from Phil Runkel on 8 August 1999.
I sympathize with Powers's sentiment that old ideas, no matter
how revered, should be taken as suspect, just as you should tread
cautiously on old floorboards. Often, the assumptions with which
we now read those ideas are not those that were in the minds of
the people who first congratulated one another on the wisdom of
their then-fresh insights.
Some savants among the ancient Greeks agreed that the universe
was arranged, approximately, in four concentric spheres. The
earth was surrounded, in order, by spheres of water, air, and
fire. The ordering was not perfect in all places, but on the
whole, that scheme must have seemed pretty obvious.
The sphericity, not to speak of the concentricity, was badly
cracked by Copernicus and Galileo. And as more people came back
from climbing high mountains and more people went up in balloons,
the idea of getting hotter from being closer to the fire of the
sun (as did Icarus) had to be given up. It became obvious,
considering the great gaps of nothing up there, that it must be
very much colder up there, not hotter.
Meanwhile, however, the idea of heat as molecular motion arose --
the idea of heat as kinetic energy. And astronomers discovered
that "empty" space contained a lot of particles of one sort or
another whizzing about at frightening speeds. In other words,
considerable amounts of matter that did occur out beyond the
sphere of air did occur in a state of "very hot" indeed.
So if you felt like harking back to the ancients, you might say,
at least from the viewpoint of one planet, that by golly those
old Greeks had it right after all.
But what those old words about the four elements, translated as
well as can be into modern languages, mean to us now is hardly
what they meant to those old Greeks. Nobody is going to advise
astronauts to keep their nose cones cool by flying low. And what
we mean now about high, low, up, down, inside, outside,
surrounding, and other relationships in the universe's space are
very different from earlier times.
I suppose I have a detail or two wrong here. Corrections
welcome.