Friday, September 01, 2006

Popping over Pluto's Demotion

Most scientists don’t bother to read Karl Popper. This famous 20th century Philosopher once stated that science progresses by falsifying previously held conclusions. I had to read his thick “The Logic of Scientific Discovery” in preparing to defend my PhD. One of my examiners threw in a few philosophical questions about my scientific theory (if a PhD is to be conferred, the student has to come up with a theory, which is nothing but an explanation about something in nature). For a decent rebuttal, I had to read Popper with popcorn to prevent my head from popping.

After all the troubles and the PhD, I came to appreciate Popper’s statements that scientific conclusions can never be proven despite the experimental evidence in support of it. But a single example contrary to the conclusion clearly falsifies it. It is impossible to prove all swans are white, but a single black one clearly falsifies the idea. So all scientific conclusions are tentative and subject to change once falsified.

What does this got to do over Pluto’s demotion as a planet to a mere “dwarf planet”?
Millions of school kids were taught that Pluto was the 9th planet. And this planet had an orbit not in the same plane as that of the other 8 planets. But this year the International Astronomical Union (IAU) defined a planet according to three criteria

1. The object must be in orbit around a star, but not be a star itself.
2. The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
3. It must have cleared the neighborhood around its orbit.

Pluto according to the IAU fails number 3. The IAU has this to say as the basis of their decision
“The proposed definition found support among many astronomers as it used the presence of a physical qualitative factor (the object being round) as its defining feature. Most other potential definitions depended on a limiting quantity (e.g. a minimum size or maximum orbital inclination) tailored for the solar system. According to members of the IAU committee this definition did not use man-made limits but instead deferred to "nature" in deciding whether or not an object was a planet”

But according to some astronomers, the Earth has been hit by space debris and thus has not really cleared the neighbourhood. So the Earth is not a planet? But in science, there is a premium for an explanation that fits observable reality. This is why the IAU eventually approved the definition. It also proposed a three type taxonomy of the planets, the “real” planets, the dwarf planets and the small Solar System objects (SSSO). And like in biological taxonomy, Pluto becomes the “type specimen” for the dwarf planets taxon. Now I have to ask the question, what is the type for the “real” planets?

The ordinary citizen may think this planet definition business isn’t important. But if we have to look for worlds with ET civilizations, we have to define what a planet is. What if a delegation from another world contacts us and they come from a dwarf planet? Will be treat them seriously? (Would you sing “Short People”?) More seriously if our own species need to look for another world, we would like to live on a planet, not a dwarf planet!

Also the planet definition business has a lot of consequences for makers of toys, scientific kits, sci-fi writers, planetariums and fans. Most appropriately, the planet definition has a lot of relevance for the practitioners of the poster-boy of non-science Astrology! (I once had a high school science teacher declare that Astrology was not a science and she was wearing a T-shirt with the Zodiac on it!) Astrologers would flip if the IAU declares in the future that gassy giants such as Jupiter and that gaudy ringed Saturn are not really planets!

Classifying is the business of taxonomy. As a biologist this controversy over planetary taxonomy doesn’t surprise me. But despite how scientists pin their egos and reputations on the nearest star (planets included), all taxonomic classifications are mere hypotheses. And if we follow Popper, if hypotheses survive repeated tests that may falsify them, then they become scientifically true.

Well for the meantime, Pluto has been demoted. The task for Pluto fans is to look for evidence that would falsify the IAU’s definition. And they have immediately started, two seconds after the IAU vote! And as for how we view our textbooks, this provides us with a humbling lesson especially for textbook writers. Science textbooks are not holy books like the Bible or Koran. All the facts in these science books can be falsified and changed. And for Astrologers to consider, as the solar system travels through the galaxy, the Zodiac would probably gain or lose some members. And probably Ophiuchus may be your sign or mine. I’m tired of being a Piscean. I want to be Ophiuchan!

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