In this series I have left out a lot regarding the Anthropic Principle, because my focus is on its value as a teleological argument for the existence of God. So, for example, I have not gone over the several types of APs that have been proposed, i.e. the Weak (WAP), Strong (SAP), Participatory (PAP), and Final (FAP) -- the latter of which Martin Gardner cleverly called the Completely Ridiculous Anthropic Principle (CRAP).
Some people think that any teleological argument is invalid in light of Darwin. Such arguments are automatically excluded from consideration, since they also apply to arguments against biological evolution. If some teleological arguments from a particular field are invalid, why doesn't that give us grounds for rejecting those from other fields? My answer is fairly simple: because the arguments against evolution don't work and the arguments from the AP do. It doesn't matter who is presenting the argument or what their motivation is: if it's valid, it's valid; and if it's invalid, it's invalid.
One thing that frustrated me about the AP when I first studied it, however, is that there seem to be examples of fine-tuning that don't serve any purpose. The example that particularly hit home with me was that our location with regards to the sun and the moon make it appear as if they just happen to be the same size in the sky. The AP shows that we have to have a moon a particular size and distance from us, and the earth has to be a particular distance from a particular kind of star during a particular burning phase; but it just seems weird to me that this results in the sun and moon appearing to be the same size in the sky. If someone rigged the game, it looks like they were rigging it to mislead us into thinking that they were the same size. Of course, the ancients were able to study the sun and the moon and determine that they're not even remotely close in terms of size. But it seems like a meaningless coincidence, and this made me suspicious that the examples of alleged fine-tuning that the AP demonstrates were similarly coincidental.
The resolution to this leads to a very interesting corollary to the AP. The surface of the earth is the only place in the solar system where an observer could see a total eclipse, in which one body blocks out the sun, but does so just barely, so that the sun's corona can be observed. For millennia, solar eclipses were one of the primary methods by which humankind could study the sun. Such study would only be possible if the sun and the moon appeared to be the same size in the sky. So the same characteristics that make life possible are also the characteristics that allow us to study and investigate the universe around us.
With the advent of the Mars Rovers, there has been a boon in the last several years on Mars studies. Below, on the left, is a series of pictures taken by one of the Rovers of Phobos, one of Mars' moons, crossing between Mars and the sun. The picture on the right is of Mars' other moon Deimos doing the same. Click here to see a very short video (a couple of seconds long) of it.
The point in showing these is that such "eclipses" (they're actually called transits or occultations) would not allow any observers to study the sun's corona.
Here's another example: the AP says that in order for life to be possible, the solar system must reside in a spiral galaxy, and lie in-between spiral arms. In the same way, we have to be between spiral arms in order to see anything beyond our own galaxy. In any other location in any other type of galaxy, the number of nearby stars and the light they produce would prevent us from seeing very far beyond them. So just as it looks like the universe and Earth have been arranged in order to support life, it looks like the universe and Earth have been arranged in order to allow for scientific discovery. Praise God.
(see also part 1, part 2, and part 3)
(cross-posted at Quodlibeta)