““The idea of an anthropic principle began with the remark that the laws of nature seem surprisingly well suited to the existence of life. A famous example is provided by the synthesis of the elements. According to modern ideas, this synthesis began when the universe was about three minutes old (before then it was too hot for protons and neutrons to stick together in atomic nuclei) and was later continued in stars. It had originally been though that the elements were formed by adding one nuclear particle at a time to atomic nuclei, starting with the simplest element, hydrogen, whose nucleus consists of just one particle (a proton). But, although there was no trouble in building up helium nuclei, which contain four nuclear particles (two protons and two neutrons), there is no stable nucleus with five nuclear particles and hence no way to take the next step. The solution found eventually by Edwin Salpeter in 1952 is that two helium nuclei can come together in stars to form the unstable nucleus of the isotope beryllium 8, which occasionally before it has a chance to fission into two helium nuclei absorbs yet another helium nucleus and forms a nucleus of carbon. However, as emphasized in 1954 by Fred Hoyke, in order for this process to account for the observed cosmic abundance of carbon, there must be a state of the carbon nucleus that has an energy that gives it an anomalously large probability of being formed in the collison of a helium nucleus and a nucleus of beryllium 8. (Precisely such a state was subsequently found by experimenters working with Hoyle.) Once carbon is formed in stars, there is no obstacle to building up all the heavier elements, including those like oxygen and nitrogen that are necessary for known forms of life. But in order for this to work, the energy of this state of the carbon nucleus must be very close to the energy of a nucleus of beryllium 8 plus the energy of a helium nucleus. If the energy of this state of the carbon nucleus were too large or too small, then little carbon or heavier elements would be formed in stars, and with only hydrogen and helium there would be no way that life could arise. The energies of nuclear states depend in a complicated way on all the constants of physics, such as the masses and electric charges of the different types of elementary particles. It seems at first sight remarkable that these constants should take just the values that are needed to make it possible for carbon to be formed in this way.””
