Claim:
The cosmos is fine-tuned to permit human life. If any of several fundamental constants were only slightly different, life would be impossible. (This claim is also known as the weak anthropic principle.)
Response:
1. The claim assumes life in its present form is a given; it applies not to life but to life only as we know it. The same outcome results if life is fine-tuned to the cosmos.
We do not know what fundamental conditions would rule out any possibility of any life. For all we know, there might be intelligent beings in another universe arguing that if fundamental constants were only slightly different, then the absence of free quarks and the extreme weakness of gravity would make life impossible.
Indeed, many examples of fine-tuning are evidence that life is fine-tuned to the cosmos, not vice versa. This is exactly what evolution proposes.
2. If the universe is fine-tuned for life, why is life such an extremely rare part of it?
3. Many fine-tuning claims are based on numbers being the "same order of magnitude," but this phrase gets stretched beyond its original meaning to buttress design arguments; sometimes numbers more than one-thousandfold different are called the same order of magnitude (Klee 2002).
How fine is "fine" anyway? That question can only be answered by a human judgment call, which reduces or removes objective value from the anthropic principle argument.
4. The fine-tuning claim is weakened by the fact that some physical constants are dependent on others, so the anthropic principle may rest on only a very few initial conditions that are really fundamental (Kane et al. 2000). It is further weakened by the fact that different initial conditions sometimes lead to essentially the same outcomes, as with the initial mass of stars and their formation of heavy metals (Nakamura et al. 1997), or that the tuning may not be very fine, as with the resonance window for helium fusion within the sun (Livio et al. 1989). For all we know, a universe substantially different from ours may be improbable or even impossible.
5. If part of the universe were not suitable for life, we would not be here to think about it. There is nothing to rule out the possibility of multiple universes, most of which would be unsuitable for life. We happen to find ourselves in one where life is conveniently possible because we cannot very well be anywhere else.
6. Intelligent design is not a logical conclusion of fine tuning. Fine tuning says nothing about motives or methods, which is how design is defined. (The scarcity of life and multi-billion-year delay in it appearing argue against life being a motive.) Fine-tuning, if it exists, may result from other causes, as yet unknown, or for no reason at all (Drange 2000).
7. In fact, the anthropic principle is an argument against an omnipotent creator. If God can do anything, he could create life in a universe whose conditions do not allow for it.
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