What do we call a theory that is no longer viable?

From a physical model of the Solar System to religious metaphor. [Credit: Gustav Dore, illustration from Dante's Divine Comedy]

From a physical model of the Solar System to religious metaphor. [Credit: Gustav Dore, illustration from Dante’s Divine Comedy]

My grumpfy rant yesterday was spurred by a particular piece of writing, but I tried to keep it as general as possible. These are habits we writers get into, after all. Sean Carroll brings up Democritus, for example, then points out how different our modern atoms are from the Greek dude’s, so I’ll absolve Sean. (I’m sure he’s happy to know that.) I know I’ve been guilty of reinterpreting geocentrism as meaning Earth is the focus of the Universe, rather than its lowest, meanest point. And that’s even after reading The Divine Comedy, where the heavens literally contain Heaven and are populated by the Blessed, while the center of Earth is the dwelling place of Satan and traitors like Judas Iscariot. Evil sinks to the center, while righteousness ascends beyond the stars.[1]

The problem is that it’s very easy and convenient to set up Straw Theories to knock down. You know what I mean: it’s fun to bring up theories that were once viable, like geocentrism or phlogiston or steady-state cosmology. Sometimes that’s to point out how scientists in the past were Teh Dumb compared with Smart Us’ns, sometimes another purpose is at work, but most often it’s just because that’s what we science writers do: it’s a reflex, a habit. If we’re talking about the atomic model of matter, we have to bring up Democritus, even if it doesn’t actually make much sense to do so.

However, physics writer/student Leah Crane sparked a thought during a Twitter conversation yesterday. She said she doesn’t want to give up using the term “Ptolemaic” just because it’s a cool word.

(Seriously, English language: we need more words starting with “pt” or similar consonant clusters. Greek has so much of an edge on us.) So, I thought of a modest proposal: what if we coin the following?

ptolemaic (adj.): pertaining to a scientific theory that was once viable and widely accepted, but no longer valid thanks to improved data and subsequent ideas.

Ptolemaic models fit the available data very well during their time, so people were not stupid for accepting them. If people continue to accept ptolemaic theories beyond their period of usefulness, that’s an entirely different matter. This is not the same as (say) Newtonian physics, which is still useful in a wide range of applications, even though it breaks down on small scales, strong gravity, and high energy. Rather, we can think of ptolemaic as similar to “obsolete”, but without the negative connotations of the latter term.

What do you all think?


  1. Dante was writing metaphorically, but (as I understand it) the Aristotelian view was that Earth’s physical laws were base, while the heavens obeyed perfect rules. At the same time, I’m not sure how fruitful it is to think of religious cosmology of that era in scientific terms.

6 Responses to “What do we call a theory that is no longer viable?”

  1. 1 Leah October 25, 2013 at 10:08

    This may be the first time anyone’s actually called me a physics writer… I just had a moment. Also, one who studies outdated theories is a “ptolemaicist” now, which is also a great word.

  2. 4 Zuulie Mars (@msjuliemars) October 25, 2013 at 10:39

    I like the coin of the phrase “ptolemaic” for outdated science theories. I’d love to start calling outdated moral codes “augustinian”.

  3. 5 rebeccaboyle October 25, 2013 at 11:35

    I like ptolemaic also because it makes me think of polemic, which is a good way to reply to those with ptolemaic views. E.g. “Her polemic against his ptolemaic views on evolution.”

  4. 6 peter October 25, 2013 at 19:33

    “..Ptolemaic models fit the available data very well during their time, so people were not stupid for accepting them. If people continue to accept ptolemaic theories beyond their period of usefulness,…”

    A point which is not minor in general (but is minor with respect to this blog): More-or-less parroting David Deutsch, I think altogether too many people are succumbing to a long discredited inductive view of science, emphasizing it merely as ‘useful for predicting’. Ptolemaic astronomy continued to ‘outperform’ Copernican until Kepler replaced circles with ellipses. But even just Copernican is far superior–it is a good explanation of the planets, not a bad one, and of course got much better with Kepler and Newton, not just in its predictions, but as an explanation of what people had puzzled about for centuries.

    Again, surely one discards phlogiston much more for its impoverished explanatory role, than for its predictive shortcomings.

    The positivists were wrong (and continue to be, in some backwaters where they still thrive), and so was Kuhn mostly, though both played somewhat useful roles in the history of science.

    And the “shut up and calculate” faux-interpreters of quantum mechanics are both wrong and to some extent harmful scientifically.

    Science is about explanation; prediction is important but secondary. Again parroting Deutsch, scientists simply do not bother checking the badness of the predictions of literally trillions of putative terrible theories, awful as explanations; his amusing example is the theory that eating a kilogram of grass is a cure for the common cold, IIRC.

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