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Fine-tuned universe
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=== Carbon and oxygen === {{Further|Triple-alpha process#Improbability and fine-tuning}} An older example is the [[Hoyle state]], the third-lowest energy state of the [[carbon-12]] nucleus, with an energy of 7.656 MeV above the ground level.<ref>[[Evry Schatzman|Schatzman, E. L.]], & Praderie, F., ''The Stars'' ([[Berlin]]/[[Heidelberg]]: [[Springer Science+Business Media|Springer]], 1993), [https://books.google.com/books?id=FtZ_cNTPv8gC&pg=PA125&redir_esc=y#v=onepage&q&f=false pp. 125β27].</ref> According to one calculation, if the state's energy level were lower than 7.3 or greater than 7.9 MeV, insufficient carbon would exist to support life. To explain the universe's abundance of carbon, the Hoyle state must be further tuned to a value between 7.596 and 7.716 MeV. A similar calculation, focusing on the underlying fundamental constants that give rise to various energy levels, concludes that the [[strong force]] must be tuned to a precision of at least 0.5%, and the electromagnetic force to a precision of at least 4%, to prevent either carbon production or oxygen production from dropping significantly.<ref>{{cite journal|last1=Livio|first1=M.|authorlink1=Mario Livio|last2=Hollowell|first2=D.|last3=Weiss|first3=A.|last4=Truran|first4=J. W.|authorlink4=James W. Truran|s2cid=4273737|title=The anthropic significance of the existence of an excited state of 12C|journal=Nature|date=27 July 1989|volume=340|issue=6231|pages=281β84|doi=10.1038/340281a0|bibcode = 1989Natur.340..281L }}</ref>
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