Electromagnetic Radiation & Optics 

• see also:
  • light
  • electromagnetic radiation
  • optics
  • matter, light and energy
  • the origin of the Universe
  • history of astronomy

A brief history of electromagnetic radiation & optics:

• Euclid:
  • light travels in a straight line
  • geometry
• Archimedes:
  • magnifying mirrors
• Ptolemy (140AD) studied refraction of light, although only a fragment of his book "Optics" survives, courtesy of the Arabs in the Dark Ages, he concluded that light was refracted at a fixed proportion to the angle of incidence - this only holds for small angles & he was criticised by Brahe in 16thC & Newton;
• Abu Ali al-Hasan (Alhazen) (b. 965AD in Iraq):
  • transformed the subjective Greek classical theories into the geometric view of optics that we take for granted today.
  • failing to control the Nile river as had been asked of him by the Egyptian king Al-Hakim, to avoid death, Alhazen pretended to be mad & was locked away, there he studied the light coming through his barred windows.
  • he convinced that light did not come from his eye as was thought by the Greeks, but was independent of the eye & was thus then able to use Euclid's elegant straight-line geometry, imagining the light flowing along lines from the sun, beaming out in all directions, with one beam hitting his eye, enabling sight.
  • after many years, when the king finally died, Alhazen now in his 50's and out of confinement, could refine his ideas.
  • working with polished metal of mirrors (in use since the Copper Age perhaps 5000yrs before), took the study of reflection to a new peak, detailing the ways that rays bounce off different curvatures of mirror from spherical to conical by painstakingly following the paths of hundreds of individual rays.
  • he discovered atmospheric refraction of light at sunsets/sunrise & then estimated how thick the atmosphere was (15-40km)
  • used a pin-hole to display an inverted image - the camera obscura
• Grosseteste (late 11thC):
  • an English monk, ranked observation above theory, contrary to the authoritarian ideas of both Greek philosophers & the Church.
  • envisaged matter to have been formed from light
  • paved the way for Bacon
• Roger Bacon (1214-1294):
  • an English monk who was prevented from writing or keeping books, but eventually was allowed to write his Opus Majus, Minus & Tertius
  • the 1st real scientist - proposing an hypothesis & then testing it.
  • worked on Grosseteste's lenses & made the 1st ever spectacles
  • argued against Aristotle's view that light could not take any time to travel, suggesting it was like sound
  • described how the rainbow could be caused by refraction & reflection within individual raindrops
  • gave a reasonable explanation of why the sun & moon appear larger near the horizon
• Leonardo da Vinci (1452-1519):
  • theoretical telescopes:
    • describes "make lenses to see moon big", "... bring image of a planet onto the base of a concave mirror. The image reflected ..will show the surface of the planet much magnified"
  • 1st to theorize that the eye worked like a camera obscura, projecting an inverted image, but it was Maurolico who suggested that the cornea & lens focussed the image onto the retina & explained near & far-sightedness, developing the theory behind Bacon's glasses.
• Hans & Zacharias Janssen (1590):
  • lens makers, assembled 1st compound microscope, but it was not until 1674, that van Leeuvenhoek, using a single lens instrument discovered bacteria.
  • this father/son team were in a boom in optical business in Holland, which was to be the centre of optical mastery for the next 100yrs.
• Leonard & Thomas Digges:
  • possibly the 1st to make refractor telescopes
• Galileo (1609):
  • invented the 1st refractor telescope with an upright image some 50yrs after the 1st telescope by Digges.
  • in 1610, discovered the 4 largest moons around Jupiter
• Rene Descartes (-1676):
  • used a bull's eye to prove the eye worked like a camera obscura
  • 1st to write that Alhazen's rule that angle of reflected ray is same as incident ray.
  • theorised Snell's law at same time that Snell developed it using experimentation
• Bartholin (1669) - discovers double refraction in calcite - "must be 2 types of light" - but the truth not discovered for 200yrs.
  • Vikings had possessed a special gem "sunstone" - could this be calcite (Iceland spa).
• Roemer (1676) calculates speed of light at 220,000km/sec
• James Gregory:
  • 1st reflector telescope - sent light back through a small hole in the main mirror
• Isaac Newton (1642-1727):
  • popularised the reflector telescope with a 90deg. mirror sending light sideways & which did not suffer from chromatic aberration as did the refractor
  • the origin of colours:
    • the prism doesn't tint light, but breaks it up into the colours of the spectrum
    • deduced the mechanism by which an object appears to have a particular colour
    • degree of refraction depended on the colour of light
  • light as small particles 'corpuscles'
  • 1704, after years fighting Hookes, finally publishes his book Opticks
• Christiaan Huygens:
  • light as wavelets in "ether" which consisted of tiny invisible compressible spheres (replacing Descartes' plenum)
• Schulze (1727) found that silver nitrate would retain a darkened image when a picture is projected onto it using a stencil
• Davy:
  • 1802: realized the potential for making pictures using light-darkened silver, but could not retain the images unless kept in total darkness.
  • 1860: 1st commercial arc light
• Herschel:
  • 1800: discovers "invisible light" by detecting increase temperature past the red from a spectrum made by a prism, which he called infra-red
  • discovers fixing of the silver nitrate image & in 1839 coined the words 'photography' & 'negative'
• Ritter:
  • 1801: repeated Herschel's expt using silver nitrate paper & detected ultraviolet light
• Thomas Young (1773-):
  • 1801: proved that light was a wave by demonstrating interference patterns & that the colours were dependent on the wavelength
  • deduced that the waves moved up & down rather than as compression - to explain polarisation - but not widely accepted for 40yrs
• Augustin Fresnel
  • fringes around a shadow could be explained by interference - diffraction patterns
