Posted by: dacalu | 2 July 2018


“And yet, it moves.”

So said Galileo about the earth. The story may be only legend, but the sentiment is true and important. We move through the heavens, both physically and conceptually. We grow and change.

I believe that science progresses. We continue to learn new things about the world. I also believe that fashions change, not always for the better. Sometimes we simply change our minds, our philosophy. Which common beliefs have changed because of scientific discovery and which have changed for other reasons? The progress of science depends on our ability to tell the difference.

The moving earth provides a great example. Our perspective has changed. Our knowledge has deepened. And yet, our familiarity with the word “earth” can hide its true significance. Science, through Copernicus, Galileo, and Newton, helped us see that the physics of earth can be applied to stars and planets. This idea that our place in the universe is not privileged, that (all things being equal) the same rules apply everywhere, has been called the Copernican Principle. I think it represents scientific progress.

All things are not equal, though. After all, we are here (on Earth) and not there (in space, on Mars, …). So, we must be careful in how we apply the Copernican Principle. It has become fashionable to say that Copernicus decentered earth and humanity. This is true, but in a limited way. A quick look at the dictionary reveals three parallel meanings for the word “earth”: soil, world, and planet. Each has a different story. Science decentered the soil, but not the world or the planet.

Earth as Soil

Soil provides the oldest meaning for earth. It refers quite tangibly to the stuff beneath our feet. Ancient Greeks thought of four elements – earth, air, fire, and water. This earth was responsible for mass and heaviness. As such, it settled downward. In a spherical universe, it formed the central sphere. Gravity made sense because all earth tended toward the middle. Water enveloped earth, then air, and fire. Finally, the heavens, unimaginably large and made of a fifth element, enveloped the fire.

This earth is a common noun. It is a kind of stuff. Many debated whether there were other clumps of earth out there. Lucretius thought that everything was falling through space and that there were many flat platforms of earth, all falling together. Mostly, though, scholars thought gravity wouldn’t work unless it all ended up in the middle.

Our ideas about matter have changed over the centuries. Earth, air, fire, and water gave way to modern elements. We discovered that gravity could hold clumps of matter together locally without a single force pushing downward (or center-ward) everywhere. And so common earth was distributed throughout the cosmos but got to keep its spherical shape locally. Copernicus decentered earth as soil. With Galileo and Newton, he spread the earth around.

Earth as World

A second meaning refers to earth as a place we find ourselves. We use the German derived “world” for the range of humanity, but the Hebrew ‘erets, Greek ge, and Latin tellus (or terra) can have the same meaning. We live on top of the soil. We came to call our place earth.

The human world may have been at the center of the earliest cosmologies. Israelites and Egyptians, for example, envisioned a sandwich of earth and sky, with humans in the middle. By the common era, scholars had a more complex perspective. The dominant view came from Plato and Aristotle (and Philo and Augustine). The human world formed a thin shell partially covering the sphere of soil. Modern authors might say the biosphere (living Earth) wraps around the geosphere (solid Earth). Many Ancient and Medieval authors thought that the world only covered one hemisphere or less.

This earth became a proper noun. Like the (U.S.) Capitol or the Federation in Star Trek, it acquired a capital letter and an attendant particle. We can speak of The Earth. It is both specific and significant. We can speak of other worlds, but we always speak hypothetically. No one would be confused about which world, which Earth, you were talking about unless you had already introduced others.

The Earth was close to the center of Ancient and Medieval cosmologies, but it was not the center. Nor was the center happy or privileged. Plato wrapped the Earth around Tartarus and Hades. Dante wrapped it around the Inferno, with Satan at the very center, the bottom of the universe. These were Hell-centered cosmologies and, for both Plato and Dante, they reflected human dysfunction. By “decentering” the world, Copernicus and colleagues freed us from the mud and muck of earth as soil.

Earth as Planet

A third meaning arose only after Copernicus’ revolution. Prior cosmologies included planets as sky-travelers. The word means “wanderer” in Greek and refers to the irregular course of planets in our sky. Stars describe a constant circle in the sky, but planets seem to move on their own. Ancient cosmologies associated planets with gods, Medieval cosmologies with angels. They were considered intelligences on their own, though they might (as in Dante) rule over heavenly spheres and subjects.

We cannot speak of earth as planet prior to Copernicus. The terms were mutually exclusive. Planets wandered; the earth stayed put. If we embrace the Copernican principle and reject the idea that earth (as soil, world, or planet) provides a privileged perspective, then we should drop the article. We do not live on The Earth, but only Earth. We occupy one place among many. That place has a proper name. No one would speak of The Mars or The Pluto; why should Earth receive an honorific? Copernicus did not demote or decenter the planet Earth. He created it. The old cosmology ended and a new one took its place. Planets, including Earth became places in space.

Being Moved

It can be easy to think of the Copernican revolution as a demotion for humans. Indeed, intellectual fashion says as much. This was not a product of science, however, but of humanism. Ancient and Medieval cosmologies were centered on value and disvalue, placing the rarified good and God in the heights, the gross bad and Hell in the depths. The humanists argued that we should not have such a Deocentric (or infernocentric) view; we should have an anthropocentric one. Or perhaps a noocentric one, defined by the intelligence that perceives, understands, and models the universe. This new perspective fit well with Enlightenment values and so was taken on. In many ways, it elevated the importance of human minds while distributing soil and human bodies. Humans have moved, but perhaps not in the way we imagined.


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