The Anthropic Principle In the early 1970's, Brandon Carter stated what he called 'the anthropic principle': that what we can expect to observe 'must be restricted by the conditions necessary for our presence as observers' (Leslie ed. 1990). Carter's word 'anthropic' was intended as applying to intelligent beings in general. The 'weak' version of his principle covered the spatiotemporal districts in which observers found themselves, while its 'strong' version covered their universes, but the distinction between spatiotemporal districts and universes, and hence between the weak principle and the strong, could not always be made firmly: one writer's 'universe' could sometimes be another's 'gigantic district'. Moreover, the necessity involved was never -- not even in the case of the 'strong anthropic principle' -- a matter of saying that some factor, for instance God, had made our universe utterly fated to be intelligent-life-permitting, let alone intelligent-life-containing. However, all these points have often been misunderstood and, at least when it comes to stating what words mean, errors regularly repeated can cease to be errors.
Has Carter therefore lost all right to determine what 'anthropic principle' and 'strong anthropic principle' really mean? No, he has not, for his suggestion that observer ship's prerequisites might set up observational selection effects is of such importance. Remember, it could throw light on any observed fine tuning without introducing God. Everything is thrust into confusion when people say that belief in God 'is supported by the anthropic principle', meaning simply that they believe in fine tuning and think God can explain it. As enunciated by Carter, the anthropic principle does not so much as mention fine tuning. Being aware of possible 'anthropic' observational selection effects can encourage one set of expectations, and belief in God another set.
If suspecting that Carter's anthropic principle has practical importance, you will be readier to believe (i) that there exist multiple universes and (ii) that their characteristics have been settled randomly, some mechanism such as cosmic inflation ensuring that all was settled in the same fashion throughout the region visible to our telescopes. True, the believer in God can accept these things too, yet he or she may feel far less pressure to accept them. Even if there existed only a single universe, God could have fine tuned it in ways that encouraged intelligent life to evolve. A possible argument for preferring the God hypothesis runs as follows.
A physical force strength or elementary particle mass can often seem to have required tuning to such and such a numerical value, plus or minus very little, for several different reasons. Random variations from universe to universe might explain why it took any particular value somewhere or other, yet how could they account for the fact that one and the same value satisfied many different requirements? Why is such consistency possible? Why does electromagnetism, for example, not need to have one strength to allow atoms to be stable, and another strength for stars to burn at a life-encouraging rate, and yet another to permit carbon (quite probably crucial to life) to be produced plentifully?
Here a religiously minded physicist could think in terms of many possible fundamental theories, God selecting a theory which permitted life's requirements to be fulfilled without contradictions. web.