geocentrism and planet movement

Every time I hear an atheist criticizing the Bible’s use of “sun rise” or a creationist criticizing the early Catholic belief that the sun revolved around the earth, I cringe. Both claims come from a fundamental lack of understanding the nature of space.

Does the Earth move or does it stay still? Well, it depends on your frame of reference. Almost everyone has had this experience: they are sitting in a car and all of a sudden the car in front of them starts slowly backing up (OR is your car slowly inching forward?). Unless your sense of balance detected movement, it is hard to tell. When looking at the car in front of you, your vision could not decipher which car was moving.

In the dead of space the problem is even worse. There are no real stable objects on which to gauge speed. There are no trees outside that serve as a frame of reference. If two rocketships are approaching each other there is absolutely no way to say how fast each is going. In fact, without a common point of reference, there is no right answer to the speed of two rocketships in space.

Now to geocentricism. Points of reference are arbitrary. People tend to say the Earth revolves around the Sun because the Sun is gigantic and exerts a lot of gravitational pull. But to say that the Earth revolves around the Sun is to assume the largest gravitational object is the correct point of reference. But that is not a rational dogma. After all, the planet on which we live seems like a better frame of reference for normal life. When I drive a car I say “I am driving 55 mph” not “55 mph plus the speed of the Earth as it goes around the Sun plus the spin of the earth”. Speaking as if the Sun a valid frame of reference for normal life would make you a crazy person.

Astronomers, instead, use the Sun when calculating orbits of planets (this makes the math easier). But astronomers quickly ditch the Sun when they want to calculate galaxy movement. Gravitational centers are not absolute references, but are a trick to make math easier.

Technically, both the Sun and the Earth revolve around each other if gravitational center was the correct frame of reference. Like a fat man swinging around a child, the fat man still has to lean back slightly to offset the weight of the child. The center of gravity is called a barycenter. While the Earth-Sun barycenter lays within the physical Sun, it is not the center of the Sun. The Sun and the Earth rotate around a point that is not the center of the Sun.

What all this means is that the Earth is a valid frame of reference, but not the only one. Any point can be chosen for which to use. I can use my cat, my sock, a bird, anything. Using my cat’s location to determine my jogging speed or the orbits of the planets would be nigh ridiculous, but not impossible. But there is no absolute frame of reference.

Here is the leading astronomy blogger on this issue:

I have two things to say that might surprise you: first, geocentrism is a valid frame of reference, and second, heliocentrism is not any more or less correct.

Surprise! Of course, the details are important.

Look, I’m human: I say “The Sun rose in the east today”, and not “the rotation of the Earth relative to the rest of the Universe carried me around to a geometric vantage point where the horizon as seen from my location dropped below the Sun’s apparent position in space.” To us, sitting here on the surface of a planet, geocentrism is a perfectly valid frame of reference. Heck, astronomers use it all the time to point our telescopes. We map the sky using a projected latitude and longitude, and we talk about things rising and setting. That’s not only natural, but a very easy way to do those sorts of things. In that case, thinking geocentrically makes sense.

However, as soon as you want to send a space probe to another planet, geocentrism becomes cumbersome. In that case, it’s far easier to use the Sun as the center of the Universe and measure the rotating and revolving Earth as just another planet. The math works out better, and in fact it makes more common sense.

However, this frame of reference, called heliocentrism, still is not the best frame for everything. Astronomers who study other galaxies use a galactic coordinate system based on our Milky Way galaxy, and the Sun is just another star inside it. Call it galactocentrism, if you want, and it’s just as useful as geo- or heliocentrism in its limited way. And none of those systems work if I want to know turn-by-turn directions while driving; in that case I use a carcentric system (specifically a Volvocentric one).

You use coordinate systems depending on what you need.

So really, there is no one true center to anything. I suppose you could say the Universe is polycentric, or more realistically acentric. You picks your frame of reference and you takes your chances.

Geocentrism is only wrong when advocates think that all the planets revolve in near circles around the Earth, rather than a strange path that can best be mapped using the Sun as a reference.

About christopher fisher

The blog is meant for educational/entertainment purposes. All material can be used and reproduced in any length for any purpose as long as I am cited as the source.
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