Carl%20Sagan%20-%20The%20Demon%20Haunted%20World

THE DEMON-HAUNTED WORLD
the air', the aether is what they had in mind. (The Russian phrase
is quite literally 'on the aether', v efir.) But of course radio readily
travels through a vacuum, one of Maxwell's main results. It
doesn't need air to propagate. The presence of air is, if anything,
an impediment.
The whole idea of light and matter moving through the aether
was to lead in another forty years to Einstein's Special Theory of
Relativity, E = mc 2
, and a great deal else. Relativity, and
experiments leading up to it, showed conclusively that there is no
aether supporting the propagation of electromagnetic waves, as
Einstein writes in the extract from his famous paper that I
reproduced in Chapter 2. The wave goes by itself. The changing
electric field generates a magnetic field; the changing magnetic
field generates an electric field. They hold each other up, by their
bootstraps.
Many physicists were deeply troubled by the demise of the
'luminiferous' ether. They had needed some mechanical model to
make the whole notion of the propagation of light in a vacuum
reasonable, plausible, understandable. But this is a crutch, a
symptom of our difficulties in reconnoitring realms in which
common sense no longer serves. The physicist Richard Feynman
described it this way:
Today, we understand better that what counts are the equations
themselves and not the model used to get them. We may
only question whether the equations are true or false. This is
answered by doing experiments, and untold numbers of
experiments have confirmed Maxwell's equations. If we take
away the scaffolding he used to build it, we find that
Maxwell's beautiful edifice stands on its own.
But what are these time-varying electric and magnetic fields
permeating all of space? What do and mean? We feel so
much more comfortable with the idea of things touching and
jiggling, pushing and pulling, rather than 'fields' magically moving
objects at a distance, or mere mathematical abstractions. But, as
Feynman pointed out, our sense that at least in everyday life we
can rely on solid, sensible physical contact to explain, say, why the
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