More on Fine Tuning

Luke Barnes has asked me to look at Part 1 of his defense of Fine Tuning against Ikeda and Jeffries' critique. Part 1 is, unfortunately, over-complicated, and, as best I can tell, the complications obscure rather than explain the underlying point.

We can concede the most basic Fine Tuning argument: The existence of life does indeed raise the probability that a life-designer exists and designed life. At a very basic (not fundamental) level, the existence of life is indeed evidence for a life-designer. This conclusion has absolutely nothing to do, however, with Fine Tuning. Even if we were to conclude that all logically possible physics guaranteed the existence of life, then it would still be the case that the existence of life was evidence for a life designer (or a life-friendly-physics designer). I don't even need to get into complicated probability math. We can simply look at the alternative: if no life existed, then that would absolutely falsify the existence of a life-designer, in just the same sense that the fact that we observe that no hoverboards exists absolutely falsifies the existence of someone who has (successfully) designed a hoverboard.

The problem with defining evidence in this sense is that it's far too broad. I used to play poker. Sometimes I would win, sometimes I would lose. Just the fact that I lost on some particular day is evidence in the above sense that someone was cheating that day. Again, in a similar sense, had I won that day, I would have known with certainty that no one was cheating.* Possibly cheating is greater than definitely not cheating. Similarly, the fact that each star in each galaxy is arranged in the particular positions we observe is evidence that it was done intentionally: had we observed a different arrangement, that would definitely falsify the hypothesis that they were deliberately arranged in the positions we do observe.

*Or if they were cheating, they were cheating to lose, against which I have no objection.

However, the fact that I lost some days and won some days, and that all the stars in all the galaxies are in the positions that we observe are also evidence for the fact that these events happened by chance. Again, observing something different would falsify the hypothesis that the specific event occurred by chance. If a specific event had not happened, then the hypothesis that the event actually happened by chance would be certainly false.

So observing the existence of life is evidence for the hypothesis that life was created, and it's also evidence for the hypothesis that life happened by chance. Wait, what? How can something be evidence for contradictory hypotheses?! Well, the hypotheses are not contradictory. They're mutually exclusive, but neither "life was designed" nor "life exists by chance" is the complement of the other. Logical consistency demands only that evidence for some hypothesis must be evidence against its complement , not against some other event that is merely mutually exclusive.

Thus, that life exists proves that the complement of the union ("life was designed" or "life happened by chance") is definitely false, which implicitly proves that both "life was designed" and "life happened by chance" have a higher ex post probability than they had ex ante. However, we still have to distinguish between the two probabilities. Hence we start doing things like conditioning on the existence of life, and we get Ikeda and Jeffries.