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Introduction

The puzzling properties of light and the ether remained through the turn of the century and up to 1904: the speed of light (as described by the equations of electromagnetism) did not depend on the motion of the observer and, stranger still, the medium in which light propagates could not be described consistently.

A final effort was made in order to understand in a ``fundamental'' way the negative result of the Michelson-Morley experiment. It was postulated (independently) by Fitz-Gerald and by Lorentz that matter moving through the ether is compressed, the degree of compression being just so that there is a negative result in the M&M experiment. The claim was that the ether wind does slow down and speed up light, but it also contracts all objects and these two effects conspire to give no effect in all experiments.

A calculation shows that an object of length l moving with velocity v with respect to the ether should be contracted to length l' given by

\begin{displaymath} \ell ' = \ell \; \sqrt{ 1 - { v^2 \over c^2 } } \end{displaymath}

(where c is the speed of light) in order to get the null result required.

So in order to understand the gamut of experimental results the ether had to be a very tenuous medium that could not be felt or tasted, nonetheless the strongest materials would be squashed by it by an amount which makes it impossible to see the ether's effects. The amount a material would be squashed, though admittedly very small, would always be there and is independent of the composition of the object going through the ether (see Fig. 6.1). This is a situation like the one I used in the `` little green men on the moon'' example (see Sect. 1.2.1): the ether has was awarded the property that no experiment could determine its presence; the ether hypothesis is not falsifiable.


 
Figure 6.1: The idea behind the Lorentz-Fitz-Gerald contraction.  
\begin{figure} \centerline{ \vbox to 3 truein{\epsfysize=4 truein\epsfbox[0 0 612 792]{6.str/l_fg.ps}} }\end{figure}


next up previous contents
Next: Enter Einstein Up: The Special Theory of Previous: The Special Theory of

Jose Wudka
9/24/1998