Fine Tuning of the Earth's Orbit
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[edit] Introduction
One common creationist claim is that the distance of the Earth from the sun is precisely fine-tuned to ensure that the Earth has temperatures suitable for life, thus revealing the hand of God in the fiat creation of our Solar System.
[edit] Example
The following statement of the argument is not atypical:
- For example, the position of the earth vis a vis the sun. Our planet is so well placed vis a vis the sun. A few feet away from the sun (compared to where we are now) , and we all freeze to death. A few feet near the sun and we all burn. [1]
[edit] Discussion
To be fair to creationists, not all of them are daft enough to claim that a few feet (or, in some cases, inches) distance from the Sun are sufficient to make the difference between freezing and burning. Some of them are quantitively vague, as in the following example:
- If the Earth were any further away from the sun, we would all freeze. Any closer and we would burn up. Even a fractional variance in the Earth's position to the sun would make life on Earth impossible. The Earth remains this perfect distance from the sun. [2]
This is rather vaguer than claims about "a few feet nearer", but again, the creationist is attempting to give the impression that the distance of the Earth from the Sun is exquisitely fine-tuned.
But how fine-tuned is it really? Well, the eccentricity of the Earth's orbit is such that over the course of a year our distance from the sun varies by about four million miles[3], which is about 3%. To see how little difference this makes to the Earth's climate, consider that we are closest to the Sun when it is winter in the Northern Hemisphere: the axial tilt of the Earth, causing the seasons, has far more effect than a variation in distance of a mere four million miles.
Furthermore, the variety of climatic conditions on the Earth suggests that the orbit could be altered considerably and still leave some zones habitable. If the Earth was ten or twenty million miles closer to the Sun, which might make an appreciable difference, then perhaps equatorial zones would be too hot for most life, but Antarctica would become habitable; if it was further out, then perhaps Canada would be covered by glaciers, but the Sahara would be pleasantly temperate.
Finally, we should note that this is one alleged case of fine tuning where the anthropic principle quite definitely applies. There are about 100,000,000,000 stars in our galaxy[4], which is not atypical; and perhaps 200,000,000,000 galaxies in the visible universe[5]; and models of solar system formation suggest that the typical solar system should resemble ours in having small rocky inner planets like Mercury, Mars, Earth, and Venus, with large gas giants as outer planets[6]. It follows that there must be lots and lots of planets suitable for Earth-type life, and of course we happen to live on one that is suitable, rather than one that isn't. Marveling at our good fortune in living on of the zillions of planets that can support life, rather than one of the admittedly much greater number that can't, is rather like being surprised that you weren't born at the South Pole, or in the crater of an active volcano, or five miles underground. This is not "fine tuning", this is a biological inevitability.