  • polarisation
• Daguerre (early 19thC): invented his Daguerretype pictures
• Michael Faraday (1846):
  • connected electricity, magnetism &  light & theorised that light would not need ether to travel in
  • electricity, when moving along generates magnetism
  • magnetism, when moving generates electricity
• Fizeau/Foucalt (1849) - measure speed of light mechanically as 298,000km/s
  • later measurements of speed of light:
    • 1931: Michelson mechanically measured it at 299,774 km/sec
    • 1980's: 299,792,457 & 299, 792,459 m/s created a problem in that the metre was defined based on wavelength of light emitted by krypton atom, thus speed of light was measured with greater accuracy than the metre!
    • 1983: the fixed speed of light in vacuum - defined as being 299,792,458 m/sec & the metre defined from this.
• Tyndall (1854):
  • attempted to explain the sky's blue colour as a scattering effect of dust - the Tyndall effect
  • discovers total internal reflection in water
    • within 10yrs, Charles Boys creates 1st glass optical fibres, but these were only a novelty, until laser was invented.
• James Maxwell (1831-):
  • built on Faraday's theory & described how light worked
  • light was the result of the interplay of electricity & magnetism at just the right speed - the speed of light
  • defined light by the forces producing it rather than by the way the eye perceives it
  • described for 1st time mathematical equation, the way 3 primaries combine to provide any hue.
  • also gave the 1st clear picture of how the eyes perceive colour with separate components picking up each of the three primaries & explained colour blindness
• Thomas Edison:
  • 1879: invents his incandescent lamp, one of the earliest practical lamps
• George Eastman (1884): produced 1st roll film to be used inside a camera and create the negatives.
• Albert Michelson (1887): proves there was no 'ether' wind, but ether theory was not fully rejected for another 13yrs.
• Heinrich Hertz (1888):
  • using an apparatus to demonstrate the strange electromagnetic waves in action, discovers waves well below infra-red "electric waves"
• Gugliemo Marconi (1895): working on the "electric waves" devises 1st successful radio equipment
• Wilhelm Rontgen (1895): working with cathode ray tube, discovers X-rays
• Lumiere brothers (1895): shows their 1st moving picture to the public
• Rutherford discovers gamma rays
• Planck still believing light was a wave, theorised atoms gave off light as chunks of energy 'quanta'.
• Einstein (1905) - the photo-electric effect & quantum theory & is his theory of relativity including the principle that nothing could go faster than the speed of light in a vacuum & that light beams should be bent by gravitational fields as part of his distorted space-time.
• Gilbert Lewis gave the packets of light a term - 'photon'
• Einstein (1917) predicts possibility of creating a chain reaction producing light - 'stimulated emission'
• Eddington (1919) proves Einstein's theory of light being bent around a massive object by photographing a solar eclipse. Using this same principle but using a galaxy as the gravitational field rather than the sun, it was possible to create a galactic lens & see stars up to 14b light years away, much further than previous.
• Bose, Einstein (1920's) - theorised a 5th state of matter - the 'Bose-Einstein condensate' - by applying intense cold or pressure to a substance.
• Einstein, Podolsky & Rosen ("EPR") in 1935, whilst double checking the quantum theory equations, realised that photons exist in a strange mixture of two possible states & that it is possible to force two photons together such that they are opposites of each other. They then proposed what they thought was impossible - the 'EPR phenomenon' - if these two photons were separated to a great distance, then looking at one to determine its type would instantaneously force the other to become its opposite! If this is true, it could form the basis of a matter transmitter!
• Land (1926), working on polarised light, develops his 'Polaroid' plastic sheet, founding the Polaroid Corp. by 1937 & making him millions.
• Feynman (1940s), - theory of quantum electrodynamics (QED) - a photon starts its life when an electron moves from one orbital to another, travels for perhaps billions of years & is destroyed by another electron's electrical field. 
  • Light is made up of particles & behaves like particles & his theory based on probability could explain all of light's characteristics without resorting to wave theory. Photons reflecting off a mirror bounce in all directions according to probability, but usually, the least probable directions cancel each other but this can be shown to happen when looking at a CD disk playing surface where the row of pits on it cut out the probability in one direction only resulting in rainbow of colours.
  • Light is fundamental to the continued existence of matter. Electrons do not collapse into the nucleus of an atom as there is a constant exchange of photons, providing just enough interaction to keep the electrons in their place, thus each atom is an absolute fireball of light, busily ensuring matter stays intact, but as it does not get outside the atom, it is invisible.
• Basov, Prochorov (1954) - develop the maser by firing microwaves to trigger a synchronised stimulated emission of photons from ammonia.
• Maiman, Gould (1960) develop the visible light maser - the laser using a ruby and mirrors
• Leith, Upatnieks (1964), using Gabor's theories of the 1950's & the new laser, produced the 1st true hologram
• John Bell (1964), proved that the absurdity of EPR to be a potential reality.
• Alain Aspect (1982) demonstrates EPR
• Charles Bennett (1993) made the leap from the reality of EPR to the possibility of teleportation
• Nimtz (1995) sends a digital version of Mozart's 40th symphony at 4 times the speed of light (in vacuum)!
• 1997, independent teams in Innsbruck & Rome demonstrate teleportation from one side of a room to another
• Hau (1998) using a Bose-Einstein condensate manages to slow light down to as low as 1 metre/sec! This raises the possibility of developing "slow glass" glass which would show an image that hit it some time in the past!
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