Wave Particle Controversy and Light

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1.  Within the field of electromagnetism, there is the concept of waves and particles

2.  What is a Wave vs. a Particle?

  • A wave is a disturbance to a medium that travels from one location to another
  • A medium is a collection of particles that are capable of interacting with one another (e.g., say water molecules or air molecules)
  • When a disturbance is brought on by some kind of release of energy, each particle within the medium interacts with the one (s) next to it
  • In turn, those particles interact with the one(s) next to them
  • This interaction goes on through the medium until the energy is fully used (all the potential energy is gone)
  • Once each particle is interacted with, it returns to its original rest position
  • The wave medium is not the wave; it merely carries or transports the wave from the source of the disturbance to other locales 1

3.  What are examples of Waves?

  • Ocean waves travel through the medium of water
  • Sound waves travel through the medium of air
  • Stadium waves travel through the medium which are the fans in the stadium

4.  What are examples of Particle Movement?

  • When a batter hit a baseball – energy is transferred from the bat to the baseball. The swinging bat is an example of particle movement and the launched baseball is an example of particle movement. The crack of the bat, that is the resulting sound, is an example of a sound wave

5.  A stadium wave is a good way to view the whole process.  Each fan is like a particle.  The crowd is like a medium.  Some action initiates the wave process (usually one fan gets the idea and starts the round).  The movement of individual fans results in interaction with the fans next to him or her.  As each fan stands and then sits, the fan next to him stands and sits.  Once the wave has passed by, the fans returns to their original starting position at rest (namely, sitting back in their seat). 2

6.  What does a Wave transport?

  • A wave transports energy – it does not transport matter
  • The particles return to their resting position as long as there are no other forces (or other types of waves for that matter) acting on them

7.  Whereas a wave doesn’t transport matter, particle movements do

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8.  In light of this, is Light a Wave or a Particle?

  • The debate around this has gone on for two millennia and has only been recently settled
  • As you look at this high-level timeline, understand that each party is putting forth proof for Light’s behaving as either a Wave or a Particle

9.  400’s BC – The Greek philosopher Democritus begins to build out his basis for the existence of atoms

  • In so doing, he theorizes that Light is a Particle or some form of solar atom 3

9.  300’s BC – The Greek philosopher Aristotle proposes that Light is really just a Wave or disturbance in the medium of air 4

10.  980’s AD – Persian mathematician Ibn Sahl first documents the concepts behind the Light refraction

  • His work lends itself to the idea that Light acts as a ray or Wave 5

11.  1100’s – The Egyptian (Arabic) scientist Alhazen writes a comprehensive treatise on optics

  • In this, he shows Light to be an emanation of Particles from the object being viewed to the eye 6

12.  1620’s – Dutch mathematician Willebrord Snell develops the Law of Refraction

  • This demonstrated that as light travels from one medium to another, it changes direction
  • This is why a straight stick that is half-submerged in water appears to bend
  • This further develops the idea of Light as a Wave
  • Note: “The refractive quality of lenses is frequently used to manipulate light in order to change the apparent size of images. Magnifying glasses, spectacles, contact lenses, microscopes and refracting telescopes are all examples of this manipulation.” – see http://en.wikipedia.org/wiki/Light 7

13.  1630’s – The French mathematician and philosopher Rene Descartes shows that Light acts very much like a wave

  • He bases this notion on the idea that the Universe was without a void – it was completely filled
  • If we presume that a universal medium e√xists (called “plenum”), then certain Light activities could be understood as Wave-like disturbances 8

14.  1670’s – Isaac Newton develops his “Corpuscular Hypothesis”

  • The central premise is that Light travels in straight lines of reflection – this is in keeping with the behavior or a Particle, not a wave 9

15.  1670’s – Danish astronomer Ole Romer uses data from the eclipses of Jupiter’s moons to get the first reasonable value for the speed of Light

  • Up until this time, many scientists believed the speed of Light was Infinite
  • Though he underestimated light’s speed by roughly 26%, science had definitive proof of the Finitude (i.e., non-instantaneous) of the speed of Light 10

16.  1690’s – Dutch mathematician Christiaan Huygens put forth his Treatise on Light

