 Many examples of fine-tuning have to do with star formation. Stars are important since life requires a variety of elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Stars contain the only known mechanism for producing large quantities of these elements and are therefore necessary for life. Lee Smolin estimates that when all of the fine-tuning examples are considered, the chance of stars existing in the universe is 1 in 10229. “In my opinion, a probability this tiny is not something we can let go unexplained. Luck will certainly not do here; we need some rational explanation of how something this unlikely turned out to be the case” (Smolin 1999, 45). Smolin is not merely claiming that all improbable events require an explanation, but some improbable events are special. (In poker, every set of five cards dealt to the dealer has the same probability, assuming that the cards are shuffled sufficiently. If the dealer is dealt a pair on three successive hands, no special explanation is required. If the dealer is dealt a royal flush on three successive hands, an explanation would rightly be demanded, and the improbability of this case isn’t even close to the magnitude of the improbability that Smolin mentioned.)  Physicists who have written on fine-tuning agree with Smolin that it cries out for an explanation. One explanation is that the universe appears to be fine-tuned for the existence of life because it literally has been constructed for life by an intelligent agent.