This is the weekly Q & A blog post by our Research Professor in Philosophy, Dr. William Lane Craig.
Hi Dr Craig, I have been watching your excursus on natural theology and am upto the part about teleology. You mention an objection to the argument, that we could have other natural laws and it could be more probable than not, with other sets of laws, that life permitting universes do exist just by chance. You say we just don't know the answer here.
Then you exclude the possibility of assessing possible worlds with other natural laws. You use the illustration of hitting a fly on a portion of blank wall, being much more improbable than probable, even if the area outside of the blank wall happens to be covered in flies. Of course in hitting flies on a wall we get to decide the portions. We get to say 'we ar looking at the probability of hitting the fly with in this area'.
But I'm confused about why we would be 'allowed' to do that when discussing the potential universes. What justification do we have to exclude worlds with other natural laws from our calculations of the probabilities?
(If the answer is, well, these are the natural laws we have so that's all we must look at, then I don't understand the goal of the project really. We could say the same thing about all the constants and quantities; since there is only one set that actually exists, that's all we must address and then end up with a properly 0% chance of any other arrangement.
Dr. William Lane Craig’s Response
Thanks for the chance to clarify the point for you, Amanda! Let’s first be clear about the nature of fine-tuning. The fine-tuning concerns the values of the fundamental constants and quantities of nature. For purposes of the argument, one holds the laws of nature unchanged but alters the values of the constants and quantities. It’s very important that the laws be held unchanged, or we wouldn’t know what would happen if, say, the force of gravity were increased or decreased. Because the laws are held unchanged, physicists can predict what would happen (e.g., the universe would expand more rapidly or else collapse).
Now the objection is that maybe in universes operating under different laws of nature, there wouldn’t be serious side effects of having a different value for the gravitational constant. The response is that we need not consider such universes in order to recognize that our universe is fine-tuned. The illustration of the fly on the wall shows why. If there is a large blank area of the wall occupied by a single fly and a single shot is fired, then it is vastly more probable that the bullet will not hit the fly but rather some other part of the blank area. This probability is independent of whether outside the blank area the wall is covered with flies, so that a randomly fired single shot would likely strike one. The point is that even if intelligent life were very probable in universes operating according to different laws of nature, it would still be the case that it is highly improbable in any universe governed by laws like ours.
Now your question is, “why we would be 'allowed' to do that [i.e., decide the portions] when discussing the potential universes. What justification do we have to exclude worlds with other natural laws from our calculations of the probabilities?” Amanda, it’s vital that you see that these are two entirely different questions. The second question is why we can ignore the worlds operating according to different laws of nature. That question has already been answered. The fly on the wall illustration shows why the flies outside the blank area are irrelevant to the probability of a single shot’s hitting the fly in the blank area. Rather the important question is the first: do we know how large the blank area of universes operating according to our laws of nature is, so as to say that a single universe randomly selected from the possible universes is probably life-prohibiting?
The answer is that physicists do have a very good grasp of what Robin Collins calls “the illuminated zone,” that is to say, the zone in which we can predict with confidence what would happen if the values of the constants and quantities were increased or decreased. Granted, we don’t know what happens outside the illuminated zone, but the illuminated zone is huge, like that large blank area of the wall in which the solitary fly sits. That’s enough to conclude that it’s highly improbable that a randomly selected universe operating according to our laws of nature should be life-permitting.
So your last paragraph misses the point. We’re not saying, “well, these are the natural laws we have so that's all we must look at.” Rather we’re saying, “What might or might not happen in universes operating according to different laws of nature is irrelevant to asking about the probability that a universe operating according to our laws of nature should be life-permitting.”