Models of the Aether

Chapter 13

By Michael Dolan

Composition of Light Corpuscular/

Emission Theory

Wave Theory

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

Descartes All space is a

plenum Vacuums and/or

voids do not exist Corpuscular

Theory

Newton Disagreed with Hooke’s notion that light

was a wave

Before Principia: “All space filled with an aether of variable density.”

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

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

Lesage Instantaneous propagation of gravity

= NO need for aether

= NO wave theory

= support for Corpuscles Corpuscular

explanation of gravity Eventually disproved

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

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

Young Constructive and

Deconstructive interference of light waves

Used analogy with water waves

Transverse vibrations

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

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

Electromagnetic Aether Faraday’s study of magnetism He breaks from traditional scientific thought

of his day

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

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

Maxwell Uses ideas from Faraday and Thomson From parts to the whole, rather than

vice versa

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.

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

http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/mmexpt6.htm

Saving the Aether Lorentz-Fitzgerald

contraction hypothesis, 1904

Kennedy-Thorndike experiment, 1932

But both experiments merely provided ad hoc parameters

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

Fall of the Aether Einstein’s theory of

relativity No longer needed one

universal frame, and therefore no longer needed the aether either

Light in a Vacuum? Einstein solved this

problem as well Considered light a

wave-particle This eventually led to

the beginning of quantum mechanics

End of the Aether Ockham’s Razor eliminates the aether

Theory of

Relativity Theory ofAether