5.  Lucretius had a great idea but it didn’t catch on.  He wrote that light and heat came from the sun in tiny atoms that have both speed and direction.  Instead, the idea that light emanated from the eye or the mind hung on for a few centuries.

7.  Grosseteste was a religious scholar who advocated reasoning and experimentation when studying nature, proposing that geometry be used to study light.

8.  Methods of studying nature and increasingly sophisticated instrumentation challenged official religious explanations of the cosmos.  According to the Catholic Church (and most others), the earth was the center of the universe, and while sin and physical corruption was evident on earth, the heavens were perfect.

9. Kepler devised a mathematical theory of camera obscura and explained how the eye works Galileo observed the moon with a telescope, noting that the bumps and craters indicated the heavens were not perfect, and even worse supported the idea that the earth orbits the sun.

11. Proposed particle theory of light Experimented with prisms to show that white light consisted of a combination of colors.

12.  Huygens, on the other hand said light is a wave traveling through ether (aether), which fills space.

13. In that case, what is space? For centuries in the west, space was thought to be filled with some kind of substance, a sort of invisible fluid called ether,or aether. (In the late 19 th century scientists realized they couldn’t measure movement through ether because it wasn’t there—ether doesn’t exist) But until then…

14. Light waving in ether might act as sound does in the air. As mathematician Leonhard Euler put it the sun is like a bell, ringing out light. This analogy wasn’t new, but Euler gave it some math muscle, with calculus. Leonhard Euler 1707-1783 Switzerland http://en.wikipedia.org/wiki/Leonhard_Euler

15. Sound is a vibration (wave) that passes through air. The pitch of a sound corresponds to the frequency of the vibration. The volume of a sound corresponds to the amount of energy in the vibration

16. Back to Euler-- Maybe light traveling through ether acted like sound traveling through air. In his New Theory of Light and Color (1746), Euler supported the vibrational theory of light. He systematically pointed out weaknesses in Newton’s view of light as particles. However, he didn’t answer all the objections to his own theory. For example, his version of the wave theory didn’t explain the many effects of diffraction.

17. Diffraction occurs when light passes sharp edges or goes through narrow slits. The rays are deflected and produce fringes of light and dark bands wordnetweb.princeton.edu/perl/webwn wordnetweb.princeton.edu/perl/webwn

18. The bending of light around objects, such as clouds and fog droplets, produces fringes of light and dark colored bands. www.srh.noaa.gov/jetstream/append/glo ssary_d.htm www.srh.noaa.gov/jetstream/append/glo ssary_d.htm

20. Thomas Young 1773-1829 England According to Young, light is a wave traveling through ether. Puzzling behavior can be explained. Compare light waves to water waves. Just shine light on an even surface then shine more light and bands of darkness will appear. The trick is to make light waves interfere with each other the way water waves can interfere with each other.

21. Take a couple of waves, make sure the peaks are lined up, put them together and you get a larger, stronger wave. Take a couple of waves, make sure the peaks of one are lined up with the troughs of the other, put them together and they cancel each other.

22. Young’s double slit experiment demonstrated diffraction and interference. Light behaves like a wave. But this did not explain everything. Waves deflected in diffractionTwo sets of waves set up to interfere

23. In 1819, Augustin Fresnel, (who didn’t know about Young) provided the best mathematical explanations of diffraction yet. He (and Young) explained another behavior of light, polarization. Augustin Fresnel 1788-1827

24. In Fresnel’s time, an experiment with two crystals showed that when the crystals were arranged in one way, light would travel through the first and then the second. When the crystals were arranged in another way, light would pass through the first, but not through the second.

25. http://www.worsleyschool.net/science/files/polarized/ light.html Ordinary visible light is a mixture of many kinds of waves. The light that enters your eye is composed of waves of a multitude of different wavelengths. Each of these different waves vibrates in many different directions as the light travels. The beam is made up of waves vibrating in all directions, as shown by the white arrows in this diagram. A brief diversion to the 21 st century helps explain :

26. We perceive light waves that vibrate horizontally as 'glare'. As light hits a particular portion of the truck's surface and returns to our eye, the waves get polarized. This means that a higher than normal number of them are vibrating one way, in this case, horizontally. When this light enters our eye, the large number of horizontally vibrating waves seem to overpower the other waves, and everything near that part of the truck is hidden by the 'glare' caused by the polarized waves. (Of course, Fresnel didn’t have a truck but he understood wave orientation.)

27. Glare is just one familiar example of light waves that have been polarized. There are many others. Whenever we change a beam of light waves so that many of the waves are vibrating in the same direction, we have 'polarized' the light beam. A beam of light where most of the waves are vibrating the same way (vertically).

28. Fresnel imagined something vaguely like this: The light waves oriented by the first crystal didn’t match the orientation of the second crystal and couldn’t get through.

29. Fresnel, like most others at the time assumed that light traveled through ether, a material substance. It was hard to imagine light waving in nothing. By the end of the19 th century, however, electromagnetism and field theory made it easier finally to let go of ether.

30.  In the 19 th century, Faraday ‘s concept that light might be propogated by an electromagnetic field was mathematically explained by Maxwell.  Maxwell realized light is a form of electromagnetism  but  he couldn’t let go of ether.

31. Taking an idea from Maxwell, Michelson and Morely figured if light traveled through ether, the invisible substance thought to exist throughout space, the effect of ether would be measurable. Their experiment ‘failed’ because it could not detect ether but their experiment succeeded because it could not detect ether because ether doesn’t exist.

32.  Einstein proposed that the velocity of light is the same, no matter what the velocity of the source of light. The speed of light is the same, no matter what the observer’s frame of reference. Copy and paste this web address for a short video explanation:  http://www.youtube.com/watch?v=WdfnRWGgbd0

33.  A quantum is a discrete piece of something.  Quantum theory states that electromagnetic radiation (including visible light) is emitted in quanta (the plural of quantum)  Quantum theory predicts and explains some odd behavior: depending on when and how it is observed light behaves like a wave and a particle. Observing a light waves up close turns light into a particle, seemingly.

34.  Copy and paste the address below for an explanation by “Dr. Quantum” with another version of the double-slit experiment.  http://www.youtube.com/watch?v=DfPeprQ7oGc