Friday, April 11, 2014

Apparent motion

Does Scripture teach geocentrism? Many unbelievers claim it does, and use that to disprove Scripture. A few Christians defend geocentrism. By way of reply:

i) Astronomers want to translate observations into objective third-person descriptions. But in ordinary language, a statement like "the sun goes around the earth" is shorthand for "I see the sun pass overhead." It's inherently indexical: a statement which takes the earthbound observer as the frame of reference.

That's the origin of the statement: the experience of the earthbound observer. 

To treat that as a geocentric claim involves translating it into a different kind of statement. 

ii) An observational statement about the apparent motion of the sun is not a statement about the sun moving in relation to the earth, but the sun moving in relation to the observer

Compare climbing a staircase to riding an escalator. 

When I climb a staircase, I'm in motion in relation to the staircase and the room, while the staircase and the room are stationary in relation to me. I go from one step to another step.

When I ride an escalator, I'm stationary in relation to the escalator, but in motion relative to the room. I remain on the same step moving up or down. I'm not moving, the escalator is.

Am I moving in relation to the room? That's ambiguous. In one sense, I'm motionless. I remain in the same position relative to the step I'm standing on. 

I'm moving in the sense that I'm being moved. The escalator is moving me from one location to another. So, in another sense, I'm in motion–even though I'm stationary.

That's like standing still on a revolving earth, and watching the sun shift position throughout the course of the day. 

And it does shift position from one side of the horizon to the other. Does that mean it shifts position by moving? But that's ambiguous in the same sense as the escalator. 

When I ride an escalator, does my position shift? In relation to the escalator? No. In relation to the room? Yes.

Biblical descriptions of apparent motion are consistent with more than one underlying explanation. They don't single out geocentrism. The language is not that specific. It's not a direct statement about the sun shifting position in relation to the earth, but a direct statement about the sun shifting position in relation to the earthbound observer, who is stationary on a revolving earth. At best, it's an indirect statement about the sun's shifting position, via the stationary earthbound observer.  

Suppose I'm in a valley. The sun is just above the eastern side of the horizon. I'm standing on the western side. Suppose I sprint to the eastern side. The sun is now shifting position in relation to my changed perspective. When I'm in motion, moving from west to east or east to west in the valley, the stationary sun shifts position. It's at a different angle, relative to me. 

Some people are impatient. In a hurry. They both ride and climb the escalator. They are moving in relation to the escalator while the escalator is moving them in relation to the room. 

iii) Here's an anecdote by William James, which exposes the ambiguities of relative motion:

SOME YEARS AGO, being with a camping party in the mountains, I returned from a solitary ramble to find every one engaged in a ferocious metaphysical dispute. The corpus of the dispute was a squirrel – a live squirrel supposed to be clinging to one side of a tree-trunk; while over against the tree’s opposite side a human being was imagined to stand. This human witness tries to get sight of the squirrel by moving rapidly round the tree, but no matter how fast he goes, the squirrel moves as fast in the opposite direction, and always keeps the tree between himself and the man, so that never a glimpse of him is caught. The resultant metaphysical problem now is this: Does the man go round the squirrel or not? He goes round the tree, sure enough, and the squirrel is on the tree; but does he go round the squirrel? In the unlimited leisure of the wilderness, discussion had been worn threadbare. Every one had taken sides, and was obstinate; and the numbers on both sides were even. Each side, when I appeared therefore appealed to me to make it a majority. Mindful of the scholastic adage that whenever you meet a contradiction you must make a distinction, I immediately sought and found one, as follows: “Which party is right,” I said, “depends on what you practically mean by ‘going round’ the squirrel. If you mean passing from the north of him to the east, then to the south, then to the west, and then to the north of him again, obviously the man does go round him, for he occupies these successive positions. But if on the contrary you mean being first in front of him, then on the right of him, then behind him, then on his left, and finally in front again, it is quite as obvious that the man fails to go round him, for by the compensating movements the squirrel makes, he keeps his belly turned towards the man all the time, and his back turned away. Make the distinction, and there is no occasion for any farther dispute. You are both right and both wrong according as you conceive the verb ‘to go round’ in one practical fashion or the other.” 
Although one or two of the hotter disputants called my speech a shuffling evasion, saying they wanted no quibbling or scholastic hair-splitting, but meant just plain honest English ‘round’, the majority seemed to think that the distinction had assuaged the dispute.

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