  • He makes a strong case for Light as a Wave construct 11

17.  1800’s – English doctor Thomas Young performs the “Double-Slit” experiment providing definitive proof that Lights is a Wave

  • The experiment clearly showed light to diffract, and thus travel as a wave
  • By passing light through a single slit before passing it through a double slit, he managed to emulate a point source of light
  • This was in keeping with Light being a Wave 12

18.  1830’s – Irish physicist, astronomer, and mathematician William Rowan Hamilton forms the basis for the field of Quantum Mechanics

  • His theory joined optics and mechanics and began to link a relationship between waves and particles
  • His ideas begin to lay the groundwork that Light might be both Particle and a Wave 13

19.  1850’s – Two French physicists Hippolyte Fizeau and Léon Foucault demonstrated that Light traveled slower through denser media

  • This is done primarily with water experiments and Light
  • The experiments with a water medium further propel the idea of Light as Wave 14

20.  1860’s – Scottish physicist James Clerk Maxwell formulates Electromagnetic Theory

  • This unites all previously unrelated observations, experiments, and equations of electricity, magnetism, and optics into a consistent theory
  • Maxwell’s work demonstrate that (1) Electricity, (2) Magnetism and (3) Light are all manifestations of the same phenomenon, namely the electromagnetic field
  • Prior to this, electricity was believed to be a kind of fluid
  • Maxwell also proved that electric and magnetic fields travel through space in the form of Waves at the speed of Light 15

21.  1890’s – British physicist JJ Thompson uses a Cathode Ray Tube to show that electricity consists of flowing Particles, namely Electrons

  • This was done by performing tests within a vacuum where no medium could exist
  • Yet, Light was still transmitted 16

22.  1900’s – German physicists Max Planck and Albert Einstein lay the basis for Quantum Theory

  • In short, this went a long way in explaining atomic and even sub-atomic processes
  • The outcome is the conclusion that Light acts as both a Wave and a Particle
  • Today, this is referred to as the Wave Particle Duality of Light 17

 

Notes:

  1. http://www.physicsclassroom.com/class/waves/u10l1b.cfm
  2. http://www.physicsclassroom.com/class/waves/u10l1b.cfm
  3. http://www.iep.utm.edu/democrit/http://www.answers.com/topic/the-nature-of-light
  4. http://www.jstor.org/discover/10.2307/301645?uid=3739832&uid=2129&uid=2&uid=70&uid=4&uid=3739256&sid=21100901740891,     http://library.thinkquest.org/C005705/English/Light/history.htm
  5. http://www.agilegeoscience.com/journal/2011/1/19/great-geophysicists-1-ibn-sahl.html
  6. http://library.thinkquest.org/C005705/English/Light/history.htmhttp://en.wikipedia.org/wiki/Wave–particle_duality
  7. http://interactagram.com/physics/optics/refraction/,   http://micro.magnet.fsu.edu/optics/timeline/people/snell.html,   http://library.thinkquest.org/C005705/English/Light/history.htm,    http://www-history.mcs.st-and.ac.uk/PrintHT/Light_1.html
  8. http://www.field.io/process/research/science/descartes,   http://en.wikipedia.org/wiki/Wave–particle_duality
  9. http://library.thinkquest.org/C005705/English/Light/history.htmhttp://www-history.mcs.st-and.ac.uk/PrintHT/Light_1.html,        http://en.wikipedia.org/wiki/Wave–particle_duality
  10. http://www-history.mcs.st-and.ac.uk/PrintHT/Light_1.html
  11. http://physics.about.com/od/lightoptics/a/waveparticle.htm
  12. http://library.thinkquest.org/C005705/English/Light/history.htm,     http://cavendishscience.org/phys/tyoung/tyoung.htm
  13. http://library.thinkquest.org/C005705/English/Light/history.htm
  14. http://library.thinkquest.org/C005705/English/Light/history.htm,      http://www.relativitycalculator.com/fizeau_fresnel_experiment.shtml
  15. http://www-history.mcs.st-and.ac.uk/PrintHT/Light_1.htmlhttp://en.wikipedia.org/wiki/James_Clerk_Maxwell,     http://library.thinkquest.org/C005705/English/Light/history.htm
  16. http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html
  17. http://www.colorado.edu/physics/2000/quantumzone/photoelectric2.html