Direct Continuation of: Birds Are Dinosaurs, But Pluto Isn’t A Planet, Part I

Earlier, I stated that recent science has found that some “birds are dinosaurs”, and also commented about how science has found that “Pluto is not a planet”. I then asked what is going on here? How can definitions change, and why do they change?

Can we be wrong when we apply a definition? Isn’t debating definitions a folly?

Earlier, I elaborated on a theory of how definitions should work in order to make conversations more efficient, and a bit of what it means for you to be wrong if you don’t pick a certain definition. I also elaborated further on how to avoid the broad fallacy of smuggling connotations I will continue this discussion in this essay.

 

A Distinction Worth Making

So why would we want one definition of planet for Pluto instead of the other? Who cares about whether a planet has cleared its neighborhood or not? And if clearing a neighborhood is an important distinction to make, such that it now makes or breaks the definition, why not tack on even more distinctions, such as declaring only stellar bodies with rings to be planets? And since all planets have individual differences, can’t we draw more and more distinctions until there is no point in even using the word planet?

The answer lies again with the criteria of practicality. All these definitions of planets are (2) sensical, (3) not circular, and (4) not vague, but they don’t meet the same merit of (1) practical. Only the three-pronged definition established by the IAU is in current common usage, and it was chosen for a reason.

So what was it that inspired this change of definition? To explain this story of Pluto, I will point to a different story: the story of Ceres. Ceres is the largest asteroid in our Solar System, and is located in the Asteroid Belt between Mars and Jupiter. Ceres is so comparatively massive that it makes up a third of the Belt by itself, though is only roughly 10% the mass of Pluto.

 

See, once upon a time, back in the early 1800s, Ceres was considered a planet. In fact, Ceres was considered a planet for nearly fifty years of its existence — back in 1830, there were eleven bodies considered planets, with Uranus being the eleventh planet from te sun: “Mercury, Venus, Earth, Mars, Vesta, Juno, Ceres, Pallas, Jupiter, Saturn, and Uranus”.

And then the definition of planet changed — what once was a query that asked “Is this an object that orbits around the Sun?” now expanded to a query that asked “Is this an object that orbits around the Sun and has a radius of 1000km or more?”

What had inspired this change? People had noticed an important distinction: there was a massive size gap between those things that were just relatively tiny asteroids (Vesta, Juno, Ceres, and Pallas) and those that were relatively large planets. And to make matters worse, those tiny asteroids were being discovered by the dozens thanks to improvements in telescopic technology, and apparently no one wanted a list of forty planets.

 

Recall that the goal of a definition is for the ease of classification of experiences that we have — we want to have communications with others that involve definitions that are easy to share, easy to get everyone on board, and easy to further study and gather even more information. The idea of a bunch of small bodies and a bunch of large bodies coexisting in the same table was just not satisfying this goal.

This size distinction was becoming a distinction worth making — the massive difference in size made it worth taking big objects like Mercury out of the growing list of small asteroids and placing it in a new list.

 

 

Polywater, H₂O, and Atoms

Depending on how the distinction is made, different things can happen to words depending on what we think is practical. Consider a few more stories, though rest assured we’re getting to Pluto, and birds as dinosaurs, shortly.

Once upon a time, there was an idea of something called polywater, a version of water that was allegedly polymerized, and thus the subject of much controversy in the 1960s. This polywater also allegedly had very different properties, despite looking like ordinary water — it was said to have a larger density, significantly higher viscosity, higher boiling point, and lower freezing point than regular water. It was thus apparently distinction worth making.

Later, though, it was found that polywater was not another substance, but merely regular water that had additional impurities due to malfunctioning lab equipment. The definition of polywater was then “water with these additional impurities”. Once this discovery was made, the impurities distinction was no longer worth making, and the word polywater went away. Nowadays, when water has impurities, we just say it is “water with impurities”.

We don’t need a word for every distinction, only the common ones that are practical to make.

