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Editorial Board: Wittgenstein, Aristotle and Pluto
By Brian M. Carney, The Wall Street Journal
Eastern edition; Sep 2, 2006, A.8
Early in the "Ethics," Aristotle cautions his readers that every field
of study should aim for a degree of precision appropriate to the
subject matter. "The same exactness must not be expected in all
departments of philosophy alike," Aristotle wrote, "any more than in
all the products of the arts and crafts." The officious astronomers who
redefined planethood to exclude Pluto are guilty of what scholars of
Aristotle like to call a "category mistake." They are striving for a
degree of precision inappropriate to their subject matter.
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Apparently Mr. Carney has no scientific training—"nothing turns
on whether Pluto is a dwarf or not" could only be stated by someone who
does not understand the nature of physics and astronomy, and so
imagines that the categories used by planetary scientists are
arbitrary. (His tossing about philosophy is equally
illiterate—by "category mistake" Gilbert Ryle was referring
specifically to treating an abstraction as if it were a concrete thing,
viz, "I have seen the classrooms, the library, and the dormitory, but
where is the university?")
At issue is the origin of Pluto—was it formed in the same way as
the Earth or in the same way as the 800 or so objects in the Kuiper
Belt? And how were those bodies formed? The
study of these objects is quite recent.
From the Wikipedia—
Over 800 Kuiper belt objects (KBOs)
(a subset of trans-Neptunian objects (TNOs)) have been discovered in
the belt, almost all of them since 1992. This was a result of advances
in computer hardware and software...
Among the largest are Pluto and
Charon, but since the year 2000 other large objects that approached and
even exceeded their size were identified.
The definition of "planet" since Copernicus is based on an orbital
pattern that Pluto has always been known to violate. Furthermore,
it posed a huge problem—how could there be four rocky
planets—Mercury, Venus, Earth, Mars—followed by four gas
giants—Jupiter, Saturn, Uranus, Neptune—and then this one
puny rock? Today we know that there are hundreds of rock-ice
bodies like Pluto beyond Neptune. We assume they are leftovers
that didn't consolidate when the Sun and the planets were formed.
The better understanding of the Kuiper Belt—and tentative
discovery of such a belt around two other stars—has in large part
prompted the need to reclassify Pluto.
Here's the current definition of Pluto—
Pluto is the second-largest known
dwarf planet in the solar system. It orbits between 29 and 49 AU from
the Sun, and was the first Kuiper Belt Object to be discovered.
Approximately one-fifth the mass of the Earth's Moon, Pluto is
primarily composed of rock and water ice. It has an eccentric orbit
that is highly inclined with respect to the planets and takes it closer
to the Sun than Neptune during a portion of its orbit.
In fact, Pluto is smaller than seven moons of the planets. Also,
many people raising opinions about Pluto apparently don't know that
Ceres was viewed as a planet for many decades (starting in 1801) until
we understood it was part of what came to be known as the Asteroid
Belt. Ceres contains 1/3rd of the mass of the asteroid belt, so
it is quite huge in comparison to the rest. Indeed, under the new
designation, Ceres is now called a "dwarf planet," just like Pluto, not
an asteroid.
The classification of Ceres has
changed more than once. At the time of its discovery it was considered
a planet, but upon the realization that it represented the first of a
class of many similar bodies, it was reclassified as an asteroid for
over 150 years. As the first such body to be discovered, its name was
prefixed by the number 1, under the modern system of asteroid
numbering. After the discovery of the trans-Neptunian object Eris, the
International Astronomical Union put forward a proposal to once again
define Ceres as a planet, along with Eris and Pluto's moon
Charon. This draft definition was not accepted, and in its place
an alternate definition of "planet" came into effect as of August 24,
2006. Under this definition, Ceres is a 'dwarf planet', and is no
longer classified as an asteroid.
As to the equally bizarre remark—"Until last month, most of us
thought that Pluto was a planet. Where was the harm in
that?"—consider that until the 19th century scientists did not
have a name for rocks that fell from the sky—the very idea of
meteorites was folklore, not science.
From http://www.unmuseum.org/rocksky.htm—
The great Greek philosopher Aristotle
thought that rocks could not fall from the sky because the heavens were
perfect and could not possibly have loose pieces floating around to
fall to Earth. When a meteorite fell at Thrace near Aegospotami,
Aristotle was forced to take the position that strong winds had lifted
an Earth rock into the sky, then dropped it.
Even after scientists accepted the
idea that rocks could fall out of the sky, it still took them a while
to come to believe that really big rocks could fall from the sky. Rocks
large enough to make craters like those seen on the moon. This was
partly because the largest meteor impact witnessed was only about a ton
in weight and had made a hole just slightly larger than itself. Most
scientists in the beginning of the 20th century thought that very large
meteors would burn up in Earth's atmosphere before they hit the ground.
Barringer's study of Meteor Crater in Arizona in the 1870s finally
turned the corner. However, the origin of the crater wasn't
established until 50 years ago—
Controversy over the origin of the
crater continued until 1957 when Eugene Shoemaker, a geology graduate
student, reexamined the site and produced additional evidence showing
that the crater was the result of an iron meteoroid about 80 feet in
diameter and weighing 63,000 tons, hitting the plain approximately
50,000 years ago. The impact released energy equivalent to a
1.7-megaton bomb.
What was the harm in that ignorance? Well, today the US
government requires NASA to search for, catalog, and predict the Near
Earth Asteroids that could crash into earth and destroy all
civilization.
From the Wikipedia—
The general acceptance of the Alvarez
hypothesis, explaining the Cretaceous-Tertiary extinction event as the
result of a large asteroid or comet impact event, has raised the
awareness of the possibility of future Earth impacts with asteroids
that cross the Earth's orbit.
Roughly 1000 near-Earth asteroids are
known, ranging in size up to ~32 kilometres (1036 Ganymed). Tens of
thousands probably exist, with estimates placing the number of NEAs
larger than one kilometre in diameter at up to 2,000.
On March 23, 1989 the 300 metre
(1,000-foot) diameter Apollo asteroid 4581 Asclepius (1989 FC) missed
the Earth by 700,000 kilometres (400,000 miles) passing through the
exact position where the Earth was only 6 hours before. If the asteroid
had impacted it would have created the largest explosion in recorded
history.
On March 18, 2004, LINEAR announced a
30 metre asteroid 2004 FH which would pass the Earth that day at only
42,600 km (26,500 miles), about one-tenth the distance to the moon, and
the closest miss ever noticed. They estimated that similar sized
asteroids come as close about every two years.
Science advances by categorizing phenomena and things, and identifying
the processes that cause them. No understanding is possible
without a meaningful categorization, a sorting, first often by
appearances, and then by causes. That's why biology started by
taxonomizing plants and animals. And why today there are dozens
of names for types of genes. And why we are busy looking for and
categorizing Near-Earth Asteroids.
To say nothing hinges on whether Pluto is called a planet or not is
like saying nothing hinges on the difference between science and
imagination.
It's remarkable and disturbing that this article was written by a
member of the WSJ Editorial Board. Or perhaps to borrow Mr.
Carney's language, I should say "an officious editor."
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Copyright © 2006 William J. Clancey. All Rights Reserved.