Abbreviated History of Optics

Transcription

1 Abbreviated History of Optics Understanding came very late historically Lack of scientific tradition prevented systematic investigation of natural phenomena Most progress since the 1600 s 500 to 200 Greeks Optics as geometry Mirrors 1000 Alhazen Optics as scientific study Middle ages Grosseteste Further studies 1600s Kepler, Galileo, Fermat, Optic laws Descartes, Snell 1700s Newton Huygens Particle theory Wave theory 1800s Young, Fresnel, Maxwell, Helmholz, Hertz Elaboration of wave theory, E&M radiation 1900s Planck, Einstein Modern quantum theory Paul Avery (PHY 3400) 1 Abbreviated History of Optics

2 The Greeks Vision / light investigated by philosophers & mathematicians y Pythagoras (550 B.C.E.) y Democritus (400 B.C.E.) y Aristotle (350 B.C.E.) De Anima y Plato (320 B.C.E.) Timaeus y Euclid (320 B.C.E.) Optics y Diocles (2 nd century B.C.E.) y Hero of Alexandra (1 st century A.C.E.) y Ptolemy (2 nd century A.C.E.) y Many others Sometimes muddied thinking about vision vs light, e.g., vision not always considered distinct from light sources y Example 1: Vision caused by light coming from eyes! y Example 2: Images carried from object to eye Much concern about reality vs appearance, illusion and deception, requirements for vision Greek strengths: Deductive reasoning and mathematics Greek weaknesses: Empirical verification through carefully designed experiments Paul Avery (PHY 3400) 2 Abbreviated History of Optics

3 Euclid, most famous for treatise on geometry (Elements), but also wrote Optics. y Deals with subjective appearances and optical illusions y Uninterested in question about sources of light rays y Some quantitative understanding about light y 1. Light travels in straight lines 2. Closer objects appear to be larger and move faster 3. Can measure object distance from known height Diocles (2 nd century B.C.E.) y Proved that a paraboloid mirror reflects rays to a point Mirror Paul Avery (PHY 3400) 3 Abbreviated History of Optics

4 Alhazen (c A.C.E.) First to completely disentangle light from vision y Successful application of reductionism Optics informs us about objective reality y Contrast to Greek thought that optics concerned with subjective aspects of what the eye sees Testable predictions vs philosophy First scientific explanation of vision using structure of eye Explained refraction, reflection, binocular vision, focussing with lenses, the rainbow, parabolic and spherical mirrors, spherical aberration, atmospheric refraction, and the apparent increase in size of planetary bodies near horizon Books translated into Latin in 1270 (no other sources survive) y 200 books in Arabic, few translated, unfortunately y Influenced Roger Bacon, Kepler Paul Avery (PHY 3400) 4 Abbreviated History of Optics

5 Middle Ages Investigation of nature to reveal God s works Study of rainbow using bowls of water Robert Grosseteste (c. 1200) Light is the first creative impulse Light spread and formed the heavens Understanding light propagation helps understand creation Paul Avery (PHY 3400) 5 Abbreviated History of Optics

6 Galileo ( ) Applied telescope to astronomy: many discoveries Made unsuccessful attempt to measure speed of light Kepler (1604) Paralipomena René Descartes (1637) Expressed modern version of law of refraction n sinθ = n sinθ Snell s law Light is real, propagates through mechanical medium Light is central to a mechanistic view of nature Pierre de Fermat (1650 s) Derived law of refraction from least time principle By the end of 17 th century, geometric optics and lens making well understood. But what is light? Paul Avery (PHY 3400) 6 Abbreviated History of Optics

7 Isaac Newton (1704): Opticks First serious attempt to study the nature of light Paul Avery (PHY 3400) 7 Abbreviated History of Optics

8 Comprehensive study of optics through rigorous experiments y Ex: Prism does not modify light, light composed of colors Using two prisms to split and then reconstitute white light Paul Avery (PHY 3400) 8 Abbreviated History of Optics

9 Corpuscular theory of light: light = particle rays Different kinds of rays hitting retina cause color sensation Strong arguments against wave theory of light Bitter argument with Hooke who argued for wave theory Forceful personality and intellectual achievements led to adoption of particle theory for 100 years! First attempt to measure color quantitatively (color wheel) Rainbow Designed telescopes, including first reflecting telescope Christian Huygens (1690) Argued for wave theory y Huygens principle of light propagation Paul Avery (PHY 3400) 9 Abbreviated History of Optics

10 Thomas Young (1802) Newton to 1900 Beautiful series of experiments on interference showed clearly that light acts as a wave Proposed that light is transverse wave Augustin Fresnel (1815) Developed beautiful theory of diffraction & interference Argued that light was a transverse wave Devised experiments to demonstrate light s wave nature Paul Avery (PHY 3400) 10 Abbreviated History of Optics

11 James Clerk Maxwell (1864) Electromagnetic theory of light is a masterpiece y Maxwell s equations unify electric/magnetic theory y Describe almost everything about electromagnetism y Speed of light in terms of E&M constants: c = 1 / µε 0 0 Heinrich Hertz (1888) Measured E&M waves from spark gap Demonstrated reflection, refraction same as for light Paul Avery (PHY 3400) 11 Abbreviated History of Optics

12 Modern Understanding Planck (1900) Quantum theory of light: emitted discontinuously E hf Einstein (1905) emission = Photoelectric theory of light y Light absorbed discontinuously y Light acts as a particle and as a wave y Received Nobel prize for this years later Photon theory of light: E hf photon = Paul Avery (PHY 3400) 12 Abbreviated History of Optics