 

H₂O vs. Water

In 1805, something startling was discovered, though the discovery was not made all at once, and thus surprised very few. Still, though a discovery: what we previously knew as water was in fact not water, but a combination of one oxygen atom and two hydrogen atoms per molecule. What did this mean for the definition of water, now that we can describe water in terms of an atomic arrangement?

Here, because the specific arrangement was so common and often studied, it is practical to still discuss something as specifically “water”, just like it is still useful to use the word sandwich to describe a specific arrangement of cheese, bread, and lettuce.

Just because we can reduce a definition does not mean we must abandon that definition, though sometimes we should.

 

The Inseparable Atom

Another adventure in definitions involves the concept of the atom. In 450 BCE, the Greek philosopher Democritus referred to the idea of atomism, though of course he didn’t call it that because he spoke Greek, not English. Instead he referred to “ἄτομος” which means the smallest unit of matter, uncuttable and indivisible.

Eventually empirical science confirmed what the philosophers had guessed about our world, that there were tiny things called atoms that all of matter was made of, when John Dalton started atomic theory in 1805.

But the thousand-year-old concept of atoms as indivisible was overthrown in 1897, by J. J. Thomson’s work with cathode rays, discovering the electron. All of a sudden, the definition of atom was no longer true: atoms were no longer indivisible, but instead made up of divisible parts. What did this mean for our definition? Did Thomson disprove the existence of atoms?

No, instead the definition of atom was simply redefined. The new definition was changed, not thrown out like in the example of polywater or kept like in the example of water, but a middle ground between the two. Here, the new notion of the atom was enough to say that atoms are no longer the smallest units, but instead everything else the idea of “atom” referred to: those things which molecules are made of, and arranged by in the periodic table.

Sometimes the current definition just needs to be tweaked when we encounter new understanding.

 

 

“Choosing” Definitions

So what was it that “forced” the “demotion” of Pluto (note the scare quotes), or rather, what was it that made the IAU decide that it was more practical not to define Pluto as a planet?

It’s actually a story very similar to Ceres, and it begins in 2005 with the discovery of Eris, now considered a dwarf planet. But here’s the problem — Eris is roughly the same size as Pluto, and fit the same definition of planet that Pluto did. The 10th planet was then discovered.

But Eris was accompanied by other discoveries of potential planets: Sedna, Haumea, Orcus, Makemake, Quaoar, and a few others that haven’t yet received cool names. The count of planets orbiting the sun under the old definition was increasing to over twenty, with potentially more on the way as telescopic technology continues to improve.

 

But with all these planets being added, like all the asteroids that joined Ceres back in the day, there was a distinction worth making. All of these new objects had massively elliptical orbits and behaved more like comets.

They also did not have a cleared neighborhood, meaning that the object is gravitationally dominant; there being no other bodies of comparable size nearby the object other than that which is under its gravitational influence, such as moons.

Furthermore, there was a strong parallel with Ceres again, because the planets which failed to clear the neighborhood also had a significantly smaller size than other planets, with the largest (potentially Eris or Pluto) being only 4% of the second smallest planet, Mercury.

 

But what is it about this definition that is compelling? Why couldn’t we just agree to stick to the previous definition of planet, provided we agree upon it?

Well, first we would be defying the common usage without a good reason. But second, we would be ignoring this glaring distinction — so much so that if we used planet to refer to all stellar bodies, we would need to invent a new word to describe those planets which have cleared their neighborhood.

This definition change was made rightfully to maximize the practicality of the words we use, as a result of new discoveries.

 

So there is a clear difference between a needless semantic quibble and a distinction worth making. One of these is the notion that some birds are dinosaurs. Again, these aren’t birds that once were dinosaurs, or the idea that some dinosaurs were once considered birds at some point, but the fact that some commonly found birds, such as the pigeon, living today, ought to be considered living dinosaurs.

In the next post, we’ll explore this further. Stay tuned.

Directly Continued in: Birds Are Dinosaurs, But Pluto Isn’t a Planet, Part III