion. Quantum mechanics is the theory developed during the1920s by such giants of 20 th -century physics as Erwin Schrodinger, Wolfgang Pauli, Werner Heisenberg, P.A.M.Dirac, Niels Bohr, and Enrico Fermi, all of whom eventually became Nobel laureates in physics. 6 § 1.2 Contemporary Physics: classical and modern This theory integrated many phenomena such as: X-ray, radioactivity, electron, radiation of blackbody, photoelectric effect, quantization of angular momentum and energy. Classical physics Modern physics Kinematics and dynamics Electromagnetism thermodynamics Relativity(special and general) Quantum mechanics § 1.3 Why must we study physics 1. What is physics? Physics is foundation to all natural sciences, technologies and engineerings. Physics education should be the education of science diathesis. Physics studies fundamental structures , fundamental interactions of substances, and fundamental laws of motion of matter in various structure level. 7 § 1.3 Why must we study physics 2. The relationships among the physics and other disciplines 1physics and astronomy astronomical observation physics § 1.3 Why must we study physics 8 § 1.3 Why must we study physics Einstein suggested that a body with a large mass will bent space. § 1.3 Why must we study physics Einstein ring and gravitation lens 9 § 1.3 Why must we study physics 2Physics and biology Organisms are made up of atoms and molecules, which obey physical laws. § 1.3 Why must we study physics A magnetic resonance image of the head Physics provides the research methods for biology and biological medicine. 10 § 1.3 Why must we study physics § 1.3 Why must we study physics The reattachment of detached retinas by means of lasers 11 § 1.3 Why must we study physics 3physics and microelectronics(computer science) Quantum physics(1925)—energy band theory of solids(1929)—Transistors(1947)— integrated circuits(1962)—large scale integration and SLSI(1970s) In 1992, IBM MOSFET memory chip 4 gigabits of memory Several hundred nanometers long Properties are quantum -mechanical 例如： *第一代电子计算机“埃尼阿克”，整机用了1万8 千多个电子管、重30吨，占地549平方米，费用 1000万美金，计算机运行速度为每秒5000次。 *第二代晶体管计算机，1956年投入军用，占地一 大间，造价为几十万美金。 *第三代大规模集成电路计算机，1964年由IBM生产 出来，尺寸和费用都已大大降低。 § 1.3 Why must we study physics 12 *第四代超大规模集成电路计算机，70年代，在一 块重约十克，几个平方毫米的芯片上（Intel-8048) 就已拥有“埃尼阿克”的全部功能，耗电量从140 瓦下降到3瓦，价格降至几美元，运算速度上升到 每秒几十万次，这就是俗称的微型机。 *第五代计算机 ——智能型（专家系统） *第六代计算机 ——神经系统电脑（量子技术、光 子技术） § 1.3 Why must we study physics § 1.3 Why must we study physics P-n junction and transistor 13 § 1.3 Why must we study physics MOSFET Quantum well Metal-oxide semiconductor field-effect transistor The moving range of electrons is 20 nanometers § 1.3 Why must we study physics 4Physics and optics information technology Signal source —laser based on the quantum physics Transmission medium --material (optical fiber, disk)based on physics Detection and treatment of the information --technologies of optical acoustics, optical magnetism, optical electronics, integrated optics ……, all based on physics. 14 § 1.3 Why must we study physics Electromagnetic theory(1860), quantum theory(1900 ), stimulated emission theory(1917) are the foundations of laser. The maser was made in 1953, the first laser was made by Maiman in 1960 Communication with optical fibers § 1.3 Why must we study physics 15 § 1.3 Why must we study physics All the materials are composed of atoms and molecules. 5physics and science of materials X-ray and the structure of materials o 50=φ § 1.3 Why must we study physics 16 § 1.3 Why must we study physics The scanning tunneling microscope § 1.3 Why must we study physics Iodine atoms on the surface of Platinum observed by the scanning tunneling microscope 17 § 1.3 Why must we study physics Individual Xenon atoms can be moved. 6physics and energy sources technology § 1.3 Why must we study physics Natural radioactivity of Uranium was discovered in 1896—E=mc 2 was given by Einstein in 1905—quantum theory was invented in 1925 –the model of proton and neutron of atom in 1932—atomic bomb in 1945—hydrogen bomb in 1952—first nuclear power station in 1954 18 § 1.3 Why must we study physics Applications of the laser: Fusion by inertial confinement with laser beams or particle beams § 1.3 Why must we study physics Fusion by magnetic confinement 19 § 1.4 What should we learn in the study of physics 1. What have we known about the universe? The whole picture for the universe Microcosmic: Molecules Atoms Nuclei Proton Neutron Electron Photon …… Macroscopical: Every thing we can see by our eyes Universal: Solar system Milky way Galaxy Neutron star Black hole Galaxies Universe § 1.4 What should we learn in the study of physics Fundamental theory Quantum mechanics Special relativity Statistic physics Newton’s laws of motion Maxwell’s electromagnetism theory thermodynamics Gravitation theory General relativity Quantum mechanics 20 § 1.4 What should we learn in the study of physics The 42 steps of Universe Four Fundamental forces of nature Category gravitational Weak electro- magnetic Strong Action distance (cm) ∞ < 16 10 ? ∞ < 13 10 ? Relative intensity 13 10 ? （ cm) Mediating particle(s) graviton？ Vector bosons photon gluons 13 10 ? 38 10 ? 2 10 ? 1 )(γ )(g § 1.4 What should we learn in the study of physics 21 § 1.4 What should we learn in the study of physics Some orders of magnitude for time 10 18 Age of universe 10 -4 Highest audible sound 10 17 Age of earth 10 -6 Half-life muon 10 7 One earth year 10 -10 Period of vibration for Cecium clock 10 5 One earth day 10 -15 Visible light wave 10 3 Class lecture 10 -19 Light to cross atom 10 0 Human heartbeat 10 -23 Light to cross proton Time(s)parameterTime(s)parameter § 1.4 What should we learn in the study of physics 2. How do we know about the universe? Observations and experiments Models and mathematics equations Compare the results with the experiments Predictions from the results of equation New observations and experiments 22 § 1.4 What should we learn in the study of physics World of sense Physics world Substantial world The theories of physics are continuously developing, our knowledge about the world is becoming more and more profound. The universe evolves and changes. Our descriptions of physics also change and improve as we develop better way of observing and studying the universe with keener insight, more sophisticated equipment, more realistic approximations , and more encompassing theories. § 1.4 What should we learn in the study of physics 3. Transfer of the ways and the means of the research 1The applications of physics methods e.g. Observation, experiment, induction, illation, simulation, hypothesis, analogy, idealization, analysis, synthesis …… 2The applications of physics knowledge e.g. Astronomy, biology, chemistry, medicine, material, communication, industry, agriculture, national defence, …… 23 3 The applications of scientific conceptions e.g. (a) KIS principle—the more simple the more universal (b) correspondence principle—most physical theories are approximations or models that accurately describe nature phenomena under certain limiting condition and idealized circumstance. (c) sustainable development stratagem –- human being is the part of the nature § 1.4 What should we learn in the study of physics Some main References 1University physics Vol.1 and Vol. 2 Ronald Lane Reese 2 Fundamental physics 6 th edation Halliday , Resnick, Krane 4 Beyond the mechanical universe Richard P. Olenick 5《大学物理学》 1~5册张三慧 清华大学出版社 6《物理学概论》上、下册 徐行可等 西南交大出版社 3 Sears and Zemansky’s University physics Vol.1 and Vol. 2 Hugh D. Young Roger A. Freedman