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

Maxwell and The Nerds
an electrical field; and (4) vice versa.
When the equations were written down like this, Maxwell was
readily able to show that E and B propagated through empty space
as if they were waves. What's more, he could calculate the speed
of the wave. It was just 1 divided by the square root of ε 0 times μ 0.
But ε 0 and μ 0 had been measured in the laboratory. When you
plugged in the numbers you found that the electric and magnetic
fields in a vacuum ought to propagate, astonishingly, at the same
speed as had already been measured for light. The agreement was
too close to be accidental. Suddenly, disconcertingly, electricity
and magnetism were deeply implicated in the nature of light.
Since light now appeared to behave as waves and to derive from
electric and magnetic fields, Maxwell called it electromagnetic.
Those obscure experiments with batteries and wires had something
to do with the brightness of the Sun, with how we see, with
what light is. Ruminating on Maxwell's discovery many years
later, Albert Einstein wrote, 'To few men in the world has such an
experience been vouchsafed.'
Maxwell himself was baffled by the results. The vacuum seemed
to act like a dielectric. He said that it can be 'electrically
polarized'. Living in a mechanical age, Maxwell felt obliged to
offer some kind of mechanical model for the propagation of an
electromagnetic wave through a perfect vacuum. So he imagined
space filled with a mysterious substance he called the aether,
which supported and contained the time­varying electric and
magnetic fields ­ something like a throbbing but invisible Jell­O
permeating the Universe. The quivering of the aether was the
reason that light travelled through it ­ just as water waves
propagate through water and sound waves through air.
But it had to be very odd stuff, this ether, very thin, ghostly,
almost incorporeal. The Sun and the Moon, the planets and the
stars had to pass through it without being slowed down, without
noticing. And yet it had to be stiff enough to support all these
waves propagating at prodigious speed.
The word 'aether' is still, in a desultory fashion, in use ­ in
English mainly in the adjective ethereal, residing in the aether. It
has some of the same connotations as the more modern 'spacy' or
'spaced out'. When, in the early days of radio, they would say 'On
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