Aristotle's Toy Universe
The title might sound condescending, but "toy" is meant in a sense similar to that in a physicist's "toy model," an oversimplified version of a physical situation. Modern physics famously has its spherical cows.
In contrast with the universe of his "scientific" descendants, the cosmos of Aristotle will undoubtedly strike modern people as small. His entire cosmos had its termination in the sphere of the fixed stars that revolved not far outside the sphere of the outermost planet. The earth, of course, sat at the center, the cosmic sump at the bottom of all things; contra Enlightenment rhetoric, the earth was the least important part of the cosmos.
Another way Aristotle's cosmos was smaller was that he had only four or five elements, as opposed to our 118 (at present). Of course, what he identified as elements were probably closer to what we call phases of matter (solid to plasma). Of course we humans can only distinguish elements by their activities. But only the coarsest macroscopic activities were readily accessible to him, hence his identification of phases of matter as elements.
Aristotle was also aware of a much smaller number of plants and animals. There's only so much one can do at the beginning of science to catalog all creatures.1
But the universe we know today is also, in a way, deeper than Aristotle's cosmos. There is much more structure on the way down. It's as if the bottom of reality, the infinite division that yields featureless matter, were farther away than he estimated. But this is a constant human tendency. Well into the 20th century biologists still thought the protoplasm of the cell was structureless, homogeneous liquid, whereas nowadays we know that it has important structure at all levels down through macromolecules to its atoms.
But it's interesting to consider how much Aristotle's cosmos was very like our conception of the universe. Our universe, most especially our solar system, still has orbiting bodies, though they don't orbit in perfect circles around the earth. We do have (chemical) elements. Most fundamentally, Aristotle was right about the need of any science to distinguish the elements of its study. As he opens the Physics:
When the objects of an inquiry, in any department, have principles, conditions, or elements, it is through acquaintance with these that knowledge, that is to say scientific knowledge, is attained. (I.1.184a10, trans. Hardie and Gaye)
And for scientists (and philosophers) to know both the form and matter of their subject:
Again, matter is a relative term: to each form there corresponds a special matter. How far then must the physicist know the form or essence? Up to a point, perhaps, as the doctor must know sinew or the smith bronze (i.e. until he understands the purpose of each): and the physicist is concerned only with things whose forms are separable indeed, but do not exist apart from matter. (II.2.194b9-12)
Aristotle described a simpler universe, but many of the right distinctions are present even there. Today the best physicists openly acknowledge that our picture of the universe is much simpler than the reality. The most remarkable thing left out of our "scientific" universe is the scientists themselves, and all humans in fact: the thinking, reflecting subjects that are somehow part of the universe without being thereby constrained to the same level as the rest of it.
Notes
1. Interesting trivia: Aristotle spent two years studying animals on the island of Lesbos. An infinity of jokes is possible from this one historical fact.
