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Models of the Aether

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  1. Models of the Aether Chapter 13 By Michael Dolan

  2. Composition of Light • Corpuscular/ Emission Theory • Wave Theory

  3. The Aether • Waves need a medium • Obvious for water, air, etc. • What about a vacuum?

  4. Descartes • All space is a plenum • Vacuums and/or voids do not exist • Corpuscular Theory

  5. Newton • Disagreed with Hooke’s notion that light was a wave • Before Principia: “All space filled with an aether of variable density.”

  6. Newton • In Principia: Kepler’s 1st and 3rd laws show that a dense aether does not exist • After Principia: Associates existence of an aether with his belief in God’s omnipresence

  7. Huygens • Against Corpuscular Theory: When two beams cross there is no scattering • Believed light waves are propagated through a very elastic medium • His views were not widely accepted

  8. Lesage • Instantaneous propagation of gravity = NO need for aether = NO wave theory = support for Corpuscles • Corpuscular explanation of gravity • Eventually disproved

  9. Stellar Aberration • Discovered by Bradley in 1728 • Used as support for corpuscular theory • Proves speed of light is constant

  10. Euler • Proponent of Wave Theory • Light sources do not lose mass • Claimed gravity was also explained by the aether that is responsible for the propagation of light

  11. Young • Constructive and Deconstructive interference of light waves • Used analogy with water waves • Transverse vibrations

  12. Wave Theory of Light • Started by Fresnel, uses aether to explain polarization • Measurement of the speed of light in water vs. speed of light in air • Supported by Poisson’s “Bright Spot” experiment <<

  13. The Elastic Solid Aether • Navier, Cauchy and MacCullagh’s mathematical equations • Riemann unifies optics and electromagnetism • Boussinesq proposes one aether, which is present (and the same) everywhere • Result: the Electromagnetic Theory of Light

  14. Electromagnetic Aether • Faraday’s study of magnetism • He breaks from traditional scientific thought of his day

  15. Thomson • Gave legitimacy to Faraday’s concept of an electric medium, “Faraday saw a medium where they saw nothing but distance” • Equated lines of (electrostatic) force to lines of heat flow (Poor) reproductions of figures 13.3 and 13.4 on p. 189 in the text

  16. Thomson (cont’d) • Analogy between E field and an elastic solid • Described B field as rotary phenomenon • Mechanical model for aether

  17. Maxwell • Uses ideas from Faraday and Thomson • From parts to the whole, rather than vice versa

  18. Maxwell (cont’d) • Vortices imply viscosity • Adamantly defended existence of the aether Whether this vast homogenous expanse of isotropic matter is fitted not only to be a medium of physical interaction between distant bodies, and to fulfill other physical functions of which, perhaps, we have yet no conception, but also… to constitute the material organism of beings exercising functions of life and mind as high or higher than ours are at present, is a question far transcending the limits of physical speculation.

  19. Michelson-Morley Experiment • Produces the null result • Challenged the belief of an absolute aether

  20. Saving the Aether • Lorentz-Fitzgerald contraction hypothesis, 1904 • Kennedy-Thorndike experiment, 1932 But both experiments merely provided ad hoc parameters

  21. Saving the Aether • Aether Drag: lessens magnitude of aether’s effects, but fails to explain other phenomena • Experiments by Hamar and Hoek again find the null result

  22. Fall of the Aether • Einstein’s theory of relativity • No longer needed one universal frame, and therefore no longer needed the aether either

  23. Light in a Vacuum? • Einstein solved this problem as well • Considered light a wave-particle • This eventually led to the beginning of quantum mechanics

  24. End of the Aether • Ockham’s Razor eliminates the aether Theory of Relativity Theory of Aether