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 1 st and 3 rd 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 http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htm

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