10/07/2006

Aristotle's natural motion and modern inertial motion

Last week, in my history of science class, we finished the unit on ancient science and medicine. At the end of the unit, I asked my students the (ill-posed) question: so is any of this stuff we've been reading science or not? (We read Plato's Timaeus, Aristotle's Physics II and On the Heavens, Ptolemy's Almagest, and bits of Epicurus as well as Hippocratic writers.)

One sentiment that came to the fore was that the ancients were (on average) more willing to countenance teleological explanations in natural sciences than we are. I think this is definitely right on the whole. But I did want to ask a question about an example sometimes forwarded in defense of this claim. Aristotle says that part of what makes the element earth earth is its tendency to move towards the center of the universe (since Aristotle thought the planet Earth was at rest in the center of the universe). Air and fire move away from the center of the universe, and the celestial matter moves in a circle around the center. These 'natural motions' are taken to appeal to final causes in a way that modern science does not: water and earth have a 'goal' or 'end' (Greek telos), viz., the center of the universe. And (so the story goes) matter from the Early Modern period onwards, starting with Descartes at the latest, is not like that at all.

I, unfortunately, cannot make out a substantive difference here -- we can describe Aristotle and the moderns in the same terms: we can make Aristotle sound more modern, or make Newton et al. sound more teleological. In the modern dynamical picture, we have inertial motion: a body in motion will maintain that motion (speed and direction), unless acted upon by an outside force. If the telos of an Aristotelian hunk of earth is the center of the universe, the telos of a modern bit of matter is (something like) self-preservation. Its goal is resistance to change (of direction and speed).

Alternatively, we can characterize Aristotle as more modern: Aristotle is describing what happens to a bit of fire or water if it's just "left alone," i.e., what does a body do when it is free of any interference? Aristotle clearly disagrees with the moderns about what a body does when "left alone"... but Einstein disagreed with Newtonians over the same issue. In other words, we can think of the difference (on this topic) between Aristotle and the moderns as a disagreement over which trajectories are the ones bodies will follow when no external forces act upon them. Teleology doesn't appear here at all.

Of course, I could be overlooking something obvious in the Aristotelian text. Hopefully any real Aristotle scholars out there reading this will tell me if I have. If you want to check the text of On the Heavens for yourself, it’s online here.

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3 Comments:

At 8/10/06, Blogger "Q" the Enchanter said...

Interesting thought. Perhaps the difference between Aristotle's cosmological-center-as-telos and your preservation-as-telos is that the former provides a framework for understanding a cosmological process to run from an initial state to a goal state over time (e.g., earth tends toward the center, hence the Earth came into being), whereas the latter is a dispositional property that is not necessarily working toward any discernible "final" goal (i.e., things just move around in a uniform state of motion (absent another force)--but they've *always* done that and always will). But that distinction might not cover other cases of Aristotle's appeal the concept of telos in his physical theories.

 
At 10/10/06, Blogger Clark Goble said...

I think you're right. Interestingly the Lagrangian formulations of Newton's laws perhaps make telos even more explicit. They are cast in a form that the system tries to reduce the difference in kinds of energy.

I remember back when first doing advanced mechanics and discovering Euler and Lagrange just how different the philosophical spin on things was. The Hamiltonian offers yet an other philosophical spin if one "reads it" literally. Yet all the formulations are mathematically equivalent.

And of course one can do similar things with quantum theory. Although I've never found trying to make things more "Newtonian" terribly satisfying. But Feynman diagrams in a sense end up being the Lagrangian again whereas traditional QM is typically variations on the Hamiltonian.

 
At 15/11/06, Anonymous Anonymous said...

Greg (if I may),

Interesting post.

The intentional sense of telos (i.e., "purpose" or "goal") should be minimized or ignored altoghether when the telos of a non-intentional substance is being considered. For while Aristotle does routinely draw analogies between intentional and non-intentional motions, such analogies are not necessary.

Instead, telos or end should be understood in the sense of terminus (Aristotle does say that the usual result of a motion is its end). I think the biological development of an embryo is an excellent example to illustrate the point.

It is an undeniable fact that the changes undergone by the embryo are according to a certain trajectory, so to speak, viz., the adult organism. That trajectory is inherent in the structure of the nascent organism, i.e., in its form or shape (Aristotle uses morphe more often that idea; the basic meaning of both is shape, but morphe suggests this more than idea because the former was not used by Plato).

It is important to note that, for Aristotle, form and end are ultimately the same. The end is the form as terminus, i.e., the shape that the fulfilled motion will take.

 

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